Experimental implementation of the laser shock peening method aimed at an increase in the fatigue properties of metals

The study is aimed at the development and implementation of an experimental setup for treating metal parts with complex geometry to induce compressive residual stresses in the surface layers. Modern methods of surface treatment demonstrated the possibility of increasing the durability of parts by several times through creation of high-amplitude residual compressive stresses. We managed to form the residual compressive stresses up to a depth of 1 mm using the titanium alloy specimens. The developed installation consists of a solid-state laser with a pulse energy of up to 10 J, a six-axis robot manipulator, and a system for measuring residual stresses by hole drilling method. The processing is realized in automatic mode with the possibility of continuous change of specimens. The geometry of parts and processing features are worked out on a digital three-dimensional model of the part. A number of tests have been carried out to reveal the dependence of the values of residual stresses on the processing conditions and demonstrate the necessity of numerical analysis and preliminary modeling of the process of laser shock peening. The distribution of residual stresses was measured by hole drilling method in the specimens before and after laser shock peening under various processing conditions, and the profiles of these stresses in depth were plotted. It is shown that along with the pulse power, the value and distribution of residual stresses are significantly affected by the number of repeated passes, the overlap degree, and the technology of preliminary preparation of the specimen surface. The analysis made it possible to choose the optimal processing mode for titanium alloys providing the values of residual compressive stresses up to 1 GPa.

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