Md. Gilchrist et N. Svensson, A FRACTOGRAPHIC ANALYSIS OF DELAMINATION WITHIN MULTIDIRECTIONAL CARBON EPOXY LAMINATES/, Composites science and technology, 55(2), 1995, pp. 195-207
Multidirectional laminates of the continuously reinforced carbon/epoxy
composite T300H/914C have been rested under static and fatigue condit
ions by the use of fracture mechanics coupons. Loadings of pure mode I
, pure mode II and different ratios of mixed mode I/II, i.e. opening t
ension and sliding shear, have been applied to double cantilever beam
(DCB), end-loaded split (ELS), fixed-ratio mixed-mode (FRMM), and mixe
d-mode bending (MMB) specimens. Optical and scanning electron microsco
py techniques were used to identify distinguishing fractographic featu
res and to establish the differences between static and fatigue fractu
re, as well as the differences between the various modes of fracture.
The cusp angle and the amount of fibre pull-out on the fracture surfac
e can be used to characterise the different loading modes. A large amo
unt of fibre pull-out is the dominant feature of a mode I fracture whe
reas cusps are characteristic features of a mode II fracture. Fatigue
fracture surfaces exhibited slightly more debris than static fracture
surfaces: this is thought to be due to the fretting nature of fatigue.
For the same reason, shear cusps (hackles) were more rounded and less
distinct in fatigue than on static fracture surfaces. In certain fati
gue cases, it was observed that polyethersulphone (PES), a toughening
agent used in the formulation of the epoxy resin, came out of the matr
ix; the reason for this is not fully understood.