AN EXPERIMENTAL-STUDY OF LOW-VELOCITY IMPACT DAMAGE IN WOVEN FIBER COMPOSITES

A study is made on the low velocity impact response and post-impact me chanical capacity of woven fiber [0/90, - 45/45,0/90], carbon epoxy co mposite plates. This complements the work done by numerous other resea rchers who have also examined low velocity impact of composites, but h ave focused on uni-directional, cross-ply or quasi-isotropic laminates . In the present study, post-impact static uniaxial tension, compressi on, as well as tension-compression fatigue tests are performed. The da mage mechanisms for woven laminates are found to be predominantly dela mination and fiber breakage, with the area of impact-induced delaminat ion increasing linearly with impact energy for the range of energies e xamined. Damage extent and type are also dependent on the curvature of the impactor tip and deformation generated by a sharp impactor is mor e localized. The existence of a threshold energy level below which no delamination discernible by C-scan occurs is noted. In contrast with p revious findings, it is observed that the peak in the impactor deceler ation-time response is not associated with the onset of fiber failure, which can occur earlier. The amount of energy absorbed when this peak occurs therefore does not indicate the energy required to initiate fi ber breakage. It is observed that residual tensile strength is a funct ion of delamination area and impactor tip radius. For static compressi on and tension-compression fatigue, the residual load-bearing capacity is only dependent on delamination area. Under compression, delaminati on promotes the micro-buckling of fibers, whereas in tension, failure is predominantly via fiber breakage. For a common impact energy and im pactor, a damaged specimen is weaker in compression than in tension.