Abstract
AbstractThe toughening effect of ligaments in a fully lamellar Ti-48Al-2Cr-2Nb alloy has been determined by evaluation of J integrals of the crack tip and crack wake regions from surface strain maps. The crack tip fracture toughness KtiP was found to vary with lamellae orientation and ranged from Ktip = 13 MPa√m for inter-lamellar fracture to Ktip = 19.5 MPa√m for translamellar fracture The bridging contribution to fracture toughness was found to arise from a bimodal distribution of ligament sizes. Fracture surface reconstructions showed a distribution of large hinges that initiated at grain or subcolony boundaries and smaller ligaments associated with delaminations within a grain. The stress-displacement functions for these two ligament populations have been determined from a large scale bridging analysis of the resistance curves along with fractographic information. The small ligamerts appear to account for the initial rapid rise in crack growth resistance; and the large hinges, for the slow continued rise in toughness at large crack extensions.
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