Effect of strength mismatch on fully plastic fields in dissimilar joints under combined loading

Via detailed finite element limit analyses, plastic limit loads, rotation factors, and crack-tip stress field are investigated for a combined tension and bending of a plane strain single-edge -cracked bimaterial specimen. Limiting bimaterial specimens are considered, consisting of an elastic/perfectly plastic material bonded to an elastic material having the same elastic properties. The limit loads of bimaterial specimens are shown to be very close to those of homogeneous specimens, so that limit load information for homogeneous specimens can be used even for bimaterial specimens. A tractable, approximate elliptical yield locus is proposed, which fits the FE results within 1%, for all ranges of tension-to-bending ratios. The plastic rotation factor of bimaterial specimens can be higher than that of homogeneous specimens as much as 25%, when the specimen is subject to small tensile forces. Results from the present analysis is applied to the analysis of typical fracture testing specimens such as compact tension specimens. For both homogeneous and bimaterial specimens, larger tensile forces are associated with substantial loss of crack-tip constraint. Bimaterial specimens have as much as 2 times higher constraint than homogeneous specimens, due to plastic strength mismatch. Tractable closed form approximations for crack-tip stresses are proposed in terms of tension-to-bending ratio.