Research On Bending Fretting Fatigue Characteristics And Failure Analysis Of40CrNi2MoA Alloy Steel

Fretting fatigue promoted micro-fatigue crack initiation and propagation rapidly, resulting in dramatically decreasing of fatigue life of the components, failure in far lower than that of fatigue limit. Fretting fatigue widely existed in mechanical, nuclear power, shipbuilding, bridge, aerospace, chemical and other industrial fields, and had became the mainly failure form of the close cooperation. According to the different types of load, fretting fatigue should be summarized into three basic modes, which were tension and compression fretting fatigue, bending fretting fatigue and torsional fretting fatigue. The domestic and international fretting fatigue research results focused on the tension and compression fretting fatigue right now, with few relatively studies on the latter two modes. This study could help to study on fretting fatigue damage mechanism in depth, and had a theoretical guidance value for resistance to bending fretting fatigue in engineering.This study had been done with the bending fretting fatigue test-bed owned by our group, and researched the bending fretting fatigue characteristics about orthogonal cylinder contact mode. With different bending load and cyclic number conditions, analyzed the damage rule of40CrNi2MoA alloy steel. The fracture specimen got observation and analysis on law of micro-crack initiation and propagation, under three aspects which were fracture analysis, morphology of wear scar and profile analysis. The work had been done to find failure mechanism of motor shaft-small gear shaft shrink fit. The main research results were as fallows:(1)The S-N curve of40CrNi2MoA alloy steel presented a shape of "C". When select bending load correspond to nose of curve, fretting was in mixed regime, and the bending fretting fatigue life was shortest.(2)The wear scar in fretting damage area had a oval shape. Contact center of sample were seriously worn, while two sides had different width wear strips under different fretting slip amplitude. With the increasing bending loads, the damage level of contact area was up, and fretting was running in partial slip regime, mixed regime and slip regime successively. The fatigue life had a characteristic of firstly decrease and increase later.(3)Fracture of fretting fatigue cracks appeared in the contact zone close to the loading end. The cracks extended obliquely at an angle under the mainly affecting of contact pressure, and then extended in depth with the help of bending loads. The crack propagation direction became vertical to sample face until fracture. (4)According to the motor shaft-small gear shaft shrink fit, the work which owned hardness test, fracture analysis and crack analysis, had been done to find invalidation mechanism.