The reference texture: A proposal of a physical explanation

The reference concept of quantitative fractography covers fatigue fractures caused by variable amplitude (cycle) loadings in which significant events occur sufficiently regularly and frequently. The reference texture is a subset of the image texture in fractographs which is common to all fractures defined above. Reference texture is unambiguously linked to the reference crack growth rate, which is related to the conventional crack growth rate by the reference factor. The physical explanation of the reference features is based on the mechanism by which overloads affect crack growth in the models of Wheeler and Willenborg. A magnitude derived in this way from the sequence of successive sizes of cyclic plastic zone is shown to imply values close to the reference factor. Application of the model to a set of nine test specimens from aluminum alloy loaded by three different loading regimes is shown. The maximal discrepancy of reference factors is about 20%. It may be argued that reference features are dominantly governed by cyclic plasticity.