Effects of a Single Overload Event on the Fatigue Crack Growth Rate of a Low Alloyed Rotor Steel

Abstract

The aim of this work is to study the effect of the overload on the fatigue crack growth rate properties of a low alloyed steel used for rotor disk. On one hand, experimental fatigue tests during which a single overload event is applied are performed on CT specimens. Different loading conditions are imposed in order to study the effects of these parameters on the retardation of the fatigue crack due to the overload. On the other hand, two dimensions elastic plastic Finite Element calculations of crack propagation using nodes release method were used to estimate the effects of a single overload event on the fatigue crack growth rate. Different loading conditions, as for the experimental tests, are used in order to study numerically the effects of these parameters on the retardation of the fatigue crack due to the overload. The experimental and numerical results show the decrease of the crack growth rate due to the overload. This decrease depends on different parameters as overload ratio, stress ratio used for the constant amplitude cyclic loading and ΔK at which the overload is applied. From experimental test results, it can be observed that the decrease is as significant as the overload ratio is high, and as the ΔK at which overload is applied and stress ratio are low. Numerical results show similarities with experimental results, for instance the decrease of the fatigue crack growth is linked to the increase of the overload ratio or to the decrease to the ΔK at which overload is applied. Differences are also observed i.e. the increase of the stress ratio seems to increase the effect of the overload in the numerical calculations in contrary of the experimental results. By comparing to the numerical results, the quality of the results obtained from simplified models has been assessed in regard of the overload effect. A modified Kim and al. model seems to be representative of the different effects of the overload on the fatigue crack growth rate. The future work to be done consists to improve the comparison between experimental and numerical studies.

Loading sequence effect on fatigue life of Type 316 stainless steel

“…In this study, this was confirmed for Type 316 stainless steel. It was noteworthy mentioning that the tensile overloading also caused the reduction in fatigue life, although, in previous studies using the compact tension specimen, the tensile overloading deceased the effective stress amplitude and caused retardation of crack growth [31,32]. The crack mouth opening behavior seemed to be different between the tension-tension loading and tensioncompression loading.…”

“…Non-cold worked [34] Cold worked (20%) [35] Cold worked (40%) [35] As discussed in Section 1, previous studies pointed out that the overloading altered the crack mouth opening point and growth rate [28][29][30][31][32]. The enhanced crack mouth opening increased the effective strain amplitude and accelerated the crack growth.…”

“…The crack mouth opening effect has been investigated in periodical overload tests in which the test results obtained using smooth or notched bar specimens showed that the periodical compressive overloading reduced the fatigue life [27]. On the other hand, the test using compact tension specimens demonstrated that the single overloading during the crack growth tests caused retardation of the crack growth due to crack closure caused by evolution of a plastic strain field [28][29][30][31][32][33], development of residual stress or crack tip blunting [32].…”