Vol.13, No2, 2013, pp. 99–108
UDC 539.3/.4

Failures of engineering structural components and structures can typically be traced to surface cracks. A serious difficulty associated with predicting structural integrity in this case is that the surface cracks are three dimensional, whereas fracture mechanics methods are based on two-dimensional assumptions. The basic requirement for the applicable fracture mechanics method are behind accuracy its simplicity and robustness. According to current FAD methods, the last two requirements are fulfilled. The increased conservatism of the results shows, however, that the requirements concerning the accuracy cannot be always fulfilled. The advance in this respect is achieved by the method presented in this paper considering that the plastic zone at the crack tip is the feature representing the ability of the most engineering material to reduce the stress peaks and thus to weaken the crack effect. The rigorous consideration of plastic zone correction by the construction of FAD in the actual codes is less advisable. The verification of the alternative approach is achieved based on experiments. The agreement with the experimental results is for the proposed method very successful. In case of R-6 Option 2 representative for current methods, in opposite, the results indicate a systematic deviation from the experimental results, which lies in the structure of the current formula of FAD.

Keywords: FAD, surface crack characterisation, plastic zone, EPFM, residual strength, verification