DEVELOPMENT OF J-R CURVES FROM OBSOLETE DATA USING NORMALIZATION TECHNIQUES

Modern elastic-plastic fracture toughness measurement often uses the J-R curve test method to characterize the ductile fracture process. However, this method requires automatic crack length measurement equipment, like elastic compliance, to provide a continuous record of crack length during the test. Before the automatic crack length systems were developed multispecimen tests were conducted from which single points of J vs crack extension were measured for each specimen. These points could be used in a extrapolation scheme to measure a single point fracture toughness value, JIC, but could not be used to develop a full J-R curve. Since the development of the single specimen J-R curve methods, these data were now considered to be obsolete. However, the recent development of the method of normalization allows the analysis of a full J-R curve from a single specimen load-displacement record without the need for automatic crack length monitoring equipment. With this method, fracture toughness test data generated before automatic crack length measurement was available can now be reanalysed to develop the full J-R curve; in particular the test records which were thought to be obsolete can now be reanalysed to yield full J-R curves. This paper describes the method for reanalysis of the older test records and takes several examples to show the success with which it can be used. The method need not only be applied to older test results. Any fracture toughness test which did not have an automatic crack length monitor, or for which the equipment failed, can be analysed by the normalization method to develop full J-R curves. © 1990.