CRACK-GROWTH RATE OF AN INCLINED SURFACE CRACK

Investigation of surface crack growth in 16MnR steel specimens with crack inclination angle beta = 0-degrees, 30-degrees and 45-degrees and under the condition of biaxial loading ratio P(x):P(y) = 0, 0.5 and 1 is reported in this paper. A formula of the stress intensity factor for surface cracked cruciform specimens loaded biaxially is calibrated using the finite element method and the line-spring boundary element method. The view that the effects of both the mode I and the mode III crack driving forces on fatigue crack growth rate cannot be neglected is proposed. In order to estimate the crack growth rate of an inclined surface crack correctly, the projection method is used and the modified Paris equation, which contains the normalized mode III stress intensity factor, is developed. The experiment data are sorted out group by group and classified in the light of the crack inclination angle and the biaxial loading ratio. Linear regression analyses and statistical tests were carried out. Consequently, the equations of the crack growth rate for inclined surface cracks in the thickness and length directions are obtained.