Multiple Deformation Mechanisms in Adiabatic Shear Bands of a Titanium Alloy during High Strain Rate Deformation

This work studies numerically the development of adiabatic shear banding (ASB) during high strain-rate compression of AISI 1045 steel. Plane strain and cylindrical axisymmetric compressions are simulated in LS-DYNA, considering rectangular and cylindrical steel samples, respectively. Also, a parametric analysis in height-to-base ratio is conducted in order to evaluate the effect of geometry and dimensional ratio of the sample on ASB formation. Doubly structural-thermal-damage coupled finite element models are developed for the numerical simulations, implementing the thermo-viscoplastic Modified Johnson–Cook constitutive relation and damage criterion, while further damage-equivalent stress and strain fields are introduced for the damage coupling. The simulations revealed that plane strain compression promotes more ASB formation, providing lower critical strain for ASB initiation and wider and stronger ASBs compared with axisymmetric compression. Further, X-shaped ASBs initially form during plane strain compression, while as deformation increases, they transform into S-shaped ASBs in contrast to axisymmetric compression, where parabolic ASBs are developed. Also, a lower height-to-base ratio leads to greater ASB propensity, reducing critical strain in axisymmetric compression. Finally, thermal softening is found to precede damage softening and dominate the ASB genesis and its early evolution, while in contrast damage softening drives later ASB evolution and its transition to fracture.

Numerical Study on the Development of Adiabatic Shear Bands During High Strain-Rate Compression of AISI 1045 Steel: A Comparative Analysis Between Plane-Strain and Axisymmetric Problems

Karantza,

Manolakos

2024

Adiabatic Shear Localization in Metallic Materials: Review

Guan,

Qu,

Wang

et al. 2024

In advanced engineering applications, there has been an increasing demand for the service performance of materials under high-strain-rate conditions where a key phenomenon of adiabatic shear instability is inevitably involved. The presence of adiabatic shear instability is typically associated with large shear strains, high strain rates, and elevated temperatures. Significant plastic deformation that concentrates within a adiabatic shear band (ASB) often results in catastrophic failure, and it is necessary to avoid the occurrence of such a phenomenon in most areas. However, in certain areas, such as high-speed machining and self-sharpening projectile penetration, this phenomenon can be exploited. The thermal softening effect and microstructural softening effect are widely recognized as the foundational theories for the formation of ASB. Thus, elucidating various complex deformation mechanisms under thermomechanical coupling along with changes in temperatures in the shear instability process has become a focal point of research. This review highlights these two important aspects and examines the development of relevant theories and experimental results, identifying key challenges faced in this field of study. Furthermore, advancements in modern experimental characterization and computational technologies, which lead to a deeper understanding of the adiabatic shear instability phenomenon, have also been summarized.

Recent Developments in Plastic Deformation Behavior of Titanium and Its Alloys During the Rolling Process: A Review

Ryu,

Kim,

Nahm

et al. 2024

Titanium (Ti) and its alloys are used in various applications, including aircraft frames, ship parts, heat exchangers, and evaporator tubes, because of their extraordinary properties, such as high specific strength, excellent corrosion resistance at high temperatures, good castability, and weldability. Plastic deformation plays a crucial role in securing the appropriate microstructure and strength of Ti and alloys in these applications. The rolling process, one of the most useful methods for plastic deformation, causes efficient deformation inside the materials, resulting in grain refinement, dislocation slip, and twinning. Recent studies on the rolling behaviors of Ti and its alloys have explored their crystallographic and mechanical properties. These investigations primarily analyzed the microstructural changes and their influence on the mechanical properties under different temperatures and rolling methods. This study elucidates a complex relationship between the processing conditions and the resulting properties. Therefore, this paper presents a comprehensive review of the state-of-the-art Ti rolling. Various key aspects for verifying the microstructure of Ti and its alloys are discussed, including electron backscatter diffraction analysis, Schmidt factor, and misorientation distribution.