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Assessment Method for the Effect of Strain Rate on Fracture Toughness

应变率对断裂韧性影响的评估方法

基本信息

批准号：
63850094
负责人：
TOYOSADA Masahiro
金额：
$ 8万
依托单位：
Kyushu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Developmental Scientific Research (B).
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1990
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-63850094/
关键词：
Strain Rate Temperature Rise Due To Plastic Work Strain Rate Temperature Parameter Constitutive Equation Dynamic Fracture Toughness Dynamic CT Test Dynamic COD Test Dynamic Thermo-plastic elastic FEM Strain Rate Tenperature Rise due to P

项目摘要

Constitutive relation between strain, stress, strain rate and temperature is conducted by using the strain rate temperature parameter defined by Bennet for the purpose of avoiding the vagued definition of quasistatic condition. For the purpose of obtaining the local temperature rise due to plastic work in the vicinity of a crack tip under dynamical condition, the dynamic thermodplastic-elastic FEM, in which the above constitutive equation and iterative method are used, is developed. It became clear that the plastic work converts around 90 percent of this into the heat and the remaining plastic work converts into another works such as the formation of slip band from the tensile test under several loading rates.CT tests under several loading rates and 3-point bend tests by using a drop weight testing machine are carried out for the purpose of measuring the strain distribution in the vicinity of a crack tip and the FEM show to give the good agreement with the measuring strain distribution.Moreover the distributions of the temperature rise near the crack tip of CT specimen due to plastic work under several loading rates are measured by using Thermo Viewer and the FEM results also show the good agreement with the experimental ones. Moreover the FEM results show that the yield stress in the vicinity of a crack tip keeps some constant level as a result of compensating effect of strain rate and temperature on the yield stress. This result supports that the experimental displacement behavior in the dynamic condition is similar to that in the static condition.From above results, the assessment method for obtaining the fracture toughness under the arbitrary strain rate is proposed by the fracture toughness test under static condition.

利用Bennet定义的应变率温度参数，导出了应变、应力、应变率与温度之间的本构关系，避免了准静态条件的模糊定义。为了获得动态条件下裂纹尖端局部塑性功温升，本文采用上述本构方程和迭代方法，建立了动态热塑性弹性有限元法。很明显，塑性功将其中约90%转化为热量，剩余的塑性功转化为另一种功，例如在几种加载速率下的拉伸试验中形成滑移带。为了测量裂纹尖端附近的应变分布，使用落锤试验机进行点弯曲试验，此外，利用ThermoViewer测量了不同加载速率下CT试件裂尖附近塑性功引起的温升分布，有限元计算结果与实验结果吻合较好。此外，有限元分析结果表明，由于应变速率和温度对屈服应力的补偿作用，裂纹尖端附近的屈服应力保持一定的水平。这一结果支持了动态条件下的实验位移行为与静态条件下的相似性，并由此提出了通过静态断裂韧性试验获得任意应变率下断裂韧性的评价方法。