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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.12, #2)
Determination of Residual Stresses in a Boron Fibre/Aluminium Matrix Composite by S. H. Gasparyan; N. P. Andrianopoulos (pp. 65-72).
In the present work residual stresses in a boron fibre/aluminium matrix composite are determined through an etching method. The inhomogeneous removal of surface layers, due to the different sensitivity of boron and aluminium to alkaline environment, requires the application of a modified technique for the estimation of deformations and the calculation of stresses. The results obtained indicate considerable deviations in both distribution and magnitude of residual stresses in the same MMC, due to different fabrication methods.
Keywords: MMC; boron; residual stresses; etching
Buckling of Sandwich Composites; Effects of Core–Skin Debonding and Core Density by Hassan Mahfuz; Syful Islam; Mrinal Saha; Leif Carlsson; Shaik Jeelani (pp. 73-91).
Foam–core sandwich composites have been fabricated using innovative co-injection resin infusion technique and tested under in-plane compression. The sandwich construction consisted of Klegcell foam as core materials and S2-glass/vinyl ester composites as face sheets. Tests were conducted with various foam densities and also with implanted delamination between the core and the face sheet. The intent was to investigate the effect of core density, and the effect of core–skin debonds on the overall buckling behavior of the sandwich. Analytical and finite element calculations were also performed to augment the experimental observations. It has been observed that core density has direct influence on the global buckling of the sandwich panel, while embedded delamination seem to have minimal effect on both global as well as local buckling. Detailed description of the experimental work, finite element modeling and analytical calculations are presented in this paper.
Keywords: foam–core; sandwich composite; buckling; delamination
A New Method to Quantify Delamination Resistance of Fibre Reinforced Polymers (FRP) under Transverse Loading by T. Kuboki; E. Gallagher; P. -Y. B. Jar; J. J. R. Cheng (pp. 93-108).
A test method, with specimen design similar to that proposed by O’Brien et al. (see [23–26]) but under 3-point bending, is proposed to measure the critical strain energy release rate (Gc) for delamination in fibre-reinforced polymers (FRP) under out-of-plane (transverse) loading. Unlike end-notch-flexure (ENF) test or double-cantilever-beam (DCB) test that are currently used, the new method does not require an insert film or a pre-crack to initiate delamination. Instead, the delamination was initiated from a FRP layer of the same composition but with different fibre orientation. Difference of the fibre orientation used in this study was 90○, i.e. one 90○ layer in the mid-thickness and the rest 0○ layers. Under 3-point bending, matrix shear cracking was firstly initiated in the 90○ layer, mimicking the mechanism for delamination initiation in the FRP when subjected to transverse loading. The matrix shear cracking led to delamination in the adjacent interlaminar regions, of which area can be measured after the test. Calculation of Gc was based on “area method”, that is, dividing the total energy loss by the delamination area. The Gc was compared with that from plate specimens of the same composition and fibre lay-up but subjected to transverse point loading. The comparison suggests that very similar Gc values were produced from the two types of testing, even though unstable crack growth occurred under 3-point bending and stable crack growth under transverse point loading. Therefore, the proposed method has the potential of quantifying delamination resistance of FRP under the transverse loading conditions.
Keywords: FRP; delamination; transverse loading
Prediction of Impact-Induced Fibre Damage in Circular Composite Plates by J. Lee; C. Soutis (pp. 109-131).
A simple analytical impact damage model for preliminary design analysis is developed on the basis of experimental findings observed from quasi-static lateral load and low velocity impact tests. The analytical model uses a non-linear approximation method (Rayleigh–Ritz) and the large deflection plate theory to predict the number of failed plies and damage area in a quasi-isotropic composite circular plate (axisymmetric problem) due to a point load at its centre. It is assumed that the deformation due to a static transverse load is similar to that occurred in a low velocity impact. It is found that the model, despite its simplicity, is in good agreement with finite element (FE) predictions and experimental data for the deflection of the composite plate and gives a good estimate of the number of failed plies due to fibre breakage. The predicted damage zone could be used with a fracture model developed by the second investigator to estimate the compression after impact strength of such laminates. This approach could save significant running time when compared to FE numerical solutions.
Keywords: circular composite plate; impact damage; fibre damage; quasi-static test; low velocity impact test; Rayleigh–Ritz method; non-linear deflection plate theory; finite element analysis