93 research outputs found
Modelling the damage evolution in unidirectional hybrid laminates
No full textAlthough composite materials are durable, strong and light, their brittleness limits their use in several industrial applications. The lack of ductility of composites can be overcome by hybridisation where low strain materials (LSM) are sandwiched between two layers of high strain materials (HSM). Hybridisation tends to improve composite properties by acting either on the overall mechanical properties or on the damage propagation mechanisms leading to failure. UD hybrid composites have complex failure mechanisms including multiple interacting damage modes, such as ply fragmentation and interface delamination. The damage mechanisms in UD hybrid composites varies with the thickness ratio of LSM/HSM. To study the behaviour of UD hybrid composites in different load and boundary conditions, a numerical model is required. The aim of this study is to simulate the damage evolution in unidirectional hybrid carbon/glass and carbon/carbon composites subjected to tensile loading by finite element models
Hybrid effect of carbon/glass composites as a function of the strength distribution of aligned short carbon fibres
No full textThis paper aims to investigate the effect of strength distribution of aligned discontinuous carbon fibre layers in carbon/glass hybrid composites on the increase of carbon fibre failure strain. The aligned discontinuous carbon layers were manufactured by the HiPerDiF (High Performance Discontinuous Fibre) method, this allows manipulating the strength distribution of carbon layers while maintaining mechanical properties comparable with continuous carbon composites. Single fibre tests were performed to obtain the statistical properties of each group of carbon fibres. Interlaminated hybrid composite specimens with aligned discontinuous carbon plies sandwiched between continuous glass plies were designed and tested in uniaxial tension. The experimental results of the hybrid effect were compared with modelling predictions.sponsorship: This work was funded under the UK Engineering and Physical Sciences Research Council (EPSRC) Programme Grant EP/I02946X/1 on High Performance Ductile Composite Technology in collaboration with Imperial College, London. Supporting data can be requested from the corresponding author, but may be subject to confidentiality obligations. Y. Swolfs acknowledges the support of the European Commission for his Marie Skłodowska-Curie Individual European Fellowship “HierTough” and FWO Flanders for his postdoctoral fellowship.status: Publishe
Deformation and failure of pseudo-ductile quasi-isotropic all-carbon hybrid FRPS with an open hole under tension
No full textsponsorship: Acknowledgements The work of SBS was financially supported by the Russian Science Foundation (project No. 18-19-00377) and partially by KU Leuven. The authors are grateful to the Toray Group for providing prepreg materials and for supporting the Toray Chair at KU Leuven, held by SVL. The authors thank laboratory staff Bart Pelgrims, Kris Van De Staey and Marc Peeters for their help and support of the experimental work. The authors thank Madhusudhan Gundappa for manufacturing some laminates and assisting some testing activities. (Russian Science Foundation|18-19-00377, KU Leuven, Russian Science Foundation|18-19-00377)status: Publishe
Weld lines in tow-based sheet moulding compounds tensile properties: Morphological detrimental factors
No full textWeld lines (WLs) are among the most detrimental defects affecting polymer composites. While they have been extensively studied in short fibre composites, their effects on tow-based composites are largely unknown. In this study, tow-based carbon fibre sheet moulding compounds were used to compression mould plates with WLs. Three different WLs configurations were considered: WLs in (1) low-flow moulding, (2) high-flow moulding with opposite meeting fronts and (3) high-flow moulding with adjacent meeting fronts. The tensile strength of the WL specimens was between 48% and 88% of the pristine material. Tows were highly distorted in the region of the WLs, both in-plane and out-of-plane, and a significant tow re-orientation parallel to the WLs was recorded. The meeting flow fronts acted as a physical barrier to each other, preventing tows to intermingle. A comprehensive characterisation of the effects and the main detrimental factors of WLs in tow-based composites was thus presented.sponsorship: The research leading to these results has been performed within the framework of the FiBreMoD project and has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 722626. YS acknowledges FWO Flanders for his postdoctoral fellowship. SVL holds the Toray Chair at KU Leuven, the support of which is acknowledged. The authors acknowledge Mitsubishi Chemical Carbon Fiber and Composites GmbH for providing material and related information. The micro-CT images have been acquired on the X-ray computed tomography facilities at KU Leuven, maintained under the supervision of Prof M. Wevers and financed by the Hercules Foundation and the Research Council of KU Leuven (project C24/17/052); help of Dr. Jeroen Soete and of Johan Vanhulst is gratefully acknowledged. (European Union|722626, FWO Flanders, Toray Chair at KU Leuven, Hercules Foundation, Research Council of KU Leuven|C24/17/052)status: Publishe
Identification of the damage in woven composites based on acoustic emission cluster analysis
No full textUnderstanding the failure mechanisms in textile composites based on acoustic emission (AE) signals is a challenging task. In the present work, unsupervised cluster analysis is performed on the AE data registered during tensile tests on 2D and 3D woven carbon and glass fibre/epoxy composites. The analysis is based on the k-means++ algorithm and principal component analysis. Peak amplitude and frequency features – peak frequency for 2D woven composites and frequency centroid for 3D woven composites – were found to be dominant in cluster analysis. Cluster bounds were identified for all composite types. These bounds do not differ with a reinforcement type, but do differ for glass and carbon reinforced composites. These bounds can be used as a starting point for AE analysis of other carbon or glass fibre/epoxy composites
Hybridisation of self-reinforced composites
No full textsponsorship: The work leading to this publication has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under the topic NMP-2009-2.5-1, as part of the project HIVOCOMP (Grant Agreement No. 246389). The authors thank the Agency for Innovation by Science and Technology in Flanders (IWT) for the grant of Y. Swolfs. I. Verpoest holds the Toray Chair in Composite Materials at KU Leuven.status: Publishe
Fibre-direction strain measurement in a composite ply under quasi-static tensile loading using digital volume correlation and in situ synchrotron radiation computed tomography
No full textDigital Volume Correlation (DVC), in concert with in situ Synchrotron Radiation Computed Tomography (SRCT), has been applied to Carbon-Fibre Reinforced Polymers (CFRPs) under quasi-static tensile loading. DVC represents a relatively novel tool for quantifying full-field volumetric displacements and implicit strain fields. The highly anisotropic and somewhat regular/self-similar microstructures found in well-aligned unidirectional (UD) materials at high volume fractions are shown to be intrinsically challenging for DVC, especially along the fibre direction. To permit the application of DVC to displacement and/or strain measurements parallel to the fibre orientation, the matrix was doped with a sparse population of sub-micrometre barium titanate particles to act as displacement trackers (i.e. fiducial markers). For the novel materials systems we have developed, measurement noise is considered along with the spatial filtering intrinsic to DVC data processing. Compared to volume images acquired through Micro-focus Computed Tomography (μCT), hold-at-load artefacts are mitigated through scan times on the order of ∼seconds using SRCT, as opposed to ∼hours. Instances of individually fractured fibres evolving into clusters of breaks are presented, together with the associated strain redistribution (imaged at a voxel resolution of 0.65 μm). It is shown that the distance over which strain is recovered in the broken fibres not only increases with the applied force, but also with the number of broken fibres, delineating aspects of the load shedding phenomenon. The study demonstrates that unprecedented, mechanistically-consistent three-dimensional (3D) strain measurements may be made in relation to fibre failure events, that can be used to validate micromechanical models for predicting UD tensile failure. We believe this work presents the first application of DVC to the SRCT imaging of failure in CFRPs, achieving significantly higher resolution than reported previously within the literature.<br/
Morphology-induced fatigue crack arresting in carbon fibre sheet moulding compounds
No full textCarbon Fibre Sheet Moulding Compounds (CF-SMCs) are tow-based composite materials. Interrupted fatigue tests, combined with computed tomography, were performed here to investigate the damage mechanisms in high in-mould flow CF-SMC. The tow-based microstructure created obstacles for fatigue damage propagation, increasing the CF-SMC's resistance against cyclic loading. Failure is shown to nucleate inside the tows, but inter-tow crack propagation tends to be hindered by the presence of the other tows. Tows oriented perpendicularly to the initial fatigue crack stop the crack itself, showing an intrinsic crack arrest mechanism. Additionally, pre-existing manufacturing cracks or voids do not propagate at all. As a result, flatter slopes of the SN diagrams were observed for CF-SMC than for other carbon or glass fibre composites with short, long and even continuous fibres
Specimen designs for accurate tensile testing of unidirectional composite laminates
No full textTensile testing of unidirectional composites based on standardized test methods nearly always leads to premature failure in the end tab region. The material near the tab section is under a complex loading state, including longitudinal, transverse, and shear stress components. The present work examines different conventional designs for tensile testing along with novel ones to find the method that minimizes the geometric discontinuity and yields the highest failure strain. Finite element (FE) models are utilized to predict the stress concentrations for all end tab designs with representation of the actual grip components. The simulation reveals that the stress concentration near the edge of the end tabs can vary significantly with end tab design. FE models are used to further optimize the geometry of end tabs. The experimental results reveal that specimens with novel arrow-shaped tabs and continuous tabs yield the highest failure strain, and hence are best at avoiding premature failure
Quasi-isotropic carbon-carbon hybrid laminate: static and low-cyclic performance
No full textThe main strategy to make composite materials more damage tolerant and less brittle is the hybridization. The interlayer hybridization is the simplest way consisting of low-elongation and
high-elongation layers. In this context, few studies have been focused on interlayer all-carbon quasi-isotropic laminates. This is the topic of the present work dealing with the
pseudo-ductile (PD) behavior of a laminate [0/45/90/-45]s both for quasi-static and low-cyclic tensile
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