Investigation of delamination and matrix cracking in quasi-isotropic GFRP laminates
Intra-laminara nd inter-laminarc rackingi n GFRPl aminatesh as beens tudied. The
epoxy matrix used gave a transparent composite and was compatible with
polyurethanee,n ablinga modifieds ystem(c ontaining2 0%u ethane)t o be investigated
in addition to the standarde poxy. Three stacking sequenceso f quasi-isotropic
laminates(,+ 45/-45/0/90),( 0/90/-45/45) and (+45/90%45/0w),e ret ested.
Dataw ereo btainedfo r the growtho f damagea ndi ts effecto n laminates tiffnessu nder
increasingq uasi-staticlo ad and as a function of numbero f fatigue cycles at two
differents tressle vels. Using the transparensty stemse nableda morec ompletes et of
damaged atat o be obtainedth anb y previousw orkers. The damagec omprised9 0-ply
crackingf ollowed by +45 and -45 crackinga nd then for (+45/-45/0/90)[3a nd to a
limited extenti n (+45/90/-45/0)xd],e lamination.T he initiation andg rowtho f damage
wase xaminedw ith regardt o matrix type ands tackings equenceT. he onseto f matrix
cracking and delaminationa re both delayedi n the urethane-containinlga minates;
fracturem echanicste stss howedt hat the urethanes ystemw as significantlyt ougher.
Moreover,a t a given quasi-statics tresso r numbero f fatigue cycles the urethano.
modified laminatesre taina greaterp roportiono f their initial modulus. The stacking
sequencein fluencesi nterlaminars tresses( thereby controlling delamination)a nd
determinesp arameterssu cha s ply thicknessa nd neighbouringp ly orientationw hich
in turn influencei ntralaminasc ocking.
Fracture mechanics has been applied to model the initiation and growth of
delamination under quasi-static and cyclic loading using a modified compliance
technique. Shear-lag models have been used to determine the stiffness loss due to
intralaminar cracking, enabling the stiffnessr eduction associatedw ith delamination to
be deduced empirically. This enables the energy release rates associated with
delamination to be derived leading to more sensible results than those obtained using
an unmodified technique