Master Curve da/dt vs C* for Creep and Creep-Fatigue Crack Growth on CT Specimens

摘要

During high temperature service, engineering components are subjected to complex loading history including creep andcreep-fatigue conditions. Fracture mechanics concepts are widely used in defect assessment procedures like A16 guide inFrance or R5 rule in Great Britain. In order to describe crack growth, these methods apply correlations between the creepcrack growth rate da/dt against the fracture mechanics load parameter C*. Some procedures are proposed to yield this mastercurve C* versus da/dt on laboratory tests especially with CT specimens.The creep crack growth rate is obtained experimentally by the potential drop technique. C* is calculated from the loadlinedisplacement rate dδ_(exp)/dt = δ_(exp). This latter value is recorded during experimental tests but it involves :- a part due to the creep behavior : δ_C (subscript C stands for Creep behavior)- a part due to the structure response related to the crack growth : δ_s (subscript S denotes Structural term)In the literature various approaches suggest to calculate C* with δ_C =δ_(exp) - δ_S. But the δ_S (non time-dependentcomponent) evaluation differs from one approach to another.The paper aims at applying the methodologies reported in the literature to CT experimental data. A discussion about therelevance of each methodology is proposed. Furthermore, some recommendations are suggested concerning the constructionof the da/dt versus C* master curve on CT specimens. Finally, the use of the master curve for other specimens subjected tocreep-fatigue loading is commented.