小尺寸CT试样断裂行为的GTN细观损伤模型研究

Study on Fracture Behavior of Mini-CT Specimen Based on GTN Mesoscopic Damage Model

基于国产A508-Ⅲ钢的单轴拉伸测试,构建了Ramberg-Osgood力学本构模型和GTN(Gurson-Tvergaard-Needleman)细观损伤模型,并对模型参数进行了标定,开展了不同温度下小尺寸CT(1/6CT)试样的断裂韧性测试,采用规则化方法计算得到裂纹扩展阻力曲线(J-R曲线),分析了测试温度对材料断裂性能的影响。结果表明,随着温度从-100℃度降低至-130℃,断口韧窝区的宽度由43μm缩减至10μm,平均韧窝尺寸从0.3μm缩小至0.05μm,材料的塑性变形能力随着温度的降低而脆化。基于构建的力学本构模型和GTN细观损伤模型,采用有限元法分析了1/6CT试样从裂纹萌生、扩展至失效断裂的过程。结果表明,J-R曲线随着温度的下降而降低,断裂韧性(J_(IC)值)和裂纹扩展量(Δa)的降幅分别为43%和3%,相对误差不超过5%。这表明,基于GTN细观损伤模型的数值方法是研究小尺寸CT试样断裂行为的一种简便、有效的方法。

To ensure the safe operation of nuclear power plants,the status of the reaction pressure vessel needs to be monitored in real time.The fracture toughness of the domestic A508-Ⅲsteel,which is the main material,can be used as the primary indicator to reflect its condition.Recently,the size of specimens used for nuclear material testing and analysis is gradually decreasing,and this trend helps to improve the accuracy and efficiency of testing.The fracture behavior of mini-CT(1/6CT)specimens from a meso-scale perspective was studied in this paper,to reveal the fracture mechanism for a better understanding of the material properties.The uniaxial tensile testing of domestic A508-Ⅲsteel was carried out with the aim of gaining insight into this fracture behavior.Based on the testing results,the Ramberg-Osgood mechanical intrinsic model and the GTN(Gurson-Tvergaard-Needleman)meso-damage model,those can accurately describe the mechanical behavior of the material,were constructed.The model parameters were also calculated and determined based on the testing data,and the reliability of the models was verified by comparing the testing data with the simulation results.Subsequently,fracture toughness tests of 1/6CT specimens at different temperatures were also conducted to understand the effect of temperature on the fracture properties of the material by analyzing the morphological characteristics of the fracture.The results show that the width of the fracture toughness zone shrinks from 43μm to 10μm,and the average toughness size shrinks from 0.3μm to 0.05μm as the temperature decreases from-100℃to-130℃.The plastic deformability of the material becomes more brittle as the temperature decreases.Based on the constructed mechanical intrinsic model and the GTN meso-damage model,the 1/6CT specimen was analyzed from crack sprouting and expansion to failure fracture using finite elements,and the results show that the J-R curve decreases with the decrease of temperature,and fracture toughness value(J_(IC))and crack extension length(Δa)decrease by 43%and 3%respectively,with an error of no more than 5%.This indicates that the numerical method based on the GTN meso-damage model is a simple and effective way to study the fracture behavior of mini-CT specimens.