Abstract: The objective of this study was to develop a Computational Fluid Dynamics (CFD) 3D model for an industrial application, to investigate how surface roughness affected pressure drop and thermal performance in the ACEPACKTM DRIVE, a commercial SiC-based power module used in traction inverters, that features a pin-finned baseplate with cylindrical pin-fins. The surface roughness of the pin-fins was modelled by using a sand-grain model available in Ansys Fluent, which represents a novelty in the literature and can pave the way for the development of accurate and computationally efficient simulations. The CFD model exhibits an error from experimental data within the range 10%–22% when the flow rate varies from 2 l/min to 12 l/min (maximum error at 2 l/min), while the validation of the thermal behaviour was obtained with a maximum error of 2.5%. Subsequently, a parametric analysis was carried out, varying the flow rate of the coolant, in order to investigate the influence of pin-fins surface roughness on performance, by considering two possible design option featuring respectively a surface roughness equal to 1 μm and 6 μm. The results showed a reduction in pressure drop from 4% to 11% and a degradation of the thermal performance, less than the 2%, when the pin-fins roughness increases.

Keywords: CFD | Pin-fins | Power module | Surface roughness

Abstract: This paper presents a method to study the reliability behavior of the ACEPACKTM SMIT, which is a top side-cooled power module employing high-voltage silicon MOSFETs in a half bridge topology. The experimental test involves power cycling: this is an accelerated stress test, which allows monitoring a temperature-sensitive electric parameter to study the thermal behavior of the package. The efficiency of heat exchange between the module and the cooling plate surfaces is strongly influenced by the thermal interface material (TIM) used between them. TIM is designed to fill gaps and voids between two surfaces, in order to to increase the effective contact area and improve thermal conductivity at the interface. In this work, the thermal performance of two different TIMs, a thermal grease and a phase change material, will be analyzed. The aim of the paper is to provide an experimental approach for characterizing the reliability behavior of power modules, considering the thermal behavior when different TIMs are considered.

Keywords: Accelerated stress test | Power Module | Reliability | Thermal Interface Material | TIM

Abstract: The use of silicon carbide (SiC) in power semiconductor modules has led to higher power density, increased maximum junction temperature, high voltage application, and more compact devices, which require efficient cooling systems. This study was to investigate the influence of the surface roughness on the pressure drop of ACEPACKTM DRIVE, a commercial SiC-based power module for traction inverter. This power module has a cylindrical pin-finned baseplate that is mounted on a dedicated cooling device (water jacket) in which coolant media flows. The analysis aimed to characterize the pressure drop between the inlet and exhaust sections of the water jacket, with the objective of optimising the coolant flow for an efficient module cooling, avoiding both excessive resistance and insufficient flow. Confocal laser scanning microscope was used to measure roughness on two different pin-fins with the same geometric characteristics but different surface roughness. Pressure drop measurements were taken at different coolant temperatures and flow rates using a hydraulic test bench. Results indicate that the pressure drop of the higher roughness configuration is 13-19% smaller than the first one, depending on the flow rate and coolant temperature. The suggested reason is that this decrease is caused by a reduction in pressure drops due to concentrated losses associated with fluid flow separation.

Keywords: CLSM | Pin-Fins | Power module | sPressure drop | Roughness

Abstract: This paper presents an experimental thermographic analysis of a directly-cooled silicon-carbide based power module, designed for automotive traction applications. The aim of this activity is related to one of the reliability assessments executed on power MOSFETs arranged in this package, named active power cycle. In this framework, thermo-sensitive electrical parameters (TSEPs) are commonly used to estimate the junction temperature of power devices. In the paper, the TSEP related to the body diode voltage drop is compared with the results obtained by using a high frame-rate thermal camera. Moreover, the heat propagation inside the module during the heating phase is showed.

Abstract: In this paper, a liquid-To-liquid thermal shock test is performed on TO-247 packages. By employing liquid with a high heat transfer coefficient as an energy transfer medium, it becomes possible to quickly couple thermomechanical stresses at the module interface. The temperature jump is achieved by maintaining the hot chamber at 150°C and the cold one at-65°C, by immerging the samples in each chamber for 8 minutes. Using ANSYS Mechanical, a numerical model was developed to evaluate the lifetime of the TO-247 under thermal shock test. In addition, this model was also used to compare the lifetime of these packages when a temperature cycle is considered. Experimental results showed differences between cold and hot ramp rate. In more detail, the average ramp rate of the 4 samples in hot environment is about 90°C/s while in the cold one it is about 65°C/s. Difference between heating and cooling rate could be addressed to the temperature effect on fluid viscosity. The numerical results show that the thermal shock test (with a soak time of 5 minutes) anticipates crack initiation compared to the temperature cycle (with the same soak time), suggesting that the difference in accumulation of inelastic work due to fatigue lies in the different ramp rates. A further comparison between two thermal shock was done, decreasing the soak time to 2 minutes, which confirmed the previous results.

Abstract: This study developed a 3D Computational Fluid Dynamics (CFD) model to compute the thermal resistance of the SiC-based direct cooled ACEPACK™ DRIVE power module, by STMicroelectronics. The model was validated with respect to experimental data. The model investigate regarding the temperature dependency of materials thermal conductivity. In more detail, two different thermal conductivity values for solder layer were considered, showing their significant impact on thermal resistance. After adjusting for this parameter and taking into account the effects of temperature-dependent thermal conductivity of the active metal brazing (AMB) substrate, the model showed good accuracy with an error ranging from 0.5% to 1.6%. Furthermore, the CFD model was used to investigate the influence of the non-linear thermal conductivity of the AMB on thermal resistance, finding that it varies as a polynomial function of flow rates and increases linearly with dissipated power.

Abstract: Automotive market requires more and more power semiconductor modules for the realization of vehicle electrification. With respect to more conventional discrete packages, power modules have more complex manufacturing flow in which there are some process parameters that play a key role for a robust design, mechanical and hydraulic integration with the vehicle. Among these parameters, the flatness of the final product must be controlled in order to guarantee the mounting of power modules on cooling system and the proper working of thermal management. This paper would introduce the technology of liquid cooling solution for electrified vehicles’ power module, pointing out the importance of power module flatness. Then, it is proposed an experimental methodology to analyze the warpage behaviour during power at the different process steps and at the end of power module manufacturing. Measurements confirm that flatness is within admitted tolerance (200 μ m), highlighting the ceramic soldering process as the most critical for warpage modification.

Keywords: Design | Flatness | Manufacturing | Power module | Tolerances

Abstract: Transfer molded modules (TMMs) are becoming more and more diffused in semiconductor industries for several automotive applications. Epoxy molding compounds are used as plastic encapsulants for TMMs thanks to their adhesion, hygroscopic ruggedness and reliability improvement in active cycle conditions. However, a numeric quantification of adhesion is of paramount importance to build up a methodology to compare different resins. The target of the activity is the characterization of the adhesion strength and mode-mixity angle for copper-resin system. Four point bending experiment and numeric model based on fracture mechanics are employed for this purpose.

Keywords: Copper | Ductile fracture | Epoxy resins | Fracture mechanics | Resins | Semiconductor device manufacture

Abstract: This work presents an integrated experimental–numerical method to characterize, model, and experimentally study the properties of transfer molded power modules, considering two different thermal interface materials (TIMs). More specifically, a thermal grease and a phase change material are considered. The aim is to select the most reliable solution by making analytical characterization and power cycling tests on the modules equipped with the two kinds of TIMs. Then, further reliability study is accomplished, in order to estimate the lifetime of the power module equipped with the best TIM, that is the phase change one. Finally, a finite-element numerical model is developed and correlated with experimental data.

Keywords: Power cycle | Power packages | Thermal interface material | Thermal simulation

Abstract: The hybrid and battery electric vehicle market is heavily increasing the demand for semiconductor power modules. The manufacturing of such products is more complex than discrete devices. Some parameters, such as module deformation (warpage), play a major role. Power modules have to comply with customer Geometric Dimensioning & Tolerancing (GD&T) targets in order to avoid coolant leakage during operation and to guarantee mechanical compatibility with the driving board. Compliance with an appropriate flatness tolerance reduces rejects during manufacturing processes such as ultrasonic welding, and the consequent impact on reliability. Due to these requirements, there is a need to implement dedicated countermeasures during manufacturing flows and to develop the proper methodologies to monitor flatness tolerances. Appropriate component selection at the design stage also limits flatness through the prediction of deformations during assembly flows using finite element model. This activity outlines the manufacturing flow for a direct cooled semiconductor power module and presents a method for product optimization in terms of flatness tolerance using a dedicated finite element model that calculates the warpage deformation induced by baseplate soldering and different ceramic substrate layouts. Furthermore, we describe experimental methodologies for measuring power module flatness and straightness across the manufacturing phases. Dedicated experiments were conducted for methodological and design validation.

Keywords: finite element analysis | flatness | Power module | straightness | tolerance

Abstract: Power modules development is becoming more and more important for switching applications, to improve electric and reliability performances. This paper presents an experimental-numerical method to characterize the reliability behavior of ACEPACKTM SMIT package, a top side-cooled module designed with a half bridge topology, which employs high-voltage silicon MOSFETs. The experimental test involves power cycling to study the reliability and thermal behavior. Then, a finite-element based model is developed to simulate test conditions, to calculate temperature behavior inside the package.

Abstract: The use of molding compound as encapsulant is nowadays increasing in semiconductor power module applications. The adhesion of package interfaces between copper components and molding compound is one of the key aspect for an improved durability. The presented activity proposes the fracture toughness characterization of copper–resin interface in a power semiconductor package due to different experimental tests and the cohesive zone method to describe interfacial fracture. Double Cantilever Beam (DCB) and Four Point Bending (FPB) tests have been executed on dedicated bi-material coupons. The scope of these trials has been to enhance two different propagation modes based on different ratio between mode-I (opening) and mode-II (sliding) according to a mixed-mode approach. Strain energy release rate (SERR) and mode-mixity have been estimated by a finite element analysis based on the virtual crack closure technique (VCCT) and the crack surface displacement method (CSD). The information about fracture toughness at two different mode mixity have been considered to predict the SERR for every arbitrary mode mixity. Finally, dedicated finite element models based on cohesive elements have been developed and calibrated considering the fracture toughness experimental values and the measured force–displacements behavior during the two considered tests. Dedicated physical analyses have been carried out to validate the proposed method.

Keywords: Cohesive zone method | Finite element analysis | Fracture toughness | Interface | Power semiconductor package

Abstract: The massive development of Hybrid and Electrical Vehicles is strongly impacting the semiconductor industry demanding for highly reliable Power Electronic components. These challenges mainly originate from Silicon Carbide MOSFET’s superior properties allowing high power, high temperature capability, fast switching transients and high electric field operations. All these features can be obtained in a significant reduced chip area. In order to benefit from the disrupting advantages of these wide band gap semiconductor based power devices, a strong focus on silver sintering, as one of the most promising die attach technologies, is needed to withstand these challenging requirements. The aim of this work is to develop an integrated methodology, numerical and experimental, to assess the Ag sintering die attach process for a SiC power MOSFET. Different process parameters have been benchmarked by means of physical analyses, performed at time zero and also after liquid-to-liquid thermal shock aging test. The sintering flakes densification process has been reproduced by Finite Element Analysis and the obtained morphological texture has been used for extracting the mechanical properties of the layer as a function of the thermo-compression process itself. A simulation method, based on the evaluation of the inelastic strain accounted per cycle has been used for matching the experimental results according to an aging model. Furthermore, it has been predicted the silver sintering performances considering an active temperature cycle. The proposed methodology has supported the optimization of silver sintering parameters and has calculated the reliability performances of the silver sintering joint due to costumer-like active temperature cycle. Negligible sintering degradation has been carried out with a predicted number of cycles over two millions, suggesting die attach failure is not a relevant reliability bottleneck.

Keywords: Active temperature cycle | Reliability | Silicon carbide | Silver sintering | Simulation

Abstract: One of the main bottleneck for power semiconductor durability is the solder joint reliability. A proper design of the interconnections between silicon chip and printed control board is needed to fulfill the strict industrial and automotive requirements. Considering that solders are alloys with melting temperature lower than 450∘C, high-temperature package processes and costumer profile condition enhances the visco-plastic solder degradation, affecting the joint dimensional tolerances and reliability. The mechanical characterization of solder compounds and processes results fundamental to achieve reliability and geometric dimensioning and tolerancing targets. The presented work proposes an analytical-experimental methodology to characterize the mechanical constitutive equation of a specific solder compound widely used in semiconductor industries that is SnAgCu. Visco-plastic solder behavior with respect to environment temperature is experimental detected employing different uniaxial tensile tests considering some scenarios in terms of strain rate and temperature conditions. These outcomes are numerically post-processed to find out the Anand parameters of the analyzed solder according.

Keywords: Anand model | Material characterization | Solder compound | Visco-plasticity

Abstract: The use of molding compound as encapsulating material is nowadays increasing in semiconductor industry. Such component guarantees excellent thermal and reliability performances than the current silicone-based gel, enabling higher working temperature for semiconductor device and mitigating the solder joint reliability bottleneck. The adhesion of package interfaces between copper components and molding compound is one of the key aspect for optimized durability. Dedicated experiments and theoretical framework based on fracture mechanic are needed for this purpose. The presented activity proposes the fracture toughness characterization of copper-resin interface in a power semiconductor package. Double Cantilever Beam (DCB) test has been executed on dedicated bimaterial coupon with an initial crack at interface. The aim of this test has been to enhance the fracture propagation mode-I (opening). Strain energy release rate (SERR) and mode-mixity have been estimated from this experiment developing a finite element analysis that is able to predict the crack length during the experimental DCB trials and to predict the energy release rate by virtual crack closure technique (VCCT). Mode-mixity has been estimated collecting displacements near the crack tip by crack surface displacement method (CSD). The proposed methodology for fracture toughness characterization represents a strong pillar to predict fracture behavior due to any load conditions and it is needed to describe interface adhesion by cohesive zone method (CZM).

Keywords: Finite element analysis | Fracture | Interfacial delamination | Power electronics | Virtual crack closure technique

Abstract: This paper proposes an experimental method devoted at characterizing the maximum continuous drain-source current sustainable by a power semiconductor device. This information, strictly related to thermal limit of the package, is being more and more important, especially for automotive applications, where the robustness must be assured, in terms of reliability. More specifically, usually it is demanded a high value of current which the device must be handled. The test vehicle used in this work is the low-voltage LFPAK package, based on a silicon MOSFET. Moreover, a finite element based model is developed in order to numerically reproduce the experiment: in this way, it is possible to study the system in a more detailed manner, and changes in device's and cooling system's designs can be quickly evaluated.

Keywords: Electric measurements | Finite element analysis | Power packages | Thermal characterization

Abstract: ilicon carbide (SiC)-based power modules in automotive applications are becoming more and more important in the framework of battery and hybrid vehicles. Consequently, the reliability concerns related to these products must be carefully assessed, considering the harsh environment of automotive applications. The aim of this work is to give some insights into the reliability assessments during the design stage of SiC modules devoted to traction applications, considering different aspects such as power cycle, thermal characterization, and solder joint reliability.

Keywords: Automobiles | Reliability

Abstract: Structural mechanics and mechanical reliability issues are becoming more and more challenging in the semiconductor industry due to the continuous trend of the device dimensional shrinkage and simultaneous increased operative temperature and power density. As main consequence of the downsizing and more aggressive operative conditions, the mechanical robustness assessment is now having a central role in the device engineering and assessment phase. The risk of mechanical crack in the brittle oxide layers, which are embedded in pad stacks, increases during the device manufacturing processes such as the electrical wafer testing and during wire bonding. This risk increases with the presence of intrinsic mechanical stress in individual layers resulting from the metal grain growth mechanisms, the stack layers’ interfacial mismatches in coefficients of thermal expansion and the temperature stress induced by doping diffusion and film deposition. The current trend of innovation in the electronic industry is going over the semiconductor material itself and it is now impacting the improvement of the Back-End of Line. Key actors are becoming the interactions between the semiconductor die and the device packaging such as adhesion layers, barriers and metal stacks. In the present work, different pad structures have been structurally analyzed and benchmarked. The experimental characterization of the pad structures has been done through a flat punch nano-indentation to investigate on the mechanical strength and the crack propagation. The considered mechanical load reproduces the vertical impact force applied during wire bonding process to create the bond-pad electrical interconnection. The obtained testing results have been compared to finite element models to analyze the stress distribution through the different layers’ stacks. Scope of this work is to demonstrate the validity of the proposed integrated numerical/experimental methodology, showing the impact of the metal connections layouts by the analysis of the stress notch factors and crack propagation behaviour.

Keywords: finite element | nanoindentation | Pad | stress analysis

Abstract: New technological and packaging solutions are more and more being employed for power semiconductor switches in an automotive environment, especially the SiC-and GaN-based ones. In this framework, new front-end and back-end solutions have been developed, and many more are in the design stage. New and more integrated power devices are useful to guarantee the performances in electric vehicles, in terms of thermal management, size reduction, and low power losses. In this paper, a GaN-based system in package solution is simulated to assess the structure temperature submitted to a Joule heating power loss. The monolithic package solution involves a half-bridge topology, as well as a driver logic. A novel integrated electromagnetic and thermal method, based on finite element simulations, is proposed in this work. More specifically, dynamic electric power losses of the copper interconnections are computed in the first simulation stage, by an electromagnetic model. In the second stage, the obtained losses’ geometrical map is imported in the finite element thermal simulation, and it is considered as the input. Hence, the temperature distribution of the package’s copper traces is computed. The simulation model verifies the proper design of copper traces. The obtained temperature swing avoids any thermal-related reliability bottleneck.

Keywords: Automotive | Electromagnetic simulation | Finite element simulation | Gallium nitride | Half-bridge | Integrated package | Power devices | Thermal simulation

Abstract: The increasing demand in automotive markets is leading the semiconductor industries to develop high-performance and highly reliable power devices. Silicon carbide MOSFET chips are replacing silicon-based solutions through their improved electric and thermal capabilities. In order to support the development of these novel semiconductors, packaging technologies are evolving to provide enough reliable products. Silver sintering is one of the most promising technologies for die attach. Due to their superior reliability properties with respect to conventional soft solder compounds, dedicated reliability flow and physical analyses should be designed and employed for sintering process optimization and durability assessment. This paper proposes an experimental methodology to optimize the pressure value applied during the silver sintering manufacturing of a silicon carbide power MOSFET molded package. The evaluation of the best pressure value is based on scanning electron microscopy performed after a liquid-to-liquid thermal shock reliability test. Furthermore, the sintering layer degradation is monitored during durability stress by scanning the acoustic microscopy and electric measurement of a temperature sensitive electric parameter. Moreover, mechanical elastoplastic behavior is characterized by uniaxial tensile test for a bulk sample and finite element analysis is developed to predict the mechanical behavior as a function of void fraction inside sintering layer.

Keywords: Finite element analysis | Mechanical characterization | Physical analyses | Reliability | Silver sintering

Abstract: Electrochemical deposited (ECD) thick film copper on silicon substrate is one of the most challenging technological brick for semiconductor industry representing a relevant improvement from the state of art because of its excellent electrical and thermal conductivity compared with traditional materials, such as aluminum. The main technological factor that makes challenging the industrial implementation of thick copper layer is the severe wafer warpage induced by Cu annealing process, which negatively impacts the wafer manufacturability. The aim of presented work is the understanding of warpage variation during annealing process of ECD thick (20 µm) copper layer. Warpage is experimentally characterized at different temperature by means of Phase-Shift Moiré principle, according to different annealing profiles. Physical analysis is employed to correlated the macroscopic warpage behavior with microstructure modification. A linear Finite Element Model (FEM) is developed to predict the geometrically stress-curvature relation, comparing results with analytical models.

Keywords: ECD | FEM | Phase-Shift Moiré | Semiconductor | Warpage

Abstract: Nowadays, solder reliability in new power electronic packages is an important research topic. Therefore, it is of paramount importance to properly understand and model the material behaviour and to develop a calculation model to predict reliability performances. This work presents a thermo-mechanical analysis of different solder layers for a low voltage discrete package. The solder joint reliability between package and PCB is also considered in the simulation. This modelling activity is possible by employing the Anand visco-plastic model and by means of a finite element model implemented in COMSOL. The number of cycles to failure can be subsequently computed, with the Darveaux method, for fatigue life estimation purpose.

Abstract: Traditionally, duplicating handmade artefacts was done primarily by moulds. To obtain multiples of the casts, the artisan laid out a layer of clay over the mould and pressed on it strongly to make sure of thorough contact. The moulds found by excavation show wear due to compression and deterioration over time. They often disintegrate and are unusable. Consequently, understanding and studying the images they contain is only possible when the moulds are re-useable for casts which, to date, are carried out in restoration laboratories by traditional techniques. It should be noted that apart from the casts’ shrinking, moulds are also subject to altered sizes and morphologies after extraction from the archetype and therefore at the end of the production line the cast image is all the more blurred due to a loss of detail. This study describes a multidisciplinary approach applied to two clay moulds from classical antiquity that differ in size and shape, and the casts they produce using traditional techniques. Using Reverse Engineering (RE) by 3D laser scanning, a computer-based method was applied to study their morphometric relationship only obtainable in a virtual environment without compromising the integrity of the physical models. Furthermore, the digitalised moulds have provided virtual casts without significant size alterations for the aims of this work, making them ‘ideal’ casts. These last casts were then converted by Rapid Prototyping (RP) into physical prototypes which have negligible geometric errors for making multiple replicas for educational or exhibition purposes. In archaeology, this method offers researchers the opportunity to study and acquire morphological data which the moulds themselves cannot, nor can their casts. So, it is possible to go back in time to images which match their archetypes even without their casts. More detailed knowledge about the form of an art object is important for its study, conservation and how it was produced. So, ancient clay moulds are studied particularly in investigating methods of mass production, their social value and the degree of specialisation of those ancient societies.

Keywords: 3D laser scanning | 3D technology in archaeology | Ancient mould | Cultural heritage survey | Morphometric analysis | Virtual model

Abstract: The presented work investigates about the deformation of semiconductor device induced by electrochemical deposited thick copper films. It enhances thermal and electric performances allowing to use copper interconnections without formations of intermetallic layers at the interfaces with consequent reliability improvement. Nevertheless, the induced deformation strongly affects manufacturability, criticizing the integration between different process steps. Experiment based on phase-shift Moiré principle has been performed to better understand the relation between warpage and temperature. Finite element model has been developed to reproduce the phenomenon in order to address the design and the process integration optimizing workability, electrical performances and reliability.

Keywords: Finite element model | Manufacturability | Power electronics | Process integration | Warpage

Abstract: Hybrid and full electric automotive market is strongly increasing the demand for power semiconductor modules. With respect to discrete packages, manufacturing of power modules is more complex and new process parameter, such as module deformation (warpage), assumes a key role for a robust design and to guarantee reliable application. The aim of this paper is to study the warpage behaviour during power module assembly flow by means of dedicated warpage measurement at different process steps. Once highlighted the most impacting process for warpage, a finite element model has been developed to reproduce phenomenology, predicting the induced deformation.

Keywords: Finite element modeling | Manufacturability | Planarity | Power module | Warpage measurement

Abstract: The valve train plays a major role in the performance of internal combustion engines by controlling the combustion process and it is therefore one of the key aspects for increasing the efficiency of combustion engines. Considering the dynamics, the spring force must be high enough to reliably close the valve preventing from seating bouncing due to surge modes after the valve closure. On the other side, the spring force should be kept as low as possible in order to reduce the engine friction losses and consequently the fuel consumption. In the high-performance engines, the valve springs have to be designed and optimized for sustaining higher stresses with compact dimensions leading to critical material and manufacturing processes. This requires a reduction of moving masses and a strong focus on design and process optimization of the coil springs for reducing the mechanical load and the friction losses at low engine speed. At the same time, valve train should be reliable at high engine speed. The calculation of stresses and contact forces for moving parts under dynamic load is essential for durability analysis. A method to calculate the contact of moving masses is described and proposed to justify valve motions experimental results. To fully understand the failure mechanism of test bed reliability trials, the dynamic stresses have been calculated modeling the real springs’ shape. The contact forces have been reproduced considering the coil clash effects and the dynamic behavior of the flexible spring.

Keywords: Coil clash | FEM | Multibody | Valve springs | Valve train

Abstract: Electrochemical deposited (ECD) thick film copper on silicon substrate is one of the most challenging technological brick for semiconductor industry representing a relevant improvement from the state of art because of its excellent electrical and thermal conductivity compared with traditional compound such as aluminum. The main technological factor that makes challenging the industrial implementation of thick copper layer is the severe wafer warpage induced by Cu annealing process, which negatively impacts the wafer manufacturability. The aim of presented work is the understanding of warpage variation during annealing process of ECD thick (~20 µm) copper layer. Warpage has been experimental characterized at different temperature by means of Phase-Shift Moiré principle, according to different annealing profiles. A linear Finite Element Model (FEM) has been developed to predict the geometrically stress-curvature relation, comparing results with analytical models.

Keywords: ECD | FEM | Phase-Shift Moiré | Semiconductor | Warpage

Abstract: Semiconductor power modules are the key hardware components of a traction inverter. It drives motor speed and torque, managing the energy exchange from battery to motor and viceversa. The increasing demand for electric and hybrid vehicle requests high performance power modules. Power semiconductor devices based on wide band gap compound, like silicon carbide (SiC), have excellent electrical properties in terms of on-state resistance, stray inductance and performance at high commutation frequency. One of the most promising solution is silicon carbide MOSFET power module in which each switch is made by several different dies placed in parallel. Embedded direct cooling system and novel materials with high conductivity (e.g., active metal brazed substrates) can be considered to enhance thermal performance. A robust method is needed to characterize and to predict power module temperature behavior considering the importance of the thermal performance to improve reliability and to optimize module weight and dimensions. According to several parallel dies inside each switch, classic method based on temperature electric sensitive parameter (TSEP) shall be validated with direct measurement. In this framework, it has been reported the thermal characterization of a power module for a traction inverter based on eight silicon carbide MOSFETs for each switch. Both TSEP and infrared measurements have been employed. Thermal behavior has been numerically reproduced, creating a simplified equivalent network and developing a predictive model by finite element method (FEM).

Keywords: numerical model | Power modules | SiC MOSFET | thermal measurements

Abstract: Belt drives are commonly used in various types of transmissions to link two or more rotating shafts. In order to transmit the motion, an effective grip on the pulley has to be set by imposing a pre-load on the belt. Moreover, the dynamics of the system is strongly affected not only by the geometrical and inertial properties but also by the imposed belt tension force as a functional parameter affecting the vibration characteristics. In the present work, it is presented an integrated methodology, experimental and numerical, to determine the dynamic behaviour of a water pump drive in a high-performance internal combustion engine.

Keywords: Belt | Internal combustion engine | Multibody model | Natural frequency | Vibration modes | Water pump transmission drive

Abstract: Solder reliability is a key aspect for the packaging of low voltage power semiconductor device. The interconnections among package components, e.g. the silicon chip and copper leadframe, and between package itself and the external printed control board (PCB) should be properly designed to ensure the automotive durability requirements. In this framework, the proposed paper introduces an experimental-numeric characterization flow with the purpose to analyze solder visco-plasticity and fatigue during passive temperature cycle. The presented methodology has included solder mechanical characterization aimed to determine the parameters of Anand model which reproduces the solder visco-plastic behavior and the mechanical properties' temperature dependency. Finite element model has been employed to calculate the inelastic work which solder dissipates during each temperature cycle. Simulation results serve as input to predict solder lifetime according to an energetic method. Moreover, failure analyses have been performed to assess the failure mechanism and to check model correlation in terms of number of cycles to failure forecast.

Keywords: finite element model | material characterization | power semiconductor package | Reliability

Abstract: This work has investigated the impact of crystallographic structure on SnAgCu (SAC) solder reliability at print board circuit (PCB) level. A detailed reliability analysis has been performed on packages with different solder thickness. The correlation between experiments and Finite Element Model results explains how NiAu metallization and the reduction of solder thickness improve the solder joint reliability performances.

Abstract: Innovation on semiconductors technology requires enhancements of all actors like adhesion layers, barriers and metal stacks, beyond of semiconductor materials themselves. In general, metallic layers influence the whole die performances. The composition and the layout of these metal layers are fundamental for the signal transmission from the frame to the die and vice versa, and therefore their improvement contributes to the die development in terms of performances and reliability. In the present work, two pad structures have been benchmarked and analyzed under the structural strength standpoint. The experimental comparison among the different pads has been done through a flat punch nanoindentation to highlight the material strength and the crack propagation phenomena. Testing results have been compared to finite element models to analyze the stress through the different layers. The findings of the work demonstrate the validity of the methodology adopted and show the importance of the metallic connections layouts for the stress concentration and crack formation analysis.

Abstract: The presented analysis has been aimed to evaluate the impact of die solder and sintering solution for automotive power modules in terms of thermal behavior. First, dedicated temperature measurements have been performed to evaluate the module thermal impedance in the two cases. Then, a lumped equivalent networks has been calculated, by means of a dedicated numeric, and finally function structures have been extracted.

Abstract: The aim of this study was to confirm the identities of numerous portraits attributed to the composer Vincenzo Bellini by using 3D-to-2D projection. This study also followed on from earlier research on three death masks of Bellini, the results of which had shown that the wax mask in Catania's Bellini museum best represented Bellini's face compared to the other two. This study used the aforementioned 3D wax death mask obtained through Reverse Engineering as a reference for a morphometric comparison with 14 other portraits. For each portrait, the linear 3D-to-2D transformation M was found which minimized the distance between the 2D landmarks in the picture and the projected landmarks on the 3D mask. This normalized the distances considering the scale of the portrait and the final dissimilarity score with the mask. In particular, the analytical results were able to identify two portraits which particularly resembled the 3D death mask providing future researchers with the chance to carry out historical-artistic evaluations. We were also able to develop a new tool – Image Mark Pro - to easily annotate 2D images by introducing landmark locations. Since it was so reliable for manually annotating landmarks, we decided to make it publicly available for future research.

Keywords: 3D death mask | 3D-2D comparison | Face recognition | Landmarks projection

Abstract: The massive development of Hybrid and Electrical Vehicles (HEV) is strongly impacting the semiconductor industry demanding for highly reliable Power Electronic components. Within the engine compartment installation space is of major concern, therefore small size and high integration level of the modules are needed. Conventionally devices are typically soldered to ceramics substrates that are vacuum soldered to water-cooled base plates. The known reliability limitations of traditional solder joints are significantly limiting the power density increase, limiting the maximum operative temperature and representing a strong constrain for using high performances devices such as wide bandgap compound like Silicon Carbide (SiC). Silver sintering today has started to replace the solder joint from chips to carrier substrates, leaving one major reliability bottleneck. Combining properly temperature, time and pressure, a strong, highly electrically and thermally conductive bond is formed. The aim of this work is to develop an integrated methodology, numerical and experimental, to assess the Ag sintering die attach process for a SiC power MOSFET. Different process parameters have been benchmarked by means of physical analyses, performed at time zero and also after liquid-to-liquid thermal shock aging test. The sintering flakes densification process has been reproduced by Finite Element Analysis and the obtained morphological texture has been used for extracting the mechanical properties of the layer as a function of the thermo-compression process itself. A simulation method, based on the evaluation of the inelastic strain accounted per cycle has been used for matching the experimental results according to an aging model.

Keywords: Die attach | Finite Element Model | Reliability | Silicon Carbide | Thermal shocks

Abstract: In the present work it is shown how stress engineering can be used in semiconductor industry to improve Power MOSFET transistor’s performance beyond simple geometrical downscaling. The aim of this paper is to present an integrated methodology, coupling modelling and experimental results, focused on the structural optimization of a power device by means of final passivation mechanical stress tuning. The proposed approach is based on a Finite Element Model that describes and predicts the mechanical strain of a singulated power device (MOSFET) validated by the correlation with interferometric experimental warpage measurements (Topography and Deformation Measurements). Scope of the activity is to engineer Power Devices with reduced intrinsic stresses in order to optimize the reliability performances. Controlled stress into a single semiconductor crystal oriented substrate can be managed at manufacturing level by several methods, including the introduction of a layer on the top of the substrate or around the gate region. From the knowledge of the mechanical boundaries, as a function of temperature, it is possible to predict the stress conditions impacting on device fabrication and on reliability performances. Moreover, according to the piezoresistive model, it has been evaluated the electrical characteristics (on-resistance) in the operative working condition range. According to the proposed approach an optimized passivation layer solution has been proposed, simulated by Finite Element model and validated by experiments.

Keywords: FEM | Moiré topography | Reliability | Silicon MOSFET | Warpage

Abstract: The interactive design for industrial applications is today carried out through methods and tools, with different level of accuracy and simulation times. Consequently, the time necessary for virtual prototyping and analysis phases are often long and may be definitely reduced by means of optimization of tools and methodologies. Compliant mechanisms are increasingly used in the industrial field and the design methods are the subject of several studies, to improve their performance and reliability. This paper provides the reader with reliable numerical expressions to describe flexural beams with large deflections in case of combined end loads and without inflection points. Most of the numerical expressions describing beam deflection already existing in the literature are based on elliptic integrals that take into account strict limitations on the maximum slope angle. Here, we go beyond these limitations at the same time trying to give an order to the most relevant formulations used for determining large deflections of beams subject to combined tip loads. The proposed method provides the same results of the comprehensive elliptic integral solution described in a recent study.

Keywords: Compliant mechanisms | Flexural beam | Large deflection

Abstract: Although the CAD parameters allow to update easily the geometrical model, the numerical models updating into Finite Elements (FE) software with different mesh result to be often heavy, due to the necessity both to create new mesh and to make usually time consuming and complex CAE calculations for updating the loading conditions. The aim of the present research is to devise a reliable methodology and at the same time to reduce computational burden in the shape optimization studies of mechanical components. In particular, an integrated Multibody (MB) and Mesh-Morphing (MM) approach was developed to perform shape optimization, in order to reduce maximum tensions. Using the RBF Morph ACT Extension plugin implemented in the commercial solver FEM ANSYS® Mechanical vers. 18.2 along with the commercial MB software MSC ADAMS® vers. 2017, shape optimizations can be obtained in a very short time, by acting directly at the mesh so updating node positions and mesh elements geometry without bringing different geometrical models of the component into the FE environment. To validate the methodology, a crankshaft for a high performance Internal Combustion Engine (I.C.E.) was chosen, as case study, to optimize the fillet zones between web and pin.

Keywords: Crankshaft | FEA | Fillet zones | Multibody | Stress analysis

Abstract: In the present work a novel rear suspension for motorcycles, able to achieve the required progressiveness in terms of rigidity by using a constant-stiffness spring and an innovative compact mechanism, is studied. The key component is an eccentric system inserted in the shock absorber head. As reference, the rear suspension of the Ducati Multistrada MY 2010, characterized by the use of a variable-stiffness spring, is analyzed. The aim of the paper is to prove that the novel proposed solution can obtain a response, in terms of wheel load, similar to that of the reference system. At first, a mathematical model to simulate the kinematics of the novel suspension is presented. This model is able to evaluate the influence of geometric dimensions of the components, checking successfully the ability to reproduce the behavior of the original suspension. After the preliminary design, the kinetostatic model is included within an optimization algorithm ad-hoc created to obtain the optimum dimensions of each component. In order to obtain the inertial parameters, two 3D models of both the suspensions are created. Finally, two multibody models of the two suspensions are implemented in Adams environment in order to evaluate their dynamic behaviour. Results confirm the goodness of the novel solution being comparable to the reference one in terms of dynamic response during the simulation of a typical experimental test performed in Ducati.

Keywords: Constant stiffness spring | Eccentric mechanism | Integrated simulation | Motorcycle rear suspension | Multibody dynamics

Abstract: In the present work, by means of an integrated approach, a new rear suspension for motorcycles, able to achieve the required progressiveness in terms of rigidity by using a constant-stiffness spring and a compact mechanism, has been studied. The key component is an eccentric system inserted in the shock absorber head. As reference, we analyzed the rear suspension of the Ducati Multistrada MY 2010, characterized by the use of a variable-stiffness spring. The aim of the paper is to prove that the new proposed solution can obtain a response, in terms of load to the wheel, similar to that of the actual system. At first, a mathematical model to simulate the kinematics of the new suspension is presented. This model is able to evaluate the influence of geometric dimensions of the components, checking successfully the ability to reproduce the behavior of the original suspension. After the preliminary design, the kinematic and static models are included within an optimization algorithm ad-hoc created to calculate the exact dimensions of each component. Two Matlab/Simulink® lumped mass models, respectively referred to the novel and reference suspension, are used to compare the dynamic responses during the travelling of a particular road profile used in Ducati’s experimental tests. Finally, an accurate modeling of the components, considering also the production processes to be used for their creation, is provided.

Keywords: Dynamics | Integrated simulation | Motorcycle rear suspension

Abstract: This work describes an integrated method of 3D modelling algorithms with a modal approach in a multibody environment which provides a slimmer and more efficient simulation of flexible component contacts realistically reproducing system impacts and vibrations. A non-linear numerical model of the impulse contact forces based on the continuity approach of Lankarani and Nikravesh is developed. The model developed can evaluate deformation energy taking into account the material's characteristics, surface geometries and the velocity variations of the bodies in contact. ADAMS®-type modelling is applied to the sliding contacts of the links of a chain and its mechanical tensioner (“blade”) in the timing of an internal combustion engine. The blade was discretized by subdividing it into smaller components inter-connected with corresponding centres of gravity through 3D General Forces. Static and dynamic tests were performed to evaluate the stiffness, damping and friction parameters for the multibody model and to validate the methodology.

Keywords: Flexible body | Friction forces | Hysteresis damping | Impact | Slip

Abstract: This work describes a simple, fast, and robust method for identifying, checking and managing the overlapping image keypoints for 3D reconstruction of large objects with numerous geometric singularities and multiple features at different lighting levels. In particular a precision 3D reconstruction of an extensive architecture captured by aerial digital photogrammetry using Unmanned Aerial Vehicles (UAV) is developed. The method was experimentally applied to survey and reconstruct the 'Saraceni' Bridge' at Adrano (Sicily), a valuable example of Roman architecture in brick of historical/cultural interest. The variety of features and different lighting levels required robust self-correlation techniques which would recognise features sometimes even smaller than a pixel in the digital images so as to automatically identify the keypoints necessary for image overlapping and 3D reconstruction. Feature Based Matching (FBM) was used for the low lighting areas like the intrados and the inner arch surfaces, and Area Based Matching (ABM) was used in conjunction to capture the sides and upper surfaces of the bridge. Applying SIFT (Scale Invariant Feature Transform) algorithm during capture helped find distinct features invariant to position, scale and rotation as well as robust for the affinity transformations (changes in scale, rotation, size and position) and lighting variations which are particularly effective in image overlapping. Errors were compared with surveys by total station theodolites, GPS and laser systems. The method can facilitate reconstruction of the most difficult to access parts like the arch intrados and the bridge cavities with high correlation indices.

Keywords: Architectural reconstruction | Area Based Matching | Feature Based Matching | Photogrammetry | SIFT algorithm

Abstract: The shipment of heritage artefacts for restoration or temporary/travelling exhibition has been virtually lacking in customised packaging. Hitherto, packaging has been empirical and intuitive which has unnecessarily put the artefacts at risk. So, this research arises from the need to identify a way of designing and creating packaging for artefacts which takes into account structural criticalities to deal with deteriorating weather, special morphology, constituent materials and manufacturing techniques. The proposed methodology for semi-automatically designing packaging for heritage artefacts includes the integrated and interactive use of Reverse Engineering (RE), Finite Element Analysis (FEA) and Rapid Prototyping (RP). The methodology presented has been applied to create a customised packaging for a small C3rd BC bronze statue of Heracles (Museo Civico “F.L. Belgiorno” di Modica-Italy). This methodology has highlighted how the risk of damage to heritage artefacts can be reduced during shipping. Furthermore, this approach can identify each safety factor and the corresponding risk parameter to stipulate in the insurance policy.

Keywords: Cultural heritage | FEM | Laser scanning | Packaging | Rapid prototyping

Abstract: The present work aims at the development of an advanced control system implemented through Adams/View-Matlab/ Simulink co-simulation for a high-performance motorcycle dynamics study. In particular, the purpose of this study is to create a model able to consider several aspects of the rider-motorbike dynamic simulation and its control system, generally treated separately in the literature, making also use of an original and accurate modelling of the rider. From a previous multi-body model of motorcycle/virtual rider, developed by the authors, a flexible tool is created to simulate system dynamics to follow any trajectory at a prescribed velocity profile. Considering high-performance motorcycle dynamics are greatly influenced by the rider's weight, his movements have been accurately replicated to obtain the most realistic results. To simulate the passive impedance of rider's arms, a torque was applied to the steering as per the literature. The aerodynamic force was modelled as a function of kinematics variables and rider's posture. The control system is very flexible and adaptable to different manoeuvres realistically reproducing engine and braking performance, steering torque and rider movements. Numerical results show that the control system can accurately direct the motorcycle/ rider system along an entire lap of the Monza circuit, following a desired path at a given velocity profile. The model developed allows a complete view of the motorbike-rider dynamic behaviour thus being useful during both design phase and set-up, with a considerable saving in terms of both cost and time; it can also evaluate the influence on the system dynamics of riders with different anatomical characteristics and driving styles.

Keywords: Co-simulation | Control | Multibody | Path tracking | Rider/motorcycle

Abstract: Interactive simulations in Virtual Reality, such as haptic interaction, are more and more used to test or optimize nonlinear mechanical systems subjected to large deformations. FE algorithms are often not suitable for such purposes due to the high computational burden and the long simulation times. This paper provides a modified version of the classic chain algorithm, referred to as modified chain algorithm (MCA), to overcome some convergency issues and reduce the simulation time. The proposed algorithm is able to reduce the number of iterations estimating two kind of average moment laws. The MCA is then integrated into a design optimization procedure for the synthesis of a double slider-crank compliant mechanism to be used as opening system for an adjustable bicycle saddle. Finally, a X-Y layered ABS prototype is manufactured by rapid prototyping technique and 3-D printer. Experimental setup to test the deflection of the prototype revealed in good accordance with results coming from the MCA.

Keywords: Adjustable bicycle saddle | Compliant mechanisms | Nonlinear finite elements

Abstract: The saddle is one of the most complex bicycle components providing both comfort and support while pedalling. Several studies have been carried out on bicycle saddles in recent years including medical ones to identify any correlated pathologies, and others to optimize design and sports performance. There are various types of commercially available saddles but they are all fixed geometry. The main identifiers of these designs are their length, nose inclination and the geometry of the support of the ischial tuberosities and pubic rami (wide, narrow, flat, furrowed etc.). So as the literature suggests, the fixed-geometry saddle on today’s market has only partly resolved the anatomical pathologies related to extended saddle time. Consequently, the aim of this study is to develop, through interactive Re-design methodology, a variable geometry saddle (VGS) prototype for amateur cyclists capable of reducing the onset of saddle pathologies and improving pedalling comfort. The VGS was developed which can be adjusted to the physico-anatomical requirements of the rider as well as to various ride conditions (uphill, flat and downhill). The simple adjusters affect nose inclination and the width of the saddle back. In particular, the nose mechanism allows on-the-fly adjustment. The VGS developed could also allow the cyclist to identify the most congenial subjective geometry to help choose among commercial alternatives. An electroneurograph test on the pudendum nerve was also performed on five male amateur cyclists to see whether there were any effects with a variable saddle geometry compared to a fixed-geometry commercial saddle.

Keywords: Bicycle seat | Cycling | Interactive design | Rapid prototyping | Reverse engineering

Abstract: A methodology for integrating the CAD-CAE design of a chain drive system is presented by evaluating meshing angles. The methodology correlates the angles of engagement with transverse vibrations and the tensile force of the chain links, showing that the dynamic behaviour of a chain drive can be significantly improved by fine tuning the meshing angles. An objective parameter was introduced to evaluate divergence from correct meshing. Here the methodology is applied to optimize the timing chain system of a high power V12 quadruple overhead camshaft engine. The reliability of the method relies on multibody modelling all the components and accurate experimental tests. Correlating the experimental measurements provided exact modelling of the contact forces, exact evaluation of stiffness and damping values and precise dynamic modelling of the tensioners and guides. Finally, the dynamic performance of the two different primary stage chain drive layouts were compared.

Keywords: Chain stiffness | Contact force model | Meshing impact | Multibody dynamics | Tensioner | Transverse vibration

Abstract: In recent years virtual anthropology has been carrying out investigations as an alternative to the traditional anthropological approach. Among various applications is the study of the death masks of historically famous people, to authenticate them and make facial reconstructions. This study describes a multidisciplinary approach applied to the only three death masks of the musician Vincenzo Bellini made from different materials in different periods. By applying virtual anthropology along with Reverse Engineering, the morphological and metrical relationships of the masks were able to be studied, a study uniquely enabled in virtual environment. So, the finds were investigated without compromising their integrity also thanks to the use physical models obtained through Rapid Prototyping. Integrated with traditional artistic techniques, these methodologies provided evaluations of the historical, technical and morphological relationships between the death masks. Nevertheless, to refer these faces to Bellini, the results were compared with Bellini's autopsy data from Prof. Dalmas.

Keywords: Additive manufacturing | Death mask | Laser scanning | Superimposition techniques | Vincenzo Bellini | Virtual anthropology

Abstract: The dynamics of a high-performance motorcycle are greatly influenced by the rider's weight and movements especially when the power-to-weight ratio is very high. Generally in motor vehicles, the driver's/rider's weight is a significant fraction of the entire system. This work is about ADAMS/View multibody modelling of a motorcycle and virtual rider who simulates handlebar interaction and saddle sliding. In the literature, the rider's influence is unrealistic being limited to considering him as a concentrated mass or in other cases as a fixed passive system. Even vehicle modelling is often inaccurate, referring at best to simplified models of rigid bodies. In this work, the vehicle and rider have been accurately modelled to most realistically reproduce the dynamic behaviour of the system. The motorcycle was modelled with 12 bodies incorporating concentrated flexibility for the two suspension units and considering the chassis as a flexible body using modal synthesis. The virtual rider is made up of 15 rigid bodies and has 28 degrees of freedom. To study the effects on the motorcycle of the rider's movements as well as the motorcycle's dynamics and performance, a monitoring system similar to that in the literature was used to read handlebar torque and engine and braking torque. Furthermore, in the literature there are simulations of standard manoeuvres whereas in this work an entire lap of Monza was simulated. There were simulations of a fixed and mobile rider validating the model in advance and thereafter monitoring the most significant dynamic parameters. The multibody model provides useful results at the design phase and insights into the whole vehicle/rider dynamic to setup all the reference parameters for immediately evaluating system effects.

Keywords: Multibody | Path tracking | Rider's effects | Rider-motorcycle system | Steering torque

Abstract: The aim of present work is the containment of the inertia forces, the stiffness components optimization and the fit tolerances of valve train in internal combustion engines (I.C.E.) 4T. The proposed methodology allows, through the development of a test machine, the evaluation of axial stiffness of tappet depending on eccentricity of the cam tappet contact, performing a functional analysis that simulate the behaviour of the system in operational condition, even if, some adjustment of tolerances of the fit between tappet and his guide, occurred. The dynamic study of the valve train, through modern computer codes, is performed by connecting lumped masses, springs and dampers that characterize each element. In numerical models the tappet is represented as constituted by the tappet and by the hydraulic element. Each of these elements is characterized by stiffness and mass. The structural rigidity of the tappet has, in fact, important effects on the dynamic behaviour of the entire valve train. The test machine makes possible the choice of the dimensional and geometrical tolerances of the fit between tappet and his guide; allows furthermore the evaluation of errors occurred during construction and integration phase. In addition, the test machine is also suitable for reverse engineering applications, makes it possible to automatically draw the cam profile in polar coordinates. © 2012 Springer Science+Business Media Dordrecht.

Keywords: Cam | Dynamics | Fit tolerance | I.C.E | Tappet | Timing system

Abstract: The valve return springs in the distribution chain of internal combustion engines constitute a fundamental component for the duration, efficiency and performance of the engine itself [1,2,3,4]. This is even more true for high-performance engines whose mechanical and thermal power leads to the premature deterioration of poorly designed components. The elevated forces in such engines necessitate, where the valve springs have not been substituted by alternative kinematic systems, progressive springs, i.e. springs with variable stiffness. Despite this fact, the literature does not contain any univocal methods for defining the geometry of this type of spring. In the present study, the question is approached on the basis of a numerical-iterative calculation, providing a general methodology which, starting from data regarding the functioning of the engine and the geometric volumes to be respected, leads to the definition of the optimal geometry of the helix, taking account of the trend of the stiffness, of the natural frequencies and of the loads over the entire operating range of the spring. Tests on springs calculated in this way were performed using multi-body software, in order to verify the correspondence between the initial design data and the real behaviour of the geometry generated. © 2011 SAE International.

Abstract: The valve return springs in the distribution chain of internal combustion engines constitute a fundamental component for the duration, efficiency and performance of the engine itself [1,2,3,4]. This is even more true for high-performance engines whose mechanical and thermal power leads to the premature deterioration of poorly designed components. The elevated forces in such engines necessitate, where the valve springs have not been substituted by alternative kinematic systems, progressive springs, i.e. springs with variable stiffness. Despite this fact, the literature does not contain any univocal methods for defining the geometry of this type of spring. In the present study, the question is approached on the basis of a numerical-iterative calculation, providing a general methodology which, starting from data regarding the functioning of the engine and the geometric volumes to be respected, leads to the definition of the optimal geometry of the helix, taking account of the trend of the stiffness, of the natural frequencies and of the loads over the entire operating range of the spring. Tests on springs calculated in this way were performed using multi-body software, in order to verify the correspondence between the initial design data and the real behaviour of the geometry generated. Copyright © 2011 SAE International.

Abstract: Accurately measuring an artefact of historical significance generally results in being able to extract information which is useful for evaluating what remains of the materials from a distant time. This allows scholars arrive at an exhaustive historical reading of the same artefact. Compared to the traditional measuring techniques, which can often be imprecise and complicated, 3D laser scanners measure the morphological characteristics of an artefact with extreme accuracy. Despite this, it is not always possible to choose the most appropriate sensors due to the geometric peculiarities, or indeed, the size of the object. The present work deals with two non-destructive analyses of an ancient stone sculpture, which for its morphology and size was scarcely compatible with the technical characteristics of either of the scanners used. Both scanners operate on the same technical principal, but are quite different from each other in terms of scale and precision. For these reasons, a complex 3D model (extremely appropriate given the original artefact) was draw out through a synergy of the two techniques. The virtual particularities of the model allowed it to be manipulated with the appropriate software. In fact, on the basis of qualitative parameters devised by researchers, it proved possible to reproduce the artefact's geometric form, both virtually and in the form of physical models, obtained through non-conventional restoration methods (R.P. techniques).It has also been possible to verify the state of degradation of the surface of the stone caused by the traditional methods of applying cataloguing or storage information to it.Finally, the results achieved provide opportunities for further research on certain geometrical characteristics of the stone which, as highlighted by the elaboration on the virtual model, seem to be traceable to non-manual, perhaps mechanical, processes. Therefore, the historical considerations which derive from this fact call certain scholars into play. © 2011 Elsevier Ltd.

Keywords: Arteafct | Rapid prototyping | Reconstructing | Scanner | Sculpture

Abstract: In the present study, the authors performed a dynamic analysis of the desmodromic timing system, where the valve lifter is realized by conjugate cams, using a methodology of modal synthesis to examine the effects of the deformability of the principal parts, and evaluating the deformations and vibrations of the components under various operating conditions. With this aim, a virtual 3D model and a multibody calculation program were used in a concentrated parameter model, requiring the choice of numerous parameters that greatly affect the results of the analysis. It was therefore important that, within the variability range of these parameters, the values adopted rendered the behavior of the analytical model as close as possible to that of the real system. Finally, the need to evaluate some of the more important aspects of the dynamic system (such as values of clearances, stiffnesses and damping at contacts, and stiffnesses and damping of shafts and belt) made it necessary to validate the model through comparison with experimental trials conducted to determine the valve motion and to measure the strain on the distribution belt.

Keywords: Desmodromic timing system | Dynamics | Flexible bodies | Modal synthesis

Abstract: In this study, a methodology based on co-simulation was developed for the multibody parametric modelling of a motorcycle with an anthropomorphic model of the rider. This co-simulation uses two different software programs, integrated to ensure a complete exchange of information between them in real time. The paper reports the effects induced by the movement of the rider's body on the dynamics and performance of a motorcycle. The legs of an anthropomorphic model were used as kinematics to control transverse movements of the motorcycle. The control system inputs are the geometric characteristics of the road (length, width and radius of curvature) and the speed of the vehicle along the track. For the dynamic behaviour of the motorcycle, the only channels currently operated by the control system are steering angle and engine torque, which are determined in accordance with the input parameters.

Keywords: Control | Dynamic | Motorcycle | Multibody | Rider

Abstract: The main purpose of the present study was to optimize a prototype hexapod robot, called Gregor I, through reverse engineering techniques. The robot is based on experimental observations of the cockroach with regard to mechanical design and the locomotion control strategy. This paper reports on the design phase of a hexapod robot, where the basic geometry of the system is defined through solid modeling and improved through kinematic and dynamic studies, using multi-body software. The dynamic simulation environment made it possible to study the performance of the system under different working conditions. Guidelines for an optimization process of the hexapod structure were drawn from these analyzes, aimed at the improvement of specific characteristics: speed, payload and climbing capabilities. Finally, the robot model and the robot prototype were compared.

Abstract: Defining a procedure for the characterization of the crankshaft and entire engine unit, based on CAD-FEM multi-body methodology, would provide an analysis tool which avoids the simplified hypotheses usually accepted when designing these components. The methodology is based on the Craig-Bampton method, i.e. on the theory of component mode synthesis. According to the Craig-Bampton theory, the deformation of a flexible crankshaft interfacing with the rest of the engine is obtained through static and normal modes, considering the discretized model with a large number of degrees of freedom and using modal truncation. It is based on the separation of interface and internal d.o.f. Using modal stress analysis has the advantage of reducing the d.o.f. of the FEA model. The multi-body model includes the elasticity of the camshaft and the reduced inertia of the gearbox and timing system. Comparing simulations performed at different engine speeds, the crankshaft evidenced the angular oscillations of generic sections of the axis and shaft, without separating the bending and torsional d.o.f. At higher engine speeds, the vibrational response showed how the harmonics with greater amplitude correspond to the crankshaft's first natural modes and are excited by some harmonics present in the engine moment.