Finite element prediction of fatigue crack growth in Super CMV hollow shafts with transverse holes under combined torsional and axial loading

Abstract

Fatigue crack growth tests have been carried out on two types of pre-cracked, hollow, Super CMV shaft specimens with transverse holes, under combined torsional and axial loading, from which crack growth patterns and crack growth data have been obtained. Experimental results show that the cracks were found to initially propagate under the Mode I condition on the planes of maximum tensile stress, and these then veered toward the planes of maximum shear stress and propagated under a mixture of Modes II and III patterns. A finite element approach is used to predict the fatigue crack growth, under the Mode I condition, in the shaft specimens tested at relatively low magnitudes of torque. A series of incremental finite element analyses, in conjunction with the use of Paris’ law, with different crack lengths and crack front profiles, are used to simulate the progressive fatigue crack growth process. The finite element predicted crack growth data are compared with the corresponding experimental data. Good agreement is obtained between the finite element predictions and the experimental results for relatively “short” crack growths, for crack lengths of up to about 1.25 mm. For the crack lengths greater than 1.25 mm, the finite element approach underpredicts the fatigue crack growth rates and overpredicts the fatigue lives. The possible reasons for the difference between the predicted and tested results are also discussed.