Crack propagation behaviour during three-point bending of polymer matrix composite/Al2O3/polymer matrix composite laminated composites

The crack propagation behaviour during three-point bending of a monolithic Al2O3 and PMC/Al2O3/PMC (where PMC denotes polymer matrix composite) laminated composites have been investigated. The laminated composites were fabricated by bonding two PMC layers on both sides of an Al2O3 plate. Carbon-epoxy and aramid-epoxy composites with two different stacking sequences, i.e. carbon(0/90)4 (C(0/90)), carbon(+45/−45)4 (C(+45/−45)), aramid(0/90)4 (A(0/90)) and aramid(+45/−45)4 (A(+45/−45)), were laminated with Al2O3 plate. The total fracture energy of the PMC/Al2O3/PMC laminated composite increased more than two orders of magnitude compared with that of monolithic Al2O3. The three-point bending process of the PMC/Al2O3/PMC laminated composite could be divided into three regimes related to the crack initiation and propagation. The PMC/Al2O3/PMC laminated composite deformed elastically in regime I. A crack was initiated and opened in the Al2O3 layer in regime II, and the outer PMC layer were deformed without complete debonding at Al2O3-PMC interface in regime III. The crack initiation stress at Al2O3 layer is proportional to the elastic modulus of PMC and the energy absorbed in regime I is the energy for elastic deformation of PMC/Al2O3/PMC laminated composites. The C(0/90)/Al2O3/C(0/90) and A(0/90)/Al2O3/A(0/90) composites, in which the laminated PMCs have higher flexural stress and modulus, fractured by the debonding at the Al2O3-PMC interface. The C(+45/−45)/Al2O3/C(+45/−45) and A(+45/−45)/Al2O3A(+45/−45) composites, in which the laminated PMCs have lower flexural stress and modulus, did not debond at the Al2O3-PMC interface but fractured by the deformation of PMC layer.