Swerea SICOMP

Mölndal, Sweden

Swerea SICOMP

Mölndal, Sweden
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Saseendran S.,Swerea SICOMP | Wysocki M.,Swerea SICOMP | Varna J.,Lulea University of Technology
Advanced Composite Materials | Year: 2017

In this work, we investigate the relationship between the rubbery modulus and the degree of cure for partially to fully cured LY5052 epoxy resin. In particular, this paper experimentally tests an existing model formulated for shear modulus by redefining for in the tensile storage modulus. Experiments to characterize viscoelastic behaviour were performed in a dynamic mechanical and thermal analysis (DMTA) instrument in the frequency domain. Master curves are then created from DMTA using general time–temperature–cure superposition. The master curves are then normalized using the model so that the master curve does not depend on the properties in the rubbery region. This results in a unique master curve that describes the viscoelastic behaviour of the LY5052 epoxy resin for the given conditions. Once the relationship between the rubbery modulus and the degree of cure has been established, the amount of experimental characterization can be reduced. This could lead to the development of simplified experimental methodologies and simplified models to characterize the viscoelasticity of low molecular weight resins like the LY5052 epoxy resin system. © 2017 Swerea SICOMP


Larsson R.,Chalmers University of Technology | Rouhi M.,Swerea SICOMP | Gutkin R.,Swerea SICOMP
ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials | Year: 2016

We propose a new and computationally efficient continuum damage based model, able to predict fibre/matrix shear failure under longitudinal compression for a UD ply. A structure tensor based continuum damage formulation is placed in context with the UD ply, where the elastic material response is governed by transverse isotropy. To represent the proper energy dissipation, an elastic damage model is formulated in the invariants of fibre/matrix shear and fibre compression, including failure initiation and progressive damage modeling. We are guided by the anisotropic elastic model to define four strain invariants, representing key features of the UD-ply microstructure. The damage model is applied to a Non-Crimp Fabric (NCF) composite and compared to a state of the art model based on kinking theory [6]. Instead of invoking the geometric instability into the material model, a key feature is to consider the geometrical fibre kinking instability on the macro-level based on a finite strain formulation. © 2016, European Conference on Composite Materials, ECCM. All rights reserved.


Varna J.,Lulea University of Technology | Loukil M.S.,Swerea SICOMP
ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials | Year: 2016

The concept of the effective stiffness of a unidirectional layer with intralaminar cracks is revisited performing 3-D FEM parametric analysis of symmetric and balanced laminates with damaged 90-layer. The effective stiffness of the damaged layer is obtained from the difference between damaged and undamaged laminate stiffness. The effective longitudinal modulus and Poisson's ratio of the layer are equal to their initial values. A very simple expression for the effective transverse modulus change with normalized crack density has sufficient accuracy and generality to be used in laminate theory to predict macroscopic elastic property change with crack density in laminates with very different lay-ups and made of different UD composites. © 2016, European Conference on Composite Materials, ECCM. All rights reserved.


Saseendran S.,Swerea SICOMP | Wysocki M.,Swerea SICOMP | Varna J.,Lulea University of Technology
ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials | Year: 2016

The aim of the presented work is to investigate the relationship between the rubbery modulus and the degree of cure for partially to fully cured LY5052 epoxy resin. In particular, this work experimentally tests an existing model defined in shear modulus by redefining into the elastic tensile modulus. Experiments were performed in a Dynamic Mechanical and Thermal Analysis (DMTA) machine in the frequency domain. After the model is tested, super-master curves generated using time-temperature-cure superposition are normalized using the model so that the rubbery modulus made independent on the state of cure, which further simplifies the super-master curves. This results in a unique master curve that describes the viscoelastic behavior of the LY5052 epoxy resin for the given conditions. This consequently could help formulate simplified models to predict viscoelastic behaviour and also develop better experimental methodologies to characterize them. © 2016, European Conference on Composite Materials, ECCM. All rights reserved.


Loukil M.S.,Swerea SICOMP | Varna J.,Lulea University of Technology
ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials | Year: 2016

The degradation of the elastic properties of composite laminates with intralaminar cracks is caused by reduced stress in the damaged layer which is mainly due to two parameters: the crack opening displacement (COD) and the crack sliding displacement (CSD). In this paper these parameters are measured experimentally providing laminate stiffness reduction models with valuable information for validation of used assumptions and for defining limits of their application. In particular, the displacement field on the edges of a [0/ +704/ -704]s glass fiber/epoxy laminate specimens with multiple intralaminar cracks is studied and the COD and CSD dependence on the applied mechanical load is measured. The specimen full-field displacement measurement is carried out using ESPI (Electronic Speckle Pattern Interferometry). By studying the displacement discontinuities, the crack face displacements were measured. A comparison between the COD and the CSD (for the same crack) is performed. © 2016, European Conference on Composite Materials, ECCM. All rights reserved.


Varna J.,Lulea University of Technology | Loukil M.S.,Swerea SICOMP
Journal of Composite Materials | Year: 2017

The old concept of the effective stiffness of a 90-layer with intralaminar cracks is revisited performing 3-D FEM parametric analysis of symmetric and balanced laminates. It is shown, focusing on the effective transverse modulus, that the expected dependence of this property on composite elastic properties and laminate lay-up is very weak and follows very simple rules. Calculations show that the effective longitudinal modulus and Poisson’s ratio of the layer are not affected at all by intralaminar cracking. Simple fitting curve for effective transverse modulus change with normalized crack density is obtained from analysis of GF/EP cross-ply laminate. It is shown, comparing with FEM results and experimental data, that this expression can be used as a ‘master curve’ in laminate theory to predict macroscopic elastic property change with crack density in laminates with very different lay-ups and made of different unidirectional composites. © 2016, © The Author(s) 2016.


Marklund E.,Lulea University of Technology | Asp L.E.,Lulea University of Technology | Olsson R.,Swerea SICOMP
Composites Part B: Engineering | Year: 2014

A multiscale approach is used to predict transverse tensile and transverse compressive strength of unidirectional non-crimp fabric (NCF) composites. Numerical analysis on fibre/matrix scale is performed to obtain the transverse strength of the fibre bundle to be further used in an analytical mesoscale model to predict the strength of the unidirectional NCF composite. Design of unidirectional layer composites with the same fibres, interface, matrix and volume fractions as in the bundle is suggested as an alternative method for bundle strength determination. Good agreement of both methods for bundle transverse strength determination is demonstrated. The simple analytical model used on mesoscale gives accurate predictions of the tensile transverse strength whereas the compressive strength is underestimated. The necessity of including bundle waviness in models when bidirectional NCF composites are analysed is demonstrated by FEM stress analysis and by experimental data showing differences in transverse cracking pattern due to bundle waviness. © 2014 Elsevier Ltd. All rights reserved.


Olsson R.,Swerea SICOMP | Block T.B.,Faserinstitut Bremen e.V. | Block T.B.,Nordex Energy GmbH
Composite Structures | Year: 2015

Core shear cracking induced by impact on sandwich panels is a critical failure mode causing severe loss of structural performance. This paper reviews previous experimental and theoretical work in the area and derives improved closed form expressions for initiation of skin rupture and core shear cracking during impact on sandwich panels with foam cores. The criterion for skin rupture is also applicable to laminates without a core. It is shown that the skin rupture load limits the achievable core shear load, and that core shear cracking can be prevented by selecting a core thickness above a certain threshold value. The criteria are successfully validated by comparison with experimental results for a range of thicknesses of skins and cores in panels with carbon/epoxy skins and a Rohacell foam core. The criterion for skin rupture is also validated for plain laminates. © 2015 Elsevier Ltd.


Grauers L.,Swerea SICOMP | Grauers L.,Chalmers University of Technology | Olsson R.,Swerea SICOMP | Gutkin R.,Swerea SICOMP
Composite Structures | Year: 2014

To develop reliable and physically based models for the crash behaviour of composite laminates, a thorough understanding of the failure mechanisms is crucial. Compression tests of corrugated Non-Crimp Fabric (NCF) laminates, made of carbon fibre unidirectional (UD) fabric with a [0/90]3S stacking sequence and epoxy, have been performed to study the energy absorbing damage mechanisms. Samples from the specimens have been studied with optical microscopy and Scanning Electron Microscopy (SEM) to identify the mechanisms involved in the crushing process. The specimens tested fail partly in bending and partly in pure compression with a mode I delamination separating these two regions. In the region failing in pure compression, the main damage mechanisms are kink band formation and matrix cracking of transverse bundles, whereas in the part failing in bending mixed mode delaminations, intralaminar shear fracture of axial bundles and kink band formation through parts of bundles are identified. © 2013 Elsevier Ltd.


Olsson R.,Swerea SICOMP
Composites Part A: Applied Science and Manufacturing | Year: 2015

This article presents analytical models for predicting large mass impact response and damage in thin-ply composite laminates. Existing models for large mass impact (quasi-static) response are presented and extended to account for damage phenomena observed in thin-ply composites. The most important addition is a set of criteria for initiation and growth of bending induced compressive fibre failure, which has been observed to be extensive in thin ply laminates, while it is rarely observed in conventional laminates. The model predictions are compared to results from previous tests on CFRP laminates with a plain weave made from thin spread tow bands. The experiments seem to confirm the model predictions, but also highlight the need to include the effects of widespread bending induced fibre failure into the structural model. © 2015 Elsevier Ltd.

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