Effect of Laser Shock Peening on Fatigue Life for FV520B Steel
FV520B steel is primarily used in the manufacturing of blades for various centrifugal compressors because of its high strength,good fatigue resistance,corrosion resistance,good toughness and plasticity,and excellent welding characteristics.The service life of impellers can be increased by improving the anti-fatigue performance.Several methods have been proposed to enhance the anti-fatigue performance of materials.Laser shock peening(LSP)is an important strengthening technology that can effectively improve the fatigue,wear,and corrosion resistance of metallic materials compared to the traditional surface treatment methods.To evaluate the effectiveness of LSP,experiments were conducted on FV520B steel-bar specimens by choosing the appropriate shock energy,laser wavelength,pulse width,circular spot diameter,shock frequency,laser power density,and spot overlap ratio.Surface hardness was measured using a digital microhardness tester(HVS-1000AT)before and after LSP.The results showed that LSP increased the surface hardness of the specimens from approximately 330 HV to 490 HV;the depth of hardening was 0.25 mm.The residual stresses of the LSP specimens were measured using a Proto-LXRD high-power residual stress tester—a residual compressive stress of approximately 90 MPa was generated on the surface of the specimens.The low cycle fatigue experiments for FV520B specimens with and without LSP were conducted for different strain amplitudes±0.5％,±0.6％,±0.7％,±0.8％,and±1.0％,respectively.The fatigue life decreased with the increasing strain amplitude for all specimens with and without LSP.The fatigue life of all specimens improved after LSP for the five strain amplitudes.For the strain amplitudes between±0.6％to±1.0％,it was observed that the higher the strain amplitude,the more significant the improvement in fatigue life of specimens.The strain amplitude of±0.5％showed the most significant improvement of 132.2％.Scanning electron microscopy(SEM)experiments for fatigue fractures on smooth and LSP specimens showed that all the fractures presented three typical regions—the crack source region,crack propagation region,and transient fracture region.Moreover,an obvious fatigue strip in the crack growth region and a secondary crack perpendicular to the direction of crack propagation were observed for the smooth specimen.On the contrary,for the LSP specimen,the fatigue source became fuzzy,and the residual compressive stress generated on the surface after LSP inhibited fatigue crack initiation and propagation.This caused the location of crack initiation to transfer from the surface to the subsurface,and the fatigue strip spacing and dimple size were reduced,which improved the fatigue life of the specimens.Further,the fatigue lives of the smooth and LSP specimens were predicted using the Manson-Coffin equation.Overall,the prediction results for the smooth specimens agreed well with the experimental results.For the LSP specimens,the predicted fatigue life was the same as that predicted for the smooth specimens,and the prediction results were conservative.Furthermore,considering the effect of residual compressive stress on the inhibition of fatigue crack initiation and propagation,a new fatigue life prediction method that can be used to predict the fatigue life with residual compressive stress is proposed by modifying the Manson-Coffin equation.The predictions for the LSP specimens using this method were in good agreement with the experimental results.The comparative analysis of the fatigue life between smooth and LSP specimens for different strain amplitudes in this study can be used to select the appropriate process parameters of LSP for FV520B materials.This fatigue prediction method provides a new concept for determining the fatigue life of materials with residual stress.
laser shock peeninglow cycle fatigueresidual stressfatigue fracturefatigue life prediction
万方数据
维普
