Composites: Part B 67 (2014) 183–191

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Composites: Part B

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Compressive behaviour of natural fibre composite

http://dx.doi.org/10.1016/j.compositesb.2014.07.0141359-8368/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Address: School of Engineering and Design, BrunelUniversity, UB8 3PH, UK.

E-mail address: mizi.fan@brunel.ac.uk (M. Fan).

Bartosz T. Wecławski a, Mizi Fan a,⇑, David Hui b

a Civil Engineering Materials Research Laboratory, Brunel University, UB8 3PH London, UKb Department of Mechanical Engineering, University of New Orleans, LA 70148, USA

a r t i c l e i n f o a b s t r a c t

Article history:Received 19 June 2014Received in revised form 4 July 2014Accepted 9 July 2014Available online 19 July 2014

Keywords:Natural fibre compositesA. YarnD. Mechanical testingE. Filament windingB. Fracture

This paper presents findings from a comprehensive study aimed at the development of sustainable nat-ural fibre composites (NFC) for civil engineering. It focuses on the compressive behaviour in an elasticregion and post collapse behaviour of NFC tubes. Deformation and fracture behaviour were examinedexperimentally and an influence of the reinforcement arrangement and tube design on mechanical per-formance was analysed. The correlation between the reinforcement arrangement, material compressivestrength and a fracture mode was established: The compressive modulus and ultimate stress of NFCsincreased with the reinforcement orientation angle. The highest stress and modulus was observed forthe reinforcement oriented at 10� to the main axis, which were four times higher than transversely ori-ented reinforcement. Four compression collapse modes were observed for the tested NFC tubes, namelymicrobuckling, diamond shape buckling, concertina shape buckling and progressive crushing, which areclosely related to the geometries of tube architectures.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Renewable construction materials bring benefits throughoutthe life cycle of buildings, such as, the reduction of embodiedenergy, increase in energy efficiency during use, reduction of wasteand other unique properties (e.g. insulation and breathability)[1,2]. Bast fibre composites are seen as an alternative to wood orglass fibre composites in applications for door elements, roof pan-els, car bodywork and interior elements in many engineering sec-tors [1,3–5]. Add reference to the Composites B about NFCdegradation.

The advantages of natural fibre composites (NFC)s include spe-cific tensile and impact performance, low density and fibre renew-ability, while some disadvantages include moisture and ultravioletlight resistance and a relatively high price at the current low volumeproduction [6,7]. NFCs are not considered as materials withstandingcompression and they perform better under tensile loading, which isusually investigated [8–10], but in order to be applicable in construc-tion industry other properties need to be examined, e.g., fire resis-tance [11]. Moreover, in real life applications, compressive loadsare unavoidable, e.g., in tensile-compressive coupling of flexuraldeformation, unbalanced stacking sequence of a laminate or if resid-

ual stresses are present in the composite. Therefore, a performanceof NFCs under compressive load should be analysed. A compositetube, either with round or square profile, is a versatile element inall aspects of engineering. This study focuses on a compressivebehaviour of natural fibre composite tubular shells in the elasticregion and the post collapse progression, which are considered ofimportance for energy absorbing structures and safety consider-ations. A series of tubular hemp composites were processed by fila-ment winding and tested in order to investigate the fracturemechanisms during compressive loading.

2. Materials and methods

2.1. Materials selection

Hemp yarns were supplied by Cyarn Ltd. These types of yarnsare processed by retting in water, bleaching and ring spinning inorder to form twisted yarn. Unsaturated polyester resin was usedtogether with cobalt in aliphatic ester accelerator (1 wt%) andmethyl ethyl ketone peroxide catalyst (1.5 wt%). The density ofthe cured resin is 1.12 g/cm3 at 25 �C. Samples were cured at120 �C and post cured for 24 h at 100 �C in accordance with BSISO 3597-1:2003. Mechanical properties of the resin are: tensilestrength rt = 53 MPa, tensile modulus E = 3.7 GPa and compressivestrength rc = 42 MPa tested in accordance with the standard BS ISO527.

Fig. 2. Diagram of the sample rotating stand used during gelling and curing.

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2.2. Tube processing

The processing routes used for composite tube constructioninclude the pultrusion, pullwinding and filament winding, whichall rely on the tensioning of a processed reinforcement. Therefore,the yarns or filaments used should be able to withstand processingloads. Unlike most synthetic man-made fibres, which are producedcontinuously, natural fibres (NF) are inherently short. NF length isnot only limited by the length (height) of plants, but also by theextraction procedures and natural defects of natural fibres. NFsare combined into yarns either by twisting of the aligned sliveror by wrapping it with an additional synthetic fibre, in order toproduce NF reinforcement continuously.

Tubular samples were prepared with pin filament windingtechnique. The equipment was designed and built to accommo-date use of natural fibre in laboratory scale (Fig. 1). The produc-tion was mainly controlled by two step motors synchronisedtogether with a Q Drive supplied by the Applied Motion Products,which allowed for the control over winding angle and processingspeed. A consistent yarn tension was facilitated by mechanicalmeans. Prior to the processing, the yarns were dried at 80 �C for24 h in order to remove moisture from the yarns (ranging from7% to 10%). The yarns were then fed through the series of loopsand were wound in accordance with the selected program. Afterthe winding procedure, the samples were manually impregnatedwith resin.

The mould with wetted-out stacking, was covered with NV153perforated release fabric, and wrapped with HST400 thermoshrinking tape supplied by Tygavac Ltd. Then, the samples wereplaced on a rotating stand (Fig. 2) throughout gelling and curingprocess, in order to prevent gravitational resin agglomeration.The thermo shrinking tape applied a uniform external pressurewhile kept in the oven for 15 min at 120 �C. Subsequently the sam-ples were removed by collapsing molds and were post-cured at100 �C for 24 h in a vacuum oven.

Fig. 1. Diagram of the filament winding se

2.3. Testing

The cured samples were machined to the dimension of 45 mmheight and 45 mm outer diameter. This geometry was used to pre-vent the creation of a global off-axis Euler buckling mechanism ofthe tube, while testing was carried out [12]. For each configuration,two repetitions and three test pieces were developed. Before testing,both ends of samples were squared, polished and covered with PTFEpaste to diminish lateral stress concentration caused by a frictionbetween sample and compression plates (Fig. 3). Tests were con-ducted on Instron 5585 universal testing machine at a compressionrate of 0.5 mm/min. The compressive stiffness, ultimate compres-sive strength and mode of fracture were recorded. Fibre densityand yarn Tex values were measured using buoyancy method withpycnometer on the 10 m samples (ISO 2060:1994). The diameter ofthe yarn and fibre were measured on composite cross-sections withan optical microscope. Rectangular test pieces with unidirectionallyarranged reinforcement were tested in accordance with the BS EN527 standard. Test pieces (250 � 25 � 150 mm3) were staticallyloaded in tension at 2 mm/min crosshead speed until failure.

t-up used for NFC tubes preparation.

Fig. 3. Testing set-up. Tube sample with visible yarn arrangement between platensprepared for the compression test.

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3. Results and discussion

3.1. Tube structures

The NFC tubes were composed of the balanced yarn reinforce-ment layers with the designed wind orientations of 10�, 30�, 45�,60� and 90�, the actually measured average winding angles ofwhich are 11.1� ± 0.9, ±28.9� ± 1.1, 45.2� ± 1.1, 57.8� ± 1.4 and89.3� ± 0.4, being denoted as the sample T10, T30, T45, T60 andT90 respectively. The slight variation of the fibre orientation maybe caused by the variation in yarn diameter as well as two stagesof tubes preparation. Fig. 4 presents the examples of four testpieces with different yarn arrangements visible as the surface tex-ture. It can be seen that the developed machine and process areable to formulate the structure of the NFC tubes. A volume fractionof the reinforcement in processed composites was measured by

Fig. 4. Examples of NFC tubes with four reinforcement arrangements: (a) T10; (b)T30; (c) T45; (d) T90.

comparing mass of dried reinforcement used and impregnatedlaminate. The Vf of the processed tubes was equal to 30%(RSD = 2%).

3.2. Yarn properties and resin distribution

The twisted yarns were used in this study in order to formulatethe continuing yarn reinforcement of the discontinuous naturalfibres and increase the strength to sustain tension load during fil-ament winding production. The 130 Tex hemp yarn surface is pre-sented in Fig. 5A as an example. The image reveals thearrangement of individual technical fibres and the yarn hairiness,which are individual fibres protruding from the main yarn struc-ture. Individual short fibres are held together with the frictionalforces induced by the yarn twist, which arranges fibres at an angleto the main yarn direction. The diagram in Fig. 5B illustrates thepositioning of cross section images and a direction of reinforce-ment angles for the tubes developed.

A group of longitudinal and transverse cross sections were pre-pared in order to illustrate fibre distribution and laminates micro-structure (Fig. 6). Fig. 6A illustrates the cross sectionmicrostructure images of the T45 tube wall (in the ‘‘A-A’’ – normalto the longitudinal direction of the tube). Fig. 5B illustrates thecross section in the ‘‘A-A’’ direction of the tube reinforced withthe yarns arranged at 0� (grey region) and 90� (darker region).Fig. 6C represents the cross section of the T90 tube wall in the‘‘B-B’’ – perpendicular to the tube direction. Fig. 6D illustrates crosssection of the T90 tube wall in the ‘‘A-A’’ direction. The darkerregions represent the cross sections of the yarns in the transversedirection or porosity. It can be seen that the overall impregnationof the technical fibres is visible together with a close packing ofindividual yarns. The resin penetrated within the yarn and ontothe surface of the technical fibres. However, it is evident that thereis uneven distribution of yarns within the tube wall (Fig. 6B and C)which may be due to the fluctuation of individual yarn diametersleading to uneven individual yarn packing. Uneven compacting(laminating) during the winding formulation can also be observed(Fig. 6C, right side); the lighter colour between the yarns shows theconcentration of resin. The diameter of the 130 Tex hemp yarnused was d = 269.3 ± 39.8 lm and a diameter of technical fibrecomposing yarn was equal to df = 14.4 ± 3.6 lm.

In order to find allowable load, which yarn can withstand whilewinding, a yarn tenacity was also measured with 250 mm gaugelength and 250 mm/min crosshead speed in accordance with ISO/DIS 2062. Additionally, samples were also tested with 4 mm gauge.This was selected in order to reduce the possible influence of fibreslipping in comparison with the standard tenacity. Mean load car-rying capacity of a yarn tested at 250 mm gauge length wasPav = 16.8 N (RSD = 23.7%), while the shorter gauge length resultedin average load equal to Pav = 22.45 N (RSD = 24.1%). The dispersionof the results is caused by a variation in fibre diameter, fibre lengthdistribution and load distribution across the yarn. Tenacity of 130Tex yarn, was calculated and equal to 13.6 cN/Tex (RSD = 16.1%).This result suggests that it is desirable to reduce the length of yarntransportation path during winding, and the yarn delivery systemmay influence the integrity of yarn as well as the NFC properties.

A scrutiny of test results indicated the impregnation of the indi-vidual fibres is complete (Fig. 7A), which is represented by filledout small spaces and surface contact hence processing parameterswere suitable for the resin viscosity. However, there may be a weeksurface bond between fibre and matrix, which resulted in delami-nation between the fibre and matrix (Fig. 7B), which could becaused by excessive pressure during polishing process, surfacecontamination or fibre shrinkage. Fig. 7C and D also indicate theexistence of porosity within the yarn visible as the darker regionsinside the yarn cross sections.

Fig. 5. (A) Hemp yarn with 130Tex with visible individual technical fibres arrangement and yarn hairiness; (B) A diagram with positioning of cross section images and anangle of the reinforcement.

Tube wall cross section

Mould resin

Longitudinal cross sections of yarnsTransverse cross sections of yarns

A

DC

B Longitudinal yarn cross section

Transverse yarn cross section

Fig. 6. (A) Cross section of the T45 tube in the ‘A–A’ direction, (B) cross section in the ‘A–A’ direction of the tube with the reinforcement oriented at 90� and 0�, (C) the T90tube in the ‘B–B’ direction and (D) the T90 tube in the ‘A–A’ direction.

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3.3. NFC Laminate properties

Tensile strength of hemp 130 Tex yarn laminate was evalu-ated with using rectangular test pieces (Fig. 8B) unidirectionallyreinforced with volume fraction of Vf = 30%, which was equal tothat of the processed tubes. Samples were tensile loaded at2 mm/min until fracture. It was found, that samples have anaxial tensile strength of 128.9 MPa (RSD = 2.5%) and a mean ten-sile stiffness of 8.9 GPa (RSD = 7.3%). A flexural strength and aflexural modulus were 165 MPa (RSD 5.2%) and 10.2 GPa (RSD4.2%) respectively.

An investigation of commercially pultruded hemp reinforcedcomposite rods (Fig. 8A) has also been carried out in the authors’research group and outcomes have been published (Peng et al.,2011). The summarised results were a compressive strength equal

to rc = 53 MPa (SD = 0.29), a compressive stiffness equal toEc = 3.83 GPa (SD = 1.09). The reported tensile strength ofhemp-polyester composite rods was equal to rt = 122 MPa and atensile stiffness equal to Et = 16.84 GPa. A comparison of the labo-ratory compression and factory pultruded hemp compositesshowed that both composites have a very similar tensile strengthwhile the tensile stiffness of the commercially pultruded compos-ites is higher. The difference in the tensile stiffness may be due tothat the commercially pultruded samples were made with hempfibres arranged at 0� by aligning fibre sliver and then wrapping itwith additional polymeric yarn, while the laminates processed inlaboratory were made with yarns with twisted architecture(Fig. 5A), which inherently changes individual fibres orientationtowards main yarn axis thus decreasing laminate modulus(Fig. 8B).

Transverse technical fibre cross sections

Hemp fibre lumens

Hemp fibre lumen

Fibre matrix delamination

Matrix

Porosity within the yarn Delamination porosity

Sample-mould delamination C

A B

DFig. 7. (A) Impregnation of individual technical fibres within the NFC tube, (B) interface of hmp-matrix within the NFC tube wall, (C) the cross section of the tube wall withporosity within the yarns visible as black areas and (D) optical image of cross section revealing delamination sites within the yarn.

Fig. 8. (A) An image of commercially pulltruded NFC rods reinforced with hemp yarns, (B) a fracture area of the rectangular test piece after tensile test.

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3.4. Mean strength and stiffness of various NFC tubes

A summarised compression test results for the thin walledtubes with various yarn orientations are presented in Table 1. Itcan be seen that the modulus and ultimate stress are inversely pro-portional to the reinforcement orientation angles. The higheststress achieved in NFC hemp tubes is 76 MPa with a fibre orienta-tion at 11�, which is about 2.5 times higher than a peak stressobserved in tubes with reinforcement aligned at 89�. The highest

Table 1Influence of the winding angle on compression properties.

Sample wind angle rmax (Mpa) SD E (Gpa) SD

T90 (89.3�) 30.1 2.4 1.5 0.1T60 (57.8�) 33.2 3.4 1.8 0.2T45 (45.0�) 53.9 2.1 3.6 0.3T30 (28.9�) 63.4 6.1 3.1 0.4T10 (11.1�) 76.2 4.2 5.6 0.6

The each ‘SD’ column represents standard deviation and each corresponds to the colum

compression modulus is 5.6 GPa achieved for samples with rein-forcement at 11�, which is 4 times higher when compared withsamples reinforced at 89�. A strain to failure for the hemp tubeswith an angle of 11� is about 2/3 that of tubes with an angle of 89�.

For the tubes reinforced at an angle close to longitudinal direc-tion, the buckling is controlled by fibre effects, such as microbuck-ling, while loading in transverse direction has more influence frommatrix when compared with longitudinal loading, and in this caseadhesion between fibre and matrix influences the load propagation

Strain at failure (mm/mm) SD MoR (MJ/m3) SD

0.0360 0.0035 0.3088 0.03260.0316 0.0056 0.2994 0.05550.0321 0.0033 0.3170 0.03910.0313 0.0044 0.5864 0.09140.0243 0.0030 0.6316 0.1900

n on its left.

Fig. 10. Relationship between the compressive modulus of the NFC tubes and theyarn wind angles.

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[13]. A comparison of compressive strength and stiffness of tubesand commercially produced solid rods indicates that the stiffnessof both elements is around 5.5 GPa. However, the strength of NFChemp tubes developed with the fibre orientation of 11� is about1/3 higher than that of the commercially produced solid.

The relationship between the wind angle and the ultimate com-pression stress is exponential (Fig. 9). The compression strengthdecreases significantly from 11� to 45� and then both results forsamples with 58� and 89� are close to 30 MPa. A scrutiny of thecompressive strength indicates that the ultimate stress of thedeveloped tubes may increase with a wind angle below 45�, sinceresin ultimate compression stress is 42 MPa. For tubes reinforcedat higher wind angles, the compression strength is decreased tobelow that of resin, because the deteriorating effect of porosityand interface delamination may be higher than the effect of thefibre reinforcement.

Similar relationship is observed between compression modulusand the wind angle (Fig. 10). Only sample with fibres arranged at11� increases the compression modulus in comparison with purepolyester resin. The rest of samples reinforcement arrangementsdeteriorate the compressive modulus. This further indicates thatthe interface strength between matrix and fibres may not besufficient.

3.5. Fracture modes corresponding to the axially compressive testedNFC tubes

Micromechanical failure theories for unidirectional compositesdescribe that the fracture of fibre reinforced composites consistsof one or more of mechanisms: microbuckling, kinking, fibre fail-ure, longitudinal cracking or their mixture [14]. Microbucklingstarts with the localized single fibre, waviness appears and delam-ination then follows. Kinking involves the fracture of fibres alongthe kink bands. Longitudinal cracking appears as cracks parallelto the fibres [13].

Travelling hinge theory describes post initial fracture behaviourof isotropic thin-walled tubular shells. It was derived from energyrelationships, which were based on hinges creation during a col-lapse of the tube incompressible walls. Tube buckles in variousways depending on wall elastic properties geometry. It can takea form of annual rings described as concertina shape buckling ordiagonal triangular hinges described as diamond shape buckling.

Alternatively, composite tubes can collapse through crushing. Itis normally observed for thick walled tubes, for which the structurefractures through crumbling on the small scale, as opposed to thebuckling of the walls. A tubular shell can be designed to crumbleunder compression load, instead of bending along the hinges. Thecrushing consists of the combined work used for microbuckling

Fig. 9. Relationship between the ultimate compression strength of the NFC tubesand the yarn wind angles.

and micro fragmentation of the material, and it is describedthrough its energy absorption capabilities in respect to volume[15]. The total energy is calculated by integrating the area belowthe stress–strain axial compression relationship [16,17].

3.5.1. MicrobucklingThe test results show that NFCs can fail through microbuckling

process, an example of NFC microbuckling is given in Fig. 11. Thisfracture modes is characterised as a localized material instabilitywhere fibres rotate within the narrow band of about 20 fibre diam-eters. As reviewed by Schultheisz and Waas [14], the microbuck-ling is controlled by matrix stiffness in shear, which results insensitivity to time, strain rate and test conditions. Moreover, themicrobuckling depends on initial processing defects of the com-posite, such as fibre misalignment or matrix shrinkage induced

Fig. 11. Microbuckling fracture (A) stress–strain response graph, (B) Examples ofT10 samples fractures in microbuckling.

Fig. 12. Diamond shape buckling fracture: (A) A stress–strain response (dashed line represent mean post buckling load), (B) Diagonal lobes formation in diamond shapebuckling collapse.

Fig. 13. Concertina shape buckling fracture: (A) A Stress–strain response, (B) Initial stage of concertina shape buckling collapse mode with first circumferential hinge.

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residual stresses and porosity [13]. This is considered of impor-tance as the hemp yarn may consist of multiple technical fibres,which increase defect content.

Fig. 11a depicts a stress–strain response of the tube T10 type.Average compressive load for this type of tubes was equal to76.2 MPa (RSD = 5.5%). It is evident that the fracture can be charac-terised by a sudden fracture, followed by force dissipation associ-ated with sliding of the tube walls. Fractures along the fibres arevisible as vertical cracks along the surface (Fig. 11b). Dotted lineindicates one of the test repetitions, showing the consistency ofthe failure patterns. It is apparent that the microbuckling reduceswith the fibre orientation angle increase. A similar observationwas made in a previous research on glass fibre reinforced compos-ite tubes [18].

3.5.2. Diamond shape bucklingAnother type of the fracture mode observed in this study for

NFC was the diamond shape buckling (Fig. 12) as described fortravelling hinge buckling. Thin walled tubes, made out of plasticisotropic material, can collapse by forming axisymmetric rings orby folding along hinge lines and creating diamond like pattern after

exceeding buckling initiation stress [12]. The process of the col-lapse depends upon geometrical relationship between the tubediameter, wall thickness and tube length. Following initial peak,which represents sample fracture, oscillation-like pattern emerges,representing the stress concentration-dissipation processes relatedwith subsequent hinges folding (Fig. 12a). Initiation load for thesamples exhibiting diamond shape buckling is approximately halfof microbuckling initiation load (Fig. 11A and Fig. 12A). However,in diamond shape buckling, a load related with the work done onbending of hinges is sustained throughout the collapse.

3.5.3. Concertina shape bucklingThe travelling hinge buckling was also observed in the tests of

the NFC, which is concertina shape buckling. In the samples T30horizontal symmetrical hinges were created in absence of diagonallines. This kind of fracture was named concertina buckling modewhile observed in isotropic plastic material tubes [12,19]. Fracturestarts from one end and progressively continues until tube col-lapses. The process is accompanied with characteristic load oscilla-tions, which relate to an appearance of subsequent lobes asindicated on the graph (Fig. 13).

Fig. 14. Progressive crushing: (A) Examples of stress–stain responses (NFC T30 and T60 tubes with the ratio t/D > 0.04. Horizontal straight lines represent mean crushingloads), (B) A crushed sample during the test.

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A compression stress–strain graphs for NFCs tubes, in compar-ison with isotropic plastic tubes, are not smooth torn. This mightbe related with the lower tensile strain to break and lower plastic-ity of the NFCs. Yarn is composed out of individual fibres andcracks will progress faster at yarn discontinuity boundary. Duringlobe formation, the tube wall is exhibiting flexural deformation,and the crack is created at the extensional side until it stops oncompressed side of the flexed wall.

The main difference between microbuckling (Fig. 11), diamondshape buckling (Fig. 12) and concertina buckling (Fig. 13) is thatthe microbuckling is initiated at higher stress levels. In the micro-buckling a dramatic load drop followed immediately after fractureinitiation, and the tube is not able to sustain additional load. Inconcertina shape buckling, similar to diamond shape buckling,the post buckling load is sustained until total collapse occurred.

3.5.4. Progressive crushingA progressive crushing fracture mechanism was observed in

this study for those NFC tubes with the wall to outer diameter ratiot/D > 0.04. The fracture starts from the localized stress concentra-tion at one end and progresses until the whole tube is crumbled.In the plastic tube field, this collapse mechanism was describedas the combined work used for micro fragmentation and localinterlaminar fracture of the composite wall [16]. Moreover, theprogressive crushing is also initiated by chamfering the end ofthe tubular sample, imperfect clamping or voids [20].

The examples of the progressive crushing stress–strainresponse for two thick walled tubes T30 and T60 presented inFig. 14A. After reaching a peak load, graphs start to oscillate aroundmean crush propagation stress indicated by dotted lines. Fig. 14Billustrates the crushed sample half-way through the test with vis-ible crumbled edges. The crushing is characterised by higherenergy absorption in comparison with other fracture mechanismspreviously discussed.

4. Conclusions

The filament winding technologies have been developed for theproduction of 3-D composites made with natural fibre (NF) yarns.The developed machine and process were able to formulate thestructure of the NFC tubes with various structural designs.

The detailed morphology with longitudinal and transverse crosssections of NFCs was produced to illustrate fibre distribution andlaminates microstructure, indicating that the resin penetratedwithin the yarn and onto the surface of the technical fibres, butthere is uneven distribution of yarns within the tube wall.

The compressive modulus and ultimate stress of NFCs wereinversely proportional to the reinforcement orientation angle withthe highest stress and modulus being 76 MPa and 5.6 GPa respec-tively with a fibre orientation at 10�, which was approximately 4times higher in comparison with samples reinforced at 90�. Themaximum load capacity of hemp fibre tubes was related to the fail-ure modes.

Four major fracture modes under compressive loading wereobserved for NFC tubes, namely microbuckling, diamond shapebuckling, concertina shape buckling, and progressive crushing.

Fracture modes were related to the orientations of hemp yarns.In thin walled structures with t/D < 0.04, the applied compressiveload resulted in the formation of lobes. The thin walled tubes ofthe T30 type fractured with concertina shape buckling character-ised by formation of circumferential lobes. T45 tubes fracturedwith diamond shape buckling characterised by formation of cir-cumferential and diagonal lobes. In T10 samples the dominatingfailure mode was microbuckling, which is characterised by highercompressive stiffness and compressive strength along with cata-strophic fracture throughout the sample length. In short and thicksamples (t/D > 0.04), the crushing fracture was observed.

The developed NFC tube filament winding technologies in thisstudy has set out a principle of using NF for the production of 3-D NFC engineering products. The established database will serveas benchmarking information for further extension of research inthe area and potential for optimised design of NFCs in buildingor other engineering constructions.

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