Mixed-mode delamination fracture toughness and fatigue growth of T300/914C composite

The delamination fracture behaviour in static and fatigue loading for T300/914C composite laminate has been experimentally investigated by MMB test. The composite laminate examined exhibited various crack growth behaviours for different Mixed-Mode rates. The results show that the total delamination fracture toughness G_c for T300/914C composite material decreases with increase in Mixed-Mode ratio m. Fractographs of MMB specimens for T300/914C show that two typical fracture mechanisms. One, the interfacial debonding was combined with deformation of the resin matrix (associated with Mode II failure). Another one was commonly matrix failure indicating relatively good adhesion between fibre and resin. The matrix failure was occurred in interface of the inhomogeneous system and the granular fracture surface was observed. Besides, the fibre breakage observed on the fracture surfaces at m > 1 indicates that the fibre bridging existed in fracture procedure. These features are typical fracture fashion for T300/914C laminate under Mode I (DCB). Moreover, as the Mode I load increased, the fracture feature of Mode I increased obviously. The transition of fracture mechanism can be observed at m = 1. The delamination growth may be controlled by Mode I loading. The Mode I loading plays a major role in the delamination failure behaviour of carbon-fibre reinforced composites under Mixed-Mode loading and the influence of Mode I loading on Mode II failure is primarily that it constrains the development of crack-tip plastic deformation (associated with the Mode II contribution). The interaction between Mode I and Mode II loading may be characterised by the interaction parameter (I_i)"M. The delamination fracture behaviour 0f T300/914C laminates was compared with the delamination fracture behaviour of T300/M10 and of HAT/6376. The difference of the delamination behaviour between T300/914 (or HAT/6376) and T300/M10 was that nature of interfacial adhesion between fibre and matrix resin. The delamination growth rates in a wide range of #DELTA#G are not much difference. The delamination growth is discontinuous with the number of cycles depending upon the #DELTA#G value and the material structure. The fatigue crack growth rate associates with the value of strain energy release rate under static loading, although cyclic fatigue crack growth occurs under stresses which would not induce fracture under static loading. As was expected, fatigue crack growth rate for MMB tests lie well between DCB and ENF tests. (orig.)SIGLEAvailable from TIB Hannover: RN 4165(1995,12) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman