Simulation of residual stress and micro-plastic deformation induced by laser shock imprinting on TC4 titanium alloy aero-engine blade

Abstract

In laser shock processing (LSP) of aero-engine blades, overlap marks due to spot overlapping cause irregular surface morphology that becomes a source of cracks under fatigue behaviors. This reduces the beneficial effect of compressive residual stress induced by LSP and undermines fatigue performance of blades. In this paper, laser shock imprinting (LSI) is proposed to improve fatigue performance of aero-engine blades. In this process, a layer of contact film with micro-grooves is placed between the absorption layer and the workpiece (blade) of the LSP. By using the double action of laser shock wave and micro-grooves in contact film, blade surface morphology is transformed towards the direction conducive to improve its fatigue performance. Using ABAQUS software, Johnson-Cook model and Fabbro model were considered to study the plastic rheological behavior of blade surface material induced by LSI. Effect of process parameters namely, peak pressure, impact number and spot overlapping ratio on residual stress and micro-plastic deformation of blade surface were studied. Simulation results showed that under the action of laser shock wave, blade surface material flowed into micro-grooves in contact film via extrusion plastic deformation. This resulted in micro-bulge morphology having geometrically specific arrangement on blade surface, which achieved accurate control of micro-plastic deformation on blade surface. Increase in peak pressure and impact number increase the surface micro-bulges height. However, increase in peak pressure lowers the stress difference between bulging edge and non-bulge zones. It was found that 33% spot overlapping impact resulted in more uniform surface micro-bulge morphology on blade surface.

Keywords

• Laser shock imprinting
• Surface morphology control
• Finite element analysis
• Residual stress
• Plastic deformation