A Study on safety assessment of structural members subjected to combined tensile and bending stress fatigue

Fatigue crack growth characteristics were investigated using center notched plate specimens. The results showed that the mean stress has effect on the growth rate and the growth rate can be expressed using following formula which takes the mean stress effect into account, da/dN=C (Kmax/ΔK) (ΔK) mExperimental work was also done to investigate fatigue crack propagation behavior of semi-elliptical surface cracks subjected to combined tensile and bending stresses. Off-centered plate specimens with mechanically introduced surface cracks were used for this test. Estimation on fatigue crack growth was then made on such cracks applying the results of theoretical analysis done by Shah and Kobayashi on stress intensity factor for semi-elliptical surface cracks. From the analysis, it was found that the larger the amount of bending the longer the extension is along the surface. Experimental results showed similar trend to analytical results with respect to fatigue crack front configurations.These results were taken into account to discuss safety in liquid containers on the basis of leak before failure concept.