Overview on the Shot Peening Principle and Its Strengshening Mechanisms for Metallic Materials

In the shot peening strengthening mechanism(SM),there exisits a new "microstructure strengthening mechanism(MSM)" except the "stress strengthening mechanism(SSM)".To prove the MSM,the mechanical behavior of microstructure modification in the target surface layer were studied by XRD,residual stresses introduced by shot peening(SP),microhardness,and fatigue tests.The results show that the compressive residual stress introduced by SP is one of the SSM,which can only improve the resistance to fatigue fracture with normal tensile fracture mode(NTFM);however,it cannot improve the resistance to fatigue fracture with shear fracture mode(SFM).The decisive role for improving the resistance to fatigue fracture with SFM is merely the microstructure strengthening mechanism(MSM).In author's opinion,there exist at least two types of SM stated above for improving the resistance to fatigue fracture.