Double-sided Laser Shock Peening

Abstract:

Laser Shock Peening (LSP) is a process that uses high-energy nanosecond laser pulses to generate compressive residual stresses in metallic materials. These materials then exhibit longer fatigue life and generally higher resistance to cracks of all kinds. The standard method of applying LSP is to focus the laser beam on one side of the sample in the area where cracks usually initiate.

When compressive residual stresses are generated, the residual stresses in the sample are redistributed. This results in compression in the target area, while tension is created around and below this area. If the sample is thin (< 7 mm), the redistribution of stress can cause macroscopic bending of the sample away from the affected area.

This geometric deformation of the sample is generally undesirable from an application perspective, and the deflection on one side must be compensated for by the same deflection on the other side by treating the opposite side of the sample. However, this method is not very accurate and cannot be used for components such as turbine blades, which require high precision. Therefore, the so-called double-sided LSP method is chosen, in which the same laser beams strike the sample or component from both sides simultaneously. Pressure is then applied to both sides of the material at the same time, and no geometric deformation occurs.

The aim of this work is to put the double-sided LSP method into practice at the HiLASE center. The LSP station currently has a U-shaped optical table that enables this method, but so far only one side of the table has been used.

The student would split the laser beam into two and set up an optical path on the other side of the table. The optical path will need to be dimensioned so that the beam reaches the sample from both sides simultaneously.

Given the nature of the topic, a certain degree of manual dexterity and interest in practical work with laser beams and optical and optomechanical elements is expected. One of the outputs of the work will also be a comparison of the original one-sided LSP with the new two-sided approach. The determining factor will be the geometric accuracy of the processed samples.

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