The finite element method has employed to simulate the laser thermal cracking process for brittle materials. The varieties of temperature and thermal stress distributions around the crack tip were studied. The effect of cracking parameters, i.e. laser power, focus moving speed, plate thickness, crack length, cooling effect¡K etc., on the crack propagation has also investigated. The stress intensity factor around crack tip is considered as the key parameter to dominate the crack propagation. The thermal-plastic-elastic finite element model was employed to simulate the temperature and stress distributions. The strain energy release rate and stress intensity factor solved from virtual crack closure technique and displacement extrapolation method are employed to illustrate the crack state in this study. Five crack length models were used to show the stress intensity factor variations around the crack tip. Numerical results indicate that the head flux on the surface, substrate thickness and adopting cooling sources may affect the crack propagation, crack delay significantly. The results in this study also demonstrate the feasibility of employing finite element method in the exploring crack propagation mechanism in laser thermal cracking process.

Because of thermal transients and gradients occurring upon rapid heating or cooling, microcomponents made from High-Temperature Co-fired Ceramics (HTCC) often fail at temperatures far below what the materials can withstand per se. This work investigates how resistance to thermal fracture in HTCC microcomponents can be increased by improving the component design, aiming at increasing the thermal performance of a microthruster with integrated heaters. The effect of four design parameters:  component and cavity geometries (circular or square), heater placement (central or peripheral), and addition of embedded platinum layers, on thermal fracture resistance was investigated experimentally through a study employing design of experiments. Components of different designs were manufactured, and their thermal fracture resistance tested by rapid heating until the occurrence of failure. Peripheral heater placement and presence of embedded platinum layers were seen to improve resistance to thermal fracture, whereas the shape of the component and the cavity did not significantly affect thermal performance. The most favourable design was then applied for a microthruster that was fabricated and evaluated with respect to thermal fracture resistance. The microthruster survived rapid heating up to 1461°C, and was operated as a cold gas microthruster at temperatures up to 772°C. None of these temperatures were limited by component failure, but by the component interface.