The investigation of fibre reinforcement effects in thermoplastic materials: interfacial bond strength and fibre end parameter

Glass fibres used in the manufacture of fibre reinforced thermoplastic composites (FRTP) are normally sized with a film former which includes a silane coupling agent to improve the interfacial bond strength between glass fibre and matrix . However, during composite failure even an optimized interface cannot stop the initia tion of cracks at the fibre ends, which can lead to large transverse cracks in the matrix or failure by fibre pull-out. In order to help better understand the failure mechanisms of FRTP, thermoplastic microbond tests and photoelasticity experiments have been used to study the interface in model single fibre composites

Study on properties of composites reinforced by heat treated glass fibres simulating thermal recycling conditions

In the present study, commercial chopped glass fibres were heat treated at 300°C, 450°C, 500°C and 600°C to imitate a composite thermal recycling process. The heat treated fibres were extrusion compounded and injection moulded with polypropylene to form composites. The heat treatment increased the susceptibility of the fibres to length degradation during the melt processing particularly at higher conditioning temperatures. Comparison with the Cox model revealed that the stiffness of the composite was affected by the reduced fibre length. The reduced fibre length did not significantly contribute to the reduction of the tensile strength and the impact strength. These properties were deteriorated by other factors such as the strength degradation of the glass fibres and the reduced fibre matrix interaction. Thus a post treatment which recovers the fibre strength and optimizes the fibre-matrix interface will be essential to produce thermally recycled glass fibre composites with high mechanical properties

Effective use of transient vibration damping results for non-destructive measurements of fibre-matrix adhesion of fibre-reinforced flax and carbon composites

Fibre-matrix adhesion affects fibre-reinforced composites' mechanical properties, a process which can be improved by applying appropriate sizing on the fibre. Transverse bending tests and Scanning Electron Microscopy (SEM) can help quantify this effect This paper investigates if modal damping measurements are a reliable alternative for quantifying fibre-matrix adhesion. When a composite sample is vibrating, part of the dissipated energy is due to the internal friction. More internal friction and slipping at the fibre-matrix interface is expected with a weaker fibre-matrix bond, hence increasing the amount of dissipated energy, which in turn is proportional to the modal damping value. This paper researches two different cases to validate this hypothesis. In the first case, we will use two composite samples of flax fibre, one with and one without sizing. In the second case, we will compare flax and carbon fibre laminates. If the only variable is fibre sizing, better adhesion is related to significantly lower damping and higher resonance frequencies. If composite laminates with different fibre and matrix type are compared, lower adhesion is not necessarily related to increased damping and lower resonance frequencies. However, when combining the damping result with SEM microscopy, it is possible to assess the relative contribution to the internal energy dissipation of the fibre, the matrix and the fibre-matrix interface individually. (C) 2016 Elsevier Ltd. All rights reserved

The processing and testing of aluminium matrix composite wires, double composites and block composites

The Composite Processing and Testing Laboratory operated for about 15 years in USA. After that, in 2004- 2005, it moved from Boston to the Budapest University of Technology and Economics One of the main results from research and development projects is that of aluminium matrix composite wires produced via continuous processing. The composite wires have experimental applications for the electrically conductive reinforcement of high voltage electric cables, for example. Ceramic continuous-fibre-reinforced MMC-wires were produced with diameters ranging from 0.1 to 2.5 mm and a fibre volume fraction of up to 60% v/o. Thanks to the high efficiency of the continuous process, interface relations are notably reduced, and this increases mechanical properties. The other principal result is one pointing to carbon fibre-reinforced block composites processed by a combination of vacuum and high-pressure infiltration. The result of these processes is fibre-reinforced aluminium matrix composite blocks. Production methods, composite wire reinforced double composites and the results of the material tests of these products are revealed. Various matrixes were made use of in the production of double composites so as to monitor the changes in the interface relations. Alongside the conventional mechanical testing methods, mechanical properties can be characterized by use of an instrumented impact test, while the solidification structure and interfacial properties can have a SEMEDS and thermoelectric measurement (Seebeck-coefficient)

XRD and EDS Investigations of Metal Matrix Composites and Syntactic Foams

Metal matrix composites (MMCs) of different composition were produced and investigated by X-ray diffraction (XRD) and energy dispersive spectrometry (EDS) analysis. Firstly unidirectionally reinforced MMCs were produced using two type carbon fibre reinforcement and commercial purity aluminium matrix. In MMCs the interface layer has significant effect on the mechanical properties of the composites therefore need to be correctly explored. The investigations showed chemical composition changes in the composites, especially at the interface layers. In the case of carbon fibre reinforced composites Al4C3 phase was formed. The amount of Al4C3 depended on the temperature and the time at temperature of the composite during production and on the quality of carbon fibres. As the second investigated MMC, SiC fibre reinforced aluminium matrix composite wires were produced by continuous pressure infiltration. In SiC reinforced MMC wires the effect of interface diffusion was observed. After long term thermal ageing at 300°C alumina was formed and Si and Ti of SiC fibres moved into the matrix. Finally, metal matrix syntactic foams were manufactured which are particle-reinforced composites, but also known as porous materials (foams), because they contain high amount of hollow ceramic microspheres. Four type hollow spheres from different suppliers with different chemical composition and mean diameters were used. In syntactic foams an exchange reaction took place between the aluminium alloy matrix and the Si content of ceramic inclusions. The reaction resulted in significant alumina formation

A numerical study on impact and compression after impact behaviour of variable angle tow laminates

Recent developments of variable angled tow (VAT) technology have indicated that variable stiffness composite laminates offer a strong potential for structural tailoring. However, the design complexity requires use of numerical analysis and novel techniques for this type of structural composites. This paper addresses the problem of the impact and compression after impact (CAI) behaviour prediction of variable stiffness composite laminates with emphasis on the effect of the interaction between fibre orientations, matrix-cracks and delaminations. An explicit finite element analysis using bilinear cohesive law-based interface elements and cohesive contacts is employed for the investigation. Examples are presented to illustrate the effectiveness of the current models for predicting the extent of impact damage and subsequent compression strength. The current study has improved the understanding of interactions between matrix-cracks and delaminations to clarify open questions on delamination initiation and how matrix cracks and fibre orientations interact. (c) 2012 Elsevier Ltd. All rights reserved.</p

An experimental and numerical study of the influence of local effects on the application of the fibre push-in tests

Accelerated corrosion tests, Cohesive crack, Finite Elements simulations Several methods have been developed to test interfacial adhesion in composite materials such as pull-out, microbond and push-in/push-out tests. Some of them can only be applied to single fibre matrix composites and others are difficult to perform on brittle fibres due to premature fracture of the fibre. Push-in tests, consisting on pushing the fibre with a micro or nanoindenter on a bulk specimen, constitute a powerful technique that can be applied directly on composite laminates. However, the interfacial adhesion values obtained from different tests (microbond, push in) often differ and even are subjected to a large scatter. This might be due to the fact that the existing analytical solutions that are typically used to interpret the experimental data take into account the constrain effect of the surrounding fibres on a simplified manner. To study this, we have carried out a careful micromechanical modelling of the push-in test, coupled with experimental adhesion testing in a glass fibre reinforced epoxy matrix composite. The model takes into account the interfacial fracture process by means of interface cohesive elements at the fibre–matrix interface and focuses on the study of the constrain effects due to the local configuration of the surrounding fibre

Influence of nanorubber toughening on the tensile deformation and tensile fatigue behaviour of a carbon fibre reinforced epoxy composite

This study investigates the effect of nanocarboxylic acrylonitrile butadiene rubber on the tensile fatigue behaviour of carbon fibre-reinforced polymer composites with dicyandiamide-cured epoxy matrix. The stress-controlled tension–tension fatigue behaviour at a stress ratio of R = 0.1 and maximum stresses between 400 MPa and 650 MPa was investigated for the case of carbon fibre-reinforced polymers with pristine and nanorubber-modified epoxy matrices with loadings of 5 phr, 10 phr, 15 phr and 20 phr. The results from the experimental tests show that the high-cycle fatigue life of the laminates with 15 phr of nanorubber-modified resin matrix was increased by a factor of two compared to the pristine matrix samples. Scanning electron microscopy images of the fracture surfaces also show an enhanced plastic deformation existing at the fibre–matrix interface and a lower extent of fibre pull-out; both contributing towards the enhancement of the fatigue performance of the carbon fibre-reinforced polymer composites. </jats:p

Effect of fibre treatments on mechanical properties of flax/tannin composites

Due to the inherent environmental benefits of using natural resin (tannin) and natural fibre (flax), flax/tannin composites could be potentially used for vehicle applications. One of the main limitations is the hydrophilic property of flax, resulting in the poor fibre/hydrophobic matrix interface quality. Alkali, acetylation, silane treatment and enzymatic treatment were selected to modify non-woven flax mats to prepare the composites. The fibre morphology was studied through scanning electronic microscopes (SEM). The effects of fibre pre-treatments on dynamic and static mechanical properties of composites were investigated through adequate experiments, such as dynamic mechanical analysis (DMA) and static tensile testing. The modified rougher fibre surface broadened the glass transition peaks of composites due to the improved surface adhesion. However, there is no big improvement of tensile strength after modifications. The pure NaOH (sodium hydroxide) treated composites remain the tensile properties and offer good flax/tannin wettability