87 research outputs found
Impact damage detection in composite plates using deflectometry and the Virtual Fields Method
No full textThis paper presents a new method for detecting damage in layered composite materials using a simple measurement technique, deflectometry. The aim is to locate the damage in a specimen and provide a “signature” from the measured surface slopes. Firstly, this method is applied to plate specimens using numerical and experimental data. Secondly, damage indicator based on a new application of the virtual fields method to compute local apparent gaps in equilibrium is presented and used to process the measurements on plates. It is shown that the damage indicator is very sensitive, allowing detection of damage that is difficult to identify directly from the strain maps
Combining fibre rotation and fragmentation to achieve pseudo-ductile CFRP laminates
No full textThe pseudo-ductility shown by thin ply angle-ply laminates has been coupled with the gradual fragmentation of unidirectional (0°0°) plies to yield a metal-like stress–strain curve for a [±θm/0n]s[±θm/0n]s laminate. This has led to a significant increase in pseudo-ductility than either angle-ply fibre rotation or 0°0° fragmentation have shown previously. Analytical modelling has been developed that accounts for the damage processes that contribute to the gradual failure of the 0°0° plies and predictions have been made taking into account the fragmentation, delamination and eventual failure of the laminate. Experimental results are shown to correlate well with the modelling, despite some variability in the responses. Analysis via X-ray computed tomography of tested specimens shows the progression of the fragmentation and delamination damage modes prior to laminate failure and provides an in-depth understanding of the process that leads to the demonstrated pseudo-ductile strains
An investigation into fatigue behaviour and damage progression in pseudo-ductile thin-ply angle-ply laminates
No full textThis paper presents a detailed investigation on the fatigue response and damage progression in pseudoductile thin-ply angle-ply laminates with two configurations: an intermediate modulus-high modulus fibre combined IM-HM [±277/0]s and a standard modulus SM-SM [±266/0]s laminate. 80% of the “yield” stress was found to be the maximum stress for both laminates, where they can withstand 106 cycles without obvious damage or stiffness reduction. When laminates containing pre-fractured 0° plies were loaded in fatigue, both of the laminates showed a delamination dominated damage mode: the delamination initiated from the pre-fractured 0° plies and propagated at the interface between the 0° and angle plies with increasing number of cycles. An estimated delamination growth rate based on the stiffness reduction and delamination initiated from 0° ply fracture are also discussed. The IM-HM laminate with broken 0° fibres can still withstand fatigue loading at 80% severity without further modulus reduction or damage progression, whilst the SM-SM failed in delamination within a small number of cycles
Identification of the local stiffness reduction of a damaged composite plate using the virtual fields method
No full textIn the present study, a damage detection problem is formulated as the identification of the spatial stiffness distribution in a damaged composite plate. Full-field heterogeneous curvature fields obtained from an optical deflectometry technique are processed by using the virtual fields method adapted to retrieve the 2D stiffness distribution map of a damaged carbon-epoxy plate. The method not only picks up the location of the damage but also provides a fairly good estimate of the stiffness reduction in the damaged area. In this paper, the procedure is described, validated on simulated measurements and some initial experimental results are given. (c) 2007 Elsevier Ltd. All rights reserved.</p
A procedure for producing reflective coatings on plates to be used for full-field slope measurements by a deflectometry technique
No full textDamage detection in composite materials using full-field slope measurements
No full textThis paper presents a method for detecting damage in layered composite materials using a simple measurement technique, deflectometry. The aim is to locate the damage in a specimen and provide a ‘‘signature’’ in the form of surface slopes. The first part of the paper presents the experimental procedure: material, lay-up and sample types, then the set-up and data extraction are detailed followed by the finite element (FE) models. Finally the results are presented and commented
Avoiding free edge delamination in quasi-isotropic pseudo-ductile hybrid laminates- By material dispersion or layer angle dispersion?
No full textMost hybrid material studies to date have been focused on Uni-Directional (UD) laminates. This paper presents two different strategies of hybridisation for multi-directional laminates and show which one is less susceptible to free-edge delamination
Hybrid effects in thin ply carbon/glass unidirectional laminates:accurate experimental determination and prediction
No full textExperimental results are presented which allow the hybrid effect to be evaluated accurately for thin ply carbon/epoxy-glass/epoxy interlayer hybrid composites. It is shown that there is an enhancement in strain at failure of up to 20% for very thin plies, but no significant effect for thicker plies. Hybrid specimens with thick carbon plies can therefore be used to measure the reference carbon/epoxy failure strain. The latter is significantly higher than the strain from all-carbon specimens in which there is an effect due to stress concentrations at the load introduction. Models are presented which illustrate the mechanisms responsible for the hybrid effect due to the constraint on failure at both the fibre and ply level. These results give a good understanding of how variability in the carbon fibre strengths can translate into hybrid effects in composite laminates.</p
Retained strength of UHTCMCs after oxidation at 2278 K
No full textIn the frame of Horizon 2020 European C3HARME research project, the manufacture of ZrB2-based CMCs was developed through different processes: slurry infiltration and sintering, radio frequency chemical vapour infiltration (RF-CVI) and reactive metal infiltration (RMI). To assess the high temperature stability, room temperature bending strength was measured after oxidizing the samples at 2278 K and compared to the strength of the as-produced materials. Microstructures were analysed before and after the thermal treatment to assess the damage induced by the high temperature oxidation. Short fibre-reinforced composites showed the highest retained strength (>80%) and an unchanged stress-strain curve
Investigating the fatigue behaviour of quasi-isotropic pseudo-ductile thin-ply carbon/glass epoxy hybrid composites
No full textThis paper investigates the fatigue behaviour of pseudo-ductile Quasi-Isotropic (QI) interlayer hybrids with un-notched and open-hole configurations. Two different types of QI pseudo-ductile hybrids were evaluated; HighC, with carbon to glass thickness ratio of 0.29, that is made of thin-ply M46JB-carbon/epoxy and thin-ply Xstrand-glass/epoxy prepregs, and LowC, with carbon to glass thickness ratio of 0.19, that is made of thin-ply T300-carbon/epoxy and standard-ply S-glass/epoxy prepregs. The hybrid configurations were loaded at 4 Hz in tension–tension fatigue without any initial damage and at different percentages of the pseudo-yield stress (σpy) at which damage initiates. It was observed that there is no stiffness reduction, after 100000 cycles, for a stress level of 80% and 50% of the σpy for the un-notched and open-hole laminates, respectively. By increasing the stress level to 90% and 70% of the σpy for the un-notched and open-hole laminates, respectively, there is a gradual stiffness reduction due to the appearance of matrix cracking and delamination in LowC, but no gradual reduction and no visible damage were observed for HighC. The final failure is more brittle and happens at a lower number of cycles for HighC compared with LowC. Different damage extents were observed for the investigated laminates before the final sudden failure due to variables such as the ply thickness, the cyclic energy release rate and the interfacial fracture toughness
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