Using a stress ratio method and F. E. analysis for establishing geometry correction factors in fracture mechanics

Abstract

When designing stressed-skin structures, one of the prime objectives is to determine accurate stress intensity factors for the specific components in question, which, in turn, depends on the production of accurate geometry correction factors. For an irregularly shaped component, this usually means applying a specific analytical theorem or using a devoted facility such as may be found in relatively sophisticated finite element packages. An alternative technique, however, is proposed whereby stress intensity/geometry correction factors can be readily evaluated using the most rudimentary of finite element programs. The method is potentially very powerful, since it uses the magnitude of the stress at the crack tip which can be obtained using a surprisingly coarse finite element model of the cracked component. It has been found to produce very accurate results when compared with alternative, more widely established method buts is, nevertheless, very easy to apply. In addition, consideration of the relevant theory indicates that although the method is only applied here to the relatively simple case of a thin centre-cracked sheet, it should be sufficiently versatile to be generally applicable to a wide variety of different structural shapes. This paper describes the technique and compares results using different mesh densities with results obtained by other methods.