Axi-Symmetrical Transient Temperature Fields and Quasi-Static Thermal Stresses Initiated by a Laser Pulse in a Homogeneous Massive Body

In the present chapter the model of a semi-infinite massive body which is heated through the outer surface by the precised heat flux, is being under study. This heat flux has the intensity directly proportional to the equivalent laser irradiation intensity. Heating of materials due to its surface irradiation by the high-power energy fluxes, which takes place during working of the laser systems, can be modelled in a specific conditions as the divided surface heat source of defined power density or heat flux of defined intensity (Rykalin et al., 1975). Laser systems are an unusual source of electromagnetic irradiation of unique properties. These properties differ essentially from the relevant characteristics of irradiation generated by traditional sources, natural and artificial one. Laser irradiation has specific, distinguishing features: high level of spatial and time coherence, high level of monochromaticity, low divergence, high spectral intensity and continuous or impulse emission process. High level of spatial coherence gives possibility to focusing laser irradiation on the surfaces of a few to several dozens squared micrometers in a size, which correspond to very high values of power intensity even 108 –1012 W/m2 (104 –1018 J/m2 or 1023 fotons/cm2). Effectivity of local surface heating mentioned above depends on: laser pulse duration, laser pulse structure (shape) and on irradiation intensity distribution. Three specific laser pulse structures are usually under consideration: rectangular-shape pulse, triangular-shape pulse and pulse shape approximated by some defined function. Likewise to the laser pulse structure, the spatial pulse structure (distribution of laser irradiation in a plane normal to the beam axis) is also complex and challenging for precised analytical description. In approximation the spatial distribution of laser irradiation can be described by the following relations: gaussian distribution (takes place during the working of laser beam in the single-mode regime), mixed (multi-modal) or uniform distribution. In addition, laser heat source shape can be changed by the electromagnetic or optical methods. Hence, the