Strain rate sensitivity and dynamic failure mechanisms of penetration-resistant ultra-high-strength armor steel
摘要
Armor steel, as a critical protective material, requires in-depth investigation of its dynamic mechanical behavior and failure mechanisms to enhance ballistic resistance. This study systematically calibrated the Johnson-Cook (JC) constitutive model and failure parameters for a novel V-microalloyed Cr-Mn-Ni-Mo medium-carbon low-alloy ultra-high-strength armor steel (UA steel) through quasi-static and dynamic test data fitting. Experimental results demonstrate that the synergistic interaction between martensite-ferrite dual-phase microstructure and morphological evolution of second-phase particles (molybdenum sulfides) under dynamic loading—transitioning from precipitation to redissolution—endows the material with both high strength (ultimate tensile strength: 2360 MPa) and exceptional toughness (dynamic tensile toughness: 253.4 MJ/m3, 179% improvement over quasi-static conditions). In ballistic tests, UA steel exhibited an average penetration depth of merely 7.3 mm against 12.7 mm armor-piercing incendiary projectiles, representing a 72% reduction compared to the in-service 675 steel. Dynamic compression tests using split Hopkinson pressure bar (SHPB) revealed significant strain rate strengthening effects within 1500 s−1–6000 s−1, with adiabatic shear band (ASB) evolution showing strong correlation to failure modes: Above 4100 s−1, the dominant fracture mechanism transitions from microvoid coalescence-induced ductile failure (dimple size: 1.43 μm) to thermal softening-driven adiabatic shear failure, accompanied by ASB width expansion from 8.3 μm (4142 s−1) to 30 μm (6000 s−1). During penetration, ASBs propagate inward from the crater base (average width: 18.2–52.2 μm), governing material failure through branching and microcrack linkage. This work elucidates the intrinsic relationship between strain rate-driven ASB evolution and fracture mode transition, providing theoretical foundations for designing high-performance armor steels and simulating their impact responses.