42 results for Pickering, Kim L.

  • A study of polyvinyl butyryl based binder system in titanium based metal injection moulding

    Thavanayagam, Gnanavinthan; Zhang, Deliang; Pickering, Kim L.; Raynova, Stiliana (Stella) Rousseva (2012)

    Conference item
    University of Waikato

    Metal injection moulding (MIM) is an innovative injection moulding technique widely used to produce complex shaped components from feedstock composed of metal powders and thermosetting or thermoplastic binders. In MIM, binder selection and formulation are considered as critical processes since binder characteristics dictate the success of MIM. The purpose of this study is to determine the feasibility of polyvinyl butyryl (PVB) based binder system in Ti-6Al-4V(wt.%)/binder feedstock, as well as to understand the effects of key parameters, such as powder loading and mixing conditions on the rheological properties of a feedstock. In this study, PVB, polyethylene glycol (PEG), and stearic acid (SA) were chosen to formulate a multi-component binder system to prepare Ti-6Al-4V based feedstock with the aid of three types of mixers: a compounder, a modified mechanical mixer and a twin screw extruder. Further, morphological analysis was performed using optical microscopy and scanning electron microscopy. Thermal analysis was performed using simultaneous differential thermal analysis and thermogravimetric analysis. Results showed that binder formulation was reasonably successful with the aid of both mechanical mixer and a twin screw extruder under certain mixing conditions, and the critical powder loading was 68 vol.%, resulting in an optimum powder loading of 63 vol.%.

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  • Studying carbonisation with raman spectroscopy

    McDonald-Wharry, John; Ripberger, Georg; Manley-Harris, Merilyn; Pickering, Kim L. (2013)

    Conference item
    University of Waikato

    Raman spectroscopy can provide fast and non-destructive analysis of carbonaceous materials. As it is able to detect nanometre-sized structural features, Raman spectroscopy is widely used in the study of carbon nanotubes, fullerenes, graphenes, and many other carbon-rich materials. Raman analysis has previously shown potential for estimating the heat treatment temperatures (HTT) employed in the preparation of Japanese cedar charcoals which suggested future usefulness in quality control . In the current work, Raman spectroscopy was used to investigate the nanostructural development which had occurred within various chars prepared and carbonised at a range of heat treatment temperatures between ≈ 340°C and 1000°C. Chars were produced from sucrose sugar as standard precursor of high purity and two sources of biomass common in New Zealand (Radiata pine wood and Harakeke leaf fibres). In chars produced at lower HTTs, signals could be detected which were interpreted as representing hydrogen-rich amorphous carbon structures. In contrast, the Raman spectra of well-carbonised chars produced at higher HTTs featured signals consistent with graphene-like structures with coherent domains limited in size to below a few nanometres across. Measurement of such signals provides the ability to evaluate the extent of nanostructural development, identify char samples which are ‘undercooked’ when compared to other char samples, and estimate effective HTTs used in the production of a given char sample. More detailed Raman analysis of Radiata-derived chars was carried out, including analysis of chars produced from carbonising pyrolysis tars. Results of Raman analysis were correlated to H/C atom ratios obtained through elemental analysis for these chars produced from Radiata pine.

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  • 3D Printing of Natural Fibre Reinforced Recycled Polypropylene

    Stoof, David; Pickering, Kim L. (2017)

    Conference item
    University of Waikato

    The adverse effects that waste plastics are having on the environment is becoming increasingly apparent. However, the plastics recycling industry in New Zealand is entirely market driven, necessitating the development of new markets to account for increasing quantities of waste. Innovations in additive manufacturing (AM) have presented opportunities to recycle thermoplastics for use as AM feedstock material. Using waste thermoplastic materials to fabricate composites in this way, adds value to the polymer by enhancing mechanical and aesthetic properties. A range of composite filaments with differing fibre and gypsum weight contents were then produced using pre and post-consumer polypropylene (PP). The most successful filaments in terms of tensile properties consisted of 30 wt% harakeke in a post-consumer PP matrix which had a tensile strength and Young’s modulus of 41MPa and 3.8 GPa respectively. Comparing these results to those of plain PP filament, showed improvements in tensile strength and Young’s modulus of 77% and 275% respectively. Finally, a novel method of measuring shrinkage in 3d printed components was developed and used to compare relative shrinkage of different composites. The composite that showed the least shrinkage consisted of 30 wt% harakeke with a shrinkage value of 0.34% corresponding to a net reduction of 84% relative to plain PP.

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  • Optimising industrial hemp fibre for composites

    Pickering, Kim L.; Beckermann, Gareth; Alam, S.N.; Foreman, Nic J. (2007)

    Journal article
    University of Waikato

    The optimisation of New Zealand grown hemp fibre for inclusion in composites has been investigated. The optimum growing period was found to be 114 days, producing fibres with an average tensile strength of 857 MPa and a Young’s modulus of 58 GPa. An alkali treatment with 10wt% NaOH solution at a maximum processing temperature of 160o C with a hold time of 45 minutes was found to produce strong fibres with a low lignin content and good fibre separation. Although a good fit with the Weibull distribution function was obtained for single fibre strength, this did not allow for accurate scaling to strengths at different lengths. Alkali treated fibres, polypropylene and a maleated polypropylene (MAPP) coupling agent were compounded in a twin-screw extruder, and injection moulded into composite tensile test specimens. The strongest composite consisted of polypropylene with 40wt% fibre and 3wt% MAPP, and had a tensile strength of 47.2 MPa, and a Young’s modulus of 4.88 GPa.

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  • Hemp fibre reinforced poly(lactic acid) composites

    Sawpan, Moyeenuddin Ahmad; Pickering, Kim L.; Fernyhough, Alan (2007)

    Journal article
    University of Waikato

    The potential of hemp fibre as a reinforcing material for Poly(lactic acid) (PLA) was investigated. Good interaction between hemp fibre and PLA resulted in increases of 100% for Young’s modulus and 30% for tensile strength of composites containing 30 wt% fibre. Different predictive ‘rule of mixtures’ models (e.g. Parallel, Series and Hirsch) were assessed regarding the dependence of tensile properties on fibre loading. Limited agreement with models was observed. Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) studies showed that hemp fibre increased the degree of crystallinity in PLA composites.

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  • The manufacture and mechanical properties of aligned long harakeke fibre reinforced epoxy composites

    Le, Tan Minh; Pickering, Kim L. (2012-07-09)

    Conference item
    University of Waikato

    Aligned long harakeke fibre reinforced epoxy composites were prepared using hand lay-up followed by compression moulding. Densities of harakeke fibre and epoxy resin were determined for the purpose of composite design. The evenness of composites fabricated by two different size moulds was compared. It was found that more even composites were produced when using a small mould than a big mould. In this work, the dependence of tensile and flexural properties of harakeke/epoxy composites on fibre content was also investigated. The results showed that the addition of fibre enhanced tensile properties of epoxy. The tensile strength and Young’s modulus increased with the volume fraction of harakeke fibre. The flexural strength and flexural modulus increased as the fibre volume fraction increased up to 0.4. Further addition of fibre did not result in an improvement of composite flexural properties.

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  • Alignment of Short Fibres: An Overview

    Sunny, Tom; Pickering, Kim L.; Lim, Shen Hin (2017)

    Conference item
    University of Waikato

    Fibre orientation is a major factor influencing composite performance; research, largely on synthetic fibre composites, supports that the best mechanical performances are achieved in composites when fibres are aligned in the loading direction. Generally, with short natural plant fibre (SNPF) composites, randomly oriented fibre mats are used as reinforcements due to the innate limits of fibre length and the difficulty of aligning short fibre. However, there are a number of methods that have been developed for aligning short fibre, again largely employed for synthetic fibres. The two main approaches employed to align short fibres relate to whether dry or wet processing is used available in literature; in wet processes, fibres are generally suspended in a liquid medium and alignment of fibre trails the fluid flow direction, whereas in dry processes, dry fibres are aligned in the direction of an induced or applied force such as pneumatic or electric. An overview of different alignment methods with their working principles is presented in this paper. This paper also describes an alignment technique currently under development to improve the alignment obtained for SNPFs.

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  • Damping properties and microstructure of magnetorheological composites based on iron sand and natural rubber

    Shuib, Raa Khimi; Pickering, Kim L. (2013)

    Conference item
    University of Waikato

    Material with high damping capability is desired from the viewpoint of vibration suppression in structures. Rubber is by far the most commonly used material for damping; here damping relies on the energy absorbed due to viscous flow that occurs during deformation in this viscoelastic materials. However, enhancement of damping through rubber modification or rubber selection to increase viscous flow, not surprisingly, generally results in a reduction in stiffness and strength [1]. More recently, a new class of damping materials, magnetorheological elastomers (MREs) have been developed such that inclusion of magnetic particles in rubber enables additional damping through magnetic particle interaction and interfacial friction. Furthermore, damping and stiffness can be varied by application of an applied magnetic field during fabrication or in service. MREs can be utilised for damping, either alone or within a composite structure such as those including steel plates.

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  • Comparison of harakeke with hemp fibre as a potential reinforcement in composites

    Efendy, M.G. Aruan; Pickering, Kim L. (2014-12-01)

    Journal article
    University of Waikato

    The objective of this study was to characterize the performance of untreated and chemically treated harakeke fibre (a leaf fibre from a plant native to New Zealand) and compare with hemp fibre to assess its use as potential reinforcement in composites. Alkali treatment is among the most popular treatments used to remove unwanted fibre constituents such as pectin, hemicellulose and waxes; it can enhance fibre properties, fibre separation, interfacial bonding and fibre dispersion within a composite. Physical and mechanical properties of untreated and alkali treated fibres were assessed using single fibre tensile testing, X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis using thermogravimetric analysis (TGA). Untreated harakeke fibre was found to be lower in tensile strength compared to untreated hemp fibre. It was also found that the tensile strength of harakeke and hemp fibres treated with 5wt% NaOH/2wt% Na2SO3 and 5wt% NaOH was not significantly affected and these fibres had good fibre separation. However, alkali treatment was found to lead to higher crystallinity index (Ic) and better thermal stability for harakeke as well as hemp fibres.

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  • Dynamic Properties of Magnetorheological Elastomers Based on Iron Sand and Natural Rubber

    Shuib, Raa Khimi; Pickering, Kim L.; Mace, Brian R. (2015-02-20)

    Journal article
    University of Waikato

    In this study, magnetorheological elastomers (MREs) based on iron sand and natural rubber were prepared. The Taguchi method was employed to investigate the effect of a number of factors, namely, the iron sand content, iron sand particle size, and applied magnetic field during curing on the loss tangent (tan δ) and energy dissipated during cyclic loading. Tan δ was measured through dynamic mechanical analysis over a range of frequency (0.01–130 Hz), strain amplitude (0.1–4.5%), and temperature (−100 to 50°C). The energy dissipated was measured with a universal tester under cyclic tensile loading. The data were then statistically analyzed to predict the optimal combination of factors, and finally, experiments were conducted for verification. It was found that the iron sand content had the greatest influence on tan δ when measured over a range of frequency, and the energy dissipated during hysteresis tests. However, none of the factors showed a significant influence on tan δ when measured over a range of strain amplitude. Furthermore, the iron sand content and magnetic field were also found to influence the width of the peak in tan δ as a function of the temperature. The morphological characteristics of the MREs were also examined with scanning electron microscopy.

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  • Interfacial modification of hemp fiber reinforced composites using fungal and alkali treatment

    Pickering, Kim L.; Li, Y.; Farrell, Roberta L.; Lay, Mark C. (2007)

    Journal article
    University of Waikato

    Increasing worldwide environmental awareness is encouraging scientific research into developing cheaper, more sustainable materials. Industrial hemp fiber is one of the strongest and stiffest available natural fibers [K. L. Pickering, M. Priest, T. Watts, G. Beckermann, and S. N. Alam, J. Adv. Mater. 37, 15 (2005)] and therefore has great potential in composite materials. Incorporated into a thermoplastic matrix, it gives a structural material that is cheap, lightweight, and recyclable. However, natural fibers are commonly incompatible with common molding thermoplastics such as polypropylene, which limits the performance of the composites produced. The main objective of the current work was to investigate the use of fungi to treat hemp fiber to create better bonding characteristics in natural fiber reinforced polypropylene composites. X-ray diffraction (XRD), ζ-potential, lignin testing, thermal analysis, and scanning electron microscopy (SEM) were used to characterize the effect of treatment on hemp fibers. A combined alkali and fungi treated fiber composite produced the highest tensile strength of 48.3 MPa, an increase of 32% compared to composites with untreated fiber.

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  • The Effect of Aqueous Urea on the Processing, Structure and Properties of CGM

    Pickering, Kim L.; Verbeek, Casparus Johan R.; Viljoen, Carmen (2012-06)

    Journal article
    University of Waikato

    Corn gluten meal (CGM) is potentially a cost-effective raw material for producing a bioderivable thermoplastic. However, CGM disintegrates to a powder subsequent to processing with polar plasticisers, such as water. The hypothesis of this study was that aqueous urea could be used to denature protein within CGM and therefore encourage protein–protein interactions leading to consolidated bioplastics when using water as a plasticiser. To assess this, the effects of aqueous urea on structure and properties of CGM with particular focus on storage were assessed. Processing of CGM with aqueous urea produced consolidated materials. FTIR analysis showed secondary structure was modified during processing, leading to increased amounts of α-helices and random coils and reduction of the amount of intermolecular β-sheets and turns. Above 6 wt% free water, the plasticising efficiency of water in processed CGM increased as the amount of denatured proteins increased. Below 6 wt% free water, protein secondary structure did not have a significant influence on thermal and flexural properties. It was found that storage environment and urea concentration influenced the rate of drying, however, the final water content was constant relative to CGM, and not urea. The materials were resistant to cracking at urea concentrations above 8 M, provided the mass loss during storage did not exceed 15 wt%.

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  • Curing kinetics and effects of fibre surface treatment and curing parameters on the interfacial and tensile properties of hemp/epoxy composites

    Islam, Mohammad Saiful; Pickering, Kim L.; Foreman, Nic J. (2009)

    Journal article
    University of Waikato

    The curing kinetics of neat epoxy (NE) and hemp fibre/epoxy composites was studied and assessed using two dynamic models (the Kissinger and Flynn-Wall-Ozawa Models) and an isothermal model (the Autocatalytic Model) which was generally supported by the experimental data obtained from dynamic and isothermal differential scanning calorimetry (DSC) scans. The activation energies for the curing of composites exhibited lower values compared to curing of NE which is believed to be due to higher nucleophilic activity of the amine groups of the curing agent in the presence of fibres. The highest tensile strength, σ was obtained with composites produced with an epoxy to curing agent ratio of 1:1 and the highest Young's modulus, E was obtained with an epoxy to curing agent ratio of 1:1.2. Alkali treated hemp fibre/epoxy (ATFE) composites were found to have higher σ and E values compared to those for untreated hemp fibre/epoxy (UTFE) composites which was consistent with the trend for interfacial shear strength (IFSS) values. Composites σ and E were found to be higher for a processing temperature of 70°C than for 25°C for both UTFE and ATFE composites, but were found to decrease as the curing temperature was increased further to 120°C.

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  • Influence of hygrothermal ageing on the physico-mechanical properties of alkali treated industrial hemp fibre reinforced polylactic acid composites

    Islam, Mohammad Saiful; Pickering, Kim L.; Foreman, Nic J. (2010)

    Journal article
    University of Waikato

    30 wt% aligned untreated long hemp fibre/polylactic acid (AUL) and aligned alkali treated long hemp fibre/polylactic acid (AAL) composites were produced by film stacking and subjected to hygrothermal ageing environment along with neat polylactic acid (PLA). Hygrothermal ageing was carried out by immersing samples in distilled water at 25 and 50 ºC over a period of 3 months. It was found that both neat PLA and composites followed Fickian diffusion. Higher temperature generally increased the Diffusion coefficient, D of neat PLA and composites, as well as shortening the saturation time. Neat PLA had the lowest D value followed by AAL composites and then AUL composites. After hygrothermal ageing, tensile and flexural strength, Young’s and flexural modulus and KIc were found to decrease and impact strength was found to increase for both AUL and AAL composites. AUL composites had greater overall reduction in mechanical properties than that for AAL composites after hygrothermal ageing. Crystallinity contents of the hygrothermal aged composites support the results of the deterioration of mechanical properties upon exposure to hygrothermal ageing environment.

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  • Influence of accelerated ageing on the physico-mechanical properties of alkali-treated industrial hemp fibre reinforced poly(lactic acid) (PLA) composites

    Islam, Mohammad Saiful; Pickering, Kim L.; Foreman, Nic J. (2010)

    Journal article
    University of Waikato

    30 wt% aligned untreated long hemp fibre/PLA (AUL) and aligned alkali treated long hemp fibre/PLA (AAL) composites were produced by film stacking and subjected to accelerated ageing. Accelerated ageing was carried out using UV irradiation and water spray at 50 °C for four different time intervals (250, 500, 750 and 1000 h). After accelerated ageing, tensile strength (TS), flexural strength, Young's modulus (YM), flexural modulus and mode I fracture toughness (KIc) were found to decrease and impact strength (IS) was found to increase for both AUL and AAL composites. AUL composites had greatest overall reduction in mechanical properties than that for AAL composites upon exposure to accelerated ageing environment. FTIR analysis and crystallinity contents of the accelerated aged composites support the results of the deterioration of mechanical properties upon exposure to accelerated ageing environment.

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  • Microstructure and mechanical behaviour of ultrafine grained Al-4wt%Cu-(2.5-10) Vol.% SiC metal matrix composites produced by powder compact forging

    Gazawi, Amro Abdul-Karim; Zhang, Deliang; Pickering, Kim L.; Mukhtar, Aamir (2011)

    Journal article
    University of Waikato

    Ultrafine grained Al-4wt%Cu-(2.5-10) vol.% SiC metal matrix composite powders were produced from a mixture of Al, Cu and SiC powders using high energy mechanical milling (HEMM). The composite powders produced were first hot pressed at 300°C with a pressure of 240 MPa to produce cylindrical powder compacts with a relative density in the range of 80-94% which decreased with increasing the SiC volume fraction. Powder compact forging was utilized to consolidate the powder compacts into nearly fully dense forged disks. With increasing the volume fraction of SiC from 2.5% to 10%, the average microhardness of the forged disks increased from 73HV to 162HV. The fracture strength of the forged disks increased from 225 to 412 MPa with increasing the volume fraction of SiC particles from 2.5 to 10%. The Al-4wt%Cu-2.5vol.%SiC forged disk did not show any macroscopic plastic yielding, while the Al-4wt%Cu-(7.5 and 10)vol.% SiC forged disk showed macroscopic plastic yielding with a small plastic strain to fracture (~1%).

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  • Reprocessing of wood fibre reinforced polypropylene composites. Part I: Effects on physical and mechanical properties

    Beg, Mohammad Dalour Hossen; Pickering, Kim L. (2008)

    Journal article
    University of Waikato

    This paper describes the effects of reprocessing on the physical and mechanical properties of composites based on radiata pine (Pinus radiata) fibre in a polypropylene (PP) matrix. Composites, containing either 40 wt% or 50 wt% fibre with 4 wt% maleated polypropylene (MAPP) as a coupling agent, were reprocessed up to eight times. For composites with 40 wt% fibre, tensile strength (TS) and Young’s modulus (YM) were found to decrease with increased reprocessing by up to 25% for TS and 17% for YM (after reprocessed eight times). Flexural tests were also carried out for 40 wt% fibre composites and flexural strength and modulus were found to decrease with increased reprocessing. Although, TS was lower for virgin composites with 50 wt% fibre than for those with 40 wt% fibre, this initially increased with reprocessing by up to 14% (after reprocessed two times), but then decreased with further reprocessing, and an overall 11% reduction of TS was found after reprocessing eight times compared to the virgin composites. YM was higher for virgin composites with 50 wt% than those with for 40 wt% fibre and also initially increased with reprocessing but decreased upon further reprocessing. Reprocessing was found to increase thermal stability. The TS of composites made by combining reprocessed with virgin materials was also assessed.

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  • Analysis of mechanical properties of hemp fibre reinforced unsaturated polyester composites

    Sawpan, Moyeenuddin Ahmad; Pickering, Kim L.; Fernyhough, Alan (2013)

    Journal article
    University of Waikato

    Different chemically treated hemp fibre reinforced unsaturated polyester composites were investigated over a range of fibre content (0–60 wt%). Although Young’s modulus of all the short fibre reinforced unsaturated polyester composites was found to be higher than that of unreinforced unsaturated polyester; however, tensile strength of the composites exceeded that of the unsaturated polyester matrix only for the combined alkali- and silane-treated fibre composites at 40 wt% fibre content. The decrease in tensile strength of the composites could be attributed to stress concentrations caused by the fibres in conjunction with the brittle matrix. Impact strength of all the treated fibre composites was higher than that of the untreated fibre composites at all fibre contents. KIc and GIc of the composites decreased initially and thenincreased as the fibre content increased because more and more fibres being available to pull-out. The mechanical properties of the composites were increased further due to the alignment of long fibres.

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  • A new method to predict optimum cure time of rubber compound using dynamic mechanical analysis

    Shuib, Raa Khimi; Pickering, Kim L. (2013)

    Journal article
    University of Waikato

    The degree of vulcanization of a rubber compound has a big influence on the properties of the final product. Therefore, precisely defining the curing process including optimum cure time is important to ensure the production of final products having high performance. Typically, vulcanization is represented using vulcanization curves. The main types of equipment used for producing vulcanization curves are the oscillating disc rheometer (ODR) and the moving die rheometer (MDR). These can be used to plot graphs of torque versus time at a constant temperature to show how cure is proceeding. Based on the results obtained, optimum cure time (t₉₀) is calculated as the time required for the torque to reach 90% of the maximum achievable torque. In this study, the use of Dynamic Mechanical Analysis (DMA) for assessment of t₉₀ was assessed. DMA was carried out using shear mode isothermal tests to measure the changes in material properties caused by vulcanization. The results revealed that the shear storage modulus (G′), shear loss modulus (G′′), and tan δ all reflect the vulcanization process, however, tan δ gave the best representation of level of vulcanization. Indeed, the curve of tan δ was able to be used to derive the t₉₀ for rubber compounds and showed good agreement with the results from an MDR.

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  • The potential of harakeke fibre as reinforcement in polymer matrix composites including modelling of long harakeke fibre composite strength

    Le, Tan Minh; Pickering, Kim L. (2015-05-30)

    Journal article
    University of Waikato

    Mechanical properties of aligned long harakeke fibre reinforced epoxy with different fibre contents were evaluated. Addition of fibre was found to enhance tensile properties of epoxy; tensile strength and Young's modulus increased with increasing content of harakeke fibre up to 223 MPa at a fibre content of 55 wt% and 17 GPa at a fibre content of 63 wt%, respectively. The flexural strength and flexural modulus increased to a maximum of 223 MPa and 14 GPa, respectively, as the fibre content increased up to 49 wt% with no further increase with increased fibre content. The Rule of Mixtures based model for estimating tensile strength of aligned long fibre composites was also developed assuming composite failure occurred as a consequence of the fracture of the lowest failure strain fibres taking account porosity of composites. The model was shown to have good accuracy for predicting the strength of aligned long natural fibre composites.

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