Effect of crack front curvature and side grooving on CTOD delta(5) and J-integral in CT and 3PB specimens

Fracture testing on compact tension (CT) and three-point bend (3PB) specime ns is preceded by fatigue precracking. Fatigue-cracks have curved crack fro nts. Nevertheless, crack front curvature is not taken into account in numer ical modeling of fracture toughness testing procedures. In this paper we an alyze actual fatigue cracks in CT specimens and show that the difference be tween crack depth at the center plane and at the surface of specimens is ty pically 0.01 to 0.03 of the specimen width. Three-dimensional elastic-plast ic finite element analyses were performed for CT and 3PB specimens with cra ck fronts of different curvatures, and the CTOD delta(5) and the J-integral were determined. It is found that the ratio delta(5)(C)/delta(5) is sensit ive to the crack front curvature and strongly affected by side grooves. It is also shown that crack front curvature variations that are within the lim its given by the test standards affect to a certain extent the eta factor e mployed for the determination of the experimental value of the J-integral u sing the area under the force versus load-point displacement record. These facts should be kept in mind when toughness is measured.