Fundamental Studies on the Limiting Velocity of Fast Dynamic Fracture in Solids

在试验方面，利用目前研制的弹簧约束加载机，对均质材料进行了动态断裂试验。结果表明，目前世界上最先进的超高速摄像机系统（最大帧率：100万帧/秒，10 ns脉冲曝光时间）成功记录了超过材料剪切波速c_s 75%的极限快速断裂，该断裂速度超过了近尖端奇异应力场理论预测的极限裂纹速度。然而，考虑到近尖端应力场的高阶项，从理论上证明了。75^c_s是可能的。进一步阐明了裂纹尖端总能量流通量（单位时间内进入裂纹尖端的总能量通量）与断口表面粗糙度之间的关系。结果表明，随着ψ_<总>的增大，断口表面粗糙度增大。断口表面粗糙度可能引发动态裂纹分支断裂。动态裂纹分支的控制条件一直是人类长期未解决的问题。在以往的实验研究中，我们已经证明了裂纹尖端总能流通量临界判据（裂纹尖端总能流通量ψ_<total> total超过临界材料值时发生动态双裂纹分支）。在实验室中，我们发展了基于Delaunay自动三角剖分（MFEMBOAT）的非常通用的移动有限元方法。利用MFEMBOAT首次成功地模拟了动态多裂纹分支现象。仿真结果表明，裂纹尖端临界总能量流准则对动态多裂纹分支也是有效的。关键词：(1)2),(3)相干梯度传感（CGS）方法，(4)超高速摄像机，(5)跨音速I界面断裂，(6)马赫冲击波，(7)1高能冲击断裂试验机

In experimental aspect, using the presently developed spring constraint loading machine, dynamic fracture tests in homogeneous materials were carried out. As the results, a limiting fast fracture that exceeds 75% of the shear wave velocity c_s of the material was successfully recorded by the presently developed world most advanced ultrahigh-speed video camera system (maximum framing rate : one million frames per second, 10 ns pulse exposure time) this fracture velocity exceeds the limiting crack velocity predicted by the near-tip singular stress field theory. However, taking account of the higher order terms of the near-tip stress field It was theoretically proved that the ultrahigh-sped straight fracture of.75^c_s is possible.to occur Furthermore, relation ship between crack-tip total energy flow flux (ψ_<totai> total energy flux in to the propagating crack tip per unit time) and fracture surface roughness was clarified. It was found that the fracture surface roughness increases for increasing ψ_<total>. Fracture surface roughness may triggers dynamic crack branching fracture.The governing condition of dynamic crack branching has been a long-term unsolved problem for humankind. In our previous experimental studies, we have proved the critical crack-tip total energy flow flux criterion (dynamic two crack branching occurs when the crack-tip total energy flow flux ψ_<total> total exceeds a critical material value)In our laboratory, very versatile moving finite element method based on Delaunay automatic triangulation (MFEMBOAT) has been developed. Using MFEMBOAT, dynamic multiple crack branching phenomena was firstly succeeded. The simulation results proved the critical crack-tip total energy flow flux criterion is also valid for the dynamic multiple crack branching.Keywords : (1) 2),(3)Coherent Gradient Sensing(CGS)Method, (4)Ultrahigh-speed Video camera, (5)Transonic I Interface Fracture, (6)Mach Shock wave, (7)1High Energy Impact Fracture Testing Machine