Effect of stress ratio and specimen thickness on fatigue crack growth of CK45 steel

Abstract

Presented are the eect of stress ratio and thickness on the fatigue crack growth rate of CK45 steel according to DIN 17200. Test results are obtained for constant amplitude load in tension with three stress ratios of R 0, 0.2 and 0.4 and three specimen thicknesses of B 6, 12 and 24 mm. Microgauge crack opening values were used to calculate DK eff values from which the da/dN A DK eff curves are obtained. Crack closure can be applied to explain the in¯uence of mean stress and specimen thickness on the fatigue crack growth rate in the second regime of the two-parameter crack growth rate relation. An empirical model is chosen for calculating the normalized load ratio parameter U as a function of R, B and DK and, for correlating the test data. Ó

Evaluation of Fatigue Crack Propagation in The Post-Service Gas Turbine Vane

“…6 that there is little difference in FCPRs between the standard and miniature size specimens, under higher ⊿K regime than about 10 MPam 1/2 . This correspondence does not conflict with the historical results, which showed that the specimen thickness effect on FCPRs was almost within a magnitude of factor of 2 or 3 in engineering polycrystalline alloys, e.g., carbon steels or aluminum alloys (14,15,18,19) .…”

“…Therefore, it is of considerable technical and financial benefit if the condition of the blades can be assessed and their remaining life determined. Whilst some efforts have been made to investigate the microstructural evolutions (2,3) or the degraded creep properties of post-service gas turbine superalloys (4) , little is known about their properties of fatigue; the most frequent failure mode (9)(10)(11)(12)(13)(14)(15)(16)(17) . Here, the properties may be often depending on the location in the components.…”

Finite element modelling and analysis of crack shape evolution in mode-I fatigue Middle Cracked Tension specimens

“…In corner crack (CC) specimens [22] the degree of tunnelling seemed to be roughly twice as much as in CT specimens [23], also due to the extent of surface regions. The effect of CT specimen thickness on FCGR was studied at room temperature by Bao and McEvily [24] on 9Cr-1Mo steel and by Costa and Ferreira [25] on CK45 steel. They observed that the FCGR increases with that thickness, which was attributed to different levels of crack closure induced by plasticity.…”

Finite element meshes for optimal modelling of plasticity induced crack closure

“…Crack closure is the contact of the fracture surfaces during a portion of the load cycle, which affects the local stress and plastic deformation fields near the crack tip and, therefore, the micromechanisms responsible for fatigue propagation [2]. Crack closure was able to explain the influence of mean stress in both regimes I and II of crack propagation [2,3], the transient crack growth behaviour following overloads [4], the growth rate of short cracks [5] and the effect of thickness [6,7], among other aspects.…”