Effect Of Laser Shock Processing On Fatigue Resistance Of TC4 Alloy

Laser shock processing?LSP?is an advanced surface modification technology which can refine the grains of surface layer and improve mechanical properties of material like fatigue resistance.Compared with shot peening,LSP widely used in aerospace and other fields has characteristics of high efficiency,ultra-high strain rate and so on.In this paper,the parameters of Johnson-Cook?JC?constitutive model of TC4 alloy under high strain rate are obtained via numerical simulation and experiments.The dynamic behavior of TC4alloy under LSP is analyzed in detail.And the effects of LSP on fatigue resistance of samples are explored compressively.The main contents of this paper are as follows:?1?Quasi-static compression tests at low strain rate of 0.01 s^-1,0.001 s^-1 and split Hopkinson pressure bar?SHPB?experiments at high strain rate of 10³¹0⁴ s^-11 are carried out at room temperature respectively to acquire the true stress-strain curves of the TC4alloy at different strain rates and to obtain the JC constitutive model parameters.And the parameters A,B,n and C are 958.1,488.3,0.46 and 0.018 respectively.?2?The finite element model of single laser shock on TC4 alloy is established with Johnson-Cook constitutive model parameters obtained from experiments.And the dynamic response process of single laser shock on TC4 alloy is investigated via ABAQUS.The deformation and residual stress distribution of sample surface after laser shock processing are numerically analyzed,which will be then compared with the simulation results acquired through 5 different constitutive model parameters in the open literatures as well as the single laser shock experiments.The results indicate the Johnson-Cook constitutive model of TC4 alloy obtained from experiments can acquire accurate results in numerically analyzing the process of single laser shock.Meanwhile,to verify the adaptability of utilizing above parameters to analyze the process of repeated laser shocks,the corresponding finite element analysis of two laser shocks on TC4 alloy using 6different parameters as well as the tests are implemented,which demonstrates the obtained parameters can depict the process of two laser shocks accurately as well.Furthermore,the method proposed in open literature is used to probe the acquisition of the constitutive model parameters at ultra-high strain rate.?3?The single edge notched specimens are fabricated according to the experimental standard and LSP experiments under different conditions and corresponding fatigue tensile tests are conducted in sequence.The surface morphologies and residual stresses before and after LSP are measured by three-dimensional profilometer and X-ray diffractometer.Moreover,the effects of different impacting areas and other factors in LSP process on samples'fatigue life are researched in accordance with the loading cycles.The scanning electron microscope are employed to analyze the fracture morphologies of the samples.Eventually,the effects of LSP on fatigue resistance of TC4 alloy are investigated in combination with experimental and simulative results.