Time-dependent deformation and fracture of steel between 20�C and 400�C

Abstract

A~traet. The time-dependent deformation and cracking behavior of the quenched and tempered steel 15 NiCuMoNb 5 was investigated in the temperature range 20°C to 400°C. Fracture mechanics tests were carried out under various loading conditions including load-hold times of up to three weeks. The time-dependent crack growth can be described by the crack resistance (JR-) curve. Only above 300°C, the JR-curves obtained from constant-load tests start to deviate substantially from constant-displacement-rate tests. In this temperature range, the C,-parameter, which has been developed for creep crack growth testing, can be used to describe crack growth rates. For practical purposes, it is important to note that hold-time effects reduce the load-bearing capacity of cracked specimens by less than 10 percent for the present material and testing conditions.

A new model for characterizing primary creep damage

“…Results of limited testing show that conclusions similar to those made in [46] can be drawn here for line pipe steel regarding time dependent effects on the J-resistance curves. These results and those of [46] mean that once a J-resistance curve is developed at a given temperature, it may be used to predict the crack growth behavior of cracked bodies experiencing creep deformation, provided that the creep is mainly primary. For our model, the J-resistance curves were developed using standard elastic-plastic loading rates and conditions and are assumed to be valid for analysis during creep conditions.…”

“…In a series of tests on compact tension specimens, Kuhnle and Riedel [46] have shown (for the material they tested) that the J-resistance curves are independent of load-hold effects for thermal conditions between room temperature and 300°F. The specimens were each subjected to various types of loading conditions, such as varying load-hold times, varying displacement rates, and constant load, and in all cases the J-resistance curves are very similar.…”

Characterization of creep-fatigue crack growth behavior in 2.25 Cr-1 Mo steel using (C t)avg

“…This process can be simulated in the laboratory by using a trapezoidal loading waveform consisting of a rise time (tr), hold time (th) and a decay time (td). AK can be used as the correlating parameter for cycle-dependent crack growth rates, da/dN, while Ct-parameter can be used to correlate the time dependent crack growth rates, da/dt [2][3][4][5][6][7][8][9][10]. However, due to experimental limitations in obtaining instantaneous values of Ct and da/dt during the hold time, average values of crack growth rates and Ct, (da/dt)avg and (Ct)avg, respectively, are used for characterizing CFCG data.…”

Room-temperature creep behavior on crack tip of commercially pure titanium

“…The J-integral can be determined by several methods, and the following equation could contain the contribution of timedependent creep [16].…”