UpperShelf ACV + BCV LowerShelfACV‐ BCV API 5L X65 pipe steel with standard Charpy specimens at temperature range [-196°C up to 20 °C]. Experimental data are reported on Figure 2. Charpy energy and fracture aspects reveal the two failure modes below and above the transition temperature. Data are fitted according to Equation (6). Values of the four constants ACV, BCV, CCV and DCV are reported in Table 5 as well as the transition temperatures TK27 and TK50. Figure 2. Charpy energy versus temperature curve for API 5L X65 pipe steel and values of parameters of Equation (6). Table 5. Values of constants of Equation (6) for API 5L X65 pipeline steel ACV (J) BCV (J) CCV (K) DCV (K) TK 27(K) TK 50 (K) 141.35 135.65 4.33 179.22 174 179 2.3. Fracture toughness transition temperature T0 Fracture toughness KIC evolution versus temperature for brittle and quasi-brittle fracture can be modelled through plasticity-temperature relationship since the fracture process needs a preliminary yielding. Plasticity is a thermally activated phenomenon which follows Arrhenius law. Fracture toughness versus temperature from brittle plateau to transition foot is given by the following Equation 7: ) exp( min K IC K E FT + = (7) Kmin is the fracture toughness threshold, E and F are constants and T is the temperature in Kelvin. Transition temperature called T0 is defined conventionally for a fracture toughness of 100 MPa√m. Lower shelf Upper shelf
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