Off-Axis Fatigue of Graphite/Epoxy Composite

Abstract

Off-axis static and fatigue behavior of AS/3501-5A graphite/epoxy was studied in an effort to characterize the matrix/interface-controlled failure. Seven different off-axis angles were tested: 0, 10, 20, 30, 45, 60, and 90 deg. Initial (static) and post-fatigue residual strength were obtained together with S-N relationships. Fracture surfaces were examined through photomicrographs and stereo (three-dimensional) scanning electron microscope (SEM) photographs, in order to delineate failure modes, and the results of these inspections are discussed. The off-axis static strength, including scatter, was fully characterized by a polynomial and a nondimensional strength parameter. Essentially, no strength or modulus degradation was observed in the specimens surviving fatigue loading of 106 cycles regardless of the off-axis angle or fatigue stress level. When fatigue stress level is normalized with respect to static strength, all data seem to fall on the same S-N curve. Fatigue failure occurred without any warning or visible damage. Matrix failure characteristics vary with off-axis angle and appear in the form of serrations and axial and transverse cracks. Large scatter in life was observed at all off-axis angles; however, since the number of specimens employed in the present study is not sufficient to provide meaningful statistical S-N data, a more detailed investigation of the off-axis (and angle ply) behavior of graphite/epoxy composites is warranted.

Modelling the crack initiation in unidirectional laminates under multiaxial fatigue loading

“…It can be defined as the macroscopic fracture plane. Observations of fracture surfaces (Awerbuch & Hahn, 1981;Shiino et al, 2012) show the wide presence of shear cusps in the matrix between the fibres, which can be reasonably thought to be the results of the initiation of multiple inclined micro-cracks in the matrix between the fibres. This seems to be also supported by the in situ observations on 45 off-axis specimens statically tested (Cox, Dadkhah, Morris, & Flintoff, 1994).…”

“…When a UD lamina is subjected to a cyclic loading condition leading to a matrixdominated response, final failure occurs without a visible (macroscopic) progressive damage (Awerbuch & Hahn, 1981;El-Kadi & Ellyin, 1994;Quaresimin & Carraro, 2013). In fact, a stable propagation phase is never observed, and when a macrocrack nucleates, it propagates unstably leading the lamina to the complete fracture in just a few cycles.…”

Examination at a Material and Structural Level of the Fatigue Life of Beams Strengthened with Mineral or Epoxy Bonded FRPs: The State of the Art

“…• Fiber load angle: Hashin and Rotem (1973) and Awerbuch and Hahn (1981) carried out an investigation to evaluate the effect of loading on the fatigue strength of FRP composites using GFRP and CFRP respectively. In these investigations, different loading angles were used.…”

Using Artificial Neural Networks to Predict the Fatigue Life of Different Composite Materials Including the Stress Ratio Effect

“…Experimental fatigue data collected from a variety of published works [19][20][21][22][23][24][25][26][27] was used to train and test the ANN. This data included results obtained for various types of composite materials with numerous fiber orientation angles subjected to several values of the stress ratio.…”