Study on S-N Curve Test for 10CrNiMo Steel under Cantilever Bend Loading

Deflection of smooth plate specimen at loaded point under different magnitude loading was calculated by Finite Element Method.S-N curve test of 10CrNiMo steel was performed under the control of load by group-method when stress ratio was- 1, and fracture appearance of the specimens were observed and analyzed.The results manifested that the deflection amount of the specimen at loaded point is in the range of effective stroke of the test machine actuator which satisfies the needs of S-N curve test within the range of test loading; S-N curves at two normal confidence degrees were attained; area of surface crack initiation and propagation at the two surfaces is nearly the same when the alternating load is larger, and surface crack initiates and propagates in one surface when the cyclic load is smaller, and starts to initiate and propagate in another surface when the specimen fracture appearance developed to some degree.The above phenomena is relative to amount of slip systems produced by different magnitude of loads for the tested material of two specimen surfaces, structure asymmetry of material and change of stress status at crack tip during its propagation.