Abstract
As the resistance of structures against the crack-tip plastic deformation, constraints has attracted much attention in the research of material fracture behaviour. In order to increase the accuracy of structural integrity assessment, many characterization parameters of in-plane and out-of-plane constraints have been considered and proposed in the last few decades. Three-dimensional finite element analyses have been conducted for five C(T)50 specimens with different out-of-plane constraint. The distributions of four constraint parameters (σ22/σ0, Tz, h and Dp) along crack fronts were calculated. To characterize the out-of-plane constraint, the capability of constraint parameters such as σ22/σ0, Tz, h and Dp were analyzed and compared. Results show that, compared with the three constraint parameters (σ22/σ0, Tz and h) based on crack-tip stress fields, the parameter Dp based on crack-tip equivalent plastic strain is more sensitive to out-of-plane constraint, and may effectively characterize the out-of-plane constraint.
Highlights
As the resistance of structures against the crack-tip plastic deformation, constraints has attracted much attention in the research of material fracture behaviour
Based on crack-tip equivalent plastic strain, a new characterization parameter Dp of out-of-plane constraint was defined as follows: Dp where DPEEQ is the gradient of equivalent plastic strain in the middle-plane area surrounded by a specific εp isoline along a evaluated specimen crack front, and Dref is the εp gradient in the middleplane area surrounded by a specific εp isoline along the crack front of a standard reference specimen with high constraint level at fracture
The reference εp gradient Dref in equation 3 was calculated at the area surrounded by the εp=0.002 isoline in the middle plane of a standard reference C(T)50 specimen with B/W=0.5 and a/W=0.5 in Table 1, which is with high constraint
Summary
As the resistance of structures against the crack-tip plastic deformation, constraints has attracted much attention in the research of material fracture behaviour. The out-of-plane constraints such as the specimen thickness relate to the specimen dimension parallel to crack front. The constraint parameter Tz introduced by Guo[4, 5] is defined as the ratio of out-of-plane stress (σzz) to sum of the in-plane stresses (σxx and σyy), and it can characterize the 3D crack-tip stress fields: TZ zz xx yy (1). Based on crack-tip equivalent plastic strain, a new characterization parameter Dp of out-of-plane constraint was defined as follows: Dp. where DPEEQ is the gradient of equivalent plastic strain (εp) in the middle-plane area surrounded by a specific εp isoline along a evaluated specimen crack front, and Dref is the εp gradient in the middleplane area surrounded by a specific εp isoline along the crack front of a standard reference specimen with high constraint level at fracture
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