Solid State Phenomena Vol. 388

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: Various heat treatments were applied to reduce quench-induced residual stresses while improving the mechanical properties of particle-reinforced aluminum composite. The residual stress distribution of samples quenched in water with different cooling media was measured. The results showed that quenching with the 30% polyethylene glycol quenchant (PAG) yields up to an 86.8% reduction in residual stress magnitude compared with cold-water quenching (CWQ). Still, the tensile properties of samples quenched in 30% polyethylene glycol quenchant were low, with a 12.5% reduction in yield strength. The experimental results show that the uphill quench (UQ) method is an effective means of reducing residual stresses induced by quenching. At the same time, the effect on tensile properties is negligible. Moreover, the study found that combining uphill quenching with short-aging treatment can further improve the residual stress, strength, and fracture toughness of SiCp/Al-Cu-Mg composites.

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: Predicting the final shape of automotive structural components after springback is a challenge to the inclusion of high strength aluminum alloys into the vehicle body-in-white. Complex deformation paths and reverse loading of sheet material during forming operations can induce significant Bauschinger effects and kinematic hardening behaviour. Capturing the through-thickness stress gradient is critical when predicting springback, which is governed by tooling dynamics, frictional forces, and material plasticity. In this study, the anisotropic behaviour of a AA6xxx-T4 aluminum alloy was characterized to calibrate a BBC2005 yield function, kinematic hardening effects were characterized through a novel uniaxial compression-tension technique, and a technology demonstrator U-shaped rail component was formed and scanned to assess the final shape after springback. Multiple model variations were analyzed in AutoForm R12, modifying simulation control parameters, binder loading condition (uniform vs. column), friction model (Coulomb vs. TriboForm), and hardening model (isotropic vs. kinematic). The use of column binder loading paired with TriboForm friction model provided the most significant improvement for thinning and springback prediction accuracy with kinematic hardening being a second order effect compared to accounting for friction and binder force.

Abstract: Accurate prediction of the forming limit curve (FLC) is critical for evaluating sheet metal formability, yet the influence of plastic anisotropy remains controversial. In this study, the yielding behavior, hardening response, and strain-rate sensitivity of DC01 steel are experimentally characterized. Different yield criteria combined with a Swift hardening law and the Marciniak-Kuczyński (M-K) model are employed to predict the FLC. The results show that the high-order non-quadratic Yld2k-2d yield criterion captures both the yielding behavior and the forming limits. Numerical experiments using this material framework are then conducted. Variations in r-values have a limited effect on the FLC, in contrast to the common notion that high r-values mean high formability, whereas the equibiaxial tensile yield stress strongly governs the right-hand side.

Abstract: Lightweighting plays a critical role in reducing vehicle emissions, a major source of air pollution in the European Union. While weight reduction during the use phase is important, environmental impacts across production and end-of-life stages must also be considered. Advanced forming technologies enable the use of high-strength materials while maintaining formability and energy efficiency. Continuous-bending-under-tension (CBT) is a promising forming technique capable of inducing higher plastic deformation than conventional processes. In this study, CBT experiments were conducted on dual-phase 1000 low-yield (DP1000-LY) steel. The material was subjected to uniaxial tensile loading combined with cyclic bending through a moving three-roll system. The effects of key process parameters, bending depth and speed ratio between the bending assembly and tensile loading, were systematically investigated. The results show that lower bending depths allow greater total deformation before fracture and result in higher tensile forces. Higher speed ratios lead to earlier failure both during and after CBT processing. Hardness measurements indicate comparable surface hardness on both sides of the specimens, regardless of single or double roll contact. These findings contribute to a better understanding of CBT process parameters and support its potential application in lightweight automotive component manufacturing.

Abstract: High-entropy alloys (HEAs), owing to their exceptionally favourable strength–ductility balance, are regarded as promising candidates for applications in the energy, automotive, and aerospace industries. A defining characteristic of face-centered cubic (FCC) high-entropy alloys is their low stacking fault energy, which facilitates deformation via mechanical twinning and promotes the activation of transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) mechanisms. The present study focuses on the development of a heterostructured material composed of CoNiFeMn and (CoNiFeMn)₉₅Mo₅ alloys. Furthermore, the Erichsen cupping test was performed to assess the formability of the produced material and to evaluate its suitability for deep drawing applications.