Papers by Keyword: Critical Damage

Abstract: The damage tolerance methodology is used here to compare impact damage from experimental testing and virtual (numerical) testing. The first part of the study aims to identify links between experimental internal (delaminated area) and external measurable damage (dent depth) for a typical aeronautical T800S/M21e laminate. Effects of the mass/velocity ratios at some level of impact energy are evaluated. It is shown that a big mass generates denser and larger delamination with about the same dent than a small mass, which is a critical case for damage tolerance analysis. A relation between the external dent depth and internal delaminated area is proposed.

Abstract: Rock’s uniaxial compression test is completed and the datum is analyzed, then relationship between loading time and AE amplitude, AE counts sum, AE total energy’s released rate come out. Rock’s critical damage is defined which equal result of one minus ratios of residual strength to critical strength. Based on strain equivalence discipline, damage constitutive models related with acoustic emission characteristic are set up. With damage constitutive models established with AE counts sum and AE total energy serving as damage variables respectively and testing datum, the relationship between rock’s damage and stress and strain is described. Then conclusions come out: 1) damage constitutive model with AE counts sum serving as damage variable manifest rock’s damage increasing process and accords with testing result better; 2) theoretical curve is well consistent with testing curve at rock’s peak strength zone.

Abstract: The damage of thin steel plate subjected to contact explosions was a very complex nonlinear process. The initial crevasse of plate subjected to contact explosions had influence upon the whole damage process, so the critical damage study was significant on the anti-explosion of ship structure. In virtue of the wave solution of the plate plastic dynamic response and the dynamic fracture theory, the critical blasting charge was derived theoretically when onset of initial circumferential crack namely critical damage happened. And the expression of critical deformation was also obtained. Lastly the results calculated using proposed method was compared with numerical simulation and the experiment in the published literature, which were almost coincided. It could be seen that the present method could perfectly solve the critical damage of thin plate under contact explosions theoretically, and provide references for defensive engineering.

Abstract: Rock is a kind of complex and high-disordered geological material, its damage and fracture process usually shows obvious criticality. In this paper, percolation theory is applied to analyze and describe this critical property. First, we discuss the critical fracture probability of rock through percolation and renormalization analysis, and present the equivalence between fracture probability and damage variable. Based on scaling law and the relationship between critical exponents, a critical fractal dimension is obtained. Furthermore, according to the analysis of relationship between damage and fractal dimension, we suggest a damage-fractal formula, ω=ω0+ (D-D0)/Dc. This formula can not only be used to describe the damage evolution through the variation of fractal dimension, but also to define initial damage in rock. Finally, the theoretical conclusions are validated by a series of model experiments, and the experimental results agree with that of theoretical.

Abstract: In the framework of percolation theory, a simple void-coalescence model combined with the constitutive relations for describing the stress relaxation and material softening during the void-coalescence process, name as the percolation-relaxation (P-R) model, is proposed to describe the dynamic tensile spallation of ductile metals. A critical damage is introduced and coupled into the model to identify the onset of the void coalescence. Mesoscopically, the critical damage corresponds to the critical intervoid ligament distance (ILD), indicating the start of transition from the void-growth to the void-coalescence.