Abstract
The low cycle fatigue tests using the replica technique for LZ50 steel under non-proportional cyclic loading were carried out, and eight groups of effective test data were obtained. The evolution behaviour of short cracks was studied based on the effective short cracks criterion. The results show that short cracks generally originate in the grain or along the grain boundary. At the microstructural short crack stage, the crack propagation is influenced strongly by the microstructure of the material, and the growth rate of the short crack slows down several times according to the number of obstacles encountered. At the physical short crack stage, the crack propagation breaks through the banded structure of pearlite. Thus, the dominant effective short fatigue crack is formed, and the crack growth rate increases rapidly. Based on the modified parameters of the uniaxial short crack model, an approach is presented to calculate the growth rate of short cracks under multi-axial non-proportional loadings, and the new model can consider the non-proportional factor F. The fitting results of the multi-axial microstructural obstacles model are compared with test data. The comparison results show that this model can reflect the trend of short fatigue crack propagation rate under non-proportional loadings.
Highlights
Multi-axial fatigue is one of the main factors that causes destruction of the metallic structure in service
The LZ50 steel used in athe railwaydiameter axle industry is a and carbon structural material, iswith the according chemical to ASTM compositions standard E466-15
The fatigue replica tests were performed under cyclic loading to study softened by acetone was pasted on the surface of non-proportional the specimens to record the initiation and short crackpropagation growth
Summary
Multi-axial fatigue is one of the main factors that causes destruction of the metallic structure in service. Materials 2020, 13, 294 the crack initiation and propagation of materials were considered in the method In this case, this method was widely used to obtain many fatigue life prediction models under non-proportional. LZ50 a commonly usedstrain material for railway in China, parameter causing the crack initiation and propagation of materials were considered in the method. As an example, the low cycle fatigue test was carried out under axial-torsion loading to study In case, this method widely used obtain many fatigue life prediction models under nonthethis short fatigue cracks’was behaviour of thetomaterial. This method widely used obtain many fatigue life prediction models under nonthethis short fatigue cracks’was behaviour of thetomaterial These models did not consider the effect of microstructure microstructure obstacles of the material is put forward to calculate short fatigue cracks’ growth rate obstacles on short fatigueloadings. In the present study, taking LZ50 steel, a commonly used material for railway axles in China, as
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