PurposeThis paper aims to systematically investigate the effect of the sintering pressure on the microstructure and tensile behavior of sintered silver at both room and elevated temperatures. In contrast to earlier studies, this research uniquely explores the combined influence of sintering pressure, strain rate, on the high-temperature mechanical response of the porous sintered silver material.Design/methodology/approachSpecimens were manufactured from a microscale silver paste using sintering pressures of 7 and 15 MPa at sintering temperatures of 230 degrees C for three minutes, to forcibly induce distinct porosity levels. Subsequently, tensile tests were carried out at strain rates of 10-4 and 10-5 s-1, and at room temperature and at 200 degrees C.FindingsThe porosity level, as extracted from optical microscopy image analysis, were computed as 24.1% and 14.7% for sintering pressures of 7 and 15 MPa, respectively. In addition, the results indicated that higher sintering pressure, that is, lower porosity, consistently improves mechanical performance across all test configurations. Statistical analysis further reveals that porosity, strain rate and loading temperature collectively govern the mechanical response, with porosity acting as a key microstructural link between processing conditions and material behavior. Notably, thermal effects were found to be more dominant than rate effects. The combined influence of porosity, strain rate, on the high-temperature mechanical properties has been unified in a bilinear isotropic hardening material model and validated with finite element simulations.Originality/valueSintered silver has become a preferred bonding solution for high-performance power electronics due to its outstanding mechanical and thermal properties. Among the various sintering parameters, applied pressure plays a critical role in determining the porosity and, consequently, the mechanical performance of the resulting bond. Although the influence of sintering pressure has been widely studied, its effects remain not fully understood, especially under elevated temperature conditions. Unlike earlier studies, this research has exclusively explored the high-temperature behavior of the sintered silver with various porosity levels. The findings of the present study highlight the importance of explicitly incorporating porosity into constitutive models to enhance the accuracy of finite element simulations for sintered silver joints in power electronic applications.

In this paper, a combination of experimental and numerical methods is presented to improve simulation capabilities for ballistic scenarios with soda-lime glass. A new concept is developed that includes confined and unconfined characterization tests for the determination of failure and yield curves for SLG with different degrees of dynamically generated pre-damage as well as the development of an improved strength model based on the new yield curves. Intact specimens as well as pre-damaged specimens were loaded quasi-statically under compression by means of a MTS machine. Intact specimens were tested with and without confinement in order to determine Young’s modulus and the strength of intact SLG under uniaxial stress and triaxial stress conditions. Confined compression tests on specimens with different degrees of pre-damage were conducted in order to measure the residual strength of failed SLG. The pre-damage had been generated and quantified by X-ray CT in previous studies. The experiments were supported by an elaborated simulative study. The results of the simulations allowed accounting for the influence of friction and the effects of the complex test setup. A new simulation concept is developed, enabling the implementation of the novel test results into a constitutive material model. The performance of this improved SLG model is investigated in a representative ballistic impact scenario, in which a 7.62 mm armor-piercing projectile with tungsten carbide core impacted a transparent armor laminate. It is noteworthy that the presented methodology of characterizing the residual strength of quantitatively pre-damaged specimens is expected to be generally applicable to other brittle materials, such as ceramics.

This work investigates whether the architecture of a unit cell, rather than the properties of its base material, can govern strain rate sensitive behavior. We focus on additively manufactured Ti6Al4V, a lightweight titanium alloy with weak intrinsic rate sensitivity, and employ it to fabricate friction unit cells. The friction cell redirects compressive loads into frictional sliding between internal surfaces produced by the LPBF (Laser Powder Bed Fusion) process. Structural characterization from quasi-static (0.01 /s) to crash-relevant strain rates (500 /s) reveals a factor of 2.5 increase in peak stress, substantially exceeding the rate sensitivity of the base material. To identify the mechanism, the dynamic friction coefficient of the as-built Ti6Al4V tribo-pair is measured across sliding velocities from 0.01 to 8 m/s at 7.5 MPa and up to 6.5 m/s at 40 MPa. The kinetic friction coefficient more than doubles between the quasi-static plateau and the crash-relevant regime. Correlating the structural and tribological data establishes velocity-strengthening interfacial friction as the dominant mechanism behind the pronounced rate sensitivity of the friction cell. These results show that meso-scale friction, embedded through unit cell geometry and surface morphology, can dictate crash-relevant rate sensitivity that the base material alone does not possess.

The numerical modelling of cold drawing in glassy polymers such as Polycarbonate (PC) is extremely sensitive to the shape of the constitutive stress–strain curve due to softening between the upper and lower yield point. This work shows that it is equally important to consider not only stress triaxiality effects but also the role of the nonlinear plastic Poisson’s ratio to accurately model the large deformation process of PC. Experimental results for the plastic Poisson’s ratio for uniaxial tensile tests on axisymmetric specimens are reported. The ratio of transverse to axial strains is measured with a unique combination of contour strain and Digital Image Correlation analysis, indicating that the plastic Poisson’s ratio varies significantly as a function of strain. An extension of Hart’s instability analysis is proposed, which considers the effect of strain-dependent Poisson’s ratio. The resulting 1D theory successfully describes neck formation and subsequent stabilisation as the interplay of cross-section area reduction due to Poisson’s effect and gradients of the stress–strain relationships. This theory delivers an intriguingly simple explanation for the characteristic change of shape of the observed force–elongation plots as strain rate is increased, if viscoplastic effects are considered. Limitations of the approach, including the incompressibility assumption underlying the Bridgman corrections and the scope of the one-dimensional stability analysis, are discussed.

This study aims to analyze the influence of continuous fiber reinforcement on the dynamic behavior of 3D-printed composites. To this end, semicircular bending (SCB) test coupons were designed and printed using the fused filament fabrication (FFF) technique. Particularly, nylon material was used as a matrix in all specimens, while fiberglass was utilized as the reinforced material. Since printing orientation has a significant influence on the mechanical behavior of 3D-printed components, the samples were printed in different directions. In a series of tests, the SCB specimens were impacted using a split Hopkinson pressure bar (SHPB) with a strain rate of 100 s-1. In this research, a high-speed photograph system was used with a focus on the SCB specimens to capture their deformation behaviors. The results of dynamic three-point bending tests indicate that the maximum force increased by 190.2% and 238.1% in the specimens printed in ZY and YZ orientations, respectively, as a result of fiber reinforcing. The documented outcomes can be used for the design and production of 3D-printed composites with enhanced structural performance and customized mechanical strength.

Among various die-attach technologies, sintered silver has emerged as a preferable bonding technology for high-performance power electronics, attributed to its exceptional mechanical and thermal properties. The sintering process parameters including pressure, temperature, and duration significantly impact the porosity and the corresponding mechanical characteristics of the sintered silver bond. The effects of these parameters are widely investigated but they remain not fully understood. This study systematically investigates the effects of sintering pressure and duration on the porosity and tensile behavior of sintered silver. Test samples were produced using micro-sized silver particles under varying pressures (7 and 15 MPa ) and durations (3 and 6 min) at a constant temperature of 230 ^∘C . Porosity levels were assessed through optical microscopy and microstructural image analysis. Extensive tensile experiments, combined with high-precision digital image correlation, were performed at two strain rates of 10^-4 and 10^-5 s^-1 . Results indicated that higher pressure and extended sintering times significantly reduced porosity, leading to improved mechanical properties such as higher elastic modulus, yield strength, ultimate tensile strength, and failure strain. Statistical analysis further confirmed that the material's mechanical response is strain-rate dependent, with porosity playing a critical role in this sensitivity. Additionally, a bilinear isotropic hardening model incorporating porosity effects was calibrated and validated through finite element simulations, showing excellent agreement with experimental results. The findings of the present investigation provide valuable insight into optimizing sintering parameters and establishing robust constitutive models for the reliable design of power electronic assemblies using sintered silver joints.

The sintering of silver paste has become a primary die-attach technology in advanced power electronics due to its excellent bonding strength, improved thermal conductivity and ability to endure high operating temperatures. However, the sintering process often results in a porous bond microstructure, which negatively affects material properties and the bond's strength. Therefore, the quantitative relationship between sintering process conditions-specifically pressure, temperature, and time-and the resulting porosity and mechanical behavior requires further interpretation. This work aims to methodically explore the influence of sintering pressure (7 and 15 MPa), sintering temperature (230 and 270 degrees C), and the process duration (3 and 6 min) on the porosity and tensile characteristics of sintered silver. Porosity was first evaluated through optical microscopy and image analysis, while tensile properties were measured at strain rates of 10-4 and 10-5 s-1 using tensile experiments combined with digital image correlation for accurate strain tracking. The results demonstrate that higher pressure, elevated temperature, and extended sintering time markedly decrease porosity, which in turn enhances elastic modulus, yield strength, and ultimate tensile strength, as well as ductility. Statistical evaluation revealed that mechanical performance is strongly influenced by both strain rate and porosity, with porosity being the more dominant factor. Furthermore, a bilinear isotropic hardening constitutive model that is adjusted for various porosity levels and strain-rate was developed and validated via finite element simulations, showing excellent agreement with experimental data. These outcomes offer practical guidance for optimizing sintering parameters and establishing accurate material models, thereby supporting the development of more reliable and durable sintered silver interconnections in power electronic assemblies.

To accurately determine yield stress curves for ductile metals, it is essential to account for the triaxial stress state that develops during necking, which complicates the extraction of the equivalent uniaxial stress state. This study introduces a simple yet effective approach to address this challenge. Using a single-camera setup with backlight illumination, silhouette images of the specimen during tensile testing are captured. From these images, the specimen contours are extracted digitally, enabling strain computation based on changes in contour geometry. Simultaneously, a novel curvature-fitting algorithm is employed to calculate stress triaxiality. The accuracy of this method is validated through comparison with finite element simulations, and its applicability spans from the onset of necking to the point of fracture. This approach is demonstrated on 303 stainless steel, showcasing the accurate recovery of equivalent uniaxial true stress-true strain relationships under varying triaxiality conditions. Furthermore, as these stress and strain measures are energy-conjugate, the mechanical work within the neck can be calculated, enabling a direct determination of the Taylor-Quinney coefficient using infrared thermography. The method offers a robust framework for experimental analysis and provides a straightforward route for mechanical and thermal coupling studies. To facilitate broader adoption, an open-source implementation of the program is made available.

ABSTRACTThe representation of material failure due to wave propagation is essential for the numerical analysis of engineering structures under high dynamic loading. Explicit time integration schemes are well established for this kind of application. In order to realistically model the failure of certain material classes, it is necessary to resolve lower scale features accurately. Concurrent multiscale approaches are therefore well suited to this task. However, they are often complex and computationally demanding. The introduction of interfaces between disparately meshed domains may additionally lead to emerging reflections for waves that contain high frequencies, which the coarse domain cannot resolve. In this article, we compare accuracy, computational efficiency, versatility, and effort for two finite element implementations of concurrent two‐scale schemes. Both offer the possibility of adding a Selected Perfectly Matched Layer (SPML) to dampen incompatible frequencies. One approach is the widely used conventional Lagrange multiplier (LM) approach; the second is a weak staggered (WS) coupling, which was designed to maintain direct solution schemes' efficiency with explicit time integration and diagonal mass matrices. It turns out that, for typical discretizations, the WS coupling achieves an accuracy comparable to the LM coupling but requires fewer computational operations and, relevant for parallel computer architectures, significantly less communication efforts. Adaptive changes of interface topology, for example, due to explicitly resolved cracks crossing the interface, can easily be represented in the WS approach, making it a suitable candidate for the application in scenarios where gross damage is expected.

Malicious acts, but likewise unintended accidental explosions, can lead to severe structural damage and resulting debris throw, which poses a significant threat to humans and facilities. Until now, risk analysis is based mainly on empirical data, since the reliable simulation of structural break-up, dissolution and emergence of secondary fragments for real structures is still challenging. In this paper, we investigate the application of a mesoscale description of concrete with finite elements to predict the dispersal of fragments out of dynamically loaded concrete specimens. We demonstrate that the approach delivers accurate predictions for maximum velocity and total debris mass. Further, it is even able to resolve the debris mass distribution with very reasonable quality, a result rarely found in literature up to today. The detailed resolution of the debris field allows furthermore a more thorough determination of the aerodynamic factors governing the subsequent flight phase. We compare the results using different assumptions in terms of flight distances and safety maps.

PurposeThis work aims to investigate the influence of sintering pressure on the creep deformations of sintered silver specimens.Design/methodology/approachTest specimens are fabricated through the stencil printing of microsized silver paste, sintered at 230 degrees C sintering temperature for 5 min. Three sintering pressures, including 15, 20 and 25 MPa are considered. Comprehensive creep tests are conducted at room temperature, and deformations are measured using advanced optical digital image correlation techniques.FindingsThe results have indicated that sintering pressure significantly influences the creep behavior of sintered silver, with higher pressures yielding samples of superior quality and increased creep resistance due to reduced void density. A power law-based creep constitutive equation is developed in this paper to incorporate the impact of sintering pressure on the steady-state creep rate, and its validity has been carefully evaluated. The findings suggest that using higher sintering pressures in the assembly of power electronic modules with sintered silver interconnects can enhance their strength and reliability.Originality/valueSintered silver bonds are one favorite option in power modules due to their excellent electrical, thermal and mechanical characteristics. The sintering process is generally controlled by the sintering temperature, the sintering pressure and the process duration. The sintering layer strength, mechanical properties and reliability are, in fact, highly influenced by the sintering process parameters, such as the sintering pressure. Therefore, the results of this work can be invaluable for designing power devices with sintered Ag bonds.

The resource wood has been optimized by nature for millions of years, leading to its exceptional lightweight potential for numerous applications. This study examines the potential of wood as a lightweight material in the automotive sector, considering its multitudinous advantageous properties. Given the stringent requirements of the industry, uncertainty exists regarding wood integration methods and forms. Therefore, requirements were identified, analyzed and used to derive requirement-oriented design approaches. Thus, this research study explores an innovative technology for embedding wood into vehicle body components, incorporating ecofriendly design principles. Preliminary simulation results reveal significant weight reduction potentials.

This study investigates the primary mechanisms contributing to damage accumulation in additively manufactured Scalmalloy (Al-Mg-Sc) subjected to tensile tests at low and high strain rates. High-speed X-ray Phase Contrast Imaging (XPCI) performed at beamline ID19 of the European Synchrotron Radiation Facility (ESRF) provide real-time, high-resolution through-volume visualization of internal void evolution processes, including void nucleation, growth, and coalescence. This advanced experimental approach facilitates the precise calibration of established physics-based fracture models, such as the Gurson-Tvergaard-Needleman (GTN) model, which otherwise relies on assumptions that are very difficult to verify experimentally. The 2D images captured during in-situ testing were segmented to identify and track individual voids using advanced computational techniques. The strain fields within the material were calculated via the Moving Least Squares (MLS) method, enabling accurate local strain estimation in materials with complex and evolving microstructures. The results show significant strain rate effects on the void evolution in Scalmalloy. At low strain rates, the void fraction increased steadily as a result of isolated void growth. In contrast, high strain rates demonstrated complex deformation behaviors, with slow initial void growth transitioning to rapid coalescence beyond a critical strain threshold, ultimately resulting in extensive internal damage. Moreover, the analysis of the time derivative of the apparent void fraction and its relationship with the local strain rate reveals proportional damage evolution at low strain rates, indicating progressive void growth. At high strain rates, the strong linear relationships observed between the rate of change of the apparent void fraction and the local strain rate, validate the applicability of the GTN model and demonstrate its ability to predict rapid void coalescence and ductile fracture under dynamic loading conditions.

The conception of ballistic personal protective equipment requires a comprehensive understanding of the human body’s response to dynamic loads. The objective of this study is to develop rib bone surrogates enhancing new anthropomorphic test devices for personal protective equipment evaluation at high dynamic impacts. These are fabricated with additive manufacturing and compared to post-mortem human subjects (PMHS) data from literature. The 5th rib of the finite element Global Human Body Model Consortium (GHBMC) male 50th percentile (M50) model was extracted and transferred to a CAD model. This CAD model was divided into 30 sections with specific cortical bone thicknesses in all directions (caudal, cranial, cutaneous and pleural) from an equivalent rib of an M50 PMHS. Three different additive manufacturing technologies (direct metal laser melting, fused filament fabrication and multi jet modeling) were used to reproduce the M50 PMHS 5th rib surrogate. A total of 57 specimens were dynamically (500 mm/s) loaded to failure in a bending scenario imitating a frontal thoracic impact. Force, displacement, stiffness, and energy at failure were determined. Also, the strain distribution using 3D digital image correlation was recorded and compared to PMHS data from literature. The rib surrogates show deviations from the PMHS characteristic values. Nevertheless, there are also common characteristics in key variables to certain age groups of the PMHS data, which will facilitate the further development and improvement of adequate surrogates for a more realistic representation of the human body’s response to high dynamic loads.

The utilisation of high-resolution in situ computed tomography (CT) in the (sub-)μm range is typically only viable in synchrotron facilities, as the deployment of a conventional loading stage in laboratory CTs with a cone beam source does not facilitate a corresponding geometric magnification. This publication presents a CT system with a novel in situ concept that allows spatial resolutions down to 0.5 μm, enabling the analysis of weakly absorbing materials capable of applying loads of up to 5 kN in both the compression and tension directions to the sample during the measurement. The necessity for a highly precise mechanical design to ensure successful measurements at magnifications approaching the theoretical limit makes the system’s development particularly demanding. The components employed are presented, along with the requisite considerations and methodologies. It can be demonstrated that the intended specifications with regard to precision and quality are met. The experimental results of a fibre-reinforced polymer demonstrate the system’s ability to detect matrix damage features below a single fibre diameter, thereby highlighting its potential for applications in materials science where traditional laboratory CTs are insufficient and synchrotron access is limited.

This study seeks to provide guidance on how top-down greenhouse gas emission reduction targets (GHG ERTs), deriving, for example, from corporate decarbonization strategies, can be translated into quantifiable targets for component measures. Furthermore, it shows how these targets need to be adjusted during the development process to account for parameter uncertainties resulting from the lack of data availability and validity in the early design stage. The scope of the analysis focuses on ecological measure magnitude (EMM) targets for mass reduction and the content of recycled material. The study is split into two sections: The first section introduces a method on how to calculate EMMs based on a partial carbon footprint assessment (CFPA). The second and main section elaborates on an analysis of how parameter uncertainties in the CFPA influence initially defined EMM targets by using perturbation analysis. In the presented paper, the method is applied exemplarily to an automotive component in an internal combustion engine vehicle. The study shows that a parameter uncertainty in the environmental impact of the mass-induced use phase or the primary material production (and semi-finished product provision) has a significant influence on the required EMMs. In the authors’ opinion, this study can increase the awareness of how CFPA parameter uncertainties can affect the credibility of EMM development targets. The used approach can help designers and engineers to minimize the risk of a non-fulfillment of GHG emission-related development targets.

Dynamic loading of concrete often leads to excessive cracking and fragmentation. Since these processes are massively influenced by the underlying heterogeneity of the material, discrete modeling of the lower-scale features strongly improves the simulation results. At the same time, the computational effort is greatly increased. We therefore propose here a mesomechanical simulation approach which is efficient in terms of model generation and computational efforts even for large 3d models. Furthermore, it is robust by limiting the application of computationally less efficient cohesive zone elements to the weak transition boundary between matrix and inclusions. Intermatrix failure is considered by a smeared crack approach and element removal after a certain crack opening has been reached. We apply an improved version of the widely used RHT concrete model, which is enhanced with a principal stress criterion. The resulting approach leads to an accurate replication of experiments in terms of crack propagation and stress wave induced dynamic fragmentation.