Length-scale-insensitive phase-field material point method for spall fracture and adiabatic shear bands in ductile metals

• Novel S-shaped shear sample design for adiabatic shear band analysis • Superposition of tension or compression on dominant shear • Ultra-high-speed strain mapping and thermal measurements • Stress-induced martensite as in-situ indicator of local stresses Formation of adiabatic shear bands (ASB) as a deformation mechanism occurs particularly at high (shear) strain rates in metallic materials. A detailed analysis of ASB nucleation and growth, and of the contributions of the underlying mechanisms such as thermal or microstructural softening, is experimentally challenging. In this study, we present newly designed S-shaped sample geometries that allow an in-situ characterization of shear banding under different stress states. Local shear deformation occurs in a geometrically well-defined shear zone during uniaxial compression of the S-shaped samples. Considering both numerical simulations and experimental measurements, we demonstrate that the predominant shear stress can be superimposed with either tensile or compressive stresses by slightly varying the geometry of the shear zone. Moreover, we show that the sample geometry is ideally suited for the application of digital image correlation for strain (rate) mapping as well as temperature measurements at high loading velocities. Metallographic preparation of the samples prior to testing enables in-situ microstructural observations during dynamic deformation. The sample geometry is validated by dynamic experiments using a Ti-10V-2Fe-3Al alloy in a Split-Hopkinson Pressure Bar (SHPB) under nominal strain rates of >10 3 s -1 (which corresponds to local shear rates up to 10 5 s -1 ). Our experimental and numerical results demonstrate that the novel sample geometry facilitates detailed investigations focused on the formation and growth of adiabatic shear bands.

Effect of nanoprecipitates on the formation of adiabatic shear band in high-entropy alloy

High-speed blanking processes are of major interest for manufacturing sheet components from high-strength materials, as not only high-quality surfaces but further excellent properties are enabled. Reason for this are adiabatic shear bands (ASB) formed in the shear zone during the process. However, up to now it is not fully understood how ASBs evolve depending on the process conditions. For the first time, surface geometry and ASB formation are investigated for an identical macroscopic stress state using different blanking speeds. A press-hardened 22MnB5 steel is blanked with punch velocities ranging from 0.12 to 17m/s using different machine drive concepts (mechanical, hydraulic and electromagnetic), resulting in nominal shear strain rates of up to nearly 100,000,000s⁻¹. The velocity significantly influences ASB length and width as well as the microstructure and hardness of the blanked surfaces. For 17m/s blanking speed, an ASB covering the full-length of the blanked surface, i.e. the complete sheet thickness, is realized. Further, for high velocities, ASBs not only dominate the appearance of the blanked surface but also lead to significantly lower roughness, when compared to conventionally blanked surfaces. This study lays the foundation for future work on tailoring functional surfaces using high-speed blanking.

Failure analysis and microstructural design for adiabatic shear banding in a Ti–Al–Mo–Cr–Fe dual-phase titanium alloy under dynamic loading

During high-speed milling, stainless steel is prone to generating adiabatic shear bands in the cutting zone, which affects the cutting quality. The main factors causing adiabatic shear are high temperature and elastoplastic instability. An energy dissipation model for stainless steel milling was established and analyzed based on adiabatic shear. A series of flood and cryogenic cooling milling experiments with liquid nitrogen (LN2) and LN2+liquid carbon dioxide (LCO2) cooling were carried out. Simultaneously, an innovative research about the effect of LN2+LCO2 on adiabatic shear was executed. The results show that the energy dissipation is mainly determined by the influence factors such as milling force and shear strength at the same milling parameters. Compared with flood cooling, the influence factors are all increased at LN2 cryogenic temperature conditions, and the energy dissipation result is also enhanced. At 200 m /min, the temperature in the cutting zone of LN2+LCO2 is below 60°C compared with 400°C of flood cooling. The formation of serrated chips is related to the brittle cutting characteristic at lower temperature. Meanwhile, the tool wear is obviously inhibited, and the machined surface is improved with a roughness of less than Ra 0.3μm at vc = 150m/min, which is lower than Ra 0.7μm of flood cooling. Conclusion: due to the instantaneous cold brittleness of LN2 and lubricating effect of LCO2, there is difficult to obtain the conditions at the shear zone for generating adiabatic shear bands, and the milling performances are improved at the same time.

A universal statistics-based material inhomogeneity “Fingerprint” governing spontaneous adiabatic shear bands in thick-walled cylinders

Quasi-static tensile strength as an indicator of dynamic compression performance and adiabatic shear banding susceptibility in a metastable β-titanium alloy

Adiabatic shear banding (ASB) is a critical failure mechanism in titanium alloys subjected to high-strain-rate deformation, and its initiation is strongly influenced by the initial crystallographic texture. The dynamic response and ASB sensitivity of extruded and annealed Ti-6Al-4V (TC4) alloy rods were investigated under dynamic compression of cubic specimens along the extrusion direction (ED) and the transverse direction (TD) at a strain rate of 2500 s-1. Split Hopkinson pressure bar (SHPB) tests combined with digital image correlation (DIC) were employed to obtain the stress-strain response and the evolution of strain localization. A dislocation density-based crystal plasticity finite element model (CPFEM), incorporating the measured texture, was established to elucidate the correlation between texture and ASB behavior. The experimental results show that TD specimens exhibit a yield strength approximately 100 MPa higher than that of ED specimens, while both orientations display comparable post-yield hardening behavior. ASB initiation occurs earlier in TD (compressive strain ~0.13) than in ED (~0.23), indicating greater ASB sensitivity in the TD orientation. The CPFEM successfully reproduces the directional stress-strain responses and the observed localization morphology, enabling mechanistic interpretation in terms of slip activity and thermomechanical coupling. The simulations indicate that ED loading is dominated by prismatic ⟨a⟩ slip, resulting in lower flow stress and more dispersed strain localization. In contrast, TD loading is governed primarily by pyramidal ⟨c + a⟩ slip, leading to elevated flow stress and intensified localization. The higher ASB sensitivity in the TD orientation is therefore attributed to texture-controlled slip-mode partitioning, enhanced thermomechanical coupling, and a more concentrated crystallographic orientation distribution that facilitates intergranular slip transfer. These findings provide guidance for tailoring microtexture to mitigate dynamic failure in titanium alloys subjected to high-strain-rate loading.

In the face of high-strain-rate threats such as explosions, collisions, and high-velocity debris impacts, understanding the failure behavior of materials and structures under impact loading is critical for improving structural protection and service reliability. This review systematically classifies the typical failure mechanisms of materials under impact conditions into three categories based on dominant factors: wave-driven failure, inertia/localization-driven failure, and brittle fracture-dominated failure. Corresponding modes include spallation, interfacial delamination, adiabatic shear banding, dynamic voiding and ductile fracture, dynamic cleavage, intergranular fracture, and fragmentation. On this basis, the paper compares the failure behaviors of monolithic components and hybrid material systems. The former are primarily governed by intrinsic material properties, showing strong strain-rate sensitivity and relatively clear, single-mode failure paths. In contrast, composite or hybrid structures exhibit significantly more complex responses due to material heterogeneity and strong interfacial effects, often involving multiple damage mechanisms interacting simultaneously. This work provides theoretical insight for material selection and structural configuration in impact-resistant systems, laying a foundation for future studies on failure modeling and structural design.

An in-situ study on the formation mechanism of adiabatic shear band in refractory high-entropy alloys

Recent studies on dynamic pore collapse have revealed significant development of shear localization, which can lead to material failure in porous structures and hot spot generation in energetic materials. These findings have dramatically improved the understanding of failure mechanisms during pore collapse but also prompt further investigation of realistic porous materials. In particular, porous media consist of many pores and porous networks. Even in low-porosity materials, pores can form in close proximity during the manufacturing process, leading to the critical question of pore–pore interaction during collapse under dynamic loading conditions. This study investigates, via plate impact experiments coupled with high-speed internal digital image correlation and shadowgraphy techniques, the collapse of two pores in shock-compressed PMMA at stresses between 0.4 and 1 GPa. The results of these experiments provide new insights into shear localization in pore collapse, in addition to distinct interactions between pores. Shadowgraphy measurements reveal novel, direct visualization of shear band development and crack evolution from pore surfaces. Spacing between adiabatic shear bands is measured over a range of impact stresses and is predicted accurately by the Grady–Kipp model. Pore interactions are found to effect a transition in the impact stress threshold at which different failure mechanisms initiate and are also found to possibly influence preferential sites for shear cracking. Throughout the study, numerical and theoretical models are leveraged to understand shear localization behavior. The role of baroclinicity and wave interactions between the pores is used to elucidate interaction mechanisms between pores.

Hf-induced transition in deformation mechanism enhances dynamic performance of NbTaTiZr refractory high-entropy alloy

Loading paths dependence of deformation behavior and adiabatic shear band failure in Mg–Al–Mn alloy under high strain rate loading

Adiabatic shear bands (ASBs) are a critical mechanism for damage initiation under high strain-rate shear impact, whereas the high-current-density-induced shear deformation mechanism of armature and rail materials remains unclear. This study employs a pulsed power source and an electromagnetic repulsion disk device to investigate the shear deformation characteristics of typical armature and rail materials under high strain rates (≥10<sup>4</sup> s<sup>-1</sup> ) coupled with high current densities (≥10<sup>8</sup> A/m<sup>2</sup> ). The results show that the ASB formation energy barrier decreases in the following order: pure copper, oxygen-free copper, CuCrZr alloy, Al<sub>2</sub>O<sub>3</sub> dispersion-strengthened copper alloy, brass, and 7075 aluminum alloy. Therefore, 7075 aluminum alloy is the most prone to ASB formation, followed by brass, while other copper-based rail materials rarely exhibit ASB features. Both 7075 aluminum alloy and brass exhibit a current-induced suppression effect on crack propagation and ASB formation. Electron backscatter diffraction (EBSD) analysis reveals that numerous fine equiaxed grains are present within the shear bands of 7075 aluminum, and the texture within the bands significantly differs from that of the surrounding matrix. With increasing current density, the grain size within the band increases, while the fraction of dynamically recrystallized grains decreases markedly. The formation of ultrafine grains and the texture evolution can be reasonably explained by mechanically assisted rotational dynamic recrystallization. The results indicate that thermal softening alone is insufficient to induce ASB formation; instead, softening caused by rotational dynamic recrystallization is the dominant mechanism. The current-induced temperature rise was calculated, and the yield strength drop under high-strain-rate loading with current was measured, based on which the width of adiabatic shear bands (ASBs) under current was determined. The theoretical predictions show good agreement with experimental results. The results indicate that the temperature rise and softening effect induced by pulsed current lead to an increase in ASB width, which intensifies energy dissipation, suppresses dynamic recrystallization, and inhibits the formation of adiabatic shear bands.

Adiabatic Shear Band versus Twinning: Hf-driven cryogenic deformation mechanism transition in NbTaTiZr at high strain rate

Evolution of adiabatic shear band in 2000 MPa grade ultrahigh strength steel during high strain rate compression

Adiabatic shear behavior of pearlitic heat-resistant steel under fragment-simulating projectile impact

Adiabatic shear bands in additively manufactured Ti-6Al-4V under high strain rate and elevated temperature conditions

Adiabatic shear bands (ASBs) are narrow zones of intense plastic deformation that form in structural materials subjected to high strain-rate impacts, often leading to catastrophic failure. While ASB formation at room temperature is well documented, their evolution under elevated temperatures remains inadequately understood. This study investigates the formation and microstructural evolution of ASBs in quenched and tempered AISI 4340 steel subjected to dynamic loading at both room temperature (25 °C) and elevated temperatures (300-600 °C) using a direct impact Hopkinson pressure bar (DIHPB). Comprehensive microstructural characterization using optical microscopy, SEM, TEM, HRTEM, and EELS reveals that ASBs consistently formed at all temperatures tested, though their morphology and internal structure evolved significantly with temperature. Room-temperature impacts led to white-etching ASBs characterized by ultrafine grain refinement, high dislocation density, and carbide dissolution. At elevated temperatures, both white- and black-etching recrystallized ASBs developed, including dynamic recovery, recrystallization, carbide retention, and reprecipitation. Despite coarser grains at high temperatures, ASBs maintained higher hardness than surrounding regions due to carbide reprecipitation effects. Microcrack initiation and propagation were observed within white-recrystallized ASBs at 600 °C, linked to carbide fragmentation and redistribution preceding the onset of high temperature effects. These findings highlight that while temperature minimally affects ASB susceptibility, it profoundly alters post-impact microstructural evolution. The results advance our understanding of thermomechanical responses in structural steels under extreme conditions and offer valuable insights for designing materials resistant to failure in high-temperature, high-strain-rate environments. • AISI 4340 steel exhibited ASBs from 25 to 600 o C during high strain-rate impacts • Evolved ASBs at high temperatures showed dynamic recovery and recrystallization • Recrystallized grains within ASBs at high temperatures due to high stored energy • Microcracks formed within ASBs at 600 o C due to carbide fragmentations