Theoretical analysis for mechanical erosion of carbon-base materials in ablation

This article derives and provides a theoretical analysis for the mechanical erosion of carbon-base materials in ablation. The theory of mechanical erosion based on a nondimensional critical roughness parameter is proposed, The important parameters in this analytical method are independent of the test, The analysis accounts for the heating, pressure, and shear forces acting on material particles exposed to the boundary-layer flow. For the validity of a theoretical analytical method a computational example is given. The theoretical results agree fairly with the experimental data.

Fracture criteria for combined cleavage and dislocation emission

A general theory of fracture criteria for mixed dislocation emission and cleavage processes is developed based on Ohr's model. Complicated cases involving mixed-mode loading are considered. Explicit formulae are proposed for the critical condition of crack cleavage propagation after a number of dislocation emissions. The effects of crystal orientation, crack geometry and load phase angle on the apparent critical energy release rates and the total number of the emitted dislocations at the initiation of cleavage are analysed in detail. In order to evaluate the effects of nonlinear interaction between the slip displacement and the normal separation, an analysis of fracture criteria for combined dislocation emission and cleavage is presented on the basis of the Peierls framework. The calculation clearly shows that the nonlinear theory gives slightly high values of the critical apparent energy release rate G(c) for the same load phase angle. The total number N of the emitted dislocations at the onset of cleavage given by nonlinear theory is larger than that of linear theory.