X-ray method of evaluating local state of stress of material at crack tip one-time loading

Previously abstracted from original as item 9204-31-1522. Fractographic peculiarities of the failure and regularities in formation of plastic deformation zones in the materials with body-centered lattice (steels 20, 40, 45, St3, 15Kh2MFA) and face-centered lattice (alloy D16 and austenite steels 40G18F, 40Kh4G18F and 03Kh13AG19) under different types of single loads (static, impact, and high-velocity pulse) are considered. It is possible to use a unified criterion h sub max /t (ratio of the maximal depth of the plastic deformation zone under the fracture surface to the specimen thickness) for estimation of the local stressed state of the materials in the crack apex under all indicated types of loading. Three regions of the local stressed state are distinguished: h sub max /t < 10 exp --2 --approaching plane deformation (PD); h sub max /t > 10 exp --1 --approaching plane stressed state (PS); and 10 exp --2 < h sub max /t < 10 exp --1 --a transition region from PD to PS. Under test of materials on static crack resistance, the known criterion t/(k/ sigma sub 0.2 ) exp 2 = > 2.5 separates in materials with face-centred lattice PS from the transition region, while in materials with a body-centered one--transition region from PS. A connection of the criterion h sub max /t and the ratio beta / beta sub 0 in materials which under failure do not experience phase transformations is described by a single curve independent of the type of loading. In regions approaching PD and PS, the beta / beta sub 0 ratio may be used for estimation of the local stressed state of the material near the crack apex.