13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Constraint Effect in Fracture: Investigation of Cruciform Specimens using the J-A2 Method Larry Sharpe1, Yuh Chao2,* 1 Department of Mechanical Engineering University of Tennessee, Knoxville, TN, USA 2 College of Material Science and Engineering, Tianjin University, Tianjin, China * Corresponding author: chao@sc.edu Abstract The structural integrity of cracked mechanical components can be assessed using the fracture toughness material property. The fracture toughness of a particular component is often dependent upon the component geometry as well as the nature of loading (e.g. uniaxial or biaxial loading). This dependence is interpreted as the constraint effect in fracture. Various methods have been developed to investigate the constraint effect, including the two parameter J-A2 method. The J-A2 method is a more accurate representation of the stress fields near the crack tip, as additional terms from the well-known HRR series solution are included. The current study applies the J-A2 method to fracture toughness data of cracked cruciform specimens subjected to uniaxial and biaxial stresses. The J-A2 results of the cruciform specimens are compared to those of other plane strain specimens described by ASTM standards, including three point bend and compact tension, to determine if loss of constraint exists. Finite element models of each specimen were analyzed to determine the A2 parameter used to quantify the level of constraint based on geometry and loading. The results reveal loss of constraint for shallow cracked specimens when compared to deep cracked specimens, and also that uniaxial loading results in loss of constraint when compared to biaxial loaded specimens. In summary, the J-A2 method appears to be a viable tool to predict failure including the consideration of the constraint effect. Keywords fracture, constraint, biaxial, cruciform 1. Introduction A material’s fracture toughness is used to determine the structural integrity of mechanical components containing cracks. Materials used in nuclear reactor pressure vessels (RPV), including A533B and A508, are of particular interest. RPVs can be subjected to conditions close to equibiaxial loading during extreme temperature gradients experienced during pressurized thermal shock (PTS). Based on such biaxial loading, it is possible that traditional methods used to determine material properties may not provide accurate results. Widely used industry standards [1, 2] used to calculate material properties related to fracture toughness utilize specimens subjected to uniaxial loading, e.g., three point bend (3PB) and compact tension (CT) specimens. Therefore, the question arises regarding whether or not a “biaxial effect” exists for loading conditions similar to that of RPVs. Much research has been conducted in recent years to determine how component geometry and applied loading affect fracture toughness. The industry standards mentioned previously typically use deep cracked (high constraint) specimens to determine the fracture toughness. But it is known that shallow cracked (low constraint) specimens exhibit higher fracture toughness, resulting in a “constraint effect” in fracture.
RkJQdWJsaXNoZXIy MjM0NDE=