Ponencias (Mecánica de Medios Continuos y Teoría de Estructuras)https://hdl.handle.net/11441/113992024-03-28T16:47:19Z2024-03-28T16:47:19ZExperimental study of the use of ultra-thin plies in quasi-isotropic laminates under cyclic tension after impacthttps://hdl.handle.net/11441/1553632024-02-20T08:51:39Z2024-01-01T00:00:00ZExperimental study of the use of ultra-thin plies in quasi-isotropic laminates under cyclic tension after impact
In this work, the authors propose an experimental study on the possible improvement of
the mechanical behaviour produced by ultra-thin plies in laminates subjected to cyclic
loading after impact. More specifically, this work introduces the use of these plies in carbon
fibre quasi-isotropic laminates, with the aim of studying the evolution of impact damage
under tensile cyclic loads. To this aim, the behaviour of quasi-isotropic laminates consisting
of conventional thickness plies is compared with laminates with 90° ultra-thin plies, keeping
the same stacking sequence. When considering the same loading level, the damage
evolution shows a lower progress and a later failure for the laminates containing ultra-thin
plies.
2024-01-01T00:00:00ZStudy of the influence of stacking sequence in the failure of crossply laminates manufactured with ultra-thin plieshttps://hdl.handle.net/11441/1553602024-02-20T08:22:05Z2024-01-01T00:00:00ZStudy of the influence of stacking sequence in the failure of crossply laminates manufactured with ultra-thin plies
Numerous studies on the use of laminates manufactured with ultra-thin composite
laminates have shown the existence of a significant delay in the appearance of damage, a
phenomenon known as the Scale Effect. To study the effect that layer thickness may have on
the damage mechanisms that appear at higher values of the load, this work analyses
whether the use of ultra-thin laminates exhibits a better behaviour in the instants prior to
failure and laminate rupture. For this purpose, different laminates have been manufactured
with ultrathin thickness material formed by the same number of laminae oriented at 0 and
90 degrees, but with different stacking sequences, distributing the laminae such that the
thicknesses of the resulting layers are different. The laminates have been subjected to
uniaxial tension up to values close to the ultimate load in order to observe and compare the
different damage morphologies that appear in the 90 and 0 degrees layers, using optical
microscopy techniques for the observation of the damage. On the other hand, the loads for
which the failure of the selected laminates happens have also been compared. The results
obtained from this study show different behaviour of the laminates depending on the
thickness of their 0 and 90 degrees layers in the moments prior to failure and at the instant
when failure occurs.
2024-01-01T00:00:00ZBehaviour of fibre/matrix interface cracks under biaxial stress state caused by edge effect in carbon/epoxy laminateshttps://hdl.handle.net/11441/1553342024-02-20T07:56:45Z2024-01-01T00:00:00ZBehaviour of fibre/matrix interface cracks under biaxial stress state caused by edge effect in carbon/epoxy laminates
A recent study about the ''edge effect'' phenomenon in cross-ply laminates made of ultrathin plies composites has shown the presence of a relevant stress component through the
laminate thickness. This fact implies that there is a biaxial stress state in the 90° ply block,
which is present both before and after the cyclic loading tests. 4 cross-ply laminates were
analysed, only varying the 90° ply block thickness. In each case, the biaxial stress state was
obtained, selecting the most detrimental one to analyse the Energy Release Rate (G) with
respect to the fibre/matrix interface crack growth. This analysis is performed using a BEM
model from a previous study of the authors. An exhaustive microscopic revision is
performed both before (only sanded and polished after curing process) and after cyclic
testing, corroborating the occurrence of different crack growth of the present longitudinal
fibre/matrix interface debonds. In conclusion, the single fibre numerical model using BEM
and the experimental microscopic observations shed light on the micromechanical
behaviour of the interface cracks which are subjected to a biaxial stress state.
2024-01-01T00:00:00ZIn-plane shear behaviour of non-crimp fabric laminates by means of 3D finite element analysishttps://hdl.handle.net/11441/1551872024-02-13T12:27:58Z2013-09-01T00:00:00ZIn-plane shear behaviour of non-crimp fabric laminates by means of 3D finite element analysis
Suleman, A.; Camanho, P.
In order to characterize the in-plane shear behaviour of NCF laminates,
experimental off-axis tensile tests of [+45,-45]2S laminates in different loading directions
(parallel to the stitching yarns: warp-SP and normal to the stitching yarns: weft-ST) were
carried out. Since the specimens were cut from the same panel, identical results were expected
for both directions. However, the experimental tests showed that the shear modulus, the shear
strength and the shear strain at failure are higher in the weft direction (ST) than in the warp
direction (SP). To identify the cause(s) of such differences, a parametric study has been
performed using a mesoscopic scale 3D FE model of the representative unit cell of a [+45,-
45]s NCF laminate. The unit cell is composed by four laminas that have been stacked with the
correspondent +45º and -45º orientations. Each lamina contains two half rectangular crosssection tows and resin pockets between them and in the top left and bottom right corners. The
stitching yarns and the waviness induced by them in the tows have been added to the unit cell
in order to evaluate their impact in the in-plane shear behaviour. The fibre waviness appears
in the thickness direction across the length of the unit cell and since it is not normal to the tows
it has been modelled according to a new approach. That is, the element’s coordinate system of
the finite elements placed in the crimped part of the tow are rotated to take into account for the
waviness of the fibres. The study revealed that neither the stitching of the tows nor the out-ofplane waviness of the fibres is responsible for the significant differences found experimentally.
On the other hand, the parametric study revealed that a misalignment between the nominal 0º
and 90º tows of the NCF panels is what contributes the most for the differences found in the inplane shear performance between SP and ST laminates.
Web del Congreso: http://www1.dem.ist.utl.pt/composites2013/
2013-09-01T00:00:00Z