基于局部法由示波冲击试验对断裂韧性的预测

研究了基于局部法由冲击试验对三点弯曲试样断裂韧性的预测。通过对X65管线钢韧脆转变温度下的示坡冲击及三点弯曲试验，得到示波冲击试验每个试样的能量-时间、载荷-时间、载荷点位移一时间的关系曲线和三点弯曲试验每个试样的断裂韧性值。利用有限元方法分析了示波冲击及三点弯曲试样裂纹尖端的应力场，通过自编程序求出示波冲击试样和三点弯曲试样的材料局部断裂参量，验证了临界成布尔应力符合局部法理论中的双参数成布尔分布，且证明了对本研究的两类试样，临界成布尔应力与试样尺寸和加载形式无关。基于局部法在脆性断裂条件下成功地实现了由示波冲击结果来预测三点弯曲试样的断裂韧性，不仅验证了局部法理论对X65管线钢的适用性，而且证明基于局部法可以通过冲击吸收功来预测和评价材料的断裂韧性。

Evaluation of Fracture Toughness of Three-Point Bend Specimen from the Instrumented Impact Test Based on the Local Approach

The prediction of 3-point bend specimen fracture toughness from the Charpy test result based on the local approach was studied. In the instrumented impact test for Charpy V-Notch (CVN) specimen, the curves of the Charpy absorbed energy, the loading point displacement and the load respectively against time were recorded for the X65 steel in the ductile-brittle transition temperature range. The finite element method (FEM) was conducted to investigate the stress/strain fields in the vicinity of the crack (for the bend specimen) and the notch (for the Charpy specimen) tips. Then the data from FEM analysis were input into a self-programmed code, and the local parameters controlling brittle fracture were obtained from the Charpy absorbed energy results and critical fracture toughness from 3-point bend tests. It was certified that the critical Weibull stress conform to two-parameter Weibull distribution and is independent of the specimen geometry and loading pattern in the local approach. Furthermore, the fracture toughness of bend specimen was predicted from the Charpy test results based on the local approach under the condition of brittle fracture. Not only did the paper prove the theory of local approach correct, but also confirmed that fracture toughness could be evaluated by the Charpy absorbed energy based on the local approach.