In case of rock breaking by microwave radiation, thermal stress caused by local heating has a great affection. As effects of shape and volume of the heated doma
in in a mass become one of the interesting probrems, authers made some calculations using the finite element method. The results show that certain amount of thermal energy is determined for the heated domain in order to obtain effective fracture in the mass. Beyond this value of energy, the volume of the heated domain 　Then authers made simulation models of rock fracture in case of mortar and granite blocks. In these simulations, using the finite element method, assumed that E
=0 in the elements of fracture, determined by stress conditions. Distribution of temperature rise in the elements was inputed by approximating formulas based on the data, obtained driving the microwave oscillator of 915 MHz frequency and 30 kW maximum power out put.
　Through these simulations and experiments authers confirmed that there was a linearly increasing relation between the amount of fracture in mortar blocks and radiated microwave energy, and in case of a granite block, appearlance of cracks.