To determine the effects of Ti and mixing entropy (ΔS_mix) on the structure and mechanical proper-ties of Zr-Ta alloys and then find a new potential energetic structural material with good me-chanical properties and more reactive elements, Ti_xZr_2.5−xTa (x = 0, 0.5, 1.0, 1.5, 2.0) alloys were investigated. The XRD experimental results showed that the phase transformation of Ti_xZr_2.5−xTa nonequal-ratio ternary alloys depended not on the value of ΔS_mix, but on the amount of Ti atoms. With the addition of Ti, the content of the HCP phase decreased gradually. SEM analyses revealed that dendrite morphology and component segregation increasingly developed and then weakened gradually. When x increases to 2.0, Ti_xZr_2.5−xTa with the best mechanical properties can be ob-tained. The yield strength, compressive strength and fracture strain of Ti_2.0Zr_0.5Ta reached 883 MPa, 1568 MPa and 34.58%, respectively. The dependence of the phase transformation and me-chanical properties confirms that improving the properties of Zr-Ta alloys by doping Ti is feasible.

This study developed a twinning-induced plasticity (TWIP) steel characterized by lightweight, high strength, and high toughness. Tensile tests were conducted at strain rates ranging from 10⁻⁴ to 6500 s⁻¹ using a universal testing machine and a Hopkinson bar to evaluate the material’s mechanical properties. A Johnson–Cook (J-C) constitutive model was developed based on the mechanical performance data for high-strain behavior. X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) were employed to analyze the microstructural evolution and fracture mechanisms of tensile specimens. The results show that the TWIP steel exhibits positive strain rate sensitivity (PSRS) under both quasi-static and dynamic strain rates. At high strain rates, the yield strength increased from 1133.0 MPa to 1430.6 MPa, and the tensile strength rose from 1494.3 MPa to 1640.34 MPa. The J-C model fits well at strain rates of 1000 s⁻¹ and 3000 s⁻¹, but fitting errors increase at higher strain rates due to the competition between thermal softening and strain hardening. XRD results reveal no significant phase transformation occurred during deformation, with twinning being the dominant mechanism. As the strain rate increased, deformation twins appeared in the material’s microstructure, inducing plastic deformation during tensile testing. The twin volume fraction increases progressively with the strain rate. At high strain rates, secondary twins emerge and intersect with primary twins, refining the grains through mutual interaction. The TWIP effect enhances the material’s mechanical performance by improving its strength and ductility while maintaining its lightweight nature.

钢框架焊接梁柱节点在地震作用下往往容易产生脆性裂纹, 裂纹的发展和损伤累积将导致节点延性降低, 发生脆性断裂。本文旨在探究节点在地震往复荷载作用下的损伤性能, 分析其主要影响因素, 提出有效的损伤评估模型, 为后续节点损伤数值模拟提供基础, 为钢框架的抗震设计提供参考。 1. 通过足尺节点试验, 分析加载幅值、加载历程和荷载峰值对节点损伤性能的影响; 2. 基于试验结果, 标定并验证3 种经验损伤

In order to study the high strain rate effect of the high-strength steel structure weld and its heat-affected zone material under the action of explosion, in this paper, the Q460JSC and HQ600 high-strength steel welded specimens were quasi-static and high strain rate tensile test of 1500/s to 5000/s using electronic universal testing machine and Hopkinson rod tester. The dynamic mechanical properties of high strength steel welded joints were studied. The results show that both the weld and its heat affected zone have strain rate sensitivity, and the strength and ultimate strain are higher than quasi-static under high strain rate. The center weld strength is higher than that of the base metal but the plastic deformation ability is weak. The strength and ultimate strain of the Q460JSC heat-affected zone are about 10% lower than that of the base metal, while the HQ600 high-strength steel has a smaller drop and better weldability.