Yan Xiang-qiao

Mixed-mode fatigue crack growth prediction in biaxially stretched sheets

Abstract Mixed-mode fatigue crack growth in biaxially stretched sheets is investigated. The modified fracture criterion proposed by Wang and Du is extended to the case of cyclic loading to predict the mixed-mode fatigue crack growth. The analysis of the mixed-mode fatigue crack growth process is very complex. Software developed recently by the authors can be used to more precisely predict the mixed-mode fatigue crack growth process. The software in which the fatigue crack growth criterion presented here is combined with the displacement discontinuity method, a boundary element method, is described in detail from a number of aspects. The analysis of the fatigue growth process of an inclined crack in biaxially stretched sheets is performed.

Mixed-mode fracture criteria for the materials with different yield strengths in tension and compression

Abstract The Nadai elastic-plastic boundary is introduced to define the core region, instead of a core region with a constant distance r from the crack tip and a core region with the Mises elastic-plastic boundary. Taking into account fracture parameters along the Nadai elastic-plastic boundary, two improved fracture criteria are presented for the two commonly used fracture criteria, the maximum tangential-stress criterion and the minimum strain-energy-density criterion. Using the two improved fracture criteria, the effect of properties of the material with different yield strengths in tension and compression on the mixed-mode crack fracture can be revealed. It is shown by analysis that the fracture of the mixed-mode crack is affected by this kind of property of the material. Many results are given by using the two improved fracture criteria, and they are compared with those obtained by using the commonly used mixed-mode fracture criteria.

An Effective Boundary Element Method for Analysis of Crack Problems in a Plane Elastic Plate

A simple and effective boundary element method for stress intensity factor calculation for crack problems in a plane elastic plate is presented. The boundary element method consists of the constant displacement discontinuity element presented by Crouch and Starfield and the crack-tip displacement discontinuity elements proposed by YAN Xiangqiao. In the boundary element implementation the left or the right crack-tip displacement discontinuity element was placed locally at the corresponding left or right each crack tip on top of the constant displacement discontinuity elements that cover the entire crack surface and the other boundaries. Test examples ( i. e. , a center crack in an infinite plate under tension, a circular hole and a crack in an infinite plate under tension) are included to illustrate that the numerical approach is very simple and accurate for stress intensity factor calculation of plane elasticity crack problems. In addition, specifically, the stress intensity factors of branching cracks emanating from a square hole in a rectangular plate under biaxial loads were analysed. These numerical results indicate the present numerical approach is very effective for calculating stress intensity factors of complex cracks in a 2-D finite body, and are used to reveal the effect of the biaxial loads and the cracked body geometry on stress intensity factors.A simple and effective boundary element method for stress intensity factor calculation for crack problems in a plane elastic plate is presented. The boundary element method consists of the constant displacement discontinuity element presented by Crouch and Starfield and the crack-tip displacement discontinuity elements proposed by YAN Xiangqiao. In the boundary element implementation the left or the right crack-tip displacement discontinuity element was placed locally at the corresponding left or right each crack tip on top of the constant displacement discontinuity elements that cover the entire crack surface and the other boundaries. Test examples (i. e., a center crack in an infinite plate under tension, a circular hole and a crack in an infinite plate under tension) are included to illustrate that the numerical approach is very simple and accurate for stress intensity factor calculation of plane elasticity crack problems. In addition, specifically, the stress intensity factors of branching cracks emanating from a square hole in a rectangular plate under biaxial loads were analysed. These numerical results indicate the present numerical approach is very effective for calculating stress intensity factors of complex cracks in a 2-D finite body, and are used to reveal the effect of the biaxial loads and the cracked body geometry on stress intensity factors.

An effective method and its application in assembling the structural stiffness matrix in material-nonlinear finite element analysis

Abstract A very effective technique for assembling the structural stiffness matrix in material-nonlinear finite element analysis is presented. Its application to the stable crack growth analysis is described in detail. A finite element analysis of the process of slow crack growth for a center-cracked specimen subjected to monotonically and slowly increased load until the point of fast fracture is reached is made by means of a material-nonlinear and quasi-three-dimensional finite element program developed by the technique, as an example to illustrate that the technique has been successfully applied to a practical problem.

A theory of cleavage characteristic stress on low-temperature cleavage fracture in mild steel-a review

Abstract A theory of cleavage characteristic stress on cleavage fracture in mild steel is briefly reviewed. The theory involves two important concepts. First, a cleavage fracture stress (termed a cleavage characteristic stress Sco) corresponding to the brittle/ductile transition in plain tension tests is a characteristic parameter resistant to low-temperature cleavage fracture of mild steel. It is intrinsically a lower bound value required to propagate an initial cleavage crack, which has advantageous stress and location conditions and has not blunted across grain boundaries. It controls cleavage fracture and brittle/ductile conditions of not only plain-tension specimens but also notched or cracked specimens of mild steel. Initiation and propagation of a cleavage crack are stochastic processes. In order to meet the probabilistic conditions of initiation and propagation of a cleavage crack, an effective yield zone has to be formed in which the maximum principal stresses are all more than or equal to Sco.

Engineering Method for the Thermal Mechanical Erosion of C/C Composite with the Mesoscale Ablation Model

A physical model to simulate the mesoscale morphology evolution of carbon fiber is established to characterize the thermal mechanical erosion behavior of C/C composite in high temperature and high pressure gas flow. The process of mechanical erosion of single carbon fiber is calculated by the DSMC method. The fracture criteria and mesoscale mechanical erosion model of carbon fiber are developed by theory of mechanics of materials. Finally, an engineering method for prediction of mesoscale mechanical erosion is formulated, and the predictions agree well with the experiment results.

Application of cleavage characteristic stress theory to low-temperature brittleness evaluation of structural steel : a review

Abstract Some applications of cleavage characteristic stress theory to low-temperature brittleness evaluation of structural steel are reviewed. Based on this theory, two basic characteristic parameters, a characteristic transition temperature and a characteristic crack (notch) size of low-temperature brittleness, were recommended as a double-parameter evaluation of low-temperature brittleness of structural steel.