Effect Of Fatigue Damage On The Dynamic Tensile Behavior Of Q235

After studying uniaxial tensile mechanical properties of Q235 steel with different cycle fatigue life score N/Nf(N/Nf= 5%-75%) under constant strain amplitude of 0.005 of fatigue loading, it found that the maximum stress of pre-fatigue specimen under uniaxial tension is higher than the specimen under pure uniaxial tension. According to this phenomenon, it shows that the traditional damage theory that the material damage accumulation associated with sample residual strength decline is not reasonable. Contrasting the pre-fatigue specimens with the specimens without the fatigue cycle, ductility parameter of specimens is all declining, such as the reduction of area and elongation. With the N/Nf value increasing, dispersion of ductility parameter is increasing obviously, however, the area of shear lip of uniaxial tensile fracture is decreasing, which shows a transition that the fracture morphology form ductile to brittle.When the value of N/Nf reaches a certain life scores, the surface of necking section of specimens appears slip bands and tiny cracks. Moreover, the stripes and the tiny cracks are more dense on the necking zone with the number of cycle increasing, and its surface derives a large number of holes eventually. Doing uniaxial tensile failure test after cutting and polishing different thickness on the surface of Q235 steel specimens under pre-fatigue cycle, it found that the crack of surface of specimen under the uniaxial tensile failure does not appear visible to the naked eye when the surface is cut and polished to a certain thickness. The above phenomenon shows that the fatigue cumulative damage in the process of tension and compression cycle priority focused on the sample surface. Based on fatigue damage discussed in this paper, the paper also studied the notch specimen fatigue problem.