Abstract: Virtual reality (VR) applications for surgical planning and mentoring are currently becoming more widespread. Within these fields of applications, haptic systems are crucial to help the understanding of the feedback provided by the tissue during the interaction with the surgical tool. The accuracy of the VR scenario is related to many aspects, among them the ability of the haptic device to provide the force feedback and thus the adoption of proper characterization and modeling of the soft tissue behavior during deformation. This paper presents the current development concerning a VR environment to be equipped with a force feedback haptic device to simulate and experience clamping in colorectal surgery. The reaction at the clamp handle is provided starting from a FEA of the contact between the surgical tool and the tissue, coupled with the kinematic analysis of the mechanism. Connecting the virtual scenario to a microcontroller board, the reaction force is applied to the the haptic device, shaped as a clamping tool handle, so that the user may experience the tissue impedence during clamping. By simulations made through Simscape, a concept is evaluated according to some simulation paths that involve common scenarios of the virtual reality experience (such as collision, partial or total clamping operation). The novelty of the research regards the system design oriented to increase the accuracy of the soft tissue material behaviour through a preliminary off-line dedicated FEA investigation. Through Simulink simulations, the system design is verified so that the VR system set-up may be carried out. The results highlighted: (a) a good correspondence among the theoretical study of the reference kinematism that the haptic device must reproduce; (b) the implementation of a bilinear material model, derived off-line from FEA, is suitable to capture hyperelastic and geometric non-linearities of the soft tissue; (c) the feasibility of the open loop haptic control in accordance to the explored kinematism. The final goal of the research is to propose a system design approach able to tune the VR experince for teaching and mentoring through a in-house set-up easy to be tailored.

Keywords: FEA | Force feedback | Metamodeling | Surgical simulation | Virtual prototyping

Abstract: The increasing demand for designing complex structures using Functionally Graded Material boosts the research on reliable joining processes. For several industrial applications in the automotive, tooling, and petrochemical industries, the joining of a stainless steel with a low-alloy steel is often required to obtain a variation of mechanical and corrosion properties when different parts of the same structure are subjected to different working conditions. Welding a stainless steel with a low-alloy steel is a challenging operation because it is not easy to control the microstructure of the welded joint and to avoid metallurgical defects such as hot cracks. Moreover, traditional welding methods can only be applied to relatively simple geometries. To design and produce multi-material components, characterised by complex geometries, Selective Laser Melting process capabilities can be exploited. In this paper, an AISI 316L stainless steel is joined to 16MnCr5 steel by carefully tuning the process parameters. Metallurgical investigations coupled with Energy Dispersion Spectroscopy analyses allowed to evaluate the soundness of the joint and the effect of the process thermal cycle on the alloy microstructures and properties. The results are very promising and show that a careful selection of process parameters allows to obtain a continuous joint.

Keywords: 16MnCr5 | AISI 316L | Functionally Graded Material | Microstructure | Selective Laser Melting

Abstract: Additive Manufacturing is becoming a widespread manufacturing system in several industrial fields such as automotive, aerospace, biomedical, etc. Design for Additive Manufacturing represents the branch of research that considers the technological constraints from the early stages of design, arriving at a geometrical model to be exported in G-code. The limitations of additive manufacturing are related to the complexity of the process, the high costs, the processing time, and the difficulties of ensuring adequate geometric and dimensional tolerances. A data-driven approach can be a solution to improve the Design for Additive Manufacturing. Artificial Intelligence and Machine Learning methods are employed in the literature to shorten the time for assessing the optimal combination of parameters and supporting decision-making. The current state of the art shows three macro-areas to apply Machine Learning methods in Design for Additive Manufacturing. These applications concern Geometrical Design Level, Process Configuration Level, and Process Monitoring Level. This paper aims to identify and classify the Machine Learning methods and algorithms most used in Design for Additive Manufacturing practices, analyzing parameters, results, processes, and materials involved.

Keywords: Additive Manufacturing | Artificial Intelligence | Design for Additive Manufacturing | Machine Learning

Abstract: Post-processing pipeline for image analysis in reverse engineering modelling, such as photogrammetry applications, still asks for manual interventions mainly for shadows and reflections corrections and, often, for background removal. The usage of Convolutional Neural Network (CNN) may conveniently help in recognition and background removal. This paper presents an approach based on CNN for background removal, assessing its efficiency. Its relevance pertains to a comparison of CNN approaches versus manual assessment, in terms of accuracy versus automation with reference to cultural heritage targets. Through a bronze statue test case, pros and cons are discussed with respect to the final model accuracy. The adopted CNN is based on the U-NetMobilenetV2 architecture, a combination of two deep networks, to converge faster and achieve higher efficiency with small datasets. The used dataset consists of over 700 RGB images used to provide knowledge from which CNNs can extract features and distinguish the pixels of the statue from background ones. To extend CNN capabilities, training sets with and without dataset integration are investigated. Dice coefficient is applied to evaluate the CNN efficiency. Results obtained are used for the photogrammetric reconstruction of the Principe Ellenistico model. This 3D model is compared with a model obtained through a 3D scanner. Moreover, through a comparison with a photogrammetric 3D model obtained without the CNN background removal, performances are evaluated. Although few errors due to bad light conditions, the advantages in terms of process automation are consistent (over 50% in time reduction).

Keywords: Close range photogrammetry | CNN | Cultural heritage preservation | MobilenetV2 | Reverse engineering | U-Net

Abstract: This paper presents a Generative Design Method (GDM) for highly customised Cultural Heritage applications concerning the exhibition and conservation of pottery. As a fundamental requirement, archaeological finds must be preserved in their structural integrity. Additionally, when present, the exposition supports must be aesthetically pleasant meaning that they must be non-invasive in the field of view of the observer. Furthermore, each artefact presents a unique geometry, hence its supporting structure must be designed accordingly. The proposed GDM considers these requirements, adopting a synergy of CAD, CAE, and optimisation tools. It is developed through two phases. The first phase, P1, concerns with the structural integrity of the fragment. In this phase, a Parametric Modelling approach is chosen for its ease of use both in the Finite Element Analysis evaluations of artefacts and in the design and optimisations of feasible supporting structures. The output of the phase P1 is the optimised configuration of the functional elements of the support ('Ci ') which are the interface region between the support itself and the fragment of pottery. They represent the input of the second phase, P2, that aims to generate lightweight concepts for the complete supporting structure considering the optimal 'Ci ' configuration. During this phase, an aesthetics criterion (related to the minimisation of the support's visibility) is also considered to achieve non-invasive supporting structures. Doing so, the GDM provides informed decisions in the early stages of the design activities with a simulation driven approach oriented to manufacturing. In this way, users are able to focus on design requirements since the concept's variants are generated by means of an optimised configuration of standardised components ('Ci') and obstacle geometries.

Keywords: Cultural Heritage | Generative Design | Parametric Modelling | Parametric Optimisation

Abstract: Additive Manufacturing (AM) is currently making the relevance of lattice structure solutions increasing, allowing the achievement of high performance/mass ratio, where performance stands for energy absorption, stiffness, and/or insulation. This paper undertakes lattice structure for lightweight design of a horse saddletree. Saddletree is the backbone of a horse saddle, and it is composed of different components. In particular, the spring steel reinforcements inside the saddletree make it the heaviest part of the horse saddle, involving also multiple processes of manufacturing and manual assemblies. This paper aims to lightweight an existing saddletree with a Voronoi lattice solution, reducing several manual assemblies. From the methodological point of view, the lightweight design has been based on a multi-scale approach, carried out via nTopology (static FEA on the original bulk design, implicit geometrical lattice generation from FEA result maps and Boolean operation among lattice results and bulk design implicit model). The original bulk design has been digitally acquired and modeled through Reverse Engineering techniques, so that a specific customized solution may be improved. A final weight reduction of 76.5% is achieved, providing an example of how topological optimization techniques coupled with AM (in particular Powder Bed Fusion technology) may reduce assembly efforts

Keywords: FEA | Horse Saddletree | Reverse Engineering | Topological Optimization | Voronoi Lattice Structure

Abstract: Lattice structures for engineering applications are patterns of unit cells designed to make a larger functional structure. Research on lattice structures ranges in many fields, from mechanical characterization and cell and pattern designs in respect of their applications, to the manufacturing process and its final shape control. From the manufacturing point of view, some kinds of lattice structures can be infeasible when approached with traditional manufacturing methods. It may offer an inevitable limitation of their adoption. However, advancements in Additive Manufacturing (AM) have solved this manufacturing issue to a great extent, allowing to obtain major complexity of the cells that can be achieved. The topology, shape of the unit cell, and the characteristics of its replication pattern allow us to obtain many kinds of structures in respect of the different engineering requirements and manufacturing constraints. Nevertheless, the necessity of new or dedicated CAD-CAE approaches arises to manage the domains of multiscale modeling. These are some of the advantages and disadvantages that may arise while approaching the design of a component using lattice structures. The aim of this paper is to provide an overview that integrates the most recent applications of lattice structures with their related design and manufacturing issues so that, from a practical design point of view, any state-of-the-art improvements may be established in respect of the related field of applications. In this article, engineers and researchers may find a practical summary of the capabilities and processes of lattice structures that are currently available from a design and development point of view.

Keywords: additive manufacturing | cellular structures | design methodologies | functionally graded materials | lattice structures | TPMS

Abstract: Laser powder bed fusion is one of the most common metal additive applications for manufacturing industry and high-level research. It is common to have in a company, mechanical workshop or laboratory, machines of different manufacturers and powders of different suppliers. Therefore, there is the need for users of this technology to transfer optimized process parameters easily and quickly from one machine to another. Despite several multiphysics models being available, they are not always easy to use, especially by technical staff. Furthermore, particularly attention must be given to machines equipped with small laser spot size (i.e., < 50 µm) that are able to produce complex geometry with a fine resolution and smooth finish. Generally, these machines produce a deeper melt pool and are employed with fine powder (e.g., 5–35 µm) and consequently small layer (e.g., 20–40 µm). In this paper, simple and analytical rules to adjust the main process parameters (i.e., layer thickness, hatch distance, etc.) and to scale the volumetric energy density on a machine with a fine laser spot size have been proposed. Relative density, microstructure, and mechanical performance have been evaluated for AISI 316L stainless steel and 16MnCr5 case hardening steel. The results show that after a careful tuning of process parameters, it is possible to obtain relative densities close to 100% for both alloys. Mechanical tests coupled with microstructural investigations also highlighted that the alloy mechanical behavior depends on heat input and cooling rates which, in turn, are affected by process parameters.

Keywords: 16MnCr5 | AISI 316L | L-PBF process parameters | Laser powder bed fusion | Mechanical properties | Microstructure analysis

Abstract: The compression behaviour in quasi-static and dynamic conditions of cellular materials is crucial for their applications both for ensuring structural strength and high energy absorption capability. Despite the recent progress made in understanding the experimental observations, analytical and numerical modelling still requires improvements in the Representative Volume Element (RVE) identification that can be uncertain due to the limited dimensions of the investigated specimens and to the cell inhomogeneity. The objective of this paper is to implement a material model able to consider the statistical distribution so that its effect can be quantitatively highlighted, mitigating uncertainty of the RVE identification. The applied methodology started with morphological and topological analyses on samples extracted from an ingot of AA7075T6 foam, which was manufactured by compact powder technology. Quasi-static and dynamic experimental compression tests have been carried out and compared with 3D mesoscale numerical simulations in order to correlate the mechanical behaviour of the foam to the cell characteristics. Finally, an equivalent material model, which is a function of the statistical distributions of cells morphology and topology, has been proposed and analytically verified.

Keywords: Aluminium foam | Cellular material | High strain rate | Homogeneous formulation | RVE | SHPB

Abstract: Mechanical design and engineering can support projects with high-added value in the Cultural Heritage field, such as restoration of artefacts like statues and architectonical decorations. Many examples have been carried out, along the recent past, in the field of ancient bronze restorations (as for Marco Aurelio, Satiro Danzante di Mazara del Vallo and Principe Ellenistico). Engineering design techniques help the assessment of structural problems through physical measurements and FEA simulations; the digital acquisition of surfaces represents a fundamental base for CAD modelling, and the inner frame design helps for guaranteeing stability and manoeuvrability requirements for transport and exhibition. Workflow peculiarities and requirements to accomplish the restorers’ activities and investigations may highlight best practices and rules. The design of the new inner frame of the Vittoria Alata of Brescia, an ancient roman bronze statue, represents a recent example of this kind. Its design workflow was provided in the loop of the restoration program, and it was assessed considering structural integrity, surfaces protection, inner inaccessibility, and dimensions. The solutions adopted are the result of a collaborative process with restorers to evaluate each proposed concept, in compliance with the studies and the constraints highlighted during the investigations. CAD-CAE tools applied starting from the 3D acquisition, helped the development and its verification, reducing the efforts during the manufacturing phase and final set-up. This paper aims to discuss the obtained result demonstrating how structural analysis and mechanical design anchored to 3D acquisitions may help restoration of bronze statues.

Keywords: CAD-CAE | Cultural heritage | Design for restoration | Structural analysis | Vittoria Alata

Abstract: Numerical simulations and Finite Element Analysis (FEA) have currently increased their applications in medical field for making preoperative plans to simulate the response of tissues and organs. Soft tissue simulations, such as colorectal simulations, can be adopted to understand the interaction between colon tissues and surrounding tissues, as well as the effects of instruments used in this kind of surgical procedures. This paper analyses through FEA the interaction between a surgical device and a colon tissue when it is fully clamped. Sensitivity analysis in the respect of the material mechanical behaviour, geometric approximation and the effect of thickness variation are investigated with the aim of setting up a virtual prototype of the surgical operation to aid mentoring and preliminary evaluation via haptic solutions. Through this investigation, the force feedback estimation that is necessary in many virtual-reality applications, may be estimated without discharging nonlinear effects that occur during clamping and that usually cannot be simulated efficiently to guarantee real-time solutions. Results are aligned with experimental data, confirming the reliability and right the set-up of FEA. Through them, the preliminary set-up of a haptic force feedback has been described and simulated through Simulink 3D animation, confirming the feasibility of the concept.

Keywords: FEA | Force feedback | Haptic device | Metamodeling | Surgical simulation | Virtual prototyping

Abstract: Hepatic diseases are serious condition worldwide, and several times doctors analyse the situation and elaborates a preoperative planning based exclusively on the medical images, which are a drawback since they only provide a 2D vision and the location of the damaged tissues in the three-dimensional space cannot be easily determined by surgeons. Nowadays, with the advancement of Computer Aided Design (CAD) technologies and image segmentation, a digital liver model can be obtained to help understand the particular medical case; even with the geometric model, a virtual simulation can be elaborated. This work is divided into two phases; the first phase involves a workflow to create a liver geometrical model from medical images. Whereas the second phase provides a methodology to achieve liver prototype, using the technique of fused deposition modelling (FDM). The two stages determine and evaluate the most influencing parameters to make this design repeatable in different hepatic diseases. The reported case study provides a valuable method for optimizing preoperative plans for liver disease. In addition, the prototype built with additive manufacturing will allow the new doctors to speed up their learning curve, since they can manipulate the real geometry of the patient's liver with their hands.

Keywords: 3D printing | Convolutional neural network | FDM | Image segmentation | Liver disease

Abstract: Nowadays, restoration is a multidisciplinary work that gathers knowledge and skills from different areas (technical, artistic, historical, architectural, …). In the field of ancient bronze statues, technical knowledge may also concern with materials behaviour and its preservation, surface quality, non-destructive diagnostics for integrity, a better understanding of the manufacturing technology, and of details, sometimes hidden, in not directly accessible sections of the artefact. This knowledge, got from different domains, can support restorers in their decision-making process. In many cases, they summarise it on pictorial views of the artefacts, or on images derived from the 3D model that is experimentally acquired through reverse engineering, to reference information on the interested areas. The aim of this paper is to explore the advantages related to a CAD-based framework able to gather the technical domains involved in the restoration of historical artifacts. Doing so, CAD functionalities and related benefits may be extended to cultural heritage applications as tools oriented for restoration, according to a life cycle perspective of the restorer’s activities and the artefact preservation and fruition. The proposed CAD-based framework has been implemented to manage the investigation for restoration and conservation of bronze statues. The approach has been applied to the Principe Ellenistico, part of the collection of Palazzo Massimo, one of the sites of Museo Nazionale Romano (in Rome). The obtained results show that the CAD-based framework may speed-up the investigation processes without losing accuracy and restorers’ good practices.

Keywords: CAD-CAE | Cultural heritage | Design for restoration | Principe Ellenistico | Virtual prototyping

Abstract: Thanks to Laser Powder Bed Fusion (L-PBF) technology, SCALMALLOY® was the first aluminum powder material designed for Additive Manufacturing (AM), achieving a fine microstructure with high performance that is comparable to other cast materials. Despite the mechanical properties that can be achieved, there are some inherent factors that can impede components performance (i.e., surface roughness). Parts produced by L-PBF are usually characterized by rough “as-built” surfaces; hence, it is fundamental during the design phase to understand and consider how the quality of surfaces impacts on the part performance. This paper aims to provide a Computer-Aided Engineering (CAE) workflow to design components with different finishing regions in accordance with the functional distinction that exists among them. To achieve this goal, a comparison of the mechanical properties achieved for SCALMALLOY® specimens with and without post-processing is here assessed to fit proper material models for numerical simulation purposes. The material models, built with/from experimental data, are fit to functionally adapt the performance of 3D-printed objects inside CAE simulations like a Functionally Graded Material (FGM). A CAE design workflow is here applied to a case study, suitable to demonstrate how the methodology may support the integrated product–process design of structural parts reducing the cost of post-processing in AM. This approach may mitigate the performance decrease of “as-built” surfaces since the experimental results show a different fatigue endurance limit between the “as-built” and CNC machined specimens about of three times.

Keywords: CAD modeling | CAE analysis | Laser powder bed fusion | Mechanical properties | SCALMALLOY®

Abstract: Thanks to Laser Powder Bed Fusion (L-PBF) technology, SCALMALLOY® was the first aluminum powder material designed for Additive Manufacturing (AM), achieving a fine microstructure with high performance that is comparable to other cast materials. Despite the mechanical properties that can be achieved, there are some inherent factors that can impede components performance (i.e., surface roughness). Parts produced by L-PBF are usually characterized by rough “as-built” surfaces; hence, it is fundamental during the design phase to understand and consider how the quality of surfaces impacts on the part performance. This paper aims to provide a Computer-Aided Engineering (CAE) workflow to design components with different finishing regions in accordance with the functional distinction that exists among them. To achieve this goal, a comparison of the mechanical properties achieved for SCALMALLOY® specimens with and without post-processing is here assessed to fit proper material models for numerical simulation purposes. The material models, built with/from experimental data, are fit to functionally adapt the performance of 3D-printed objects inside CAE simulations like a Functionally Graded Material (FGM). A CAE design workflow is here applied to a case study, suitable to demonstrate how the methodology may support the integrated product–process design of structural parts reducing the cost of post-processing in AM. This approach may mitigate the performance decrease of “as-built” surfaces since the experimental results show a different fatigue endurance limit between the “as-built” and CNC machined specimens about of three times.

Keywords: CAD modeling | CAE analysis | Laser powder bed fusion | Mechanical properties | SCALMALLOY®

Abstract: For the past few decades, topology optimization (TO) has been used as a structural design optimization tool. With the passage of time, this kind of usage of TO has been extended to many application fields and branches, thanks to a better understanding of how manufacturing constraints can achieve a practical design solution. In addition, the advent of additive manufacturing and its subsequent advancements have further increased the applications of TO, raising the chance of competitive manufacturing. Design for additive manufacturing has also promoted the adoption of TO as a concept design tool of structural components. Nevertheless, the most frequent applications are related to lightweight design with or without design for assembly. A general approach to integrate TO in concept designs is still missing. This paper aims to close this gap by proposing guidelines to translate design requirements into TO inputs and to include topology and structural concerns at the early stage of design activity. Guidelines have been applied for the concept design of an inner supporting frame of an ancient bronze statue, with several constraints related to different general design requirements, i.e., lightweight design, minimum displacement, and protection of the statue’s structural weak zones to preserve its structural integrity. Starting from the critical analysis of the list of requirements, a set of concepts is defined through the application of TO with different set-ups (loads, boundary conditions, design and non-design space) and ranked by the main requirements. Finally, a validation of the proposed approach is discussed comparing the achieved results with the ones carried out through a standard iterative concept design.

Keywords: Design methodology | Lightweight design | Restoration of ancient statues | Topology optimization

Abstract: The interesting properties of Al 6061 aluminum foams have boosted the research on the correlation between foam composition and morphology and its mechanical response under dynamic conditions. In this study, ingots of an Al 6061-T4 foam were sectioned and analyzed in order to determine their microstructural and morphological characteristics, and then quasi-static and dynamic tests (10−3 to 3 × 102 s−1) were carried out to determine the material mechanical behavior. Dynamic tests, carried out by using the split Hopkinson bar, highlighted that the studied foam is characterized by a very good energy absorption capability, due to its ductile behavior. Nevertheless, the conducted research showed that cell morphology and distribution affect its mechanical behavior in dynamic conditions in which localized cell collapse may result in a decreased energy absorption and efficiency of the foam.

Keywords: Aluminum foams | Failure mechanisms | Fracture behavior | Hopkinson bar

Abstract: Mechanical behavior of metallic foams suffers from scattering due to morphology and distribution of cells. FEA modeling, at mesoscale level, may assist design of metallic foam components or the development of a proper model able to consider the effects of this variability. This paper discusses a foam modeling approach based on a surface tessellation provided by a Voronoi diagram, investigating its ability to obtain a final model that respects an assigned cell morphology. Results show that a wide range of void volume fraction can be achieved, with good agreement between assigned cell morphology and modeled cell distribution. Absence of non-manifold geometry and STL optimization speed-up the FEA checks on the solid mesh creation, so that, many models may be systematically simulated to investigate the role of cell morphology during deformation.

Keywords: Aluminum foam | FEA | Mesoscale geometric modeling | Non-linear analysis | Voronoi Diagram

Abstract: Close-Range Photogrammetry is a widespread and efficient technique in the 3D acquisition of artefacts, particularly in fields like Cultural Heritage. Despite this wide usage, also due to a convenient quality/cost ratio, it shows some limitations due to light conditions as well as the artefact surface finishing. In this paper, we would like to report the assessment of a photogrammetry approach to 3D capture metal reflective surfaces, such as bronze, which is a widely used material in ancient statues. To this aim, we propose a photogrammetry workflow based on systematic steps capable of overcome some of the main issues of reflective surfaces. To validate this approach, the developed 3D model is compared to a more accurate model of the same artefact, obtained with a 3D scanner. As a case study, we selected the Principe Ellenistico, an ancient bronze statue conserved in the Museo Nazionale Romano (Rome, Italy), of which a photogrammetric model is firstly developed and then compared to the scanned one.

Keywords: 3D acquisition | Bronze statue | Close-Range Photogrammetry | Principe Ellenistico | Systematic approach

Abstract: The use of continuum mechanics, especially Finite Element Analysis (FEA) has gained an extensive application in the medical field, in order to simulate soft tissues. In particular, colorectal simulations can be used to understand the interaction between colon and the surrounding tissues, and also, between colon and surgical instruments. Although several works have been introduced considering small displacements, FEA applied to colorectal surgical scenarios with large displacements is still a challenge. This work aims to investigate how FEA can describe non-linear effects induced by material properties and different approximating geometries for colon. More in detail, it shows a comparison between simulations that are performed using well-known hyperelastic models (principally Mooney-Rivlin and, in one case, Yeoh) and the linear one. These different mechanical behaviours are applied on different geometrical models (planar, cylindrical and a 3D-shape from digital acquisitions) with the aim of evaluating also the effects of geometric non-linearity. Increasing the displacements imposed by the surgical instruments, the adoption of a hyperelastic model shows lower stresses than the linear elastic one that seems to overestimate the averaged stress. Moreover, the details of the geometrical models affect the results in terms of stress-strain distribution, since it provides a better localisation of the effects related to the hypothesis of large strains.

Keywords: computer assisted surgical planning | Finite element analysis | segmentation of medical images | soft tissues simulation | surface modelling

Abstract: Cellular materials have a bulk matrix with a larger number of voids named also cells. Metallic foams made by powder technology represent stochastic closed cells. The related inhomogeneity leads to a scattering of results both in terms of stress-strain curves and maximum strength. Scattering is attributed to relative density variations and local cell discontinuities and it is confirmed also in case of dynamic loading. Finite element simulations through geometrical models that are able to capture the void morphology (named “mesoscale models”), confirm these results and some efforts have been already done to quantify the relationship between shape irregularities and mechanical behavior. The aim of this paper is to present the dynamic characterization of an AA7075 closed cell material and to calibrate its mesoscale finite element model according to the related cell shape distribution. Specimens have been derived from a small ingot (45x45x100 mm) divided along sections so that morphological analysis and experimental tests have been carried out. Specimens extracted from a half of the ingot have been used for dynamic compression tests by means of a split Hopkinson bar, meanwhile specimens extracted from the other half of the ingot have been dissected for porosity distribution analyses carried out by means of image analysis. Stress-strain curves obtained from the mechanical tests have been discussed in terms of strain rate and statistical descriptors of the porosity. Successively a 3D-model of the specimen has been generated starting from the Voronoi algorithm, assigning as input the above-mentioned statistical distribution of the porosity. Due to the peculiarity of the cell morphology (e.g. single larger cells), stress-strain localization has been demonstrated as one of the reasons of the scattering found during the experiments. A material model, to reproduce the investigated foam mechanical behavior, has been calibrated. Despite the difference among experiments the material model is able to reproduce all of them. Difference between the model coefficients quantifies roughly the difference due to the local geometry of the cells.

Keywords: Aluminum foams | Image analysis | Impact test | Porosity distribution | Strain rate effect | Voronoi model

Abstract: In Automotive and Aerospace industries, Topology Optimization (TO) is being used for the last few decades to produce lightweight structures. On the other hand, TO produces very complex geometrical features (i.e. irregular shape and hidden cavities along the thickness) that is sometimes difficult to be manufactured even with Additive Manufacturing (AM) and Casting techniques. In this paper suitable design and manufacturing constraint (MC) are applied during TO process that act as an Optimization Tool (OT) and improves geometrical features of the mechanical structures for easy manufacturing. Three mechanical structures with different geometries and boundary conditions have been considered for analysis purpose. Topology Optimization based on linear static analysis has been performed using OptiStruct (HyperWorks) solver. Finally, results of analysis conclude that the proposed OT produces lightweight structures with very simple geometries that can easily be manufactured with the help of AM or Casting techniques.

Keywords: FEA | Lightweight Design | Linear Static Analysis | Manufacturing Constraints | OptiStruct (HyperWorks) Solver | Structural Optimization | Topology Optimization

Abstract: In injection molding production, automatic inspections are needed to control defects and evaluate the assigned functional tolerances of components and dies. With the “Smart Manufacturing” approach as a point of view, this paper resumes part of a wider research aiming the integration and the automation of a Reverse Engineering inspection process in components and die set-up. The paper compares two fitting approaches for recognition of portions of cylindrical surfaces. Therefore, they are evaluated in the respect of an automatic voxel-based feature recognition of 3D dense cloud of points for tolerance inspection of injection-molded parts. The first approach is a 2D Levenberg Marquardt algorithm coupled with a first guess evaluation made by the Kasa algebraic form. The second one is a 3D fitting based on the RANdom SAmple Consensus algorithm (RANSAC). The evaluation has been made according to the ability of the approaches of working on points associated to the voxel structure that locally divides the cloud to characterize planar and curved surfaces. After the presentation of the overall automatic recognition, the cylindrical surface algorithms are presented and compared trough test cases.

Keywords: Injection molding | RANdom SAmple Consensus algorithm | Tolerance inspection

Abstract: Mechanical properties of the soft tissues and an accurate mathematical model are important to reproduce the soft tissue’s material behavior (mechanical behavior) in a virtual simulation. This type of simulations by Finite Element Analysis (FEA) is required to analyze injury mechanisms, vehicle accidents, airplane ejections, blast-related events, surgical procedures simulation and to develop and test surgical implants where is mandatory take into account the high strain-rate. This work aims to highlight the role of the hyperelastic models, which can be used to simulate the highly nonlinear mechanical behavior of soft tissues. After a description of a set of formulations that can be defined as phenomenological models, a comparison between two models is discussed according to case study that represents a process of tissues clamping.

Keywords: FEA | Hyperelastic mathematical models | Soft tissues behavior

Abstract: Reverse Engineering (RE) may help tolerance inspection during production by digitalization of analyzed components and their comparison with design requirements. RE techniques are already applied for geometrical and tolerance shape control. Plastic injection molding is one of the fields where it may be applied, in particular for die set-up of multi-cavities, since no severe accuracy is required for the acquisition system. In this field, RE techniques integrated with Computer-Aided tools for tolerancing and inspection may contribute to the so-called “Smart Manufacturing”. Their integration with PLM and suppliers' incoming components may set the information necessary to evaluate each component and die. Intensive application of shape digitalization has to front several issues: accuracy of data acquisition hardware and software; automation of experimental and post-processing steps; update of industrial protocol and workers knowledge among others. Concerning post-processing automation, many advantages arise from computer vision, considering that it is based on the same concepts developed in a RE post-processing (detection, segmentation and classification). Recently, deep learning has been applied to classify point clouds, considering object and/or feature recognition. This can be made in two ways: with a 3D voxel grid, increasing regularity, before feeding data to a deep net architecture; or acting directly on point cloud. Literature data demonstrate high accuracy according to net training quality. In this paper, a preliminary study about CNN for 3D points segmentation is provided. Their characteristics have been compared to an automatic approach that has been already implemented by the authors in the past. VoxNet and PointNet architectures have been compared according to the specific task of feature recognition for tolerance inspection and some investigations on test cases are discussed to understand their performance.

Keywords: Deep learning | Injection molding | PointNet | Reverse engineering | Tolerance inspection

Abstract: In sheet metal forming, springback represents a major drawback increasing die set-up problems, especially for ultra-high strength steels. Finite Element Analysis is a well-established method to simulate the process during design, and multicriteria optimizations, for example, via surrogate models, are investigated in order to develop integrated design. Since to take into account also springback compensation die design may involve a large number of geometric variables, this paper presents a robust design formulation, based on the adoption of the shape function optimization, to describe springback in terms of weights directly associated to global shape variations of the die shape. Doing so, multicriteria optimization, which involves also die compensation, can be set up in a more intuitive approach, as requested in the preliminary steps of die design. After the introduction of the industrial problem, the mathematical formulation of the shape function optimization is presented together with its novel extension to Robust Design, which is based on the Dual Response Surface. Through a test case derived from the head part of a B-pillar, stamped from a Dual Phase sheet 1.5 mm thick, this novel extension investigates the effect of 6% variation from nominal values of initial yield stress and thickness. Results demonstrate the feasibility of the procedure, underlying that an optimal compensation may not be optimal in terms of process robustness.

Abstract: Interventions of ancient bronze statues restoration may last long periods, involving several activities from material and structural analysis to set-up of museum exhibitions, passing through reconstruction of fragments. In this paper, we describe procedures and methods used for evaluation of the current posture of “Principe Ellenistico”. In fact, the statue seems to present some inaccuracies, in the fragments assembly, made during the last restoration activity (one of this effect is clearly observed in the spear inclination). The final aims are: (1) evaluation of differences among the postures before and after the last restoration; (2) recognition of the original fragments embedded in a previous restoration; and (3) the study of a possible better positioning of them. Methods applied are related to feature recognition on acquired point clouds, image analysis through control points and algorithms to find centerline of the elements that could need to be repositioned. In the final part, a concept design for a new inner-support is presented, giving the possibility to avoid assembly inaccuracies. Future developments are presented as the prospect of additive manufacturing the support, firstly with a FDM prototype and then through SLM or similar technologies.

Keywords: 3D-reconstruction | Bronze statue restoration | Cultural heritage | Feature recognition | Virtual prototyping

Abstract: The research reported in this paper applies an explicit non-linear FEA solver to simulate the interaction between a clamp and a hyper-elastic material that aims to mimic the biological tissue of the colon. More in detail, the paper provides new results as a continuation of a previous works aimed at the evaluation of this solver to manage contact and dynamic loading on complex, multiple shapes. Results concern with the evaluation of the contact force during clamping, thus to the assessment of the force-feedback. The analysis is carried out on two geometries, using the hyper-elastic Mooney-Rivlin model for the mechanical behavior of the soft tissues. A pressure is applied on the colon to simulate the surgical clamp, which goes progressively in contact with tissue surface. To assess FEA criticality, and, then, its feasibility, the stress-strain and the contact force are analysed according to geometrical model and thickness variation, leaving the pressure constant. Doing so, their effect on the force-feedback can be foreseen, understanding their role on the accuracy of the final result.

Keywords: Computer assisted surgical planning | Finite element analysis | Segmentation | Soft tissues simulations

Abstract: Chronicles of sieges to castles or fortresses, using "machinae", can often be found in historical sources. Moreover, archaeological excavations of castles or fortresses has brought to light rocks or projectiles whose carving suggests a military usage. Nevertheless, chronicles and discoveries alone, are seldom enough to propose a faithful reconstruction of these machines. Therefore, the aim of this research is the development of methodologies for reconstructing virtual scenarios of sieges, starting from the scarce information available. In order to achieve it, a procedure for the virtual reconstruction of the siege machine has been set up, focusing on typology and dimensions of the machines, also investigating possible fire positions according to topography. The entire procedure has been developed using the siege of Cervara di Roma's Rocca as a case study. Late medieval chronicles (end of 13th Century) report the siege brought by the papal army in order to restore the jurisdiction on the Cervara's stronghold, following the insurrection of a group of vassals headed by a monk named Pelagio. The discovery, in the area of the Rocca, of a stone that could have been used as a projectile confirms what reported. The proposed methodology is composed of two parts. The first one is connected to the study of the "internal ballistics", to understand the performances and to build virtual models of siege machines. The second part is the study of the "external ballistics", then to the positioning and shooting ability of possible machines, analysing the topography of the area. In this paper, we present the feasibility of this methodology through the preliminary results achieved correlating internal and external ballistics.

Abstract: Ancient bronze statues mainly require material integrity assessment and restoration. Restoration may include also the update of the museum exhibition, defining new structural frames and fragment re-composition to preserve the statue and improve the interpretation of the original aspect. This paper proves how engineering methods (such as Finite Element Analysis, Computer Aided Design modelling, Reverse Engineering) may assist cultural heritage experts and restorers in these tasks. It presents the activities made together with the Museo Nazionale Romano and the Istituto Superiore per la Conservazione e il Restauro, on the so-called "Principe Ellenistico" (Hellenistic Prince). This bronze was found in pieces (body, left arm and right leg), at the end of 19th century during an excavation made in Rome. No visual or reference sources can say its origin and its final posture was defined by restorers at the end of the 19th century according to their hypothesis and studies. In the 20th century, a further restoration was made on the critical areas of the surface, together with some structural improvement of the inner frame. Nowadays, after a review of its position inside the Museum, new experimental and numerical analyses have been carried out to better understand surface weakness and correct left arm positioning.

Abstract: In this paper, we aim at providing results concerning the application of desktop systems for rapid prototyping of medical replicas that involve complex shapes, as, for example, folds of a colon. Medical replicas may assist preoperative planning or tutoring in surgery to better understand the interaction among pathology and organs. Major goals of the paper concern with guiding the digital design workflow of the replicas and understanding their final performance, according to the requirements asked by the medics (shape accuracy, capability of seeing both inner and outer details, and support and possible interfacing with other organs). In particular, after the analysis of these requirements, we apply digital design for colon replicas, adopting two desktop systems. The experimental results confirm that the proposed preprocessing strategy is able to conduct to the manufacturing of colon replicas divided in self-supporting segments, minimizing the supports during printing. This allows also to reach an acceptable level of final quality, according to the request of having a 3D presurgery overview of the problems. These replicas are compared through reverse engineering acquisitions made by a structured-light system, to assess the achieved shape and dimensional accuracy. Final results demonstrate that low-cost desktop systems, coupled with proper strategy of preprocessing, may have shape deviation in the range of ±1 mm, good for physical manipulations during medical diagnosis and explanation.

Abstract: Lattice materials can overcome the need of light and stiff structures in the aerospace industry. The wing leading edge is one of the most critical parts for both on-board subsystem and structure features: it must withstand to the aerodynamic loads and bird-strike, integrating also the anti-ice system functions. Nowadays, this part is made by different components bonded together such as external skin, internal passageways, and feeding tubes. In the present work, a single-piece multifunctional panel made by additive manufacturing will be developed. Optimal design and manufacturing are discussed according to technological constraints, aeronautical performances and sustainability.

Keywords: Additive manufacturing | DOE | Metamodeling | Pareto optimality | Response surface | Virtual protyping

Abstract: Finite Element Analysis (FEA) has gained an extensive application in the medical field, such as soft tissues simulations. In particular, colorectal simulations can be used to understand the interaction with the surrounding tissues, or with instruments used in surgical procedures. Although several works have been introduced considering small displacements, as a result of the forces exerted on adjacent tissues, FEA applied to colorectal surgical scenarios is still a challenge. Therefore, this work aims to provide a sensitivity analysis on three geometric models, taking in mind different bioengineering tasks. In this way, a set of simulations has been performed using three mechanical models named Linear Elastic, Hyper-Elastic with a Mooney-Rivlin material model, and Hyper-Elastic with a YEOH material model.

Keywords: Computer assisted surgical planning | Finite element analysis | Soft tissues simulation | Surface modeling

Abstract: Mesoscale geometric modeling of cellular materials is not strictly related only to tomography reconstruction, but it can be applied also in Finite Element Analysis: (a) to better understand load distribution at the interfaces; (b) to develop and calibrate material models; (c) for sensitivity analysis to different loads or shape parameters. This paper aims to examine some of the most applied techniques for geometric modeling of cellular materials at a mesoscale level discussing their advantages and disadvantages for Finite Element Analysis. Among them, two of the most applied techniques, the Voronoi approach and the reverse engineering reconstruction, are here applied to simulate the behavior of aluminum foams under compression. These applications compared to some experimental evidences confirm the capability of mesoscale analysis, highlighting possible enhancement of the geometric modeling techniques.

Keywords: Cellular materials | Finite Element Analysis | Representative Volume Element | Reverse Engineering | Voronoi Diagram

Abstract: This work presents Reverse Engineering and Computer Aided technologies to improve the inspection of injection moulded electro-mechanical parts. Through a strong integration and automation of these methods, tolerance analysis, acquisition tool-path optimization and data management are performed. The core of the procedure concerns the automation of the data measure originally developed through voxel-based segmentation. This paper discusses the overall framework and its integration made according to Smart Manufacturing requirements. The experimental set-up, now in operative conditions at ABB SACE, is composed of a laser scanner installed on a CMM machine able to measure components with lengths in the range of 5÷250 mm, (b) a tool path optimization procedure and (c) a data management both developed as CAD-based applications.

Keywords: Computer Aided Tolerancing &amp; Inspection | Feature Recognition | Injection Moulding | Path Planning | Product Data Management | Quality Inspection | Reverse Engineering | Segmentation

Abstract: Nowadays, the most updated CAE systems include structural optimization toolbox. This demonstrates that topological optimization is a mature technique, although it is not a well-established design practice. It can be applied to increase performance in lightweight design, but also to explore new topological arrangements. It is done through a proper definition of the problem domain, which means defining functional surfaces (interface surfaces with specific contact conditions), preliminary external lengths and geometrical conditions related to possible manufacturing constraints. In this sense, its applicability is possible for all kind of manufacturing, although, in Additive Manufacturing, its extreme solutions can be obtained. In this paper, we aim to present the general applicability of topological optimization in the design workflow together with a case study, exploited according to two design intents: the lightweight criterion and the conceptual definition of an enhanced topology. It demonstrates that this method may help to decrease the design efforts, which, especially in the case of additive manufacturing, can be reallocated for other kind of product optimization.

Keywords: Additive Manufacturing | Conceptual Design | Design Intent | Lightweight Design | Topological Optimization

Abstract: This paper presents the advancements of an automatic segmentation procedure based on the concept of Hierarchical Space Partitioning. It is aimed at tolerance inspection of electromechanical parts produced by injection moulding and acquired by laser scanning. After a general overview of the procedure, its application for recognising cylindrical surfaces is presented and discussed through a specific industrial test case.

Keywords: Computer aided tolerancing &amp; inspection | Hierarchical space partitioning | Injection moulding | Reverse engineering

Abstract: Foams are able to absorb energy and bear stress more uniformly and efficiently than the correspondent bulk materials. This makes them ideal candidates to increase the specific structure's absorption efficiency.Concerning their characterisation, there are still some open issues needing further investigations, such as the experimental analysis of their dynamic behaviour with alloy types, strain rates and foam density changes.This paper focuses on the above mentioned issues presenting the results of a dynamic characterisation by means of a direct tension-compression Hopkinson bar. Tests are carried out on AlSi7 alloy foam specimens obtained from a large ingot made by compact powder technology. The results are discussed mainly in terms of strength and energy absorption efficiency, considering the effects of strain rate and of the variation of foam density, due to the manufacturing process.

Keywords: Aluminium foams | Dynamic crushing | Hopkinson bar | Mechanical characterisation

Abstract: Several methods are available for making metal foams. They allow to tailor their mechanical, thermal, acoustic, and electrical properties for specific applications by varying the relative density as well as the cell size and morphology. Foams have a very heterogeneous structure so that their properties may show a large scatter. In this paper, an aluminum foam produced by means of foaming of powder compacts and another one prepared via the infiltration process were analyzed and compared. Image analysis has been used as a useful tool to determine size, morphology, and distribution of cells in both foams and to correlate cell morphology with the considered manufacturing process. The results highlighted that cell size and morphology are strictly dependent upon the manufacturing method. This paper shows how some standard 2D morphological indicators may be usefully adopted to characterize foams whose structure derives from the specific manufacturing process. © 2013 ASM International.

Keywords: aluminum foams | compact powder process | infiltration process | morphometric analysis

Abstract: In the aerospace sector, tolerance allocation and inspection of many components must provide not only for ease of manufacturing and cost reduction but also for reliability and safety requirements. Computer Aided Tolerancing and Inspection (CAT&I) methods based on Reverse Engineering techniques may enhance production quality assessment with significant reduction of the time-to-market. This paper presents an original reverse engineering methodology that is being developed to achieve the complete automation of the inspection process starting from the design requirements (dimensional and geometrical tolerances) as they generally appear in the component's official drawings. After a brief presentation of the proposed methodology and its possible implementation oriented to non-planar surface recognition, an aeronautical component made by beta-forging of Ti6Al4V Titanium Alloy powders is presented as test case. The discussion of the procedure allows to point out its benefits in terms of (a) more efficient management of the inspection process and data consolidation; (b) more thorough comprehension of the real component; and (c) a better understanding of possible feedbacks to be applied in design or manufacturing. Finally some remarks about the limits of the proposed methodology are shown and possible enhancements, that have been already planned to be applied, will be described. © 2014 IEEE.

Keywords: beta-forging | Computer Aided Tolerancing and Inspection | Reverse Engineering | Segmentation | Ti6Al4V Titanium Alloy powders

Abstract: ABSTRACT: This paper presents a point cloud segmentation based on a spatial multiresolution discretisation that is derived from hierarchical space partitioning. Through part type recognition it aims to simplify Computer Aided Tolerance Inspection of electromechanical components avoiding cloud-CAD model registration. A voxel structure subdivides the point cloud. Then, through a suitable surface partitioning, it is linked to component volumes by means of the morphological components of the binary image that is derived from voxel attributes (‘true state’ if points are included in a specific cluster or ‘false state’ if they are not). The proposed approach is then applied on a din-rail clip of a breaker, made by injection moulding. This case study points out the suitability of the approach on box-shaped components or with normal protrusions, and its limits concerning the assumptions of the implementation.

Keywords: computer aided tolerance inspection | reverse engineering | segmentation

Abstract: This paper shows the procedures needed to calibrate a numerical model intended for ductile damage estimation of bulk materials. For this purpose, an extensive experimental campaign has been carried out on three steels used for offshore/onshore pipe applications. Tests have been performed providing very different stress states: tensile and compressive uniaxial tests, multiaxial tensile tests on round notched bars, 3-point bend tests, again on notched geometries, and plane strain tensile tests on large grooved specimens. Based on the gathered results, a standard plasticity model has been tuned and then the damage model parameters have been identified for each investigated material. The chosen theoretical formulation can take into account all of the experimental evidence: hence, the numerical model represents a useful tool for finite element simulation of engineering problems where information concerning the materials ultimate resistance capability is needed. Moreover, the proposed calibration technique has general validity and can be used to tune other similar damage models. © 2013 The Author(s).

Keywords: constitutive stress-strain relations | Ductile damage estimation | mechanical testing | offshore/onshore pipelines | plasticity

Abstract: Computer-aided engineering methods are extensively applied to sheet metal forming integrated design. The adoption of a new class of materials, the advanced high strength steels, has increased the occurrence of springback, and consequently the request for tools oriented to springback reduction and optimization. This paper presents an approximated formulation to compute the springback field after stamping through the finite element analysis of the process. This can be found assuming that the residual field of nodal forces after stamping produces a springback shape referable to a linear combination of n modes of vibration of the nominal shape of the component. The aim of this formulation is not that of substituting the finite element analysis of the springback but rather to make use of the coefficients of the linear combination, so to define a global quality function for springback. In this way, Robust Design methods or other current optimization procedures to improve the stamping process as for structural defects (such wrinkling, necking and flatness) can be applied also for the reduction of springback. The meaning of these coefficients will be shown through three test cases and the consistency of the formulation will be discussed according to the number of modes of vibration included in the computation. © 2012 Springer-Verlag London Limited.

Keywords: Computer-aided engineering | Robust Design | Sheet metal forming | Springback

Abstract: Foams and porous materials with cellular structure have many interesting combinations of physical and mechanical properties coupled with low specific weight. By means of replication casting it is possible to manufacture foams from molten metal without direct foaming. A soluble salt is used as space holder, which is removed by leaching in water. This can be done successfully if the content of space holding fillers is so high that all the granules are interconnected. One of the main advantages of using the replication casting is a close control of pore sizes which is given by the distribution of particle sizes of the filler material. This contrasts with the pore size distribution of the materials foamed by other processes where a wider statistical distribution of pores is found. On the other hand, the maximum porosities that can be achieved using space holders are limited to values below 60%, whereas the other methods allow for porosities up to 98%. Temperature of the mould and infiltration pressure are critical process parameters: a typical problem encountered is the premature solidification of the melt, especially due to the high heat capacity of the salt. In this work foam properties such as cell shape, distribution and anisotropy and defect presence are investigated by using digital image processing technique. For this purpose replicated AlSi7Mg0.3 alloy foams are produced by infiltrating preforms of NaCl particles, varying the metal infiltration pressure and the mould preheating temperature. An original procedure based on image analysis has been set up to determine size, morphology and distribution of cells. The paper demonstrates that this methodology, coupled with microstructural analysis, is a useful tool for investigating the effects of process parameters on foam properties.

Keywords: Aluminium foams | Foam morphology | Image analysis | Replication casting | Watershed method

Abstract: The actual foam density affects its mechanical energy absorption capabilities. Making structural elements starting from the cutting of semi-finished items may produce uneven results due to the lack of homogeneity in the foam. The subject of this work is the study of AlSi7 metallic foams, the focus being on the evaluation of the effective density distribution throughout large ingots. This is the first step required to establish a correlation between manufacturing process parameters and mechanical properties. The results highlighted that the void density increases from the centre toward the ingot outer wall and that specimens coming from different regions of the ingot have a very different mechanical behaviour. This is probably due to the difficulty in controlling temperature gradients and cooling rates throughout big mould cavities during the production process. © 2012 Elsevier B.V.

Keywords: Aluminium alloy foams | Cellular materials | Mechanical characterisation

Abstract: Physical and mechanical properties of metallic foams derive from their micro- and macrostructure. Unfortunately these foams have a very heterogeneous structure so that their properties may show a large scatter. In this paper image analysis has been used to determine size, morphology and distribution of cells in three aluminium alloy foams produced by means of different manufacturing processes. The study highlighted that difficulties deriving from cell cavity coalescence can be overcame by using the assistedwatershed method. The morphometric analysis of cells showed that cell size, shape and distribution are strictly related to the manufacturing process. The proposed and analysed method appears to be a useful tool to correlate cell morphology with the manufacturing parameters and then to tailor foam properties to given applications. © 2012 Taylor & Francis Group.

Abstract: In cold rolling some surface defects, known as pits, are due to lubricant that, entrapped in the deep valleys of the surface roughness, is nearly incompressible and acts like an inclusion avoiding microcavity elimination. During the rolling process, when specific favorable conditions can be set up, the lubricant may be expelled by the microplasto-hydrodynamic lubrication (MPHL) mechanism and pits may be recovered. In this paper the Λ m parameter, index of the MPHL, is investigated together with the neutral point position to better understand the practical process recommendations for surface defect recovery. By means of finite element analysis of a Sendzimir'cold rolling process, the sensitivity of these objective functions are studied by means of a design of experiment analysis changing the major process variables like back tension, friction coefficient, reduction parameter, initial thickness, and roll diameter. © 2011 Springer-Verlag London Limited.

Keywords: Cold rolling | Finite element analysis | Microplastic hydrodynamic lubrication | Neutral point | Surface quality

Abstract: In finite element analysis of sheet metal forming the use of combined isotropic-kinematic hardening models is advisable to improve stamping simulation and springback prediction. This choice becomes compulsory to model recent materials such as high strength steels. Cyclic tests are strictly required to evaluate the parameters of these constitutive models. However, for sheet metal specimens, in case of simple axial tension-compression tests, buckling occurrence during compression represents a serious drawback. This is the reason why alternative set-ups have been devised. In this paper, two experimental arrangements (a cyclic laterally constrained tension-compression test and a three-point fully reversed bending test) are compared so as to point out the advantages and the disadvantages of their application in tuning the well-known Chaboche's hardening model. In particular, for tension-compression tests, a new clamping device was specifically designed to inhibit compressive instability. Four high strength steel grades were tested: two dual phases (DP), one transformation induced plasticity (TRIP) and one high strength low alloy material (HSLA). Then, the Chaboche's model was calibrated through inverse identification methods or by means of analytical expressions when possible. The proposed testing procedure proved to be successful in all investigated materials. The achieved constitutive parameters, obtained independently from the two experimental techniques, were found to be consistent. Their accuracy was also been assessed by applying the parameter set obtained from one test to simulate the other one, and vice versa. Clues on what method provides the better transferability are given. © 2012 American Society of Mechanical Engineers.

Keywords: Chaboche's model | cyclic plasticity | high strength steel | sheet metal forming | tension-compression test | three-point bend test

Abstract: Two different closed-cell aluminium foams, manufactured by compact powder technology starting from 7075 and 6061 alloys, were studied with the aim of investigating the effect of heat treatments on their axial crushing behaviour. By means of scanning electron microscopy/energy-dispersive spectroscopy analyses, the crushing response was investigated in an attempt to understand how heat treatments may improve the absorbing efficiency of crashboxes. © 2009 Acta Materialia Inc.

Keywords: Aluminium alloy | Aluminium foam | Crashworthy design | Heat treatment | Microstructure

Abstract: Optical Reverse Engineering systems are evermore used to check dimensional and shape conformity of manufactured components; their main advantage is the short acquisition time. Dedicated CAD software tools allow comparing the acquired data (clouds of points) with the 3D CAD model. Generally, they support the automatic global shape measurement; from the designer viewpoint this is not sufficient. The desired functional behavior of component is respected only when specific geometrical tolerances are verified. Our aim is the definition of methods to automate this last control process using Full of Information (FoI) CAD models. We define them as 3D model containing tolerance attributes and methods to check them. They allow comparing the toleranced features with the corresponding parts of point clouds. The present paper describes the approach and the developed method for datum identification usable for orientation and localization geometrical tolerances control. © 2008 CAD Solutions, LLC.

Keywords: Geometrical tolerances | Quality control | Reverse engineering

Abstract: Three different aluminium foams, manufactured by compact powder technology starting from 7075, 6061 and AlSi7 alloys were studied by performing microstructural and morphometric analyses, with the aim of explaining their different behaviour during axial crushing. Void distribution coupled with material microstructure justifies the behaviour of load-displacement curves obtained during axial crushing of the foams. The results show that 7075 alloy seems to be the material having the best behaviour during crushing, at least when the foam is removed of the external walls. Despite that outer skin presence coupled with the intrinsic brittle behaviour of this alloy may cause instability, if it is used to fill hollow components like crashboxes. During deformation process 6061 and AlSi7 alloys that are more ductile, give in and maintain contact adapting to the encasement deformation. © 2007 Elsevier B.V. All rights reserved.

Keywords: Aluminium alloy | Aluminium foam | Crashworthy design | Heat treatment | Microstructure

Abstract: This work studies how a nonlinear kinematic model aimed for cyclic plasticity could be put into effect and used within a FEM code. A correct modeling of cyclic elasto-plastic behavior can be exploited in low-cycle fatigue life investigation as well as in manufacturing problems related to springback prediction. The chosen formulation has been proposed by Chaboche, and it is implemented in most of the commercial codes used for nonlinear FEM simulations. At first, a procedure for the proper identification of unknown material model parameters has been put forward. This calibration, based on the data collected from experimental low-cycle fatigue tests, has been performed by means of an inverse method. Laboratory tests differ according to the type of material under investigation. A classification can be operated distinguishing between specimens obtained from bulk materials or from sheet metals. For the former, standard tension-compression tests have been performed, while for the latter, a dedicated testing equipment for three-point bend cyclic tests has been devised. Then, further experimental tests have been run to check model transferability: different strain per cycle amplitudes, asymmetric strain cycling and different stress triaxiality levels have been investigated. For each of these tests, experimental vs. FEM results have been analyzed to show the level of agreement that has been reached. © 2008 Springer Science+Business Media B.V.

Keywords: Cyclic plasticity | Inverse methods | Kinematic hardening | Parameter identification | Transferability tests

Abstract: A reliable prediction of ductile failure in metals is still a wide-open matter of research. Several models are available in the literature, ranging from empirical criteria, porosity-based models and continuum damage mechanics (CDM). One major issue is the accurate identification of parameters which describe material behavior. For some damage models, parameter identification is more or less straightforward, being possible to perform experiments for their evaluation. For the others, direct calibration from laboratory tests is not possible, so that the approach of inverse methods is required for a proper identification. In material model calibration, the inverse approach consists in a non-linear iterative fitting of a parameter-dependent load-displacement curve (coming from a FEM simulation) on the experimental specimen response. The test is usually a tensile test on a round-notched cylindrical bar. The present paper shows a novel inverse procedure aimed to estimate the material parameters of the Gurson-Tvergaard-Needleman (GTN) porosity-based plastic damage model by means of experimental data collected using image analysis. The use of digital image processing allows to substitute the load-displacement curve with other global quantities resulting from the measuring of specimen profile during loading. The advantage of this analysis is that more data are available for calibration thus allowing a greater level of confidence and accuracy in model parameter evaluation. © Springer Science+Business Media B.V. 2007.

Keywords: Damage mechanics | Image analysis | Inverse methods | Machine design | Parameter identification

Abstract: This paper presents a computer-aided design (CAD) module able to analyze different manufacturing configurations of tubes used in mechanical assemblies, such as exhaust system manifolds. It can be included in the knowledge-based expert system category and has been implemented into a CAD platform as a dedicated module able to take into account manufacturing requirements related to tube bending, hydroforming, and cutting. The expert's knowledge, in terms of set of rules and criteria, has been implemented by means of the automation tools of CATIAV5R10 according to the socalled methodological formal approach. The resulting module is able to join different tubes starting from their geometrical models, obtaining a set of manufacturing alternatives. Each of them is verified with respect to collisions with a bending machine and also in terms of hydroforming process feasibility. Only those solutions that satisfy these checks are accepted as feasible and ranked according to three evaluation criteria related to manufacturing cost and easiness. The system is completely automatic and able to analyze more than 100 different configurations in <10 min. The feasible solutions are saved as CAD model to allow FEA of hydroforming and other possible CAE activities. Unfeasible solutions are deleted but reported and documented in a log file. The feasible solution rank is given in a table and has been developed according to a multicriteria approach to make optimal solution detection easier. The proposed test case aims to show and discuss these capabilities. By this module, two or more components of the exhaust system manifold can be manufactured in one stroke as a single component, starting from the same pipe and next trimmed to obtain the desired final parts. This capability can be used to reduce scraps and improve cycle time of the manufac-turing process. Copyright © 2007 by ASME.

Keywords: CAE | Design to manufacturing | Knowledge based expert system | Tube bending | Tube hydroforming

Abstract: This paper is concerned with small strain measurement utilizing the numerical processing of digital images. The proposed method has its theoretical basis in digital signal analysis and, from a methodological point of view, it can be considered as an extension to digital images of the well-known white light speckle photography technique. That conventional method is based on the analysis of photographic plates that are exposed twice (before and after the specimen deformation) with the image of a random speckle pattern that has been previously printed on the test piece surface. The digital speckle correlation advantages consist of requiring a very simple specimen preparation and, mainly, of allowing the strain field computation just by numerical elaboration of the acquired images. In this paper, the theoretical basis of the technique and some valuable improvements to the known analogous methodologies are presented. Finally, test results for an application of digital speckle correlation are shown and advantages and disadvantages of the technique are elaborated. In addition, further developments in this area are discussed.

Keywords: Image processing | Speckle correlation | Speckle methods | Speckle photography | Strain analysis

Abstract: In the field of new stamping technologies, hydroforming represents one of the most attractive solution both to reach a better quality and reduce lead-times. This paper presents a study that is being carried out to assess an optimal hydroforming process for production of automotive panels. The major economical advantages are due to the need of only one dedicated shape-defining tool, this leads also to a more flexible production system. The research starts from the analysis of two different process arrangements: hydro-punch versus negative or positive die. Their numerical simulations (performed by LS-DYNA3D) are used to define the values of control factors (maximum pressure, blankholder force) and to highlight, in terms of shape and strain field accordance, the pros and cons of each solution. To assess the better arrangement an economical evaluation is carried out using a decision making approach. The discussion is based on press shop experience related to three different components: an exterior panel of a bus, a detail of bus luggage van and a bus roof. Copyright © 2000 Society of Automotive Engineers, Inc.