T-stress And Its Effects On The Crack Propagation Path In The Fracture Of The Engineering

The crack is often contained in the rock, concrete and other engineering materials. It is particularly important problem that how to avoid the crack extension and finally result in fracture about the overall structure. Crack propagation is mainly caused by the stress concentration near the crack tip. In addition to the stress singularity, the constant term stress (ie. T-stress) that is near the crack also plays an important role in the crack propagation path. In order to clarify the relationship between the fracture parameters and T-stress, interpret of mechanism of crack propagation paths in the engineering materials, the in-depth and systematic theoretical analysis and numerical calculation are carried out. The main work includes the following parts:1. In photoelastic experiments, the non-linear relationship between the stress intensity factor (ie. K), T-stress and line stripes arithmetic progression that near the crack tip are deduced by using stress-optical law. And then the stress intensity factors and T-stress are determined by solving nonlinear equations using the least squares method. Through research on T-stress that in the crack-tip stress field, it is found that the T-stress's sign and magnitude can affect the crack tip photoelastic fringe shape, size and inclination. Therefore, it is necessary to consider the impact of T-stress in simulating the crack propagation path. It is also necessary to consider T-stress's effect when the small scale yielding plastic zone that at the top of the crack is amended.2. Because the micro-crack tip stress field's T-stress have a greater effect on the crack propagation angle and the fracture toughness, the results of crack growth and fracture toughness that are predicted by using traditional the maximum tangential (MTS) stress criterion have large deviations. The modified maximum tangential stress criterion that is combined with T-stress is presented. In biaxial compression fracture experiments, the modified MTS is applied to simulate the crack growth path. The exponential function is used to describe the rough interface degenerate of the rock's crack in the growth path simulated. It can be found that the modified MTS results by using the extended finite element method (XFEM) and the experimental results are consistent.3. The crack's stress problem in the strip plate aroused by heat exchange in a difference of temperature field is studied. In this paper, the superposition principle and the Fourier transform are used, singular integral equation are solved. The crack tip stress field's the stress intensity factor and T-stress respectively relation about the Biot number, the crack length and time are analysed in the unsteady state temperature field. The analysis results and the finite element simulation results are consistent. In the heat loads of the PMMA material fracture experiments, the finite element simulation results that combination of T-stress are more consistent with experimental results.4. In the three-phase materials concrete, the spring-layer interface model is introduced to calculate the stress intensity factor and T-stress when the influence of the aggregate and the bonding layer are considered. It is found that the aggregate and the bonding layer have great effect on the stress intensity factor and T-stress. Because the T-stress influence the crack tip plastic zone, the crack growth and the fracture toughness of the concrete are studied by using two-parameter K-T model. In this paper, the finite element simulate fracture about Galve concrete beam are completed. Because of based on the random aggregate, the concrete specimens random aggregate model are automatic partitioned by using the Monte Carlo and the Delaunay triangulation principle. The junction zone the between the mortar and aggregate is used by triangular element. The simulations of crack growth trajectory are consistent with the range of test results.