INFLUENCE OF NOTCH TIP STATE OF STRESS ON THE FRACTURE CHARACTERISTICS OF A HSLA STEEL

Effect of dimensional parameters on the notch toughness values of a HSLA steel has been studied. The notch mouth opening displacement, notch root contraction and load point displacements were measured experimentally during the test. Experimental data obtained from SEN three point bend specimens showed that the toughness as indicated by NTOD and J increases with increasing width, thickness, notch root radius and decreasing notch depth to width ratio. The yielding constraint factor, M and the general yielding constraint, m appeared to lie in the range of 1.3 to 2.3 in the various notched specimens investigated. The sizes of dimple in the notch or crack tip region seem to be largely influenced by the stress state prevailing at the crack tip, and the dimple size is found to be increasing with increasing triaxiality level. The state of stress at notch tip (ρ ≃ 0.2 mm) is found to be mixed type and at the crack tip it is triaxial, as indicated by σm/≃ values (≃ 0.5~1.2 for ρ=0.2 mm and about 3.2 for ρ≃0).