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Description:
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A finite element model based on the layer -wise theory and the von Kármán type
nonlinear strains is used to analyze damage in laminated composite beams . In the
formulation , the Heaviside step function is employed to express the discontinuous
interlaminar displacement field at the delaminated interfaces . Two types of the most
common damage modes in composite laminates are investigated for cross -ply laminated
beams using a numerical approach .
First , a multi -scale analysis approach to determine the influence of transverse
cracks on a laminate is proposed . In the meso -scale model , the finite element model
based on the classical laminate theory provides the material stiffness reduction in terms
of the crack density by computing homogenized material properties of the cracked ply .
The multiplication of transverse cracks is predicted in a macro -scale beam model under
bending loads . In particular , a damage analysis based on nonlinear strain fields in
contrast to the linear case is carried out for a moderately large deformation . Secondly , the effect of delamination in a cross -ply laminated beam under
bending loads is studied for various boundary conditions with various cross -ply laminate
lay -ups . The crack growth of delamination is predicted through investigating the strain
energy release rate .
Finally , the interactions of a transverse crack and delamination are considered for
beams of different configurations . The relationships between the two different damage
modes are described through the density of intralaminar cracks and the length of the
interlaminar crack .
It is found that geometric nonlinearity plays an important role in progression of
interlaminar cracks whereas growth of intralaminar cracks is not significantly influenced .
This study also shows that the mixture of fracture mode I and II should be considered for
analysis of delamination under bending loads and the fracture mode leading
delamination changes as the damage develops . The growth of delamination originated
from the tip of the transverse crack is found to strongly depend on the thickness of 90 -
degree layers as well as the transverse crack density . Further , the effect of interfacial
crack growth on the transverse cracking can be quatitatively determined by the
delamination length , the thickness of 90 -degree layers and the transverse crack density . |