Analysis of the residual stress level and depth dependences originating from the laser radiation parameters in simulating the laser impact machining of flat samples made of the titanium alloy

The paper analyzes effect of the laser radiation parameters on the residual stresses level and depth in mathematical simulation of the laser impact machining of a 2 mm thick titanium alloy plate. The laser machining impact mathematical model is verified by computing residual stresses in a titanium alloy after machining the plate in the modes similar to the modulated ones. Simulation results appear in good agreement with the experimental data. Simulation included two stages. The first involved simulating the elastic-plastic waves propagation based on the Johnson-Cook relationship. The second involved static computation of the residual stress distribution. It was identified that laser impact treatment without an overlapping resulted in the non-uniform distribution of the residual compressive stresses in depth depending on the machined surface zone. Therefore, it became apparent with the increasing laser radiation power density. The laser spots junction zones had the minimum residual compressive stresses. For uniform distribution of the residual stresses by depth, the paper recommends to perform the laser impact machining with the 50% overlap over the spots. With an increase in the laser passes number, the level and depth of residual compressive stresses on the treated surface increase, but tensile stresses in the sample volume are also growing. Laser impact machining of both sides of the plate leads to a decrease in the residual compressive stresses profile and provides for leveling out the near-zero residual compressive stresses on the opposite side. However, the double-sided machining causes an increase in the residual tensile stresses in the junction zone between the laser radiation spots up to 0.82 rel. units. The paper recommends the second pass with the same laser radiation parameters as the first, since this leads to an increase in the residual compressive stresses depth. With an increase in the laser spot size from 1 to 3 mm at the same pressure (5.27 GPa), the residual stresses level increases from -0.3 to -1.1 rel. units. The residual compressive stresses depth remains unchanged (0.6 mm). Varying the laser pulse parameters leads to an alteration in geometric parameters of the plate surface layer by 1 ... 5 ?m.
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