Showing papers in "Composites Part A-applied Science and Manufacturing in 2012"

Critical review of recent publications on use of natural composites in infrastructure

Abstract: Compared to most synthetic fibers, natural fibers are low-cost, are easier to handle, have good specific mechanical properties, and require only around 20–40% of the production energy. Using natural materials and modern construction techniques reduces construction waste and increases energy efficiency while promoting the concept of sustainability. Several drawbacks of natural composites which would be even more pronounced in their use in infrastructure include their higher moisture absorption, inferior fire resistance, lower mechanical properties and durability, variation in quality and price, and difficulty using established manufacturing practices when compared to synthetic composites. Many researchers have been working to address these issues, with particular attention paid to the surface treatment of fibers and improving the fiber/matrix interface. Because of their positive economic and environmental outlook, as well as their ability to uniquely meet human needs worldwide, natural composites are showing a good potential for use in infrastructure applications.

Composites Part A: Applied Science and Manufacturing

Abstract: Reference EPFL-ARTICLE-184271doi:10.1016/j.compositesa.2012.08.001View record in Web of Science Record created on 2013-02-27, modified on 2017-05-10

Effect of fiber surface treatments on mechanical and abrasive wear performance of polylactide/jute composites

Abstract: The main focus of this work is to improve the adhesion of jute fiber with polylactide (PLA). For this purpose, surface of the jute fiber was modified by alkali, permanganate, peroxide and silane treatments. The surface modified fibers were characterized by FTIR spectroscopy. Unidirectional composites were prepared with treated jute fibers and PLA matrix by hot pressing of solvent impregnated prepregs. Surface treatments resulted in enhancement of tensile and flexural properties and reduction in Izod impact strength. Dynamic mechanical analysis (DMA) results showed that, treated composites have higher storage modulus and lower tangent delta with respect to untreated composite. The degree of interfacial adhesion between the jute fiber and PLA was estimated using adhesion parameter obtained through DMA data. The results of thermogravimetric analysis (TGA) showed a higher thermal stability for silane treated composites. Experimental results on abrasive wear tests revealed that the wear resistance of composite is sensitive to fiber/matrix adhesion.

The effects of alkali-silane treatment on the tensile and flexural properties of short fibre non-woven kenaf reinforced polypropylene composites.

Abstract: Kenaf fibre reinforced polypropylene composites were manufactured by compression moulding. The kenaf fibre was considered in three forms; untreated, treated with sodium hydroxide solution and treated with sodium hydroxide solution followed by three-aminopropyltriethoxysilane. The effects of these chemical treatments on the tensile and flexural properties of the composites were investigated. Mechanical test results show that alkali treatment followed by three-aminopropyltriethoxysilane treatment (alkali–silane treatment) significantly improves the tensile and flexural properties of short fibre non-woven kenaf polypropylene composites. In particular, the specific tensile and flexural strengths of alkali–silane treated kenaf composites with 30% fibre mass fraction are, respectively, only 4% and 11% lower than those of composites made using glass fibre. Scanning electron microscopy examination shows that the improvements in the tensile and flexural properties resulting from alkali–silane treatment can be attributed to better bonding between the fibres and matrix.

Effect of ball-milling time on mechanical properties of carbon nanotubes reinforced aluminum matrix composites

Abstract: Carbon nanotubes reinforced pure Al (CNT/Al) composites were produced by ball-milling and powder metallurgy. Microstructure and its evolution of the mixture powders and the fabricated composites were examined and the mechanical properties of the composites were tested. It was indicated that the CNTs were gradually dispersed into the Al matrix as ball-milling time increased and achieved a uniform dispersion after 6 h ball-milling. Further increasing the ball-milling time to 8-12 h resulted in serious damage to the CNTs. The tensile tests showed that as the ball-milling time increased, the tensile and yield strengths of the composites increased, while the elongation increased first and then decreased. The strengthening of CNTs increased significantly as the ball-milling time increased to 6 h, and then decreased when further increasing the ball-milling time. The yield strength of the composite with 6 h ball-milling increased by 42.3% compared with the matrix. (c) 2012 Elsevier Ltd. All rights reserved.

Continuous tow shearing for manufacturing variable angle tow composites

Abstract: Automated fibre placement (AFP) is the key technology for manufacturing variable angle tow (VAT) composites with tailored fibre paths. Although it was developed in the 1980s, much research still focuses on the minimization of the process-induced defects because the fundamental principle has not been changed. In this work, a novel fibre placement technique using the shear deformation characteristic of dry tow has been developed, which was named ‘Continuous Tow Shearing (CTS)’. Through the prototype tests, it is shown that CTS could significantly reduce process-induced defects such as fibre wrinkling, resin rich areas and fibre discontinuity. Also, an intuitive notation for defining a curved tow path using piecewise quadratic Bezier curve is developed.

Crosslinked natural rubber nanocomposites reinforced with cellulose whiskers isolated from bamboo waste: Processing and mechanical/thermal properties

Abstract: Crosslinked natural rubber (NR) nanocomposites were prepared using cellulose nanowhiskers (CNWs) that were extracted from bamboo pulp residue of newspaper production, as the reinforcing phase. The coagulated NR latex containing bamboo nanowhiskers (master batch) was compounded with solid NR and vulcanizing agents using a two-roll mill and subsequently cured to introduce crosslinks in the NR phase. No evidence of micro-scaled aggregates of cellulose nanowhiskers in NR matrix was observed in Scanning Electron Microscopy (SEM) images. The addition of CNWs had a positive impact on the tensile strength, E-modulus, storage modulus, tan delta peak position and thermal stability of the crosslinked NR. Theoretical modeling of the mechanical properties showed a lower performance than predicated and therefore further process optimization and/or compatibilization are required to reach the maximum potential of these nanocomposites.

Microstructure and strengthening mechanism of bimodal size particle reinforced magnesium matrix composite

Abstract: One kind of (submicron + micron) bimodal size SiCp/AZ91 composite was fabricated by the stir casting technology. After hot deformation process, the influence of bimodal size particles on microstructures and mechanical properties of AZ91 matrix was investigated by comparing with monolithic A91 alloy, submicron SiCp/AZ91 and micron SiCp/AZ91 composites. The results show that micron particles can stimulate dynamic recrystallized nucleation, while submicron particles may pin grain boundaries during the hot deformation process, which results in a significant grain refinement of AZ91 matrix. Compared to submicron particles, micron particles are more conducive to grain refinement through stimulating the dynamic recrystallized nucleation. Besides, the yield strength of bimodal size SiCp/AZ91 composite is higher than that of single-size particle reinforced composites. Among the strengthening mechanisms of bimodal size particle reinforced composite, it is found that grain refinement and dislocation strengthening mechanism play a larger role on improving the yield strength.

A finite fracture mechanics model for the prediction of the open-hole strength of composite laminates

Abstract: A new model based on finite fracture mechanics is proposed to predict the open-hole tensile strength of composite laminates. Failure is predicted when both stress-based and energy-based criteria are satisfied. The material properties required by the model are the ply elastic properties, and the laminate unnotched strength and fracture toughness. No empirical adjusting parameters are required. Using experimental data obtained in quasi-isotropic carbon–epoxy laminates it is concluded that the model predictions are very accurate, resulting in improvements over the traditional strength prediction methods. It also is shown that the proposed finite fracture mechanics model can be used to predict the brittleness of different combinations of materials and geometries.

Woven hybrid biocomposites: Dynamic mechanical and thermal properties

Abstract: The dynamic mechanical and thermal analysis of oil palm empty fruit bunch (EFB)/woven jute fibre ( J w ) reinforced epoxy hybrid composites were carried out. The storage modulus ( E ′) was found to decrease with temperature in all cases, and hybrid composites had showed better values of E ′ at glass transition temperature ( T g ) compared to EFB and epoxy. Loss modulus showed shifts in the T g of the polymer matrix with the addition of fibre as reinforcing phase, which indicate that fibre plays an important role in case of T g . The Tan δ peak height was minimum for jute composites and maximum for epoxy matrix. Complex modulus variations and phase behaviour of the hybrid composites was studied by Cole–Cole analysis. Thermal analysis result indicates an increase in thermal stability of EFB composite with the incorporation of woven jute fibres. Hybridization of EFB composite with J w fibres enhanced the dynamic mechanical and thermal properties.

Preparation, mechanical and thermal properties of functionalized graphene/polyimide nanocomposites

Abstract: Graphene oxide sheets with isocyanate functional groups (GO NCO) were firstly synthesized and functionalized graphene/polyimide (FGS/PI) nanocomposites were subsequently prepared by typical solution casting and thermal imidization. The chemical changes of GO NCO during the preparation of FGS/PI nanocomposites were carefully characterized by Fourier transfer infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. As a result, the morphology analysis indicated that the FGS were dispersed in the PI matrix and were aligned more orderly with increasing the FGS contents. The tensile strength and the modulus of FGS/PI nanocomposites were significantly increased by 60% with a small quantity of 0.75 wt% FGS incorporated and decreased beyond that dosage. Moreover, the thermogravimetric analysis (TGA) results revealed that the thermal stability of PI was slightly improved by the incorporation of FGS.

Carbon fiber/epoxy composite property enhancement through incorporation of carbon nanotubes at the fiber–matrix interphase – Part I: The development of carbon nanotube coated carbon fibers and the evaluation of their adhesion

Abstract: A new method to realize the uniform coating of carbon nanotubes (CNTs) to carbon fibers (CFs) has been developed, which enables the scalable fabrication of CNT containing CF/epoxy composites. In this method, CNTs are treated by cationic polymers, then, the CNTs are coated to CFs by immersion into a CNT/water suspension. Good dispersion is achieved by repulsive force between positively charged CNTs and uniform coating of the CNTs is achieved by attractive forces between positively charged CNTs and negatively charged CFs. It is found that the use of specific cationic polymers including polyethyleneimine (PEI) results in stable CNT/water suspensions, and uniform coating of the CNTs. Single fiber fragmentation tests of the CF/epoxy composites were conducted to evaluate the strength of interface and interphase under shear loading. The results show that the combination of epoxy resin sizing and PEI treated CNT coating to CFs results in high interfacial shear strength.

Influence of drying on the mechanical behaviour of flax fibres and their unidirectional composites

Abstract: The microstructure of flax fibres can be considered as a laminate with layers reinforced by cellulose fibrils. During a single fibre tensile test the S2 layer is subjected to shear. At room temperature, natural fibres contain water absorbed in the cell-walls. This paper examines the influence of this water at two scales: on the tensile behaviour of the flax fibres and on unidirectional plies of flax reinforced epoxy. Drying (24 h at 105 °C) is shown to reduce both failure stress and failure strain significantly. Analysis of normal stresses at the accomodation threshold provides an estimation of the shear strength of secondary cell walls as 45 MPa for fibres containing 6.4% by weight of water and only 9 MPa for dried fibres. Results from tensile tests on unidirectional flax/epoxy composites, reinforced by as-received and dried fibres, confirm the influence of drying on strength properties.

Experimental study on the CO2 laser cutting of carbon fiber reinforced plastic composite

Abstract: Promotion of massive application of carbon fiber reinforced plastics (CFRPs) in the industry can be accomplished by using faster and more flexible technologies such as laser cutting. The anisotropic and heterogeneous features of the CFRP make laser processing very challenging. A comprehensive study on the cut performance of a CO2 laser to process sheets (3 mm thick) of a CFRP composite is presented. A high-beam quality CO2 laser has been used in order to ascertain the capabilities of CO2 laser cutting machines, widely used in metalworking applications, on the machining of this material. On the other hand, the influence of processing parameters, in both CW and pulsed mode, on the cut quality was studied. Cuts with a minimum heat affected zone, about 540 μm, were achieved using a high-beam quality CO2 laser working in pulsed mode. In consequence, the CFRP strength remains practically unaffected compared to more conventional mechanical machining.

Effects of hemicellulose extraction on properties of wood flour and wood–plastic composites

Abstract: Hygroscopicity, low durability, and low thermal resistance are disadvantages of lignocellulosic materials that also plague wood–plastic composites (WPCs). Hemicellulose is the most hydrophilic wood polymer and is currently considered as a sugar source for the bioethanol industry. The objective of this research is to extract hemicellulose from woody materials and enhance the properties of WPC by diminishing the hydrophilic character of wood. Hemicellulose of Southern Yellow Pine was extracted by hot-water at three different temperatures: 140, 155, and 170 °C. Wood flour was compounded with polypropylene in an extruder, both with and without a coupling agent. Injection molding was used to make tensile test samples. The thermal stability of wood flour was found to have increased after extraction. Extraction of hemicellulose improved the tensile strength and water resistance of composites, which may indicate a decrease in the hygroscopicity of wood flour, better compatibility, and interfacial bonding of the filler and matrix.

Mode II interfacial toughening through discontinuous interleaves for damage suppression and control

Abstract: An investigation is described concerning the interaction of propagating interlaminar cracks with embedded strips of interleaved materials in E-glass fibre reinforced epoxy composites. The approach deploys interlayer strips of a thermoplastic film, thermoplastic particles, chopped fibres, glass/epoxy prepreg, thermoset adhesive film and thermoset adhesive particles ahead of the crack path on mid-plane of Double Cantilever Beam (DCB) specimens. During these mode I tests, the interlayers were observed to confer an apparent increase in the toughness of the host material. The crack arrest performance of individual inclusion types are discussed and the underlying mechanisms for energy absorption and the behaviour of the crack at the interaction point of the interleave edge were analysed using scanning electron microscopy.

Thermal conductivity and dielectric properties of Al/PVDF composites

Abstract: Polymeric composites with relatively high thermal conductivity, high dielectric permittivity, and a low dissipation factor are obtained in the present study. Three types of core–shell-structured aluminum (Al) particles are incorporated in poly(vinylidene fluoride) (PVDF) by melt-mixing and hot-pressing processes. The morphological, thermal, and dielectric properties of the composites are characterized using thermal analysis, a scanning electron microscope, and a dielectric analyzer. The results indicate that the Al particles decrease the degree of crystallinity of PVDF, and that the particle size and shape of the filler affect the thermal conductivity and dielectric properties of Al/PVDF. No variation in the dissipation factor is observed up to 60 wt.% Al. Thermal conductivity and dielectric permittivity values as high as 1.65 W/m K and 230, respectively, as well as a low dissipation factor of 0.25 at 0.1 Hz, are realized for the composites with 80 wt.% spherical Al.

Study on graphene-oxide-based polyacrylamide composite hydrogels

Abstract: In this paper, graphene oxide (GO) is added into poly(acrylamide) (PAM) hydrogels to modify their mechanical and thermal properties. The original PAM hydrogels, which are commonly crosslinked by N,N-methylenebisacrylamide (BIS), generally exhibit pronounced weakness and brittleness. After adding the GO into the hydrogel (BIS-gel), the GO–BIS-gels become very tough and exhibit fairly good tensile properties. The mechanical and thermal properties of GO–BIS-gels vary greatly by changing GO or BIS content. This phenomenon is probably caused by the microstructure, which related to the specific combination of GO sheets and BIS, acting as multifunctional crosslinking agents in the GO–BIS-gels. However, the BIS-gels have higher equilibrium swelling ratio than that of corresponding GO–BIS-gels. Contents of GO and BIS can be adjusted for preparing hydrogels with different applications.

Tensile properties of carbon fibres and carbon fibre–polymer composites in fire

Abstract: The effect of fire on the tensile properties of carbon fibres is experimentally determined to provide new insights into the tensile performance of carbon fibre–polymer composite materials during fire. Structural tests on carbon–epoxy laminate reveal that thermally-activated weakening of the fibre reinforcement is the dominant softening process which leads to failure in the event of a fire. This process is experimentally investigated by determining the reduction to the tensile properties and identifying the softening mechanism of T700 carbon fibre following exposure to simulated fires of different temperatures (up to 700 °C) and atmospheres (air and inert). The fibre modulus decreases with increasing temperature (above ∼500 °C) in air, which is attributed to oxidation of the higher stiffness layer in the near-surface fibre region. The fibre modulus is not affected when heated in an inert (nitrogen) atmosphere due to the absence of surface oxidation, revealing that the stiffness loss of carbon fibre composites in fire is sensitive to the oxygen content. The tensile strength of carbon fibre is reduced by nearly 50% following exposure to temperatures over the range 400–700 °C in an air or inert atmosphere. Unlike the fibre modulus, the reduction in fibre strength is insensitive to the oxygen content of the atmosphere during fire. The reduction in strength is possibly attributable to very small (under ∼100 nm) flaws and removal of the sizing caused by high temperature exposure.

Ablative properties of carbon black and MWNT/phenolic composites: A comparative study

Abstract: In this work, we investigated the ablative properties of two carbon nanofiller-based composites. In particular, carbon black (CB) and multi-walled carbon nanotubes (MWNTs) were used to produce highly loaded (50 wt%) phenolic composites. The thermal properties and the ablative response of the composites were studied through the pre and post-burning morphology of the burnt surfaces and an evaluation of the in-depth temperature profiles. When compared to the CB-based counterpart, the MWNT-based composite exhibited a higher thermal diffusivity and an erosion rate that was exactly localized above the flame plume. The CB-based system showed a thin charred region whilst the MWNT-based was characterized by a thick and wide pyrolyzed zone.

The effect of milling conditions on microstructures and mechanical properties of Al/MWCNT composites

Abstract: Strengthening efficiency of multi-walled carbon nanotubes (MWCNTs), depending on their morphology and interface structure, is investigated for aluminum-based composites. The composites were fabricated by hot-rolling the powders which were ball-milled under various conditions. Milling variables affect the dispersion, dimension and interface structure of MWCNTs. With an insufficient milling intensity, MWCNTs are mostly located on the surface of powder, exposed to severe impact, and readily damaged. As the milling intensity increases, MWCNTs are embedded inside the powder and then dispersed through plastic deformation of the powder. Furthermore, aluminum infiltrates the core of MWCNTs during milling, increasing the diameter of MWCNTs. The outer surface of the Al-infiltrated MWCNTs sticks to the matrix, providing a strong interface by mechanical interlocking. The Al-infiltrated MWCNTs exhibit superior strengthening efficiency. On the other hand, the composite with unfilled MWCNTs, fabricated with a higher milling intensity, exhibits better ductility and pull-outs of the tubes in tensile fracture.

Recycled carbon fibre-reinforced polypropylene thermoplastic composites

Abstract: Comingled carbon fibre (CF)/polypropylene (PP) yarns were produced from chopped recycled carbon fibres (reCF) (20 mm in length, 7–8 μm diameter) blended with matrix polypropylene staple fibres (60 mm in length, 28 μm diameter) using a modified carding and wrap spinning process. Microscopic analysis showed that more than 90% of the reCF were aligned along the yarn axis. Thermoplastic composite test specimens fabricated from the wrap-spun yarns had 15–27.7% reCF volume content. Similar to the yarn, greater than 90% of the reCF comprising each composite sample made, showed a parallel alignment with the axis of the test specimens. The average values obtained for tensile, and flexural strengths were 160 MPa and 154 MPa, respectively for composite specimens containing 27.7% reCF by volume. It was concluded that with such mechanical properties, thermoplastic composites made from recycled CF could be used as low cost materials for many non-structural applications.

Grafting effects of polypropylene/polyethylene blends with maleic anhydride on the properties of the resulting wood–plastic composites

Abstract: In the presented study, polypropylene (PP) and high density polyethylene (PE) were blended at the ratios of 80/20 and 20/80 to simulate recycled waste thermoplastic mixtures. The effects of in situ grafting of PP/PE blends with maleic anhydride through the extruder on the mechanical and rheological properties of resulting wood/plastic composites were investigated. Different ratios of PP and PE in the blends created distinct properties in the resulting composites. Grafting of PP and PE blends improved the tensile and flexure properties of the resulting composites. The composites exhibited a reduced water uptake and resultant dimensional swelling due to grafting with maleic anhydride. Grafting of the blends also considerably improved the interfacial bonding and enhanced the dispersion of wood in the matrix, as evidenced by rheological analysis and scanning electron microscopy.

Compressive characteristics of metal matrix syntactic foams

Abstract: The compressive behaviour of eight different metal matrix syntactic foams (MMSFs) are investigated and presented. The results showed that the engineering factors as chemical compositions of the matrix material, the size of the microballoons, the previously applied heat treatment and the temperature of the compression tests have significant effects on the compressive properties. The smaller microballoons with thinner wall ensured higher compressive strength due to their more flawless microstructure and better mechanical stability. According to the heat treatments, the T6 treatments were less effective than expected; the parameters of the treatment should be further optimised. The elevated temperature tests revealed ∼30% drop in the compressive strength. However, the strength remained high enough for structural applications; therefore MMSFs are good choices for light structural parts working at elevated or room temperature. The chemical composition – microballoon type – heat treatment combinations give good potential for tailoring the compressive characteristics of MMSFs.

Effect of water absorption on the mechanical properties of nanoclay filled recycled cellulose fibre reinforced epoxy hybrid nanocomposites

Abstract: Recycled cellulose fibre (RCF) reinforced epoxy/clay nanocomposites were successfully synthesized with different weight percentages (0%, 1%, 3% and 5%) of organoclay platelets (30B). The objective of this study was to investigate the effect of water absorption on the physical and mechanical properties of the RCF reinforced epoxy/clay nanocomposites. TEM images indicated a well-intercalated structure of nanoclay/epoxy matrix with some exfoliated regions. Water absorption was found to decrease as the clay content increased. The flexural strength, flexural modulus and fracture toughness significantly decreased as a result of water absorption. However, the properties of impact strength and impact toughness were found to increase after exposing to water. The addition of nanoclay slightly minimized the effect of moisture on the mechanical properties. SEM images showed that water absorption severely damaged the cellulose fibres and the bonding at fibres–matrix interfaces in wet composites.

Damage accumulation in a carbon/epoxy composite: Comparison between a multiscale model and computed tomography experimental results

Abstract: High-resolution computed tomography has been carried out for carbon/epoxy laminates loaded in situ to failure. The experimental data allows major damage mechanisms to be quantified in 3D, in an unambiguous and mechanically representative way, where previous experimental analysis is limited. A multi-scale model that predicts damage accumulation in tensile loaded composites is compared to the experimental analysis, to validate the underpinning assumptions within the model and overall performance. The model considers the random nature of fibre-strengths, stress transfer resulting from fibre breaks, fibre/matrix debonding and viscosity of the matrix. Assumptions within the model are made to reduce computational times whilst considering the microscopic behaviour of the whole structure. Both model and experimental results indicate failure of the composite progresses via single fibre breaks, which, at higher loads, evolve into clusters of broken fibres. The model resulted in reasonable predictions of the preceding damage accumulation and final failure load of the structure.

Characterising the shear–tension coupling and wrinkling behaviour of woven engineering fabrics

Abstract: Modelling the forming process for engineering fabrics and textile composites using a mechanical approach, such as the finite element method, requires characterisation of the material’s behaviour under large shear deformation. For woven engineering fabrics, a coupling between in-plane tension and both shear compliance and the onset of wrinkling is to be expected. This paper focuses on a novel testing technique, the biaxial bias extension test, as a means to investigate this shear–tension coupling and fabric wrinkling. Novel methods of determining the wrinkling behaviour are demonstrated. The main difficulty with the technique lies in extracting the material contribution to the recorded signal. To do this, an experimental method is proposed and demonstrated using a plain weave glass fabric. Biaxial bias extension test results are compared against picture frame and uniaxial bias extension results.

Diameter dependence of the apparent tensile modulus of hemp fibres: A morphological, structural or ultrastructural effect?

Abstract: The aim of this paper is to investigate the origin of the diameter-dependence of Young’s modulus in hemp fibres. In view of the considerable experimental difficulties encountered when determining the 3D morphology of elementary fibres, the influence of the fibre morphology and size on the E -modulus is studied using a mathematical model. An approach based on the 3D elastic theory is used to construct a model of the fibre structure, and to predict its mechanical properties. We clearly show that the modulus is dependent on the size of the lumen and on the outer fibre diameter. This structural effect, induced by the cylindrical geometry, the multi-layered organisation, and the orientation of the cellulose microfibrils only partly explains the large, experimentally determined dispersion of apparent E -modulus, as a function of fibre diameter. Ultrastructural parameters, such as cellulose crystallinity and microfibril angles, are identified to be the main factors involved in this dependence.

Atomistic simulations on multilayer graphene reinforced epoxy composites

Abstract: We use molecular dynamics simulations to characterize multilayer graphene reinforced epoxy composites. We focus on two configurations, one where the graphene layers are parallel to polymer/graphene interface and a perpendicular case, and characterize the in situ curing process of the resin and the thermo-mechanical response of the composites. The yield stress of the composites under uniaxial loading normal to the interface is in all cases larger than that of the bulk polymer even after the constraint of the reinforcement to transverse relaxation is taken into account. While both the parallel and normal configurations have very similar strengths, the parallel case exhibits cohesive yield with strain localization and nano-void formation within the bulk polymer while the case with graphene sheets oriented normal to the interface exhibit interfacial debonding. These two mechanisms lead to different post yield behavior and provide key insight for the development of predictive models of carbon fiber polymer composites.

Acoustic emission source location in composite materials using Delta T Mapping

Abstract: The location capability of the acoustic emission (AE) technique is often considered its most powerful attribute. However, assumptions made in the calculation of location by current algorithms can be limiting in complex geometries and materials. This work forms a detailed study into the use of a novel mapping technique for AE source location in fibre reinforced composite materials. Both the performance and the robustness of the approach are assessed using artificial and real AE sources. Furthermore a large fatigue specimen was used to demonstrate detection and location of damage onset and development, where findings were validated using a thermo-elastic stress analysis (TSA) system. Substantial improvements in location accuracy were observed and early detection of damage onset was seen to outperform TSA.