Failure assessment diagrams. IV The inclusion of constraint parameters

Abstract

Recent discussions of the relation between R-curve analysis and failure assessment diagrams of the type used in R6 and PD6493 are generalized to the situation where the material resistance is defined by a function depending not only on the crack extension but also on other parameters which measure the constraint at the crack tip. There is thus a resistance surface if only one other parameter in addition to the crack extension is involved. The analysis is formulated for any number of generic constraint parameters which can be defined in terms of a generic constraint function which depends on the independent variables used in the characterizing parameter functions. These variables are here taken to be the crack length a and the load L on the structure. The analysis is developed in detail for the parameter T . It is shown that, provided the R-curve image (RCI) of the previous work is generalized to a curve called the projected growth path image (PGPI) the relations between R-curve analysis and the failure assessment diagram (FAD) can be extended to this more general situation while still retaining a two dimensional fad. The methods previously developed for testing the consistency or conservatism of an engineering fad can thus be extended to generalized diagrams which allow for crack tip constraint. An illustrative example showing the effect of including constraint is given and some general implications are considered.