Papers by Keyword: Anisotropy

Abstract: Predicting the deformation behavior of rolled and extruded light metal alloys is a challenging task. Due to the high cost of experimental analysis, finite element simulations are often required. A variety of material models at different scales are available for practical use. In this work, the viscoplastic self-consistent (VPSC) approach is employed to consider microstructural effects. These can be incorporated by using measured crystal sizes and orientations - called texture - of the alloy under consideration. For each integration point in the FE mesh, a corresponding texture is assigned and individually deformed in LS-Dyna^®, where VPSC is implemented as a user-defined material model - referred to as FE-VPSC. This study focuses on preprocessing of texture data as well as their compression for accurate and faster FE simulations. For verifying the simulations, a comparison with digital image correlation (DIC) of experimental puncture tests was conducted.

Abstract: This paper revisits the long-standing question of how to fully characterise the in-plane plastic anisotropy of sheet metals without assembling evidence from multiple standardised tests. The central idea is pragmatic: a single, well-designed heterogeneous biaxial experiment can replace the conventional combination of uniaxial and equibiaxial tests if the specimen and the inverse identification method are co-designed to (i) activate informative stress states and (ii) maintain low strain gradients for accurate digital image correlation measurements. The proposed cruciform specimen is deliberately conceived as a benchmark configuration for full-field inverse identification, with known locations and stress-strain states at which relevant material information is embedded. The approach is coupled with a Finite Element Model Updating framework, enabling all anisotropy parameters of the YLD2000-2d model to be identified from a single full-field dataset. Sensitivity and identifiability analyses demonstrate that a physically based parameter formulation significantly improves the conditioning of the inverse problem. Virtual experimentation confirms the robustness and accuracy of the proposed “one-test” identification strategy.

Abstract: The efficient development of high-quality sheet metal components increasingly depends on predictive numerical simulations conducted prior to forming operations. Achieving such accuracy requires precise calibration of models that represent the complex mechanical behaviour of metals. Mechanical testing provides the essential data for calibration, revealing material anisotropy, strain hardening, and ductile fracture. However, traditional characterisation approaches are often labor-intensive, time-consuming, and prone to operator variability. Within the phenomenological framework, numerous tests are typically required to capture the full material response, including repeats for statistical reliability, leading to high costs and extended lead times. To address these limitations, this study introduces an automated mechanical testing platform designed to rapidly acquire experimental data useful for material models. The use of a cobot enables fully automated test sequences, ensuring high repeatability and reducing manual intervention. When combined with automated model calibration, this approach provides a direct link between the physical material (metallic sheet) and its virtual mechanical representation.

Abstract: Medium-Mn steel (MMnS) and quenching and partitioning (QP) steels are two representatives of third-generation advanced high-strength steels (3^rd Gen AHSS), developed to achieve an optimal balance between strength and ductility. In forming applications, global formability reflects a material’s resistance to necking, while local formability indicates its resistance to fracture. Both aspects are essential for assessing mechanical performance. Global formability is often characterized by the forming limit curves at necking and is highly sensitive to work hardening behavior. Similarly, the forming limit curves at fracture determined from different stress states can be applied to evaluate the local formability. In addition, these deformation characteristics can be influenced by anisotropy introduced during sheet processing. Rolling process introduces orientation-dependent variations in both plastic flow and fracture behavior, which significantly affect necking development and fracture initiation. This study investigates and compares the global and local formability of various 3^rd Gen AHSS grades, with a focus on the influence of anisotropy. To investigate the anisotropic effects on plasticity and ductile fracture under different stress states, tensile tests were conducted on specimens with various geometries and orientations cut from sheet materials. Based on the tensile tests, the forming limit framework of Shen et al [1] was broadened to include anisotropic effects.

Abstract: The influence of the stress state on damage evolution, fracture behavior, and component performance is well established for proportional loading conditions. In contrast, many industrial sheet-forming processes involve non-proportional loading paths, which can significantly alter material hardening and fracture responses. Recent results have shown, that load direction changes affect damage evolution in the dual-phase steel DP800. This paper aims to investigate to what extend these results can be transferred to the aluminum alloy AA6082-T6. Therefore, specimens are first prestrained in uniaxial tension and subsequently reloaded either in the same direction or orthogonally, using additional tensile tests. Fracture strains during the subsequent tensile tests are determined by Aramis DIC. Orthogonal load direction changes lead to an increased fracture strain for DP800, but decreased fracture strain for AA6082. While the observed behavior of DP800 can be attributed to the void morphology, which is established during prestraining, the results of AA6082 indicate different damage mechanisms which cause this behavior.

Abstract: The present study aims to investigate the anisotropic creep behaviour of aluminium alloy 2139 during artificial ageing, through in situ thermomechanical loadings under Electron Backscattered Diffraction (EBSD). EBSD analysis enabled the characterisation of microstructural parameters and the identification of grain misorientations which were further correlated with macroscopic creep strain. In situ analyses were conducted within a Scanning Electron Microscope (SEM) using a micro‑tensile stage that allows simultaneous heating and mechanical loading. Creep tests were performed at 160°C under 50, 100 and 150 MPa along three different orientations in order to investigate the creep behaviour of the alloy. Kernel Average Misorientation (KAM) maps showed a progressive increase of the average KAM values for the different loading conditions, reaching a saturation value after 10 hours. Ex situ tensile tests were conducted on creep‑aged specimens using Digital Image Correlation (DIC). The main mechanical property evolutions (averaged across all orientations) are a 45 % increase in yield stress, a 10 % increase in ultimate tensile stress and a reduction in ductility, characterised by a notable decrease in elongation. Further works will focus on the result repeatability, as well as on the influence of prior deformation on the creep strain.

Abstract: Despite remarkable advances in additive manufacturing (AM), the uncertainty in direction-dependent strength and fracture behavior of metallic components still poses major challenges for their reliable structural application. The layered nature of laser powder bed fusion (LPBF) produces highly anisotropic textures and microstructure architectures that influence both plastic flow and fracture. While numerous studies have characterized tensile anisotropy, the coupling between build-induced anisotropy and stress-state-dependent fracture remains largely unresolved, yet it governs the structural integrity of AM parts under multi-axial loading. In particular, the extent to which anisotropy alters the ductile-to-brittle transition or fracture locus is still unknown. This study addresses this gap by combining experiments and advanced constitutive fracture modelling for two typical AM metals, austenitic 316L stainless steel and AlSi10Mg aluminum alloy. The goal is to formulate a unified, physically based description of anisotropic plasticity and fracture that is applicable across various material classes. LPBF samples of 316L stainless steel and AlSi10Mg were built at multiple orientations between 0° and 90° relative to the build direction. Uniaxial tensile tests were carried out with digital image correlation to capture full-field strain evolution and to determine r-values as a measure of plastic anisotropy. Complementary fracture tests under different stress states ranging from simple shear to plane strain tension were designed to evaluate the fracture dependence on stress states and anisotropy. It can be concluded that both alloys exhibit orientation-dependent flow and r-value during plastic deformation. The fracture strain decreases with rising triaxiality, yet its rate of decrease depends strongly on orientation, demonstrating a clear coupling between anisotropy and stress state.

Abstract: Triply Periodic Minimal Surfaces (TPMS) structures, such as the Gyroid, can exhibit nearly isotropic mechanical behaviour over specific relative density ranges, as predicted by the Zener anisotropy ratio. In contrast, the Laser Powder Bed Fusion (L-PBF) process may induce anisotropy in the material due to thermal gradients and residual stresses, potentially influencing the overall structural response. This work investigates how the anisotropy generated by the L-PBF process interacts with the inherent isotropy of Gyroid architecture. Gyroid lattices in 316L stainless steel were produced with varying unit cell sizes and wall thickness. Quasi-static compression tests were performed along directions parallel and perpendicular to the build axis to evaluate orientation effects. Numerical simulations, using both isotropic and anisotropic material properties, were employed to estimate the effective elastic response and the Zener anisotropy ratio. The combined experimental and numerical study aims to assess whether and to what extent the Gyroid architecture partially mitigates the transmission of process-induced anisotropy to the effective elastic response, contributing to a better understanding of the mechanical behaviour of additively manufactured metallic lattices. In particular, the study clarifies whether the theoretically isotropic Gyroid architecture is able to attenuate or transfer L-PBF-induced material anisotropy at the lattice scale.

Abstract: Cold rolling forces are strongly affected by lubrication and material properties, and maypotentially be used to estimate material property variations along the coil. The 1D slab method iscommonly used to estimate rolling forces as it is computationally inexpensive. By model definition,the pressure distribution as modelled in the slab method has a single peak or friction hill in the rollbite. However, it has been observed in several studies that multiple local peaks can appear in thepressure distribution in the roll bite. Additionally, material anisotropy also affects the contact pressuredistribution and steady state roll force. In the present work, a 2D plane strain finite element rollingmodel is used for a detailed sensitivity study of the multitude of parameters that affect the verticalpressure distribution and the steady state roll force. The considered model parameters are materialanisotropy, entry sheet thickness, roll radius, tensions, coefficient of friction and roll gap.

Abstract: Thermoelectric generators (TEGs) are vital, reliable energy sources for both extreme environments such as deep space exploration and off-grid terrestrial applications, as well as emerging fields like wearable energy harvesters and biocompatible medical sensors. This study focuses on tin selenide (SnSe) combined with ductile silver sulfide (Ag₂S) to leverage their complementary properties: SnSe’s promising thermoelectric performance and mechanical robustness for homojunction TEGs, and Ag₂S’s exceptional ductility and thermal sensitivity ideal for flexible, biocompatible devices. Materials were synthesized using scalable powder metallurgy and spark plasma sintering (SPS) techniques, ensuring reproducibility and microstructural control tailored for these diverse applications. Our Bi-doped polycrystalline SnSe exhibits a unique polarity switching phenomenon and anisotropic behavior influenced by dopants (Bi, Ag, In), enabling optimized thermoelectric and mechanical properties that reduce interfacial stresses and enhance durability in harsh conditions. Meanwhile, the Ag₂S materials combine thermoelectric efficiency with fast thermal response and flexibility, suited for continuous physiological monitoring in wearable systems. The hybrid integration of SnSe homojunctions with flexible Ag₂S devices opens new possibilities for durable, efficient thermoelectric energy harvesting across wide temperature gradients in aerospace and biomedical fields.