As I know, fibre orientation with 90 degree can allow better load transmission, so fibre orientation with 90 degree should have better fatigue life cycle. comparison in terms of percent of ultimate tensile strength. Thank you.
At 90 degre the fatigue life is completely dominated by matrix behavior. In case of thermosetting resins the fatigue behavior is quite poor.
At 45 degrees fatigue behavior is partly due to the fibers. Then, in this case the fatigue behavior is relatively flatter than at 90 degrees.
I would be wary of generalisations like your statement. Fatigue performance in off-axis directions depend on so many factors that I don't think there is one answer to that question.
Just think about interphase properties, fiber volume fraction, fiber anisotropy (like in carbon or kevlar), viscoelastic properties of the matrix (effects of test frequency, mean cyclic stress, time at load,...).
First of all, i mean the fibre direction is parallel to load applied. Then, the other parameters (frequency, fiber volume fraction...) are same for the specimens during testing.
Then, you meant between +/-45° and 0°. At 45′, you are loading the matrix in shear an matrix and interface properties are prevalent factors of fatigue life. At 0°, fibre properties govern the fatigue behaviour.
However, it is still hard to give a general trend as constituent nature and volu.e fractons are still important factors. What is true for 60% vf carbon-epoxy may not be for 35% vf glass-polyester.
For glass-epoxy, you can have a lool at the conference paper and Upwind reports listed in my publications.
In the attached file I am enclosing a graph reporting series of fatigue data taken from FAA (Federal Aviation Administration) report on "open hole" fatigue characterization.
The experimental data refer to three different stacking sequences of (0/ -45+45/90) laminate with 20 plies. The contract notation of the laminates is a/b/a ( where "a" , "b", "a" are the percent laminae at (0) , (+45 and - 45 ) and (90) degrees, respectively).The following stacking sequences are illustrated: 10/80/10, 25/50/25 and 0/100/0. The last sequence is for a fully +45 -45 degrees laminate (no laminae at 0 and 90 dgrees).
Looking at the data it appears immediately that the laminates are not comparable exhibiting very different strengths. For instance the laminate with higher content of laminae at o degrees does exhibit longer fatigue life).
Anyway the fatigue behavior of 0/100/0 laminate(fully +45, -45 sequence) appears very much flatter than the other sequences.
For completeness, the experimental data are taken from the following report:
-1. DOT/FAA/AR-10/6 (2011) “Determining the Fatigue Life of Composites Aircraft Structures Using Life and Load-Enhancement Factors” http://www.tc.faa.gov/its/worldpac/techrpt/ar10-6.pdf
while, the lines passing through the experimental points are model predictions based on our modelling approach that appeared recently. Please see:
- A. D’Amore, M. Giorgio, L. Grassia, Modeling the residual strength of carbon fiber reinforced composites subjected to cyclic loading, International Journal of Fatigue 78, pp. 31–37 (2015)
- A. D’Amore, L. Grassia "Constitutive law describing the strength degradation kinetics of fibre-reinforced composites subjected to constant amplitude cyclic loading" Mechanics of Time-Dependent Materials Volume 20, Issue 1, February 2016 ISSN: 1385 (Print) 1573-2738 (Online), -(2016)
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