试样厚度对韧脆转变温度区间的影响

Effect of specimen thickness on the shift of the ductile-to-brittle transition curve

关键词:  断裂韧性  试样厚度  韧脆转变温度  裂尖拘束

Key words:  fracture toughness  test specimen thickness  ductile-brittle transition temperature  crack-tip constraint

摘要:

根据BSI 7448 Part I标准，测定了海洋平台用钢E36以裂纹尖端张开位移(CTOD)为表征的韧脆转变温度曲线. 通过改变试样厚度，研究面外拘束对韧脆转变温度区间的影响并分析了其变化规律. 结果表明,E36钢具有典型的韧脆转变特征，其韧脆转变温度曲线可以用Boltzmann函数进行拟合，具有良好的相关性；试样厚度越大，韧脆转变温度越高，断裂性能下降. 通过有限元模拟分析三维裂纹尖端应力状态，选择了面外拘束参数Tz，用来阐述厚度效应对韧脆转变温度的影响，具有良好的相关性.

Abstract:

According to BSI 7448 Part I, this paper designed three types of CTOD specimens with different thickness B of E36 steel, and CTOD tests were carried out at various temperatures to determine their ductile-brittle transition temperature curve. The test results revealed that E36 steel shows typical ductile-brittle transition characteristic and its ductile-brittle transition curve can be fitted well by Boltzmann function. What’s more, with the increase of the test specimen thickness(TST), the ductile-brittle transition curve shifts to higher temperature. In order to investigate the TST effect on the fracture toughness, an elastic-plastic finite element method (FEM) is used to analyze the stress distributions ahead of crack tips. We found that the out-of-plane constraint parameter Tzcan demonstrate the TST effect on the ductile-brittle transition temperature.