INTRODUCTION TO COMPOSITE DECKS FIBROUS LAMINATES

In materials science, a composite laminate used in decks
industry, is an assembly of layers of fibrous materials. The individual layers
consist of high-modulus, high-strength fibers impregnated in an appropriate
polymeric, metallic, or ceramic matrix material. Layers of different materials
may be used, resulting in a hybrid laminate. The individual layers generally
are orthotropic or transversely isotropic with the laminate then exhibiting anisotropic, orthotropic, or quasi-isotropic properties. Quasi-isotropic
laminates exhibit isotropic in plane response but are not restricted to isotropic
out-of-plane response. Depending upon the stacking sequence of the individual
layers, the laminate may exhibit coupling between in plane and out of plane
response. An example of bending-stretching coupling is the presence of
curvature developing as a result of in-plane loading. The properties of a
composite laminate depend on the geometrical arrangement and the properties
of its constituents. The exact analysis of such structure – property relationship is
rather complex because of many variables involved. Therefore, a few
simplifying assumptions regarding the structural details and the state of stress
within the composite have been introduced. The deformation of a plate
subjected to transverse loading is caused either by flexural deformation due to
rotation of cross-sections, or shear deformation due to sliding of sections or
layers. The resulting deformation depends on the thickness to length ratio and
the ratio of elastic to shear moduli. When the thickness to length ratio is small,
the plate is considered thin, and it deforms mainly by flexure or bending;
whereas when the thickness to length and the modular ratios are both large, the
plate deforms mainly through shear. Due to the high ratio of in-plane modulus
to transverse shear modulus, the shear deformation effects are more pronounced
in the composite laminates subjected to transverse loads than in the isotropic
plates under similar loading conditions.
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