A Study on the Applicability of Dynamic Linear Fracture Mechanics and Its Extension

对动态断裂力学的研究进行了综述，指出已有许多关于冲击断裂韧性K_<Id>和快速裂纹扩展韧性K_<Id>的特殊行为的报道，这些特殊行为阻碍了线性动态断裂力学的发展。指出了开发一种可靠的测量动态断裂韧性K_<Id>和K_<Id>的方法的重要性，以及明确衬垫动态断裂力学的适用范围的必要性。本文首先对动应力强度因子K (t)的有限元计算精度进行了研究，并基于欧拉-伯努利梁理论提出了确定冲击单点弯曲试件K (t)的简单公式。利用单点弯曲冲击试验机和上述简单公式，对碳化硅、硅藻土、PSZ、氧化铝和氧化铝-氧化锆复合材料在高达1200℃的温度下进行了冲击断裂韧性K_<Id>试验。确认了裂纹表面存在接触力，并讨论了接触力对K_<Id>值的影响与加载率、试样尺寸和断裂时间等试验条件的关系。测定了铝粉/铝复合材料和铝纤维/铝复合材料在200℃温度下的冲击断裂韧性K_<Id>。C采用一点弯曲冲击试验机。在试验温度下测量了杨氏模量、泊松比和屈服应力，并通过塑性区修正计算了动应力强度因子。通过考虑基体的蠕变，对实验结果进行了定性解释。本文对短断裂时间范围内用焦散法测量K_<Id>进行了有限元模拟。由于应力发展缓慢，足以对焦散产生显著影响，因此存在检测裂纹起裂的延迟时间。考虑焦散度法检测裂纹扩展的延迟时间，对K_<Id>的一些特殊实验数据进行了解释。少

The researches on the mechanics of dynamic fracture have been reviewed and it has been pointed out that there are many reports on peculiar behaviors of impact fracture toughness K_<Id> and fast crack propagating toughness K_<ID>, and that these peculiar behaviors prevent the development of the linear dynamic fracture mechanics. The importance of developing a reliable method for measuring the dynamic fracture toughnesses K_<Id> and K_<ID> and the necessity for clarifying the extent of applicability of the liner dynamic fracture mechanics have been also pointed out.In this research, firstly the accuracy of the finite element calculation of the dynamic stress intensity factor K (t) has been studied and a simple formula for determining K (t) of an impacted one-point bend specimen has been proposed based on the Euler-Bernoulli beam theory. By using the one-point-bend impact tester and the above simple formula, an impact fracture toughness K_<Id> test has been carried out on silicon carbide, … More sialon, PSZ, alumina and alumina-zirconia composite at temperatures up to 1200^。C. The existence of the contact force acting on the crack surfaces has been confirmed and its effect on the measured K_<Id> value has been discussed in relation to test conditions such as loading rate, specimen size and time-to-fracture.The impact fracture toughness K_<Id> of alumina-powder/aluminum composite and alumina-fiber/aluminum composite has also been measured at temperatures up to 200^。C by using a one-point bend impact tester. Young's modulus, Poisson's ratio and yield stress were measured at testing temperatures, and the dynamic stress intensity factor has been calculated by applying the plastic zone correction. The experimental results has been qualitatively explained by taking the creep deformation of the matrix into consideration.A finite element simulation of measuring K_<Id> by the caustics method in the range of short time-to-fracture has been performed. It has been found that there exists a delay time to detect crack initiation because of the slowness of the development of the stress high enough to have a significant effect on caustics. Some of the peculiar experimental data of K_<Id> have been explained by taking the delay time of detection of crack extension by the caustics method into consideration. Less