DEVELOPMENT OF DYNAMIC FRACTURE TOUGHNESS TESTING APPARATUS

本年度，利用目前开发的动态断裂韧性测试系统，对某核压力容器钢A508 3级在自下至上架子的宽温度范围内的动态韧性值进行了评估，并与文献中三点弯曲试验得到的静态值进行了比较。结果表明，动态韧性数据比静态韧性数据小30 ~ 50%，转变温度向更高温度范围移动了40 ~ 50℃。在上架温度范围内，动态韧性数据与静态数据相比也略有降低。表面力加载试验得到的韧性数据与体力试验得到的韧性数据吻合较好，但表面力加载数据数量很少。结果表明，裂纹尖端附近的焦耳加热对断裂韧性数据的影响在实际应用中几乎可以忽略不计。此外，为了准确地描述动态韧性断裂现象，似乎必须同时考虑高应变率相关的塑性和惯性力。然后，基于隐式粘塑性公式和动态非线性断裂力学，开发了有限元分析程序，用于对动态韧性数据进行重新评估。结果表明，在断裂参数计算中考虑应变率效应后，上架温度范围内的动态韧性数据提高了约5%。但是，修改后的动态数据仍然比静态数据小。采用基于计算机图像处理技术的动态应变测量系统，对j积分等断裂力学参数进行了实验评估。该方法根据塑性变形理论，对图像处理技术测得的应变分布计算应力分布。然后根据通常的路径积分方案计算J积分。得到的J积分值具有良好的路径独立性，且与COD法得到的J积分值吻合。由于该方法利用的是非常接近裂纹尖端的应变-应力数据，因此可以应用于计算任意形状二维裂纹试样的j积分。少

In this year, using the dynamic fracture toughness testing system developed so far, the dynamic toughness values of a nuclear pressure vessel steel A508 class 3 were evaluated in a broad temperature range from lower self to upper shelf, and compared with the static values obtained from the three point bending test in literature. It was shown that the dynamic toughness data seemed about 30 to 50% smaller than the static ones, and that the transition temperature shifted by 40 to 50 deg to the higher temperature range. In the upper shelf temperature range, the dynamic toughness data were also a little reduced compared with the static data. The toughness data obtained from the surface force loading test were well coincident with those from the body force ones although the number of surface force loading data was very small. It is expected from the result that the influences of the Joule heating at the vicinity of the crack tip on the fracture toughness data are almost negligible in practic … More e.Also, it seems that the high-strain-rate dependent plasticity as well as inertia forces must be taken into account simultaneously in order to describe accurately the dynamic ductile fracture phenomena. Then we depeloped the finite element analysis program based on an implicit visco-plastic formulation as well as a dynamic and nonlinear fracture mechanics, which was utilized to re-evaluate the dynamic toughness data. The results showed that the dynamic toughness data in upper shelf temperature range increased by about 5% in consideration of strain-rate effects for the fracture parameter calculation. However, the modified dynamic data were still smaller than the static data.The dynamic strain measurement system based on the computer picture processing technique was applied to experimentally evaluate fracture mechanics parameter such as the J-integral. In this method, basing on the deformation theory of plasticity, one calculates the stress distribution for the strain distribution measered by the picture processing technique. Then the J integral can calculated according to the usual path integration scheme. The obtained values of the J-integral had the good path independence and the coincidence with the J integral value from the COD method. The present method can be applied to calculate the J-integral of any shaped two-dimensional cracked specimen since it utilizes the strain-stress data very close a crack tip. Less