Plastic η-factor (η_p) of fracture specimens with deep and shallow cracks

Slip line field solutions for several commonly used fracture mechanics specimens are summarized. From these solutions analytic expressions of the plastic η_p factors are derived. These results are then compared with those η_p factors obtained using the EPRI's finite element analyses for power law strain hardening materials in order to assess the extent to which they can be approximately applied in J-integral tests with these specimens containing both deep and shallow cracks. It appears that in the deep crack specimens the η_p factors are approximately equal for all hardening materials implying that the η_p factors derived from slip line field solutions are accurate enough for J-integral evaluation. In the shallow crack specimens, with the exception of the double-edge cracked panels and pure bend specimens, the η_p factors to not agree very well and reasons for the discrepancies are discussed.