A review of the effect of a/W ratio on fracture toughness (II) —experimental investigation in LEFM

Abstract

In part I of this series, experimental investigation in EPFM (elastic-plastic fracture mechanics) had been discussed. In this paper, experimental investigation in LEFM (linear elastic fracture mechanics) is given. Fracture toughness tests had been carried out on three different strength steels, using both through-cracked specimens with different a/W ratio and semi-elliptical cracked specimens with variable crack size and shape. Results show that the fracture toughness K _IC increases with decreasing a/W when a/W<0.3 for three-point-bend specimens, and that for a/W>0.3, it is independent of a/W. Shallow crack specimens, both through-cracked and surface-cracked, gave markedly higher values than deeply notched specimens. However, the effect of crack shape on fracture toughness is negligible. Results also show that the LEFM approach to fracture is not tenable for design stresses where a _c is often very small, far less than 2.5(K _IC/σ _y)².

Keywords

fracture toughness K _IC / a/W ratio / through-cracked / surface-cracked

References

[1] Methods of test for plane strain fracture toughness (K _IC) of metallic materials[S]. B.S.5447.

[2] ROOKE D P, CARTWRIGHT D J. Compendium of stress intensity factors [R]. Her Majesty’s Stationery Office, 1976.

[3] Zhang D Z, Yan S Y, Meng M. A comparison on the effect of the ratio a/W on the fracture behaviour between ductile and brittle materials [J]. Eng Fracture Mech, 1992, 43: 1097-1101

[4] Li Q F, Hu S H, Pan X J. Effect of crack depth and shape on fracture toughness in a spring steel [J]. Engng Fracture Mech, 1990, 36(1): 1-7

[5] Li Q F, Hu S H. A further study about the effect of crack depth and shape on fracture toughness [J]. Engng Fracture Mech, 1991, 39: 219-227

[6] Li Q F, Guo Y J, Yan S Y. On the effect of plastic constraint on ductile tearing [J]. Materials Science and Engineering, 2003, 251: 197-202