窒化けい素セラミックスのクラックフリーレーザ加工 : 第2報, 過渡熱応力とクラックの生成挙動

Thermal-stress-induced cracks are generated during the laser-processing of ceramics. This paper describes the temperature profile and thermal stress propagation for silicon nitride ceramics heated by Gaussian heat flux. The thermal stress distribution is calculated with consideration of the temperature dependence on material properties, the influence of laser pulse duration and its repetition rate using FEM. The tensile stress in circumferential, radial and axial directions induces the radial lateral and median cracks, respectively. The use of short laser pulses below 20μs with a repetition frequency under 10 kHz is experimentally recommended to reduce thermal stress and to avoid crack formation.