Fatigue Response and Modelling of Variable Stress Amplitude and Frequency in AS-4/PEEK Composite Laminates, Part 2: Analysis and Formulation

Abstract

The tension-tension fatigue features at variable cyclic loadings in APC-2 composite laminates of three lay-ups, including cross-ply [0/90]4 s, quasi-isotropic [0/45/90/−45]2 s and angle-ply [±45]4 s, were investigated. The parameters involved are maximum stress, frequency, and stress ratio. First, the fatigue tests of two-step and multi-block loadings were accomplished. Next, based on Marco-Starkey cumulative damage theory, we proposed the nonlinear cumulative damage theory and nonlinear reduced undamage theory associated with damage parameters in Part 1 and developed the well-established fatigue failure criterion of multi-block loading to predict the life due to variable fatigue loadings. The difference of cycle fraction between two damage loading conditions was obtained, so that we could easily shift to different damage curve and predicted the life due to multi-block fatigue loading. The measured lives in glass/epoxy and carbon/PEEK composites are found well close to those predicted by our proposed models.

Two‐stage fatigue loading of woven carbon fibre reinforced laminates

“…Unfortunately the high variation of the data does not allow us to identify a damage curve which could, as a first approximation, be used to generally represent the behaviour described. As already discussed in the Introduction, only the data from Lee and Jen 15,16 and Gamstedt and Sjögren 20 follow an opposite trend with the low‐to‐high sequence less damaging than the high‐to‐low one: it is worth noting, however, that at least in the former case the data are obtained on thermoplastic matrix laminates.…”

“…For many metals, the reverse situation occurs in terms of the sequence of the two‐stage fatigue loading. In two cases only, 16,20 a more detrimental effect of the high‐to‐low sequence has been reported for FRP composite materials.…”

“…For a more exhaustive analysis of the available models we refer the reader to the reviews by Hwang and Han 25,35 . More recently, some other models suitable to account for the cumulative fatigue damage have also been presented, such as those reported in references 16,19 , 21,34 , 41–45 …”

“…The situation is much more difficult for the more realistic case of variable amplitude loading, since a structural member is usually subjected to a load spectrum far from the constant amplitude case. Hence there are very limited experimental data, 1–31 some of which 22–31 are on glass reinforced plastics, for the fatigue of FRP composites subject to variable amplitude loading conditions.…”

Statistical tensile and flexural fatigue lives of unidirectional CF/PP laminates

“…1 Therefore, many reports have described studies of life prediction methods for CFRPs based on damage metrics such as the strength degradation, stiffness degradation, and others. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] Furthermore, the life of CFRP is highly dependent on the environmental effects of temperature, water absorption, and other characteristics. Many reports of the relevant literature have described CFRP durability under actual environmental conditions.…”