1,721,002 research outputs found
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
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
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
Get PDFTensile 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
Get PDFThe 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
PROPER TENSILE TESTING OF UNIDIRECTIONAL COMPOSITES
Get PDFTensile tests are a basic characterization method for composite materials, but the specimens often do not fail properly. Obtaining reliable results in tensile testing requires avoiding stress concentrations near the grips. The material near the tabbed section is under longitudinal, transverse and shear stress concentrations, which leads to underestimated results and conservative design. This study therefore examines different geometries to find the best testing method that yields the maximum failure strain. The experimental results show that the novel arrow shape end tabs and continuous tab specimens allow reaching the highest failure strain value
Discontinuities in Aligned Discontinuous Fibers Composites: Microstructure Orientation Effect on Local Stress Concentration Factors
No full textThe complexity of the microstructure in composites has led to major generalizations when predicting the strength of composites. In recent years composite strength predictions have progressed by improving the fidelity of randomly packed unidirectional models. Taking it one step, further we created digital twin models of real microstructures for discontinuous aligned composites. In these models we evaluated the impact of the mean fiber direction on the local stress concentration factors. We found that the local stress concentration factors can vary 71% within a 20 ° range of rotation. Nonetheless, this variation is load dependent and will be reduced with load progression
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
A novel particle-filled Carbon-Fibre Reinforced Polymer model composite tailored for the application of Digital Volume Correlation and Computed Tomography
No full textThis paper presents the development of novel Carbon-Fibre Reinforced Polymer (CFRP) laminates, tailored for the application of Digital Volume Correlation (DVC) and Computed Tomography (CT) to experimental mechanics analyses of these materials. Analogous to surface-based Digital Image Correlation (DIC), DVC is a relatively novel volumetric method that utilizes CT data to quantify internal three-dimensional (3D) displacements and implicit strain fields. The highly anisotropic and somewhat regular/self-similar microstructures found in well-aligned unidirectional (UD) materials at high fibre volume fractions are intrinsically challenging for DVC, especially along the fibre direction at microstructural length-scales on the order of a few fibre diameters. 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 particles to act as displacement trackers (i.e. fiducial markers). Barium titanate particles (400 nm, ∼1.44 vol. %) were found to offer the most favourable compromise between contrast in CT images and the ability to obtain a homogeneous distribution in 3D space with sufficient particle compactness for local DVC analyses. This property combination was selected following an extensive Micro-focus Computed Tomography (µCT)-based qualitative assessment on a wide test matrix, that included 38 materials manufactured with a range of possible particle compositions, mean sizes and concentrations. By comparing the tensile behaviour of the particle-adapted material alongside its particle-free counterpart, we demonstrate through the application of in situ Synchrotron Radiation Computed Tomography (SRCT) that the macro- and micromechanical responses of the newly developed CFRP are consistent with standard production materials indicating its suitability as a model system for mechanistic investigations
Microstructural correlations in short-aligned glass fiber composites
No full textResearch shows that in unidirectional composites, fiber breaks and clusters of fiber breaks play a role in the failure onset of the composites [1]. So far, we know no attempts to the date have been made to analyze the fiber break development in short-aligned fiber composites, specifically using E-glass HYBON 2026. O[1]ur challenge is to determine whether there is a similar behavior in aligned short composites and its relationship with the microstructural parameter of fiber orientation distribution. This is important as it is measurable parameter to add value to recycled fiber composites. The more aligned the composite the higher mechanical properties and the higher the added value for recycling. We focused on using synchrotron x-ray computed tomography while performing hold-at-displacement scans to evaluate the fiber microstructure. We found the fiber breaks do not have the same orientation distribution as the non-broken fibers
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