In this study, the effect of matrix properties on the acoustic emission response of glass fibre reinforced plastic tubes has been investigated. Two kinds of composite materials have been considered, differing essentially in the matrix: one is polyester-based composite and the other a vinylester-based composite. It is shown that the viscoelastic behaviour of the matrix can affect the acoustic emission response (i.e. the damage accumulation rate of the composites). This is observed throughout different experimental methods, essentially by checking the effect of the influence of hygrothermal ageing, which influences the rheological properties of the pure matrix on the Felicity ratio measurement, and also by measuring the influence of strain rate on the mechanical response of the tested composite.

Creep and strain controlled low-cycle fatigue tests with an imposed hold time at maximum tensile strain were carried out, mainly at 600°C, on two heats of 316L stainless steel. Very long times to failure (≃ 104 h) corresponding to low applied strain and long dwell period (24 h) were investigated. Both fatigue and creep damage were measured by quantitative metallography. Creep intergranular surface cracking shortens the initiation stage of fatigue cracks, while creep intergranular bulk cracking accelerates the average fatigue crack growth rate. These observations are the basis for a creep-fatigue interaction model previously proposed using intergranular damage as a life correlating parameter. The applicability of this model is tested with results of 104 h creep-fatigue tests showing a saturation effect. The saturation in creep-fatigue life observed for long dwell periods is explained by an improvement in creep ductility. This intergranular damage approach is discussed in the light of the creep dominated regime concept. It is shown that pure creep failure data cannot provide reliable prediction of creep fatigue life. The need to use a model that takes into account the effect of creep intergranular damage on fatigue crack propagation is emphasized.

Eight creep-fatigue interaction models are identified on a set of LCF experimental data.

In order to predict long-term behavior of a high-creep resistant low-carbon Type 316L stainless steel under low-cycle fatigue with long hold times, a series of tests of fatigue relaxation was undertaken at 550, 600, 650, and 700°C for medium strain ranges (Δεt = 0.7, 1.2, and 1.6 percent). Hold times up to 5 h were introduced at the maximum tensile strain. It has been shown that a reduction of fatigue life occurred, generally associated with intergranular cracking when hold times increased. A maximal effect was observed at 600°C. Different methods for extrapolating results for very long hold times, such as those encountered on fast breeder reactor components (∼1000 h) were proposed. These methods were based on a time-temperature equivalence comparable to those used for extrapolating creep rupture data. A correlation between reduction of fatigue life with the amount of stress relaxation during hold times was also used. Predictions by these methods are compared with ASME N47 fatigue design curves.