Effects of fabric parameters on the tensile behaviour of sustainable cementitious composites

The mechanical behaviour of fabric-reinforced composites can be affected by several parameters, such as the properties of fabrics and matrix, the fibre content, the bond interphase and the anchorage ability of fabrics. In this study, the effects of the fibre type, the fabric geometry, the physical and mechanical properties of fabrics and the volume fraction of fibres on the tensile stress–strain response and crack propagation of cementitious composites reinforced with natural fabrics were studied. To further examine the properties of the fibres, mineral fibres (glass) were also used to study the tensile behaviour of glass fabric-reinforced composites and contrast the results with those obtained for the natural fabric-reinforced composites. Composite samples were manufactured by the hand lay-up moulding technique using one, two and three layers of flax and sisal fabric strips and a natural hydraulic lime (NHL) grouting mix. Considering fabric geometry and physical properties such as the mass per unit area and the linear density, the flax fabric provided better anchorage development than the sisal and glass fabrics in the cement-based composites. The fabric geometry and the volume fraction of fibres were the parameters that had the greatest effects on the tensile behaviour of these composite systems.     

Determining the effect of voids in GFRP on the damage behaviour under compression loading using acoustic emission

Defects in composite structures, such as voids, have a major influence on the damage behaviour and mechanical properties. Based on the conducted experiments the influence of voids on the mechanical properties of multi-axial glass fibre non crimp fabric composites under quasi-static compression load was examined. Optical in-situ inspection and acoustic emission measurement were applied to detect the failure behaviour during compression tests, while paying special attention to the early stages of damage appearance where the Young’s modulus is determined. The specimens were produced by resin transfer moulding with different processing parameters to obtain various void contents and morphologies.     

Characterisation of the draping behaviour of unidirectional non-crimp fabrics (UD-NCF)

Thin composites shell structures manufactured from stitched unidirectional non-crimp fabrics (UD-NCF) in a liquid composite moulding process provides high lightweight design capabilities. However, draping behaviour of UD-NCF has been investigated only sparsely, in contrast to research on woven fabrics or biaxial non-crimp fabrics. Hence, this contribution focuses on fundamental investigations of the draping behaviour of UD-NCF. Within this investigation picture frame tests and uniaxial bias extension tests are performed to examine the in-plane shear behaviour of UD-NCF. Furthermore, a new method is presented to examine ambivalent tensile behaviour of UD-NCF transverse to the carbon fibre roving orientation. In particular, the influence of thin glass fibres on transverse tensile behaviour of UF-NCFs is investigated using a new clamping mechanism in tensile testing. Finally, hemisphere tests are performed to observe the forming behaviour of UD-NCF in a realistic forming process and to evaluate the proposed material characterisation methods regarding its suitability for UD-NCFs.     

Thermomechanical properties of bio-based composites made from a lactic acid thermoset resin and flax and flax/basalt fibre reinforcements

Low viscosity thermoset bio-based resin was synthesised from lactic acid, allyl alcohol and pentaerythritol. The resin was impregnated into cellulosic fibre reinforcement from flax and basalt and then compression moulded at elevated temperature to produce thermoset composites. The mechanical properties of composites were characterised by flexural, tensile and Charpy impact testing whereas the thermal properties were analysed by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The results showed a decrease in mechanical properties with increase in fibre load after 40 wt.% for the neat flax composite due to insufficient fibre wetting and an increase in mechanical properties with increase fibre load up to 60 wt.% for the flax/basalt composite. The results of the ageing test showed that the mechanical properties of the composites deteriorate with ageing; however, the flax/basalt composite had better mechanical properties after ageing than the flax composite before ageing.     

Characterization of a novel natural cellulose fabric from Manicaria saccifera palm as possible reinforcement of composite materials

Identifying novel natural fibers/fabrics with proper properties as reinforcement material is a new challenge in the field of bio-composites. Hence, the aim of this paper is to study the possibility of using a natural fabric extracted from Manicaria saccifera palm as a novel reinforcement in composites. This fabric was extensively characterized by chemical composition analysis, infrared spectroscopy (FTIR) analysis, morphological studies (SEM), thermo-gravimetric analysis (TGA) and physical /mechanical properties studies. From SEM analysis it was identified globular protrusions spread uniformly over the fiber which could help the mechanical interlock with the resin. As well, Manicaria fabric showed good thermal stability, low density, low moisture content and good tensile properties. Further, their properties are comparable to most natural cellulose fabrics and some synthetic fabrics, such as fiber glass fabrics. Manciaria saccifera fabric showed to be a suitable candidate as natural reinforcement material for the development of bio- composite.     

Notch and strain rate sensitivity of non-crimp fabric composites

The notch and strain rate sensitivity of non-crimp glass fibre/vinyl-ester laminates subjected to uniaxial tensile loads has been investigated experimentally. Two sets of notch configurations were tested; one where circular holes were drilled and another where fragment simulating projectiles were fired through the plate creating a notch. Experiments were conducted for strain rates ranging from 10⁻⁴ s⁻¹ to 10² s⁻¹ using servo hydraulic machines. A significant increase in strength with increasing strain rate was observed for both notched and un-notched specimens. High speed photography revealed changes in failure mode, for certain laminate configurations, as the strain rate increased. The tested laminate configurations showed fairly small notch sensitivity for the whole range of strain rates.     

Experimental measurement of wrinkle formation during draping of non-crimp fabric

A rig and image analysis methodology is described to characterise wrinkle formation during draping of non-crimp fabrics. The circular fabric blank is draped over a male hemispherical mould, partly constrained by a circular clamping ring around the periphery of the blank. The three-dimensional shape of the fabric is derived from a shape-from-focus analysis of a stack of photographs of the deformed blank. Wrinkles are identified from the deviation of the shape from a smoothed shape. Wrinkle formation is strongly dependent on the fabric architecture and increases progressively with increased punch displacement. Triaxial fabrics have the highest wrinkle amplitude, unidirectional and 0/90° biaxial fabrics the lowest amplitude. The clamping force reduces the wrinkling for some fabrics but, for the maximum force applied, is not effective at eliminating wrinkling.     

The influence of the stitching pattern on the internal geometry,quasi-static and fatigue mechanical properties of glass fibre non-crimp fabric composites

This paper discusses the experimental results of a study comparing several aspects of the mechanical behaviour of two quasi-unidirectional non-crimp fabric composites based on non-crimp fabrics that differ only in stitching pattern. A NEW stitching pattern was compared to an industry common type (ICT). The properties studied include fabric and laminate thickness, fibre volume fraction, static tensile modulus and strength in longitudinal and transverse direction, high-speed tensile strength and tension–tension fatigue life. Statistically significant differences were observed for fabric and composite thickness, which was found to be higher for the ICT type composite. A higher fibre volume fraction was observed for the NEW stitching pattern material, as well as a higher longitudinal tensile strength at high and low speeds and a slightly higher fatigue life.     

Microstructure,flexural properties and durability of coir fibre reinforced concrete beams externally strengthened with flax FRP composites

This study investigated the flexural behaviour of plain concrete (PC) and coir fibre reinforced concrete (CFRC) beams externally strengthened by flax fabric reinforced epoxy polymer (FFRP) composites. PC and CFRC beams without and with FFRP (i.e. 2, 4 and 6 layers) reinforcement were tested under three- and four-point bending. The microstructures of coir fibre, coir/cement matrix, flax/epoxy matrix, and FFRP/concrete interfaces were analysed using scanning electronic microscope (SEM). Test results indicated that the peak load, flexural strength, deflection and fracture energy of both PC and CFRC specimens enhanced proportional to an increase of FFRP layers. Coir further increased load, strength and energy of the specimens remarkably. It was also found that the thickness and coir influenced the failure modes while the test method influenced the load and energy of the specimens remarkably. SEM studies showed effective bond at coir/cement, flax/epoxy and FFRP/concrete interfaces. Therefore, it concluded that natural FFRP composites can be used to repair or retrofit existing concrete structures.     

Effective elastic, piezoelectric and dielectric properties of braided fabric composites

Composites based upon 3D textile preforms have found broad structural application. This paper presents an analytical methodology for functional composites using piezoceramic fibers in a 3D braided preform. The effective elastic, piezoelectric and dielectric properties of 2-step braided composites with a polymeric matrix have been investigated. In the analytical approach, the effective properties of the braider and axial yarns of the unit cells are determined first using a 3D connectivity model. Then, the effective properties of the 2-step braided composite are predicted using an averaging technique. Results of a numerical example illustrating the variation of elastic, piezoelectric and dielectric constants with the braider yarn angle are provided. Textile preforming technique in general offers the potential of near net shape forming and 3D fiber placement. The present work provides the analytical basis for 3D piezoceramic textile composites.     

Flammability,thermal and physical-mechanical properties of cationic polymer/montmorillonite composite on cotton fabric

The flammability, thermal and mechanical properties on cotton fabric were improved by being finished with the composite containing montmorillonite. To this aim, polymer dimethyl diallyl ammonium chloride-allyl glycidyl ether (P_DMDAAC-AGE) was prepared and its structure characterized by Fourier transform infrared (FT-IR) and Nuclear magnetic resonance (¹H NMR). The quaternary ammonium salt copolymer/montmorillonite composite (P_DMDAAC-AGE/MMT) was obtained by polymer intercalation method. The X-ray diffraction (XRD) indicated that the MMT interlayer spacing increased after the polymer intercalation. Composite materials were loaded onto the cotton fabrics by a dip-pad-dry method. The thermo gravimetric analysis (TGA), vertical flame test and limiting oxygen index (LOI) results showed that the thermal and flammability properties of the cotton fabric were improved after it was finished with the composite. Tensile testing revealed an increase on mechanical properties of the finished fabric, but the physical properties hardly changed from the bending length and whiteness results. Scanning electron microscope (SEM) and energy disperse X-ray spectroscope (EDX) results verified the improvement of those properties due to the presence of montmorillonite in the composite.     

The influence of weave architecture on the mechanical properties of self-reinforced polypropylene

The weave architecture is vital for hot compaction and the mechanical properties of self-reinforced polypropylene. Low compaction quality resulted in early damage initiation and reduced tensile strength. Interleaved films and decreased crimp in the weave architecture increased the compaction quality. The best compaction quality and tensile properties were obtained by standard fed weaves with interleaved films. The penetration impact resistance and peel strength was independent of the weave architecture. Interleaved films increased the peel strength drastically, but the impact resistance only slightly decreased. These conclusions help to select the correct weave architecture and facilitate the hot compaction process.     

Effect of fabric compaction and yarn waviness on 3D woven composite compressive properties

3D-woven fabrics incorporate through-thickness reinforcement and can exhibit remarkable inter-laminar properties that aid damage suppression and delay crack propagation. However, distortions in the internal architecture such as yarn waviness can reduce in-plane properties, especially in compression. The degree of yarn waviness present in a 3D woven fabric can be affected by a range of factors including weave parameters and manufacturing-induced distortions such as fabric compaction. This paper presents a thorough analysis of the effect of fabric compaction and yarn waviness on the mechanical properties and failure mechanisms of an angel-interlock fabric in compression. Tests were conducted on coupons moulded to different volume fractions and data compared to previous measurements of local yarn angle. Major findings show the importance of yarn straightness on compressive strength and how this can be affected by optimising moulding thickness. Failure initiation was also found to be heavily influenced by weave style and yarn interlacing.     

Kenaf/polypropylene nonwoven composites: The influence of manufacturing conditions on mechanical,thermal, and acoustical performance

The kenaf/polypropylene nonwoven composites (KPNCs), with 50/50 blend ratio by weight, were produced by carding and needle-punching techniques, followed by a compression molding with 6-mm thick gauge. The uniaxial tensile, three-point bending, in-plane shearing, and Izod impact tests were performed to evaluate the composite mechanical properties. The thermal properties were evaluated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The performance of sound absorption and sound insulation was also investigated. An adhesive-free sandwich structure was found to have excellent sound absorption and insulation performance. Based on the evaluation of end-use performance, the best processing condition combination of 230 °C and 120 s was determined, and the correlation between mechanical properties and acoustical behavior was also verified by the panel resonance theory.     

Rate dependent modelling of the forming behaviour of viscous textile composites

A predictive approach to modelling the forming of viscous textile composites has been implemented in two finite element codes; Abaqus Standard™ and Abaqus Explicit™. A multi-scale energy model is used to predict the shear force–shear angle–shear rate behaviour of viscous textile composites, at specified temperatures, using parameters supplied readily by material manufacturers, such as fibre volume fraction, weave architecture and matrix rheology. The predictions of the energy model are fed into finite element simulations to provide the in-plane shear properties of two different macro-scale constitutive models implemented in the finite element codes. The manner of coupling predictions of the multi-scale energy model with the macro-scale models is shown to affect the rate-dependent material response in the simulations. These coupling methods are evaluated using picture frame test simulations.     

On the effect of stacked fabric layers on the stiffness of a woven composite

Most micromechanical models for stiffness prediction of woven composites assume independence of the Q-matrix on the number of fabric layers in the composite. For example, the moduli of single and 10 layer composites are assumed to be equal in the case when all layers have the same in-plane orientation. Although this statement is likely to be true for isotropic materials or even for unidirectional laminated composites, it may not be valid in some cases of woven composites.

This paper contains experimental and theoretical investigations of plain weave carbon fiber/polyester composites. Specimens with one single and eight layers of fabrics are tested and observable differences of mechanical properties are obtained.

The theoretical part of this article consists of derivation and application of several micromechanical models on these particular composites. The use of those simplified models finally allows us to find the main mechanisms which cause the observed effects.     

Properties of yarn pull-out in para-aramid fabric structure and analysis by statistical model

The aim of this study is to analyze and determine the pull-out properties of para-aramid woven fabrics. Para-aramid Kevlar29® and Kevlar129® woven fabrics were used to conduct the pull-out tests. They have high and low fabric densities. A yarn pull-out fixture was developed to test various fabric sample dimensions. Data generated from single and multiple yarn pull-out tests in various dimensions of Kevlar29® and Kevlar129® woven fabrics included fabric pull-out forces, yarn crimp extensions in the fabrics and fabric displacements. The regression model showed that yarn pull-out forces depend on fabric density, fabric sample dimensions and the number of pulled ends in the fabric. Yarn crimp extensions depend on the crimp ratios of the fabric and fabric density. Fabric displacements depend on fabric sample dimensions and the number of pulled yarns.     

Synergetic effect of conducting polymer composites reinforced E-glass fabric for the control of electromagnetic radiations

The use of fibril materials as substrate for reinforcing polymers has wide industrial applications. In this article, we discuss polyaniline and polypyrrole as conducting polymers to provide electronic conductivity in E-glass fabric reinforced conducting composite with varied degree of composition and conductivity using industrially important polymers polymethylmethacrylate and polyvinyl chloride as a host matrix. Aromatic sulphonic acids such as PXSA, OXSA, PSA, PDSA, RDSA, OCPSA and MCSA were used as a dopant. The influence of the aromatic ring substituents in these dopants over the conductivity and processibility due to various interactions has been studied. The study shows that due to bulk nature of conductivity, shielding effectiveness (SE) increases with increase in conductivity and thickness of a composite. The test samples were characterized by conductivity and electromagnetic shielding effectiveness (EMI SE). The electromagnetic shielding effectiveness was measured by co-axial transmission line method in the frequency range of 0.01–1000 MHz. These composites with both side shielded by polypyrrole offered a uniform shielding effectiveness of 69 dB.     

Fabrication and mechanical behaviors of cementitious composites reinforced by 3D woven lattice sandwich fabrics

Glass fibers were firstly woven to form three-dimensional (3D) woven lattice sandwich fabrics (WLSFs) which then were applied to reinforce cementitious foams and mortars to fabricate novel ductile cementitious composites. Failure behaviors of WLSF reinforced cementitious composite structures were studied through compression and three-point bending experiments. The WLSF greatly enhances the strength of cementitious foams at a level of four times. For cementitious mortars, compression strength of WLSF reinforced blocks is a little greater for the fraction of the textile is small as well as the compression strength of the textile pillars is not strong. But in flexure, excellent stretching ability of the glass fiber textiles greatly improves the flexural behavior of WLSF reinforced cementitious composite panels. Load capacity and ultimate deflection of these composite panels were greatly enhanced. Flexural capacity of the WLSF reinforced beam is four times greater. Reinforced by WLSF, failure of the cementitious composite is ductile.     

Evaluation of the mechanical behavior of epoxy composite reinforced with Kevlar plain fabric and glass/Kevlar hybrid fabric

In this study, composite plates were manufactured by hand lay-up process with epoxy matrix (DGEBA) reinforced with Kevlar fiber plain fabric and Kevlar/glass hybrid fabric, using to an innovative architecture. Results of the mechanical properties of composites were obtained by tensile, bending and impact tests. These tests were performed in the parallel direction or fill directions of the warp and in a 90° direction. FTIR was used in order to verify the minimum curing time of the resin to perform the mechanical tests, and scanning electron microscopy was used to observe reinforcement and matrix fractures. Composites with Kevlar/glass hybrid structure in the reinforcing fabric showed the better results with respect to specific mechanical strength, as well as bending and impact energy.