R. Jones et al., A PRELIMINARY-STUDY INTO THE MATRIX DOMINATED NONLINEAR BEHAVIOR OF GRAPHITE-EPOXY LAMINATES, Composite structures, 30(2), 1995, pp. 193-199
The potential of composites for weight-saving is now widely recognized
and they are used extensively in both control surfaces and doors. How
ever, if major weight-saving is to be realized it is essential that co
mposites be used in 'primary' components, i.e. wing and fuselage skins
. Before this can be achieved it must be shown that composites are an
adequate substitute for thin-skinned metallic components, particularly
in regions where they undergo large strains and/or post-buckling defo
rmations. For stiffened composite panels one potential failure mechani
sm is the separation of the skin from the stiffeners; resulting from e
xcessive 'through the thickness' stresses. To address this potential i
nterlaminar mechanism, the present paper discusses the non-linear, tim
e-dependent, response of a T300/914C, [0/90], graphite/epoxy laminate.
Initially a series of ASTM standard, D4255-83, shear rail tests were
performed and the equivalent sigma(eq)-epsilon(eq) curve for the lamin
ate was derived using combined experimental and computational techniqu
es. In general, the shear behaviour of the laminate was very similar t
o that observed for epoxy adhesives with extensive strain rate effects
, stress relaxation and creep even at room temperature. To further sub
stantiate these results a series of ASTM standard, D3518-76, tests wer
e then performed on +/-45 degrees laminates. These tests revealed that
the sigma(eg)-epsilon(eq) curve was indeed rate dependent, often with
a significant inelastic behaviour. Furthermore, the failure stresses
and strains were found to be strongly dependent on the loading rate.