Behavior Of Surface Cracks Research Articles

Stress intensity factors for half-elliptical surface cracks subjected to complex crack face loadings

The disagreement in the literature on the stress intensity factors for surface cracks is considerable. It is also noted that not enough attention has been given to the behaviour of surface cracks in stress fields more complex than uniform tension and bending, although such solutions are needed for crack problems in, e.g. thermal and residual stress fields. In the present paper, stress intensity factors (Mode I) are presented for nine crack geometries in combination with six load cases. The finite element method using 20-node collapsed quarter point singular elements was employed. By a proper modelling of the problem, the number of degrees of freedom was significantly reduced and high accuracy achieved. For the cases of uniform stress and bending, the results agree very well with those of Refs. [8,10], (1–3% for most cases) except one, ( a c = 0.2 , a t = 0.75 ) for which the present results are 10–17% lower than those in [8]. (For this case other published results deviate up to ± 50%). The K-factors for the more complex loadings will be useful in analysing surface cracks in complex stress fields.

Three-dimensional elastic-plastic finite element analysis of small surface cracks

Three-dimensional, elastic and elastic-plastic finite element analysis of small surface cracks was performed. The elastic analysis is in good agreement with other solutions. For a round surface with a radius equal to six times the crack depth, the K at the surface is about 4% higher than the K for a flat surface. The results of the elastic-plastic analyses show a unique variation of the effective K (J-integral) along the crack front with a decrease in K at the surface due to a lack of plane strain constraint and an increase in the effective K at the maximum depth point with increasing plasticity. Similar behavior was observed for a semielliptical crack. Increasing the strain hardening exponent from 10 to 20 produced similar results with slightly higher effective A's for high applied strains. These results are useful in understanding the fracture behavior of small surface cracks.

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.