应力波载荷下电阻点焊基本结构的冲击响应与破坏机理研究

In order to reveal the effects of stress wave on impact response and fracture mechanism of structures with resistance spot welds (RSW), fundamental tests (FT) for elementary RSW structures (ERSWS) impacted by simplified projectiles (SP) are to be presented highlighting basic character and law. An advanced experimental investigation for the deformation and fracture of ERSWS induced by the SP-ERSWS coupling loading and the base-RSW material interface effect is to be performed by using Photron Fastcam Ultima APX-RS, VIC-3D strain measure system and VISAR and to be microscopically examined by using SU-70 SEM. Base and RSW materials are to be quasi-statically and dynamically tested in different types of classical specimens to explore high strain rate constitutive equations (HSRCE) capturing both small and large strains and dynamic fracture locus (DFL) with pressure and Lode dependence of these materials. The explored HSRCE and DFL of base, RSW and heat-affected zone (HAZ) materials are to be used to theoretically analyze and numerically simulate the dynamic response and fracture mechanism of ERSWS in FT including stress wave reflection, interaction, and induced tensile fracture (TF) at high stress triaxiality (ST), TF at low ST and shear fracture. The primary results of FT for ERSWS impacted by SP are important to optimizing RSW vehicle design and to providing experimental verification of HSRCE and DFL of base, RSW and HAZ materials used in impact crash simulation codes.

为揭示含电阻点焊的结构冲击响应与破坏机理的应力波效应，提出简化撞击物撞击电阻点焊基本结构的基础性撞击试验，凸显基本特性与规律。探索采用高分辨率高速摄影跟踪分析及激光干涉测速技术等，试验研究由撞击物-电阻点焊结构耦合的冲击载荷及母材-电阻点焊区界面效应引起的结构与材料的变形与断裂历程，并显微分析损伤演化机理。为探求与压力及罗德角相关的母材、电阻点焊区材料的高应变率本构方程及动态断裂轨迹，研究不同类型试件的准静态及动态力学实验，且探讨至大应变复杂状态。研究得到的这些材料及热影响区材料的动态本构与断裂特性用于理论分析与数值模拟基础性撞击试验中呈现的冲击响应与断裂机理，其中包括应力波从自由面反射、与物质界面相互作用等及其引起的高、低应力三轴性状态下的拉伸断裂以及剪切断裂。基础性撞击试验的结果可应用于优化含电阻点焊的运载体设计，也可为含电阻点焊的结构撞毁数值模拟所用的本构方程与断裂轨迹提供实验验证。

实验研究弹丸撞击TRIP800钢/QP980钢电阻点焊（RSW）基本结构的瞬态应力波响应以及终态变形与破坏效应。气炮驱动弹丸撞击RSW试件，VISAR测试试件背部自由面速度历史，SDDM及SEM观测回收试件。从应变受控的动态拉伸实验，得到QP980钢在高应变率加载下的TRIP效应，构建了QP980钢的计及相变的动态本构方程。基于对QP980钢RSW熔化区（FZ）马氏体的采用DIC技术的准静态及动态一维应力 压缩试验，提出了FZ马氏体的动态压缩本构方程。设计QP980钢RSW层裂试验，由VISAR测试结果，得到层裂强度为1977-2784Mpa。对于小型多弹丸撞击RSW试件实验，基于应力波理论，分析VISAR测试结果和回收试件的母材界面分离。从理论与实验的结合上揭示如下机理：旁侧稀疏波使冲击波衰减为弯曲的应力波，具有弹性先驱波的弯曲应力波与RSW试件中诸多的材料界面和自由面相互作用，造就试件各处随时间变化的应力三轴性和应力罗徳角，引起VISAR测到的复杂波形以及回收试件的母材界面分离。对于较大的多弹丸以较高的速度撞击，RSW试件的母材分离可导致RSW焊点的崩裂，此种断裂机理不同于层裂。对于大型单弹丸撞击RSW试件实验，揭示了RSW试件缺口顶端（notch tip)的冲击响应特性：塑性应变在此处高度集中，局域化应变或引起裂缝，或劈裂焊点。数值模拟显示了焊点的被劈裂过程：裂缝发生在notch tip ,传播横过焊点界面並劈裂焊点。数值模拟也再现了典型实验的全过程，展现了RSW试件特征位置中特征点的应力三轴性和应力罗德角随时间的变化，对应于不同机理的变形和破坏，其中包括动态拉伸断裂和剪切断裂。回收试件的SEM分析表明，RSW焊点的动态断裂属于脆性断裂和延性断裂的混合。