Failure behavior of composite laminates under four-point bending

بحث بعنوان
Failure behavior of composite laminates under four-point bending
Murat Koc, Fazil O Sonmez, Nuri Ersoy and Kenan Cinar
Abstract
In this study, failure behavior of fiber-reinforced composites under four-point bending is investigated. First, the tests are
modeled analytically using the classical lamination theory (CLT). The maximum allowable moment resultants of [12]Toffaxis laminate as well as balanced and symmetric angle-ply [3/3]s composite laminates as a function of fiber orientation
angle, , are obtained using Tsai-Wu, maximum stress, maximum strain, Hashin, Tsai-Hill, Hoffman, quadric surfaces,
modified quadric surfaces, and Norris failure criteria. Second, the same tests are simulated using the finite element
method (FEM). Thermal residual stresses are calculated and accounted for in the failure analysis. An analysis is conducted
for optimal positioning of the supports so as to ensure that intralaminar failure modes dominate interlaminar (delamination) failure mode. A test setup is then constructed accordingly and experiments are conducted. The correlation of
the predicted failure loads and the experimental results is discussed. The quadric surfaces criterion is found to correlate
better with the experimental results among the chosen failure criteria for the selected configurations.
Keywords
Laminated composites, failure criteria, residual stresses, out-of-plane loading, four-point bending, classical lamination theory, finite element modeling
Conclusions
In this study, the failure behavior of [12]T off-axis
laminate and symmetric angle-ply [3/3]s laminates
under four-point bending is investigated. A four-point
bending test setup is designed and constructed such that
intralaminar failure modes are more critical than
delamination. Experiments are conducted for [12]T
and [3/3]s layup sequences for fiber angles of 0,
5, 15, 30, 45, 60, 75, and 90. Both CLT and
FEM are utilized to simulate the four-point bending
tests. Maximum allowable moment resultant, Mmax,
predictions of nine different failure criteria are compared with the experimental results.
For unidirectional laminates, [12]T, finite element
model based predictions of Tsai-Wu, Tsai-Hill,
Hoffman, quadric surfaces, modified quadric surfaces,
and Norris criteria are very close to the experimental
results with an average error of 11–12%. Maximum
stress, maximum strain, and Hashin criteria predict a
slight increase in strength in the first few degrees of the
orientation angle, which is in conflict with the experimental findings. The strength of [7512]T laminates is
found to be lower than that of [9012]T laminates. Only
Tsai-Wu and quadric surfaces succeed in correctly predicting this failure trend.
As for angle-ply [3/3]s laminates, if the residual
stresses are not included in the structural analysis, predictions of Tsai-Wu, Tsai-Hill, Hoffman, quadric surfaces, modified quadric surfaces, and Norris criteria
correlate well with the experimental results except
that they overestimate the strength of [603/603]s
laminate. Besides, they all fail to predict the failure
trend that the minimum strength occurs at about 60.
If the residual stresses are included, the criteria underestimate the failure loads.
The FEM-based predictions of the chosen failure
criteria correlate better with the experimental results
as compared to the analytical ones. The reason for
this may be the better representation of the boundary
conditions in the FE model and partially the use of 3D
solid elements.
Correlation of the predicted failure trends with the
experimental results is also examined for plates having
the same configurations, [12]T and [3/3]s, subjected
to uniaxial in-plane loads by comparing the predictions
with previously reported experimental results. If the
tensile strength of the material in the fiber direction is
lower than its compressive strength, Tsai-Wu and
Hoffman criteria predict an increase in strength under
uniaxial in-plane loads as the fiber angle is varied from
0 to 10–12, which is in conflict with the empirical
results. Overall, quadric surfaces is better in predicting
the failure trends for the chosen configurations [12]T
and [þ3/3]s under uniaxial in-plane and out-of plane
loading conditions.
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