Mölndal, Sweden
Mölndal, Sweden

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Pupurs A.,Lulea University of Technology | Varna J.,Lulea University of Technology | Loukil M.,Swerea SICOMP | Mattsson D.,Swerea SICOMP
16th European Conference on Composite Materials, ECCM 2014 | Year: 2014

Simple approach based on Classical Laminate Theory (CLT) and effective stiffness of damaged layer is suggested for bending stiffness determination of laminate with intralaminar cracks in surface 90-layers. The effective stiffness of layer with cracks as a function of crack density is back-calculated comparing in-plane stiffness of laminates with and without damage. The accuracy of the CLT and effective stiffness approach is demonstrated comparing with bending stiffness results from FEM simulated 4-point bending test on laminate with damage. Analytical model for damaged laminate stiffness is presented which gives similar values for effective stiffness as FEM calculations for unit cell. Effect of local delaminations initiated from transverse cracks is analyzed.

Pupurs A.,Lulea University of Technology | Varna J.,Lulea University of Technology | Loukil M.,Swerea SICOMP | Ben Kahla H.,Lulea University of Technology | Mattsson D.,Swerea SICOMP
Composites Part A: Applied Science and Manufacturing | Year: 2016

Simple approach based on Classical Laminate Theory (CLT) and effective stiffness of damaged layer is suggested for bending stiffness determination of laminate with intralaminar cracks in surface 90-layers and delaminations initiated from intralaminar cracks. The effective stiffness of a layer with damage is back-calculated comparing the in-plane stiffness of a symmetric reference cross-ply laminate with and without damage. The in-plane stiffness of the damaged reference cross-ply laminate was calculated in two ways: (1) using FEM model of representative volume element (RVE) and (2) using the analytical GLOB-LOC model. The obtained effective stiffness of a layer at varying crack density and delamination length was used to calculate the A, B and D matrices in the unsymmetrically damaged laminate. The applicability of the effective stiffness in CLT to solve bending problems was validated analyzing bending of the damaged laminate in 4-point bending test which was also simulated with 3-D FEM. © 2015 Elsevier Ltd. All rights reserved.

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.

Stromberg K.-O.,Flexprop AB | Borgenvall S.,Saab | Loukil M.,Swerea SICOMP | Noharet B.,Swedish ICT ACREO | And 3 more authors.
SAE Technical Papers | Year: 2015

Lightweight Production Technology (LWPT) is today a well-established technology in the automotive industry. By introducing light weight fixtures manufactured from Carbon Fiber Reinforced Plastics (CFRP) in aeronautical applications, new challenges as well as possibilities of in-situ health monitoring emerges. The present paper present results from experimental investigations using optical fibers with multiplex Bragg gratings (FBG) as strain gauges in an industrial CFRP fixture. Fixtures were manufactured of laminates made from CFRP. Measurements have been performed on a single CFRP beam with dimensions (8000 × 500 × 500 mm), used as a structural part in a larger assembly (9000 × 4000mm). The optical fibers were placed in between two laminates on two sides of the beam. The measurement data from the FBGs were compared and correlated to the measured displacements of the beam and the applied loads. The results show that for an eight meter long CFRP beam, it is possible to measure and detect displacements of 0.12 mm (load = 36kg), and resolve a displacement of 0.02 mm (Δload = 4.75kg). The experimental results were also compared to FEM calculations on the displacement of the beams when subject to the same load. Here measurements and calculations showed very good agreement. Overall the results imply that FBGs show a high potential as a suitable in-situ health monitoring of lightweight fixtures for the aeronautic industry as well as other applications. Copyright © 2015 SAE International.

Wagih A.,University of Girona | Wagih A.,Zagazig University | Maimi P.,University of Girona | Gonzalez E.V.,University of Girona | And 5 more authors.
Composites Part A: Applied Science and Manufacturing | Year: 2016

The study of the damage sequence in polymer-based composite laminates during an impact event is a difficult issue. The problem can be more complex when the plies are thin. In this paper, quasi-static indentation tests were conducted on thin-ply laminates to understand qualitatively the damage mechanisms and their sequence during low-velocity impact loading. TeXtreme® plain weave plies were used with two different thicknesses, 0.08 mm and 0.16 mm (referenced as ultra-thin-ply and thin-ply, respectively), and tested under different load levels. Load-displacement curves were analyzed and the extent of damage was inspected using optical microscopy and ultrasonic technique. The results showed that the damage onset occurs earlier in thin-ply laminates. The damage onset in thin-ply laminates is matrix cracking which induces delaminations, whereas for ultra-thin-ply laminates is due to delaminations which are induced by shear forces and small amount of matrix cracking. Moreover, the fiber breakage appears earlier in ultra-thin-ply laminates. © 2016 Elsevier Ltd. All rights reserved.

Paajanen A.,VTT Technical Research Center of Finland | Korhonen T.,VTT Technical Research Center of Finland | Sippola M.,VTT Technical Research Center of Finland | Hostikka S.,VTT Technical Research Center of Finland | And 2 more authors.
Safety, Failures and Robustness of Large Structures | Year: 2013

Computational modelling of fire-structural response requires interoperability of various models describing different physical phenomena. Typically, the most advanced sub-models are found within independent simulation software incapable of interoperability. To address this issue, we have developed a tool for coupling two of such programs: Fire Dynamics Simulator and ABAQUS. We present the main features and theory behind the coupling approach and use an example case to demonstrate how a coupled fire-structural analysis is set up. We also discuss potential applications and present limitations of our approach.

Sippel M.,Launcher | Kopp A.,Launcher | Sinko K.,ELTE | Mattsson D.,Swerea SICOMP
18th AIAA/3AF International Space Planes and Hypersonic Systems and Technologies Conference 2012 | Year: 2012

A new EU-funded study called CHATT (Cryogenic Hypersonic Advanced Tank Technologies) has been initiated early 2012. The project CHATT is part of the European Commission's Seventh Framework Programme and run on behalf of the Commission by DLR-SART in a multinational collaboration. One of the core objectives is to investigate Carbon Fiber Reinforced Plastic (CFRP) cryogenic pressure tanks. Four different subscale CFRP-tanks are planned to be designed, manufactured, and tested. The paper outlines the study logic of CHATT, gives a detailed presentation of the technology development tasks, and summarizes all major research results already available. © 2012 by DLR-SART.

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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