Yp. Siow et Vpw. Shim, AN EXPERIMENTAL-STUDY OF LOW-VELOCITY IMPACT DAMAGE IN WOVEN FIBER COMPOSITES, Journal of composite materials, 32(12), 1998, pp. 1178-1202
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.