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Damage mechanisms in thin stitched laminates subjected to low-velocity impact
No full textThis study examines the influence of stitching on the structural and damage response of thin carbon/epoxy [02/902]s laminates subjected to low-velocity impact. Impact tests were carried out on unstitched and stitched laminates and the nature and extent of damage at various impact energies was characterized by radiographic analyses. The main results of the study are illustrated and discussed to highlight the role and the potential of stitches for improving the impact damage resistance of this class of laminated composites
Effect of core density on the low-velocity impact response of foam-based sandwich composites
Get PDFThe paper presents the results of an investigation into the effect of core density on the low-velocity impact
response of foam-based sandwich composites. Drop-weight tests were conducted on sandwich panels with
carbon/epoxy facesheets and a 10 mm thick PVC foam core. Three foam core densities (65, 100 and 160 kg/m3)
and two facesheet layups ([0/903/0], [03/ ± 45]S) were examined in the study. The analyses show that the
influence of core density on the damage resistance of the panels is strongly correlated to the layup of the skin.
While the damage developing in [0/903/0] panels is not affected by core density, the damage area in [03/
± 45]S panels reduces with increasing core density. The different influence of core properties on the damage
response of [0/903/0] and [03/ ± 45]S sandwich panels may be attributed to the different bending stiffness of
the facesheets, with a response to impact dominated by global bending in panels with thin [0/903/0] skins as
opposed to one mainly governed by local shear rigidity in panels with thicker [03/ ± 45]S skins. FE analyses
were finally carried out to assess the capability of a model developed by the authors to capture the role of foam
density in the impact damage response of the panels
Damage mechanisms in the CAI failure of thin z-pinned composite laminates
Full text linkThe results of an experimental investigation into the compression after impact (CAI) performance of thin z-pinned carbon-epoxy laminates are reported in this paper. Unpinned and z-pinned [02/902]S and [0/±45/90]S samples were impacted at energies varying between 2 J and 35 J and then subjected to compression loading until failure. The amount and nature of the damage induced by impact and the damage mechanisms leading to CAI failure were characterized by X-radiography and through visual observation of the sample surfaces. The study shows that the effect of z-pins may be beneficial or detrimental to the post-impact strength of the laminates depending on the energy of the impact. The sequence of the main damage mechanisms observed on the laminates during the compression tests is illustrated and discussed to clarify the role of z-pins in controlling the residual strength of the impacted laminates over the full range of examined impact energies
Effect of stitching on the flexure after impact behavior of thin laminated composites
No full textThe paper investigates the effect of stitching on the post-impact flexural performance of two classes of thin carbon/epoxy laminates. Unstitched and stitched laminated samples were first impacted with energies ranging between 1 J and 8 J by an instrumented drop-weight testing machine. The residual flexural properties of impacted samples were then assessed by three-point bending tests. The damage induced by impact and by post-impact bending was characterized in detail by visual inspection and penetrant-enhanced X-radiography. The results of the experimental analyses are illustrated and discussed to highlight the correlation between the residual flexural properties and the key fracture modes occurring in the laminates. The study shows that even though stitching is capable of improving the delamination resistance of the laminates, it may also drastically reduce their flexural strength. It is also seen that the residual post-impact flexural properties, which are controlled by the peculiar impact damage mechanisms of stitched and unstitched laminates, may be greatly degraded by impacts with energy above a critical threshold value
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