Shot peening is known to improve the fatigue performance of materials. The improvement in fatigue is that plastic deformation in the surface increases hardness, yield stress and microstrain of thinning Crystal block and dislocation density, and formed advantaged compress residual stress that are introduced into the near-surface of the components and which hinder crack initiation and growth. But over peening effect is produced when shot peening strengthening goes beyond a certain limit, which was adverse to improve surface quality. This paper adopted the optimization of the critical peening parameters to avoid appearing over peening effect. The experimental result showed that arc high value of optimal shot peening was 0.40mm.

The decision making of Prognostics and Health management under uncertainty is addressed in this paper. Dempster-Shafer theory is adopted to tackle this problem and some modification about this method is made to accommodate with practice. The decision-making method and decision process are detailed.

The ideal of genetic algorithm was introduced in optimizing tap parameters for internal thread cold extrusion of high strength steel. The use of genetic algorithm was analyzed in the optimization design of the extrusion tap. Based on optimal result, the extrusion tap was machined to reduce the extrusion force effectively. It was completely feasible to using genetic algorithm to optimize tap parameters for internal thread cold extrusion of high strength steel. Results from this study provide important basis for practical application of internal thread cold extrusion of high strength steel.

From the laser welding actual process, the welding heat source model of laser welding process was established, that is, superposition heat source. According to the knowledge of thermodynamics, the establishment of a welding process, the mathematical model of temperature distribution of laser welding process was obtained by laser welding heat source. Finally, the finite element simulation of welding temperature distribution was used. The simulated results were compared with the analytical results of mathematical model of temperature field, it was proved consistent between simulated results and analytical results, at the same time it can account for the correctness of the mathematical model of temperature field.

The heat source model and the heat input model were built by analyzing welding process. The rationalities of model were verified by finite element simulation. The method of prestressed welding was employed in order to reduce welding residual stress. The welding residual stress would be widely impacted by imposed prestress of 90% yield strength welding. At the same time the propagation of welding heat cracking in the heat-affected zone was properly controlled by prestressed welding.