Papers by Author: Yong Yu Gu

Abstract: Laser shock forming in oblique angle of metal sheet is involved due to the complexity of parts profile and multiple points forming by laser shock. The influence of incident laser angle and constraint pore diameter of the mold on the forming characteristics of metal sheet is investigated according to the experiment and finite element simulation. The results show there is a horizontal deviating deformation in the place of the maximum deformation in oblique shock, as the incident angle deviating vertical direction increases, the vertical displacement amount decreases nonlinearly and the horizontal deviating amount increases gradually; and the vertical displacement amount of sheet increases with the increase of the mold constraint pore diameter in a certain range, but decreases above this certain range. The metal sheet fractures when shock times increase, the extended crack is paralleled to roll direction of metal sheet in vertical angle shocking, but the extended cracks in oblique shocking, some is paralleled to roll direction of metal sheet, another is vertical to this direction. The forming characteristics of metal sheet under laser shocking in oblique angle is very important, which provides evidence for the large area precision forming and parameters optimization by laser shock forming.

Abstract: Laser shock processing (LSP) employs high-energy laser pulses from a solid-state laser system to create intense shock waves into a material, which can induce compressive residual stresses in the target surface and improve its mechanical property efficiency. Residual stress of Ti6Al4V alloy both before and after LSP with multishocks was analysised. The depth of compressive residual stress was found to have a dependence on the number of shocking layers and a slight dependence on the level of irradiance. Surface stress improvements of more than 50% increases are possible after laser shock processing with either large spot or small spot patterns. The large spot gave a surface stress of 432MPa and a depth of over 1mm. The low intensity small spot gave a surface stress of 285MPa with a depth comparable to the large spot. Laser shock processing induces a compressive residual stress field, which increases fatigue crack initiation life and reduces fatigue crack growth rate.