Volume 18, Issue 4 (July 1990)
Stress Intensity Factors for Side-Grooved Fracture Specimens
Analytical support was sought for using Freed and Krafft's concept of effective thickness, (BBN)1/2, in ASTM plane strain formulas for elastic stress intensity factor, K, for side-grooved fracture specimens. Three-dimensional, elastic, finite-element analysis of various smooth and 20% side-grooved specimens yielded K values which not only supported this idea but also showed it to be slightly conservative. This result was expected to be generally true for all elastic fracture specimens because the finite-element K calculation was based on the elastically singular Gauss point stresses right near the crack front. Constraint at these points was constant through the thickness and nearly equal to its plane strain value. This result was insensitive to the presence of side-grooves and applied to most of the specimen thickness just ahead of the crack. Therefore the use of (BBN)1/2 in K formulas was supported not only for the elastic portion of J-integral testing (ASTM E 813 and E 1152) but for plane strain fracture toughness testing (ASTM E 399).