Abstract
The effects of crack shielding, finite thickness of the composite and fiber content on fiber/matrix debond growth in thin unidirectional composites are investigated analyzing Representative Volume Elements (RVEs) of different ordered microstructures. Debond growth is characterized by estimation of the Energy Release Rates (ERRs) in Mode I and Mode II using the Virtual Crack Closure Technique (VCCT) and the J-integral. It is found that increasing fiber content, a larger distance between debonds in the loading direction and the presence of a free surface close to the debond have all a strong enhancing effect on the ERR. The presence of fully bonded fibers in the composite thickness direction has instead a constraining effect, and it is shown to be very localized. An explanation of these observations is proposed based on mechanical considerations.
Highlights
Stimulated by the ever more stringent requirements in terms of weight and mechanical performances of the aerospace industry, in recent years the composite community has returned its attention to the mechanisms of intralam5 inar crack initiation with a focus on thin-ply laminates
F tent has a drastic effect on the Energy Release Rate at the tip of the fiber/matrix interface crack
Energy Release Rate (ERR)’ values are very similar for Repeating Unit Cells (RUC) with 11 × 11 and 21 × 21 fibers, though they are slightly higher for the larger RUC where the debonded fiber and the free surface are further away from the debonded fiber
Summary
Stimulated by the ever more stringent requirements in terms of weight and mechanical performances of the aerospace industry, in recent years the composite community has returned its attention to the mechanisms of intralam inar crack initiation with a focus on thin-ply laminates. 30 of fiber/matrix interface cracks (referred to as debonds in the following) at lower levels of strain in thinner plies, while at the same time coalescence of debonds and through-the-thickness propagation of transverse cracks in thin plies were delayed and even suppressed as ply thickness decreased. They reported the first onset of debonds at 0.4% for n = 1, 2 and 0.7% for n = 4. A aries of the RUC, the accelerating effect of the interaction between debonds of fibers located on the same vertical line is studied
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