Advances in Micro-Scale Laser Peening Technology

Recent advances in laser peening technology, also known as laser shock processing (LSP) are reported. Specific emphasis is placed on its development in the micro scale regime. LSP imparts desirable residual stress distributions into the target material in order to improve the fatigue life of the material. In modeling improvements, plasma expansion is modeled as laser supported combustion wave, in which radial and axial expansions are considered. Stress/strain analysis is extended to three-dimensional and takes into account of finite geometry, which is important for micro-scale LSP. Fatigue tests are designed to demonstrate that micro-scale LSP can improve fatigue performance of the materials while offering a level of flexibility. The influence of LSP on the microstructures of the materials is studied quantitatively using Orientation Imaging Microscope (OIM) technique, and grain size and subgrain structures are analyzed. The experimental results of strain/stress distributions are compared with that of simulations in overlapped LSP using conventional X-ray diffraction measurement. The potential of applying the technique to micro components, such as micro gears fabricated using MEMS is demonstrated. The investigation also lays groundwork for possible combination of the micro scale laser shock processing with laser micromachining processes to offset the undesirable residual stress often induced by such machining processes.