The Effect of Specimen Geometry on JIc

Abstract

Rigid-plastic slip line field analysis shows that fully plastic flow fields and hydrostatic stress elevation are greatly influenced by geometry. This argues against a one parameter fracture criterion, such as JIc, which purports to work in the plastic range. Two specimen geometries, a center cracked panel and a bend bar were tested to provide a critical evaluation of the JIc concept. An intermediate strength Ni-Cr-Mo-V rotor steel was used in the investigation. Results show that JIc is a consistent fracture criterion for plane strain behavior for essentially elastic to fully plastic conditions. This work supports the contention that a plastic crack tip singularity is a dominant consideration for crack initiation even in fully plastic bodies. Bend bars of two thicknesses were tested to show that nearly plane strain behavior can be achieved with conventional geometries as much as an order of magnitude smaller than sizes required for linear elastic plane strain fracture toughness tests. The method used for calculating the J integral for experimental load versus deflection curves is explained in detail.

Review of fracture toughness (G, K, J, CTOD, CTOA) testing and standardization

“…Among the pioneers, Begley and Landes [99] and Landes and Begley [100] at the Westinghouse R&D Center first successfully measured the J-integral and its critical value J Ic at crack initiation using the energy principle and multiple compact specimens with mode-I tensile cracks. Kobayashi et al [89] also obtained approximate J Ic values from a set of center-cracked specimen tests through using the Dugdale model [30] with a plasticity modification factor.…”

The problems in determining the selected mechanical properties of 41Cr4 steel

“…Tablica III zawiera tak- że wartości całki J Q oszacowane metodą pierwotnie zaproponowaną przez Begeleya i Landesa w latach 1971÷1974 [19,20]. Analiza tego zestawienia wskazuje, że zastosowanie różnych metod daje różne wyniki -patrz tabl.…”

“…Dla badanego materiału dwie różne normy [4 i 5] oraz trzecie podejście zaproponowane przez Begeleya i Landesa [19,20], które jest podstawą normy [5], niejednoznacznie określają odporność na pękanie w postaci krytycznej wartości całki J. Według normy [5] przeprowadzone próby są nieważne, według drugiej normy [4] -wyniki dla tego materiału nie są miarodajne -podobne wnioski można wyciągnąć dla metody opisanej w [19,20]. Zaprezentowana analiza dotyczyła materiału, o którym wcześniej nie wiedziano, jak się zachowuje -nie znano jego charakterystyki: granicy plastyczności, wytrzymało-ści na rozciąganie, stopnia umocnienia, udarności czy nawet odporności na pękanie.…”

Crack Propagation and Arrest in Pressurized Containers

“…and by observin g that the differential equation (9) and the Models I to IV, i.e., (11), (12), (10) and (19) are of the form dt f(a,P)…”

“…A quantitative modelin g of fully-yielded net ligament in shells is somewhat more complicated. However, in this case too adequate results may be obtained by properly considering the plasticity effects [1,8,9]. On the other hand, it would be no exaggeration to state that the crack propagation phase of the fracture failure following thu ,iet ligament rupture is not understood at all.…”