基于局部法定量表征面外拘束效应对转变区间断裂韧度的影响

拘束效应制约了主曲线法表征转变区间的断裂韧度,局部法作为一种细观解理断裂力学方法有望用来解决这个问题。利用两种不同拘束配置的三点弯曲试样,通过交点法标定了国产压力容器用钢Q345R的局部法参量,借助于韧性换算思想将低拘束的试样断裂韧度结果换算成高拘束的结果。通过对比高拘束实测参考温度T 0值,验证了模型的正确性。基于此提出了一种预测不同面外拘束试样参考温度的方法,通过改变厚度的大小,研究了三点弯曲试样厚度对T 0的影响。结果表明,试样厚度越大,韧脆转变温度越高,断裂韧性下降,当厚度大于25.4 mm后会出现一个韧性平台,接近平面应变状态;厚度低于该值会造成严重的拘束缺失,T 0值远大于真实值会造成危险评估,尤其对于低硬化材料,这种现象更为明显。

Quantitative Analysis of the Effect of Out-of-plane Constraint on the Fracture Toughness of Transition Zone Based on Local Approach

The constraint effect constrains the fracture toughness of the master curve method to characterize the ductile-to-brittle transition region.The local approach is expected to solve this problem as a mesoscopic cleavage fracture mechanics method.The three-point bending specimens of two different constraint configurations were used to calibrate the local approach parameters of the China-made pressure vessel steel Q345R by the intersection method,and convert the fracture toughness results of low-constrained specimens to those of high-constrained specimens by means of the thought of toughness conversion.The correctness of the model was verified by comparing the high-constrained measured reference temperature T 0 with the predicted value.Based on this,a method for predicting the reference temperature of different out-of-plane constraint specimens was proposed.By changing the thickness,the influence of the thickness of the three-point bending specimen on T 0 was studied.The results show that the larger the thickness of the specimen,the higher the ductile-brittle transition temperature and the lower the fracture toughness.When the thickness is greater than 25.4 mm,a toughness platform will appear,which is close to the plane strain state.A thickness below this value will cause serious constraint loss,and the T 0 value is much larger than the true value,resulting in a hazard assessment,especially noticeable for low hardening materials.