FAILURE ASSESSMENT DIAGRAMS .4. THE INCLUSION OF CONSTRAINT PARAMETERS

Recent discussions of the relation between R-curve analysis and failur e assessment diagrams of the type used in R6 and PD6493 are generalize d to the situation where the material resistance is defined by a funct ion depending not only on the crack extension but also on other parame ters which measure the constraint at the crack tip. There is thus a re sistance surface if only one other parameter in addition to the crack extension is involved. The analysis is formulated for any number of ge neric constraint parameters which can be defined in terms of a generic constraint function which depends on the independent variables used i n the characterizing parameter functions. These variables are here tak en to be the crack length a and the load L on the structure. The analy sis is developed in detail for the parameter T. It is shown that, prov ided the R-curve image (RCI) of the previous work is generalized to a curve called the projected growth path image (PGPI) the relations betw een R-curve analysis and the failure assessment diagram (FAD) can be e xtended to this more general situation while still retaining a two dim ensional FAD. The methods previously developed for testing the consist ency or conservatism of an engineering FAD can thus be extended to gen eralized diagrams which allow for crack tip constraint. An illustrativ e example showing the effect of including constraint is given and some general implications are considered.