断裂仿真中的网格尺寸效应与断裂曲线修正

MESH SIZE EFFECT AND FRACTURE CURVE CORRECTION IN FRACTURE SIMULATION

有限元仿真模拟方法可实现对结构材料从变形到破坏全过程的有效预测,而仿真模型建立的精度对于预测的准确性至关重要。应用有限元对标优化方法建立DP780材料的光滑拉伸、缺口拉伸及剪切拉伸试样的准静态仿真模型。划分不同网格尺寸,逆推得到材料的大变形本构曲线,以及各试样的应力三轴度、罗德角参数,系统研究了网格尺寸对材料拉伸本构曲线及韧性断裂参数逆推结果的影响。基于Lou-Huh(2012)断裂准则模型建立了不同网格尺寸下的断裂曲线。采用GISSMO理论建立断裂应变的网格尺寸效应修正函数,并对平面应力条件下的断裂曲线进行修正。研究结果表明:随着网格的细化,塑性应变-真应力曲线的对标结果向大应变方向延伸并趋于收敛,相同试样所标定的应力三轴度值与临界断裂应变值增大。随着网格尺寸的增大,临界断裂应变呈现指数形式递减,网格尺寸大于2 mm后趋于平稳。基于网格尺寸效应修正的韧性断裂模型可有效降低材料断裂仿真分析对网格尺寸的敏感性。

The finite element simulation method can effectively predict the whole process of structural materials from deformation to failure,and the accuracy of simulation model establishment is crucial for the accuracy of prediction.The finite element benchmarking optimization method was used to establish the quasi-static simulation model of smooth tensile,notched stretch and shear tensile specimens of DP780 material.The influence of grid size on the tensile constitutive curve and ductile fracture parameters of the material was systematically studied by inverting to obtain the large deformation constitutive curve of the material,as well as the stress triaxial degree and Rhode angle parameters of each sample.Based on the fracture criterion model of Lou-Huh(2012),the fracture curves under different mesh sizes were established.The GISSMO theory is used to establish the mesh size effect correction function of the fracture strain,and the fracture curve under the plane stress condition is corrected.The results show that with the refinement of the grid,the benchmarking results of the plastic strain-true stress curve extend to the direction of large strain and tend to converge,and the triaxial value of stress calibrated and the critical fracture strain value of the same specimen increase.With the increase of grid size,the critical fracture strain decreases exponentially,and the grid size tends to be stable after being greater than 2 mm.The ductile fracture model based on grid size effect correction can effectively reduce the sensitivity of material fracture simulation analysis to mesh size.