Numerical Study Of Glass Breakage And Crack Propagation Under Thermal Loading

Window glass as a weak component of building fire protection has always been ignored in design. Glass breaks and even falls out in fire conditions when thermal stress induced by heating exceeds the critical breaking stress. The breakage of glass will further cause fire spreading to other regions, which increases the fire risk.For predicting the glass fallout in fire conditions, the process of crack evolution, the first breaking time and its influential factors, the temperature field, the stress field, the process of quasi-static and dynamic crack growth are studied in this work based on the previous studies.The evolution law of crack of window glass under radiant heating is studied. The results show that the outer two cracks among all cracks initiated from shaded edges propagate initially in the opposite direction. The increase of number of main breakage can increase the number of cracked islands. The number of cracked islands and their areas at the certain range obey an exponential function distribution when the area ratio of cracked island is under 12%.The program of heat transfer of glass under fire conditions is studied and developed, and the influence of geometrical dimension parameters of glass, mechanical parameters, thermal parameters, and incident heat flux of glass surface on the first breaking time is analyzed. The numerical results show that the time to the first crack increases as the thickness of glass, the breaking stress or absorption length increases. Reducing the coefficient of linear expansion, the Young’s modulus or the incident heat flux can extend the first breaking time. The influence of the thickness of glass, shaded width and heat flux on the temperature field is studied. The numerical results show that the temperature difference between temperature at the heated side and at the ambient side increases gradually as the thickness of glass increases. The smaller the thickness of glass is, the faster the temperature of the glass edge rises and the smaller the temperature difference between temperature at the edge heated side and at edge ambient side is. The temperature rise becomes slowly at the center of shaded region as shaded width increases.Programs of quasi-static crack growth under thermal loading are respectively developed based on the singular edge-based smoothed finite element method (sES-FEM), the edge-based smoothed finite element method (ES-FEM) and the finite element method (FEM). The numerical results show that the sES-FEM has better accuracy and convergence rate than FEM and ES-FEM. The path of crack propagation under thermal and mechanical loadings locates between the path of crack growth under the thermal loading and the mechanical loading and turns to the side increasing the load.The lumped mass matrix and consistent mass matrix of five-node crack-tip elements are constructed, and programs of dynamic crack growth are respectively developed based on the sES-FEM, the ES-FEM and the FEM. The numerical results agree well with theoretical results and experimental results. The numerical results show that there is the periodic oscillations using the lumped mass matrix and structured mesh for a stationary crack. The better results can be derived by using the consistent mass matrix than the lumped mass matrix for the same mesh. It has a little effect on the results for a moving crack with the refined mesh around the crack tip using the consistent mass matrix or the lumped mass matrix.The program of dynamic crack growth developed by the FEM is used to simulate the experiments with varying shaded widths. The numerical results are in good agreement with experimental results for the first breaking time. The average value of the first breaking time decreases first and then increases, which is explained by using analysis of two limit states that are both without shaded width and glass pane covered completely by shading.