Research On A Criterion For Crack Propagation Based On The Radial Strain Energy At Plastic Core Region And Numerical Simulation

The study of problems involving crack initiation, propagation and arrest is always the interest of fracture mechanics. The MISES yield criterion is firstly used to determine the shape and size of the plastic core region, and it is drawn a conclusion that a new formulation which is to define a variable radius based on MISES yield function for the non-dimensional variable radius of the core region is presented for mixed mode (K_Ⅰ-K_Ⅱ) fracture under different loading conditions. Sequentially, the r_min -criterion is modified and introduced to determine the initial crack angle .The solution supported by the modified r_min -criterion is compared with other criteria. In this work, we propose secondly a new criterion (D-criterion) for mixed mode Ⅰ-Ⅱ crack initiation angles based on thecharacteristics of the plastic core region surrounding the crack tip--anew criterion for crack propagation based on radial strain energy along at the crack tip plastic core region. It is also drawn a conclusion that the crack always propagate along the shortest radius from the high strain area of plastic core region to the low strain area of elastic region.The D criterion states that the crack extends in the direction of the radius at the crack tip. The radial strain energy at plastic core is a ruler of measuring the material intensity of anti-rupture. Fracture toughness is represented as a material constant K_c whenever which kind of crack type the object is subjected to. And then a concept of critical intrinsic zone of crack propagation is introduced, crack propagation happens when the tress or strain status of the zone reaches to the material critical rupture value. According to this concept, the mixed mode I-II initial crack angles and the generalized crack propagation stress σ_c(πα)^1/2/K_IC under different conditions is determined. The proposed criterion is formulated for variousloading conditions and is compared with other available criteria against the limited available experimental data. It is shown that the proposed criterion provides a better agreement with the experimental data.In this paper finally, by means of the maximum circle tensile stress oncurve of constant Q) and stress intensity factors by a path independent contour integral method. The trajectories of maxed mode crack propagationare simulated through numerical manifold method, the crack propagation is traced dynamically by modifying the neighboring connection between crack-top and nodes within element in the calculating process. This method has the advantages such as less modifying area, easily programming, more realizable and so on. Then the single sharp nicked specimen is used to verified the numerical result. It is shown that the provided method is reasonable and effective.