Fatigue crack propagation behaviour derived from S–N data in very high cycle regime

Abstract

The crack propagation law was derived from the S–N data in the very high cycle fatigue of a bearing steel. The propagation rate, da/dN (m/cycle), of surface cracks was estimated to be a power function of the stress intensity range, ΔK (MPa√m) with the coefficient Cs = 5.87 × 10−13 and the exponent ms = 4.78. The threshold stress intensity range was 2.6 MPa√m. The crack propagation from internal inclusions was divided into Stages I and II. For Stage I, the coefficient of the power law was C0 = 3.44 × 10−21 and the exponent m0 = 14.2. The transition from Stage I to II took place at ΔK = 4.0 MPa√m. For Stage II, the coefficient was Ci = 2.08 × 10−14 and the exponent mi = 4.78. The specimen size and loading mode did not influence the surface fatigue life, while the internal fatigue life was shortened in larger specimens and under tension–compression loading. For ground specimens, the surface fatigue life was raised by the compressive residual stress, while reduced by the surface roughness introduced by grinding. For shot‐peened specimens, fatigue fracture did not take place from the surface because of a high surface compressive residual stress. The internal fatigue life was reduced by the tensile residual stress existing in the interior of the specimens.

Very high cycle fatigue behavior of Ti-6Al-4V alloy

“…The fracture occurred even exceed 10 8 cycles. Some researchers obtained similar S-N curves with stepwise in the fatigue test of other materials [10][11] .This phenomenon was originally observed in high strength steel and surface treatment steel [12][13] . Whether there are some relationships between the stepwise and fatigue limit haven't been discovered.…”

High Cycle Fatigue Property of Carburized 20Cr Gear Steel under Axial Loading

“…In other words, the inclusion size is large enough and exceeds the critical size corresponding to ΔKFGA, and fatigue crack can directly enter into the stable crack propagation stage under cyclic loading; i.e., the formation period of a fisheye outside of inclusion. Figure 10 Based on Tanaka's theory [20], the interior crack growth rate from the inclusion to the fisheye, da/dN, can be described by the Paris law:…”

“…Combined with the evaluated sizes of inclusion and fisheye, as well as the S-N data, the values of C and m can be obtained. Thus, the interior crack growth rate equation from the inclusion to the fisheye can be expressed as: Based on Tanaka's theory [20], the interior crack growth rate from the inclusion to the fisheye, da/dN, can be described by the Paris law:…”

Effect of Ductile Thermal Spray Coatings on Fatigue Performance of 7075-T651 Aluminum Alloy

“…Such increases result from residual compressive stresses inhibiting the motion of dislocations, retarding or even preventing the initiation and growth of cracks [7,18,19]. The location of the initiation sites observed in the data presented in Table III also indicates the presence of residual compressive stresses near the surface with initiation occurring away from the surface regions affected by shot peening.…”