A Viewpoint on the Failure Assessment Diagram

Abstract

This paper presents the results of a study to evaluate certain features of interest in the failure assessment diagram (FAD). The concept of one universal calibration curve of interpolation between the two extremes of linear elastic and plastic collapse behavior is examined. One universal curve is implicit in the Dugdale strip yield elastic-plastic model, and this is examined in the light of trends that other elastic-plastic models suggest. Material work hardening, variable constraint, and geometry were identified as variables to consider by the other models. However, in some cases the universal calibration curve concept is not appreciably affected by these additional variables. A major problem area is the consistency of load normalization by limit-load equations. These generally are imprecise estimates of the collapse load which impart a detrimental influence on the calibration curve shape and introduce the weakest link into a universal curve based FAD methodology. Three examples are given on the use of key curves to develop FAD calibration curve Kr values (elastic KI/elastic-plastic KR). A good fundamental relationship was shown to exist which, in effect, showed that FAD calibration curves represent another form of dimensional analysis. The key curve could also be used to study ways to reduce the deleterious effects associated with plastic collapse load determination problems. A procedure was shown on a way to apply FAD calibration curves to develop K-applied curves for conventional R-curve analysis.