With the development of the design and manufacture technology, composite
materials are widely used in the aeronautical industry. But, one of the main
concerns which affects the application of composites is foreign object impact.
The damages induced by the Low Velocity Impact (LVI), which can significantly
reduce the strength of the structures, can’t be easily inspected routinely. The
so-called Barely Visible Impact Damages (BVID) due to LVI typically includes
interlaminar delamination, matrix cracks and fibre fracture at the back face.
Previous researches have shown that the results of LVI test are similar to that of
the Quasi-Static Load (QSL) test. The initiation and propagation of delamination
can be detected more easily in the QSL test and the displacement and reaction
force of the impactor can be controlled and measured much more accurately.
Moreover, it is easier to model QSL tests than dynamic impacts.
To investigate the impact damage induced by LVI, a Finite Element (FE) model
employing cohesive elements was used. At the same time, the ply clustering
effect, when several plies of the same orientation were stack together, was
modelled in the FE model in terms of damage resistance and damage size. A
bilinear traction-separation law was introduced in the cohesive elements
employed to simulate the initiation and propagation of the impact damage and
delamination.
Firstly, a 2D FE model of the Double Cantilever Beam (DCB) and End Notched
Flexure (ENF) specimens were built using the commercial FEM software
ABAQUS. The results have shown that the cohesive elements can be used to
simulate mode I and mode II delamination sufficiently and correctly.
Secondly, an FE model of a composite plate under QSL but without simulating
damage was built using the continuum shell elements. Agreement between the
FEA results with published test results is good enough to validate the capability
of continuum shell elements and cohesive elements in modelling the composite
laminate under the transverse load condition (QSL). Thirdly, an FE model containing discrete interface delamination and matrix
cracks at the back face of the composite plate was built by pre-setting the
cohesive failure elements at potential damage locations according to the
experimental observation. A cross-ply laminate was modelled first where fewer
interfaces could be delaminated. Good agreement was found in terms of the
delamination area and impactor’s displacement-force curve.
Finally, the effect of ply clustering on impact damage resistance was studied
using Quasi-Isotropic (QI) layup laminates.
Because of the limited time available for calculation, the simulation was only
partly completed for the quasi-isotropic laminates (L2 configuration) which have
more delaminated interfaces. The results showed that cohesive elements
obeying the bilinear traction-separation law were capable of predicting the
reaction force in quasi-isotropic laminates. However, discrepancies with the test
results in terms of delamination area were observed for quasi-isotropic
laminates. These discrepancies are mainly attributed to the simplification of
matrix cracks simulation and compressive load at the interface in the thickness
direction which is not taken into account.
| Identifer | oai:union.ndltd.org:CRANFIELD1/oai:dspace.lib.cranfield.ac.uk:1826/7310 |
| Date | 01 1900 |
| Creators | Liu, Hongquan |
| Contributors | Zhang, Xiang |
| Publisher | Cranfield University |
| Source Sets | CRANFIELD1 |
| Language | English |
| Detected Language | English |
| Type | Thesis or dissertation, Masters, MSc by Research |
| Rights | © Cranfield University 2011. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright owner. |
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