Laser peening fundamentals
Laser shock peening is an established metal surface processing tool, which can improve integrity of advanced structures used in critical service conditions by creating near surface compressive residual stress state. Currently the application of this technique is limited mainly to very high value applications due to the high cost of the process. In current state the process requires an ablative layer on the workpiece and water environment to generate the shock waves, which is not practical and cost ineffective. Furthermore the laser used for the commercial process is a very high pulse energy system developed for laser fusion applications, which is not necessary the most optimum approach. The aim of this project is to obtain fundamental understanding of the process to make it more efficient and cost effective to enable use in various applications.
In laser shock peening a short pulse of laser energy generates vapours on the surface, which are them transformed into high energy plasma by absorbing more of the incident laser energy. The recoil pressure from the plasma results in a shock wave, which creates a compressive stress field when propagated through the component. In order to apply the technique as a mechanical rather than thermal process, an ablative layer is applied on the surface of the component. Also to confine the plasma and direct the shock wave a laser transparent di-electric medium (usually water) is used. The current research programme aims at understanding of the fundamental correlation between the laser-material interaction parameters and the shock wave generation which leads to strain hardening and formation of the compressive residual stress field. The most cost efficient way of generation of shock wave is sought. A state of the art holographic imaging will be used to investigate the generation and propagation of shock waves. Also a range of different pulsed laser sources will be used to find the most optimum energy requirement for generation of shock waves. The main emphasis is put on maximising generation of compressive stresses and minimising laser cost without the necessity of using the ablative layer and water environment.
Part of the EPSRC-funded HiDepAM project.