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Fracture toughness of pipe line steels Maiti, Ranen

Abstract

The fracture toughness of two acicular ferrite, HSLA pipeline steels was investigated utilising the linear elastic fracture mechanics analysis (K[sub Ic] testing according to ASTM Standard E399-74) as well as the elastic-plastic fracture mechanics analysis (J-Integral and crack opening displacement COD methods). The tests were conducted at a static strain rate of 10⁻⁵/sec, K = 10 ksi√in/sec with H inch thick compact tension specimens. A resistance curve test technique developed by Landes and Begley was employed to obtain the J[sub Ic] fracture toughness; whereas the British Standard for COD testing was followed for measuring the δ[sub c] fracture toughness. The anisotropy in fracture toughness and the tensile properties of the two x-70 steels were measured and explained in terms of sulphur content and rare earth additions. An attempt was made to correlate the linear elastic fracture toughness K[sub Ic] or K[sub Q] values with the elastic-plastic fracture toughness, J[sub Ic],and COD data for both steels for tests in each of three notch orientations i.e. parallel to the rolling direction (T-L); parallel to the pipe axis; transverse to the rolling direction (L-T). Tests were performed at temperatures throughout the transition range i.e. from RT down to - 196°C. Finally the static fracture toughness data as generated in this study, was compared with the dynamic fracture toughness as obtained from IIT test for both steels.

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