Research Of The Effect Of Stress Distribution And Fatigue Life On Aluminum Alloy With Fastener Hole Subjected To Laser Shock Energy

Fastener holes with large numbers in airframe are one of the structures that may generate fatigue fracture easily. Laser shock processing(LSP), to some extent, can improve the fatigue life of hole structures effectively. Traditional opinions always believe the direct proportion relationship between fatigue life of hole specimen and laser shock energy. Thus, it has important theoretical significance and engineering value to conduct the research of corresponding relation between fatigue life of hole specimen and laser shock energy which will improve the anti-fatigue performance and lay the foundation of engineering practice.The effect of fatigue life and stress distribution of aluminium alloy hole specimen under different laser shock energy was studied through theoretical analysis,simulation and experiment in this paper. Main research work and achievement are as follows:(1) The generation mechanism of residual compressive stress under laser shock and the inhibition effect of residual compressive stress to crack growth were discussed theoretically. The surface and hole-wall residual stress distribution feature of hole specimen under shock energy was analyzed. And according to the stress distribution feature, it is deduced that fatigue life of hole specimen will increase first and then decrease with the increasement of shock energy on per unit area.(2) Finite element analysis software ABAQUS was used to simulate the effect of stress distribution in hole specimen subjected to LSP. The result shows that residual compressive stress on material surface increases gradually until it reaches saturation with the increasement of shock energy on per unit area from the surface stress distribution of hole specimen. Also the depth of residual compressive stress increases with the increasement of shock energy on per unit area from the inside stress distribution of hole specimen. While the residual tensile stress at the hole center increases rapidly in this process.(3) High frequency fatigue tension test was conducted with aluminium alloy hole specimen subjected to 2.8GW/cm2, 5.7GW/cm2 and 8.5GW/cm2 laser powerdensity. The result shows that average fatigue life can increase by 62.1%, 168.3% and47.3% respectively after LSP. That is to say fatigue life will increase first and then decrease with the increasement of laser power density for hole specimen after LSP,and it agrees with the residual stress distribution regularity of hole surface under different shock energy.(4) The fatigue crack initiation(FCI) on fracture surface transfers from the hole corner into the hole surface after LSP from the macrography. And the initiations are condensed from stripped distribution to a center point on specimen thickness where has the largest residual tensile stress from simulation with the increasement of shock energy on per unit area.(5) Fatigue striation space(FSS) on fracture surface decreases compared with the untreated ones after LSP from the micrography. And the change of FSS decreases first and then increases on corresponding fracture with the increasement of shock energy on per unit area. Namely FSS has the minimal change and fatigue crack growth(FCG)has the lowest speed on the fracture when the laser power density is 5.7GW/cm2, thus the specimen has the highest fatigue life.It can be achieved from the research of laser shock energy to the stress distribution and fatigue life of hole specimen that inside the material suitable laser shock energy can induce the best residual stress field distribution under which the specimen has a better fatigue life. Thus, it is of great importance to select the suitable shock energy in engineering practice.