| |
Composite
materials are good in tension because the fibers are stable until they fracture
in this configuration. Their performance in compression is less good
as the fibers are now loaded in compression and can become unstable to buckling
before the onset of plastic deformation. This behavior is illustrated in
the diagram.
Sample (a) has a low density of fibers and the lowest
energy for the distortion puts the buckling of the fibers out of phase. The
'high n' mode shown, rather than the single curve of the n = 1 mode expected
for a free column, comes about because the elastic energy stored in the matrix
is lower. This case is not of commercial interest because VF
is too low.
For sample
(b), the fibers buckle in phase, again with a high n buckling mode. The
shear modulus of the matrix, GM, is important in this case, and the approximate value
of the stress that causes buckling is given by: sC
= GM ( 1 - VF). |
|
|
|
|
|
|
|
|
|
|
|
