THE LOAD SEPARATION AND ETA-PL DEVELOPMENT IN PRECRACKED SPECIMEN TEST RECORDS

Load separation is the theoretical basis for the single specimen J for m and the incremental calculation of J-R and J(M)-R curves. It is base d on the assumption that the load can be represented as a multiplicati on of two separate functions; a crack geometry function and a material deformation function. Until recently, the main experimental basis for such an assumption was the approximate agreement between the experime ntal results of the single specimen J form and the energy rate interpr etation of J in blunt notched bending geometries. The load separation assumption has been also implied in the growing crack records in order to develop the R-curve analysis. Both the crack geometry and material deformation functions were assumed to maintain their forms as the cra ck grows. Recently, an experimental study investigated the load separa tion in the test records of stationary crack specimens of different ge ometry, material, and constraint. The study showed that the load can b e represented by a separable form for the entire plastic region except for a limited region at the early region of plastic behavior. Also, i t was found that the load separation is not limited to a certain geome try, material, or constraint but it is a dominant property in the duct ile fracture behavior of stationary crack specimens. The study also sh owed that the crack geometry function is a power law function. Hence e ta(pl) is a constant equal to the power law exponent of the geometry f unction. The objective of this study is to investigate the extension o f load separation to growing crack records. Sets of test records from three different materials are used in this study. For each material th ree or four precracked specimen test records and one blunt notched rec ord are analyzed for the compact specimen geometry. The study will dis cuss the main condition to have a separable behavior in a growing crac k test record. It will also construct the geometry and deformation fun ctions for the materials studied, these functions are compared with th ose obtained from stationary crack records.