不同材料延性断裂韧性与裂尖拘束的关联及其影响因素分析

Correlation between ductile fracture toughness of different materials and crack-tip constraint and analysis of influencing factors

基于不同材料、不同几何尺寸试样的延性断裂韧性数据,结合有限元计算,研究得到不同材料的标称化延性断裂韧性J_(c)/J_(ref)与统一拘束参数A_(d)之间的线性关联方程,其可用于基于J-A_(d)二参数法纳入面内/面外统一拘束的结构断裂预测和评定中。进一步基于GTN(Gurson-Tvergaard-Needleman)延性损伤模型的有限元法,数值分析了影响材料J_(c)/J_(ref)-A_(d)关联线的因素。结果表明,影响材料J_(c)/J_(ref)-A_(d)关联线的主要因素包括材料的应变硬化指数n,屈服强度σ_(0)和断裂特性。其中n对J_(c)/J_(ref)-A_(d)关联线斜率的影响最大;断裂特性的影响次之;σ_(0)的影响最小。低硬化指数n,低断裂阻力和低屈服强度σ_(0)的材料的延性断裂韧性对裂尖拘束的变化较敏感。对于这类材料的结构,在断裂预测和评定中要着重考虑裂尖拘束对断裂韧性的影响。

Based on the ductile fracture toughness data of different materials and different geometric sizes of specimens,in combination with finite element calculations,linear correlation equations between the normalized ductile fracture toughness J_(c)/J_(ref) and the unified constraint parameter A_(d) of different materials were obtained.These equations can be used in the J-A_(d) two-parameter method for fracture prediction and assessment of structures incorporating the in-plane and out-of-plane unified constraint.Furthermore,based on the finite element method of the GTN(Gurson-Tvergaard-Needleman)ductile damage model,the factors affecting J_(c)/J_(ref)-A_(d) correlation line of the material were numerically analyzed.The results show that the main factors affecting the J_(c)/J_(ref)-A_(d) correlation lines of materials are the strain hardening exponent n,the yield strengthσ0 and the fracture characteristics of materials.Among them,n has the greatest effect on the slope of the J_(c)/J_(ref)-A_(d) correlation line,followed by the fracture characteristics,and the yield strengthσ_(0) has the least effect.For the materials with low hardening index n,low fracture resistance and low yield strengthσ_(0),their ductile fracture toughness is more sensitive to the change of the crack-tip constraint.For the structures made of this type of materials,the effect of the crack-tip constraint on fracture toughness should be considered particularly in fracture prediction and assessment.