Using tailored fibre placement technology for stress adapted design of composite structures

Abstract

The tailored fibre placement technology, which has been developed at the Leibniz Institute of Polymer Research Dresden, is well capable for manufacturing textile preforms for composite parts with fibre layouts of arbitrary direction using standard embroidery technology. Additionally, a new design tool, advanced optimisation for principal stress, has been recently developed to improve the mechanical properties of prospective lightweight composite structures. Two optimisation strategies for composites with non-unidirectional layout were implemented. Within the tailored fibre placement process chain the advanced optimisation for principal stress tool enables the use of these optimisation strategies, and the transfer of corresponding results to the manufacturing process and to computational analysis. As an example, an unequal wide loaded tensile plate has been optimised, manufactured, experimentally tested and, finally, numerically calculated to verify its strain behaviour. A good coincidence between numerical and experimental results was found.     

Tensile,flexural and impact properties of jute fibre-based thermosetting composites

Abstract

The present study reports static and impact mechanical properties of jute fibre-based thermosetting composites using woven and flat braided jute fabrics. Tensile, three-point flexural and low-to-medium energy drop-weight impact tests were conducted and mechanical properties were evaluated to study their dependence upon surface modifications of the fibre materials due to bleaching and coating treatments. Full-bleaching (longer and rigorous) treatments improved interfacial bonding and tensile strength properties of the woven jute composites compared to unbleached and half-bleached counterparts. Bleaching treatments did not seem to improve the flexural strength of composites. Unbleached (natural) jute composites have relatively better flexural strength due to reduced microstructural waviness or fibre crimping to facilitate flexural failure. With coated jute yarns, the tensile properties of the resultant flat braided composites slightly degraded, whereas the flexural properties showed clear improvements. The changes in the mechanical properties were broadly related to the accompanying modifications and to the state of microstructural imperfections, namely fibre/matrix interfacial adhesion, severity of resin matrix shrinkage during the curing process, fibre/matrix debonding and distribution of disbonds within the matrix region, and also to the relative fibre filament density along the loading axis, in the cured composite structure. There was a clear indication that natural woven jute composites could be more effective in applications requiring better impact damage resistance, energy absorption capability and improved progressive crushing behaviour.     

Experimental studies on fracture of unidirectional glass-fibre-reinforced plastics composites with V-notch

Abstract

The digital speckle correlation method is used to study the deformation and fracture behaviour of glass-fibre-reinforced plastics (GFRP) composites with V-notch under tensile loading. The deformation images surrounding the notch tip at varying load levels were captured; both the horizontal and vertical displacement fields are acquired. At the same time, the strain evolution information at the notch tip during the whole damage and fracture process of the notched sample is recorded by a three-element strain gauge. The effects of notch angle and notch depth on deformation and fracture of notched GFRP are analyzed. Some microscopic fracture characteristics such as interfacial debonding, fibre fracture and matrix damage are shown.     

Effect of alkali treatment on properties of unidirectional isora fibre reinforced epoxy composites

Abstract

Unidirectional isora fibre reinforced epoxy composites were prepared by compression moulding. Isora is a natural bast fibre separated from Helicteres isora plant by retting process. The effect of alkali treatment on the properties of the fibre was studied by scanning electron microscopy (SEM), IR, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Mechanical properties such as tensile strength, Young's modulus, flexural strength, flexural modulus and impact strength of the composites containing untreated and alkali treated fibres have been studied as a function of fibre loading. The optimum fibre loading for tensile properties of the untreated fibre composite was found to be 49% by volume and for flexural properties the loading was optimised at ～45%. Impact strength of the composite increased with increase in fibre loading and remained constant at a fibre loading of 54·5%. Alkali treated fibre composite showed improved thermal and mechanical properties compared to untreated fibre composite. From dynamic mechanical analysis (DMA) studies it was observed that the alkali treated fibre composites have higher E' and low tan δ maximum values compared to untreated fibre composites. From swelling studies in methyl ethyl ketone it was observed that the mole percentage of uptake of the solvent by the treated fibre composites is less than that by the untreated fibre composites. From these results it can be concluded that in composites containing alkalised fibres there is enhanced interfacial adhesion between the fibre and the matrix leading to better properties, compared to untreated fibre composites.     

A comparative investigation of interfacial adhesion behaviour of polyamide based self-reinforced polymer composites by single fibre and multiple fibre pull-out tests

Abstract

Interfacial adhesion of composite materials plays an important role in their mechanical properties and performance. In the present investigation, analysis of the interfacial properties of self-reinforced polyamide composites by using microbond multiple fibre pull-out test is emphasised. Microbond specimens prepared through thermal processing are tested for their interfacial properties by multiple fibre bundle pull-out tests and compared with that of traditional single fibre pull-out test specimens. Multiple fibre pull-out addresses the volume fraction as well as eliminates the possibility of fibre breakage before matrix shear. Higher scatter in the data in the samples is addressed in the present studies. FTIR and Fractographic studies are carried out for deep understanding of the post pull-out interfacial adhesion.     

Evaluating unidirectional composite thermal conductivities through engineered interphase

ABSTRACT

Effect of fibre/matrix interphase parameters, including thickness and material properties on the equivalent thermal conductivities of unidirectional fibre-reinforced polymer composites. A unit cell-based micromechanical method is proposed to evaluate the thermal conductivities of unidirectional multi-phase composites. The longitudinal thermal conductivity of unidirectional fibre-reinforced polymer matrix composites is seen to be independent of interphase region. When the thermal conductivity of interphase is higher than that of matrix, the increase of interphase thickness leads to an improvement in transverse thermal conductivity of fibre-reinforced polymer composites. The influences of fibre volume fraction, orientation angle and shape of cross-section as well as temperature on the thermal conducting behaviour are widely examined. The model predictions are in good agreement with the experimental data reported in the literature.     

Mechanical properties of interfaces within a flax bundle – Part I: Experimental analysis

In order to model the tensile behaviour of flax fibre based composites, the properties of each of the constituents need to be determined. In addition to the fibres, the matrix and the fibre/matrix interface, the fibre/fibre interface present within a bundle of flax fibres is an element which is rather hard to characterize but whose properties also need to be taken into account to understand properly the deformation and rupture modes of the derived composites. In the first part of this study, the protocol used to determine these properties is described; the results of the mechanical tests and the microscopic observations carried out on pairs of fibres are given and exploited to lead to the fibre/fibre interface properties. In the second part, various cohesive zone models will be evaluated using these interface properties and numerical simulations will be performed for the purpose of validation.     

Studies on recyclable composites: nylon fibre reinforced high density polyethylene composites

Abstract

A commercial grade of high density polyethylene (HDPE) matrix reinforced with nylon fibre up to 30 wt-% of HDPE was studied as a potential candidate for recyclable composites. These composite materials show improvement in mechanical properties such as tensile strength and flexural strength. Modification using styrene maleic anhydride – grafted HDPE significantly improved the mechanical and thermal properties. The HDPE/nylon composites/blends obtained by recycling of the composites also show good mechanical properties.     

Integrated compounding and injection moulding of short fibre reinforced composites

Abstract

Composites of high density polyethylene (HDPE) and carbon fibre (C fibre) were compounded and moulded into tensile test bars in compounding injection moulding (CIM) equipment that combines a twin-screw extruder and an injection moulding unit. Two HDPE grades exhibiting different rheological behaviours were used as matrices. The mechanical properties of the moulded parts were assessed by both tensile and impact tests. The respective morphologies were characterised by scanning electron microscopy (SEM) and the semicrystalline structures of the matrices investigated by X-ray diffraction. The final fibre length distribution and fibre orientation profiles along the part thickness were also quantified. The composites with lower viscosity exhibit higher stiffness, higher strength and superior impact performance. Both composites exhibit a three layer laminated morphology, featuring two shell zones and a core region. Interfacial interaction is favoured by a lower melt viscosity that enhances the wetting of the fibre surfaces and promotes mechanical interlocking. The composites display a bimodal fibre length distribution that accounts for significant fibre length degradation upon processing. The dimensions of the transversely orientated core differ for the two composites, which is attributed to the dissimilar pseudoplastic behaviour of the two HDPE grades and the different thermal levels of the compounds during injection moulding. Further improvements in mechanical performance are expected through the optimisation of the processing conditions, tailoring of the rheological behaviour of the compound and the use of more adequate mould designs.     

Combustion characteristics of cellulosic loose fibres

The aim of this paper is to study the combustion characteristics of loose fibrous cellulosic compounds through cone calorimeter measurements. The challenge in studying loose fibrous materials by cone calorimeter in a reproducible manner is met by optimizing various process parameters such as sample weight, heat flux and grid type. The method is validated using cotton fibres and fabrics with a range of flame retardant properties. Good correlations are obtained between the flame retardant content of samples and the heat release parameters for both the fibres and the fabrics. In addition, fibres from specific cotton cultivars showed statistically significant differences in heat release characteristics. This shows that valuable data concerning the combustion behaviour and the corresponding kinetics of loose fibrous compounds can be successfully gathered using a cone calorimeter. Thus, such data can be exploited to well define future fibre breeding programmes or fibre modification research. Copyright © 2012 John Wiley & Sons, Ltd.     

Fire reactions of ceramic and polymer moulding composites

Abstract

Abstract

Low cost ceramic dough moulding compounds/composites (CDMC) are composed of inorganic metal silicates and chopped fibre reinforcements. This paper investigates the fire reactions of these materials under severe thermal and heat conditions. This research is targeted to potential applications in the replacement of glass fibre reinforced polymeric insulation materials such as phenolic composites as engine heat shields which experience high temperature and heat transmission. The materials developed can provide good properties, including heat insulation with high thermal stability for engine drafts, where traditional glass/phenolic composites were used and gave a very short life cycle. This work compares the thermal properties of the glass fibre reinforced phenolic composites and metal silicate composites produced under the same processing conditions. The results show that CDMC possesses significantly better thermal stability and heat resistance in comparison with phenolic moulding composite (phenolic dough moulding composites). The indication was that under the testing condition of heat flux of 75?kW?m^?2 intended for materials used for applications in marine, transport and possibly nuclear waste immobilisation, the integration of the CDMC was kept intact and survived as a high temperature insulation material.     

Large strain and toughness enhancement of poly(dimethyl siloxane) composite films filled with electrospun polyacrylonitrile-graft-poly(dimethyl siloxane) fibres and multi-walled carbon nanotubes

Unfilled cross-linked poly(dimethyl siloxane) (PDMS) is a weak material and is generally filled with high levels of particulate fillers such as silica, calcium carbonate and carbon black to improve its mechanical properties. The use of fibrous fillers such as electrospun nanofibres and multi-walled carbon nanotubes as fillers for PDMS has not been widely studied. In this study anew copolymer, polyacrylonitrile-graft-poly(dimethyl siloxane) (PAN-g-PDMS), is used as fibrous filler for PDMS. The graft copolymer is electrospun to produce the fibre filler material. It is shown how the PDMS content of the graft copolymer provides increased compatibility with silicone matrices and excellent dispersion of the fibre fillers throughout a silicone matrix. It is also shown that it is possible to include multi-walled carbon nanotubes in the electrospun fibres which are subsequently dispersed in the PDMS matrix. Fibre mats were used in the non-woven and the aligned forms. The differently prepared fibre composites have significantly different mechanical properties. Conventional composites using fibrous fillers usually show increased strength and stiffness but usually with a resultant loss of strain. In the case of the composites produced in this study there is a dramatic improvement in the extensibility of the non-woven PAN-g-PDMS fibre mat filled silicone films of up to 470%.     

Durability of non-crimp fabric composites in aqueous environments

Abstract

Glass fibre composites subjected to hot water exhibit a reduction in stiffness and strength owing to a combination of matrix plasticisation and fibre/matrix interfacial degradation. If the composite system is subjected to some form of mechanical damage such as cracking from an external impact, the net consequence of water exposure is more difficult to predict.

This paper reports on the effects of water exposure at two temperatures (65 and 93°C) on non-crimp, quadriaxial, glass fabric systems with a polyester matrix. The residual properties are measured using the compression after impact test. It is shown that the residual properties of laminates tend to reach a minimum plateau after extended exposure to water, the value of which is dependent on the temperature of the water. It is also seen that the effects of impact damage vary depending on whether or not the impact is experienced before or after the water exposure. Impacting after conditioning produces a greater density of through thickness damage, which results in a lower compression after impact strength than impacting before conditioning.     

Dynamic mechanical,mechanical and morphological properties of reactive thermotropic liquid crystalline polymer/unsaturated polyester/glass fibre hybrid composites

Abstract

Unsaturated polyester (UP) reinforced with self-synthesised reactive thermotropic liquid crystalline polymer (TLCP)–methacryloyl copolymer (LCMC) and glass fibre (GF), the hybrid composites of UP/GF/LCMC were prepared by moulding technology. The dynamic mechanical analysis indicated that storage modulus and glass transition temperature (T _g) of hybrid composites increased significantly because of the addition of LCMC. The effect of LCMC content on the mechanical properties of LCMC/UP/GF hybrid composites such as impact strength, specific strength and modulus and load–displacement relationship were also investigated through static mechanical tests. The mechanical properties of hybrid composites increased significantly because of the addition of LCMC. The crystal behaviour analysis of LCMC/UP blend was investigated by X-ray diffraction and polarising optical microscopy. The results showed that the crystal phase and texture structure of LCMC still existed in the blends after blending with UP. The morphology of fracture surfaces of hybrid composites containing different TLCP contents was observed by scanning electron microscopy. The present paper discussed the mechanism for the improvement of dynamic mechanical and mechanical properties.     

Effect of surface modification of Kevlar fibre on friction and wear properties of UHMWPE composites

Abstract

The effects of Kevlar fibre additions and, particularly, the surface modification of the Kevlar fibres, on the sliding wear behaviour of the ultra high molecular weight polyethylene (UHMWPE) composites were investigated. The results showed that the sliding friction coefficient of the UHMWPE composites increased with the fibre content increase. The wear resistance of the UHMWPE composite was highest when the Kevlar fibre content was ～10 vol.-% and decreased as the applied normal load was increased. It was found that the silane modification of the Kevlar fibres improved the wear resistance and tensile strength of the UHMWPE composites as well.     

Mechanical properties of polypropylene composites reinforced with long glass fibres and mineral fillers

Abstract

The mechanical behaviour of long discontinuous glass fibre (LGF) reinforced polypropylene (PP) composites filled with talc or calcium carbonate fillers was studied. Sample specimens were processed by injection moulding, after which tensile and impact properties were analysed. In addition, scanning electron microscopy was used to analyse the morphology of the fracture surfaces. The results showed that the use of talc as a hybrid filler in LGF reinforced PP leads to a better tensile strength and toughness than in a corresponding hybrid composite based on calcium carbonate. Furthermore, it was observed that the matrix had a dominant role at low fibre content, whereas at high fibre loading, the effect of fibres was more evident.     

Damage assessment of alumina fibre-reinforced mullite ceramic matrix composites subjected to cyclic fatigue at ambient and elevated temperatures

The damage evaluation behaviour of alumina fibre-reinforced mullite ceramic matrix composites subjected to cyclic fatigue was investigated by means of acoustic emission (AE) monitoring and forced resonance techniques. AE technique provided sufficient information about the damage initiation and progression in real time whilst the forced resonance (FR) technique allowed the detection of changes in elastic modulus (E) and internal friction (Q⁻¹) that occurred with increasing number of cyclic fatigue at room temperature. From the two non-destructive detection techniques results combined with microstructural observations, it is concluded that the composite cyclic fatigue damage evolution begins with multiple crack formation within the matrix and is followed by delamination (interfacial failure). Final failure of the composite is caused by fibre fracture and extensive cyclic sliding along the fibre/matrix interface. The strong bonding between mullite matrix and alumina fibre caused by the glassy phase within the mullite matrix determined the fatigue performance of the composite at 1350°C. Regions with glassy phase failed catastrophically as a result of early fibre fracture.     

The role of the interface in glass fibre reinforced cement

Glass fibre reinforced cement (GRC) provides an interesting example of interaction between a brittle fibre and a porous brittle matrix which is reactive towards the reinforcement. It is also a case in which the composite fails by multiple fracture. The durability of GRC produced from ordinary Portland cement and an alkali-resistant glass fibre recently developed in the U.K., has been studied over a period of three years under different environmental conditions by measuring the variations in the mechanical properties of these composites with age. The experimental results are interpreted in terms of the micromechanics of failure for these composites and an assessment is made of the role of the interface in controlling the behaviour of the composite at various stages of its life. It is concluded that the properties of the interface in GRC change with time, partly due to chemical attack on the fibre which weakens the reinforcement but also due to changes in the physical properties of the fibre bundle and porosity and volume changes in the matrix as it sets and hardens. It has, however, not yet been possible to characterise the materials nature of the interface in GRC composites.     

Short glass fibre reinforcedpoly(butylene terephthalate) Part 2 –Effect of hygrothermal aging onmechanical properties

Abstract

The mechanical properties of injection moulded poly(butylene terephthalate) (PBT) containing various loadings of short glass fibres (SGF) have been investigated. Properties studied include tensile, flexural, and impact. Effect of hygrothermal aging on the mechanical properties was investigated by immersing the respective specimens in distilled water at 30, 60, and 90°C. All the materials tested showed poor retention in mechanical properties upon exposure to hygrothermal aging. The effect became particularly pronounced at an immersion temperature of 90°C. Fractographic inspection of the fracture surfaces revealed that both PBT and SGF–PBT composites embrittled owing to a hydrolitic degradation process. Hydrolysis not only suppressed the matrix ductility but also reduced the bonding quality between PBT and SGF. Poor interfacial bonding was indicated by the absence of polymer matrix adhering to the fibre surfaces. The decrease in the impact strength of hygrothermally aged SGF–PBT composites provided further evidence that hygrothermal aging at high temperature reduces the contribution of fibre related toughening mechanisms. The residual mechanical properties of both PBT and its composites were not fully recovered after redrying. The permanent damage to these materials was attributed to severe hydrolytic degradation of PBT.     

The influence of zirconia fibre on ablative composite materials

ABSTRACT

Zirconia fibres have excellent high temperature ablation resistance and have been widely used in ablative materials. In this paper, zirconia fibre was used for reinforcing the ablative composite materials to study the influence of zirconia fibre had upon the mechanical properties and the high temperature ablation properties of such composites. The results showed that the bending strength of the material was also good and reached a maximum of 13.05?MPa. After sintering at 1400°C, the bending strength was also great which could reach 13.05?MPa. In addition, the corrosion resistance of the composites was excellent and the oxygen-acetylene line ablation rate was 0.03?mm?s^?1 when the fibre content was 30?wt-%.