Zenichiro Maekawa

Effect of interfacial silane network structure on interfacial strength in glass fibre composites

Abstract The effect of crosslinked structure of silane condensates on the interfacial strength between silane-treated glass fibre and epoxy resin was examined using a dialkoxysilane, γ-aminopropyldimethoxymethylsilane (APDS), and a trialkoxysilane, γ-aminopropyltrimethoxysilane (APTS). Glass fibres were treated with aqueous solutions of APDS, ATPS or mixtures of both to change the silane crosslink density, and then washed with methanol to leave only chemically bonded silane at the surface. As an index of interfacial strength, the interfacial stress transmissibility was determined using a modified single-filament test. The interfacial strength decreased in the order APDS, mixtures of APTS and APDS, and APTS, showing that siloxane crosslinking of the silane condensates reduces the interfacial strength. This result suggests that the crosslinked structure depresses the penetration of the resin into the interphase and hinders reaction between silane organofunctional groups and the resin. In addition, treatment of the glass fibre with the various APDS-APTS mixtures reduced the interfacial strength in all cases, compared with the strength after APDS treatment alone. This indicates that the silane interphases formed in the present system do not lead to the formation of interpenetrating networks with the resin molecules.

Tensile Properties of Carbon Fiber Triaxial Woven Fabric Composites

Triaxial woven fabrics are attractive for industrial applications as a rein forcement of composite materials. In this article, tensile properties and fracture behaviors of carbon fiber triaxial woven fabric composites were discussed by comparing with biaxial woven fabric composites. Moreover, the effect of weave structure on the tensile properties of the triaxial woven fabric composites was investigated. Triaxial woven fabric composites were isotropic in modulus, and anisotropic in strength. Tensile properties of basic woven fabric composites were superior compared to the Bi-Plain and biaxial woven fabric com posites. The fracture mechanisms of triaxial woven fabric composites varied with fiber ori entation. This was observed from experimental data of AE (acoustic emission) mea surement and numerical analysis.

Influence of silane coupling agents on interlaminar fracture in glass fibre fabric reinforced unsaturated polyester laminates

The relationship between the adhesive properties of the interphase of glass fibre/resin and the resultant composite Mode I delamination fracture toughness in glass fibre fabric laminate (GFFL) was studied. The Mode I interlaminar fracture toughness of GFFL was obtained by using a double cantilever beam (DCB) specimen. The delamination resistance of GFFLs which have two silane coupling agents and three concentration finishes is discussed on the basis of interlaminar fracture toughness. The crack propagation behaviour of DCB testing was mainly divided into stable and unstable manners. The fracture toughness and the crack propagation behaviour were dependent on the types and concentration of silane coupling agents.

Investigation of the interphase of a silane-finished glass fibre/vinylester resin using a microscopic. FTi.r. spectrometer

Abstract The vinylester resin around a silane-finished glass fibre was measured using a microscopic FT i.r. spectrometer. It is argued that the silane affected the curing process of the vinylester resin at a great distance compared to the thickness of the silane interphase.

Mechanical Behavior and Fracture Mechanism in Flat Braided Composites. Part 1: Braided Flat Bar:

In this article, the tensile behaviors of braided flat bar are discussed. Braided flat bars are fabricated with glass fiber and epoxy resin. Consequently, it can be confirmed that reinforcements which continuously orient in braided composites highly contribute to the rise of tensile properties. Moreover, the numerical analysis method is proposed for estimating the tensile behaviors of braided flat bar. An analytical model can be developed to consider the continuity and crimp of fibers, and can faithfully express the braiding structure. The calculation time and the waste can be reduced by using this analy sis method, because an analytical model consists of few nodes and elements. The validity of this analysis method is examined by comparing predicted results with experimental data and then the predicted results well agree with experimental data. Accordingly, it was clear that the tensile behavior of the braided flat bar could be estimated by this analysis method.

Evaluation of interfacial properties in glass fibre-epoxy resin composites — reconsideration of an embedded single filament shear-strength test

An embedded single-filament shear-strength test was employed to explore the effect of the reinforced interface on the fracture of single filaments in glass fibre-epoxy resin composites. The interfacial effect was evaluated not only by critical fibre length but also by the fracture process of an embedded single filament observed by applying tensile load to the composites. The mean fragment length, measured at different tensile stresses, decreased with an increase in stress and finally reached a value correlated with critical fragment length. Interfacial reinforcement by silane treatment affects the fracture process rather than the critical fibre length. The behaviour was examined in several factors, such as filament diameter, the tension of filament on the moulding of composites, and the scatter of the composites in mechanical properties. A useful method was proposed to exclude such scatter: specimens treated on a half-length of embedded filament were subjected to this test. The present method leads us to confirm that the reinforced interface has no effect on the critical fibre length, while it does promote the progress of the fracture.

Computer Simulation of the Deformation of Weft-Knitted Fabrics for Composite Materials

A new method for predicting the deformation behaviour and the related mechanical properties of weft-knitted fabrics is presented. A two-dimensional hexagonal mechanical model is derived, which is based on the geometrical structure of plain-stitch fabric. An analytical method of converting the experimental data of the knitted fabric into the parameters of the model is proved to be effective. By using the model-knitted fabric, the elongation deformation is simulated, and the calculated results are compared with the experimental data in order to verify the validity of the model. Moreover, the slippage effect experienced with knitted fabrics is introduced into the model to simulate the greater deformation which occurs with improved accuracy. The model can also predict deformation and related mechanical quantities in the case of three-dimensional deformations.

Weight changes of a randomly orientated GRP panel in hot water

Abstract This paper deals with the weight change mechanism in randomly orientated E glass fibre mat reinforced unsaturated polyester (GRP) panels immersed in hot water. GRP panels were immersed in distilled water at 60°C and 80°C, after which the wet and re-dried specimen weights were measured. In this case, the weight change mechanism was divided into three phases. In the first phase, water absorption occurred in the resin matrix, while matrix dissolution with negligible water absorption occurred in the second phase. In the third phase, once again water absorption with continual dissolution of fibre/matrix interface ensued. The delay time for matrix dissolution and water absorption was defined as the difference between the saturation time for GRP and unreinforced resin.

Mechanical Properties of Warp-Knitted, Fabric-Reinforced Composites

A study of the mechanical properties of basic warp-knitted, fabric-rein forced composites is presented. Three basic knitted structures have been adopted. It is found that knitted structures greatly affect the in-plane anisotropic nature, tensile strength, and modulus of warp-knitted, fabric-reinforced composites. The density of the knitted structure, which influences the tensile properties has also been taken into account. From the observation of fracture surface, two fracture modes are suggested: fracture that occurs at the extreme low volume fraction region in the course direction, and fracture that occurs due to stress concentration at the loop interlocking region in the wale direction

A comparative study of failure criteria in probabilistic fields and stochastic failure envelopes of composite materials

Abstract One of the major objectives of this paper is to offer a practical tool for materials design of unidirectional composite laminates under in-plane multiaxial load. Design-oriented failure criteria of composite materials are applied to construct the evaluation model of probabilistic safety based on the extended structural reliability theory. Typical failure criteria such as maximum stress, maximum strain and quadratic polynomial failure criteria are compared from the viewpoint of reliability-oriented materials design of composite materials. The new design diagram which shows the feasible region on in-plane strain space and corresponds to safety index or failure probability is also proposed. These stochastic failure envelope diagrams which are drawn in in-plane strain space enable one to evaluate the stochastic behavior of a composite laminate with any lamination angle under multi-axial stress or strain condition. Numerical analysis for a graphite/epoxy laminate of T300/5208 is shown for the comparative verification of failure criteria under the various combinations of multi-axial load conditions and lamination angles. The stochastic failure envelopes of T300/5208 were also described in in-plane strain space.