Proposal of new damage model for thermal shock based on dynamic fracture on the brittle materials

Abstract

In the current paper, we propose that the mechanical resistance of the brittle materials under dynamic loading can be used to predict the thermal shock damage resistance via a new proposed damage criterion. The increase of the mechanical resistance based on high loading rate has been investigated by experimental methods for ‘Lead Crystal Glass’ including the static and dynamic loadings by universal ‘INSTRON’ and ‘split Hopkinson pressure bars (SHPB)’. The relationship between the measured static and dynamic strengths of materials has been compared and developed via Tuler and Butcher’s dynamic criterion. ‘Modified Brazilian disk (MBD)’ specimens are used to obtain indirect tensile stress concentration at notch tip. The fracture process under various loading rates has been observed by optical and scanning electronic microscope (SEM) to study the fracture phenomenon according to the high loading rate effect for Lead Crystal Glass. The dynamic stress due to high loading rates can be considered as the thermal stress during thermal shock phenomenon with high heat convection coefficient values which leads to high gradient temperature, low duration time and intrinsic damage feature like cracks and flakes for concerned material. The transient thermal stress analysis has been carried out by numerical method for MBD specimen subjected to rapid cooling condition. The numerical results and experimental dynamic resistance of selected material are utilized to develop a new semi-empirical damage criterion based on the continuum damage mechanics (CDM) including dynamic material resistance, critical thermal shock time which corresponds to maximum transient thermo-mechanical stress and heat convection coefficient evolution according to the thermal shock severity.