Abstract
Carbon fiber (CF) reinforced epoxy (CF/EP) laminates laid up in different ways (cross-ply and quasi-isotropic) with and without various adhesive interlayers (A) were studied under three-point bending using instrumented low-energy impact at single and multiple bounces. Interleaves were a modified EP resin on polyester fabric, a modified EP resin, and a polyethersulphone (PES) film. The impact response depends strongly on whether the CFs are oriented longitudinally (L) or transversely (T) to the hammer edge in the outer bounced ply. The threshold incident energy (E in,th) associated with severe damage to the laminates was much lower with the longitudinal outer ply.
The impact fatigue response of the transverse cross-ply (TCP) and quasi-isotropic (TQI) composite beams showed that stiffness degradation starts at a certain a threshold number of impact (NOI) and follows a logarithmic decay as a function of NOI. This is in close analogy to fatigue tests under usual conditions. Deterioration in stiffness can be assigned to the relative change in the secant slope (E max/x max) of the load-displacement (F-x) traces. The related load-time (F-t) traces flatten due to impact fatigue so that their load maximum (F max) shifts toward higher contact time.
The efficiency of the interleaving was assessed in both single (atE in,th≈3 J) and repeated impact (atE in=1 J). The first technique allowed us to differentiate between the various interleaves, whereas the latter contributed to finding the optimum stacking and position of the interleaves.
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Yuan, Q., Friedrich, K. & Karger-Kocsis, J. Low-energy charpy impact of interleaved CF/EP laminates. Appl Compos Mater 2, 119–133 (1995). https://doi.org/10.1007/BF00569254
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DOI: https://doi.org/10.1007/BF00569254