Composites Part B 105 (2016) 60e66
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Mechanical and damping properties of resin transfer moulded jute-carbon hybrid composites Sam Ashworth, Jem Rongong, Peter Wilson, James Meredith* Department of Mechanical Engineering, University of Shefﬁeld, Sir Frederick Mappin Building, Mappin Street, Shefﬁeld, S1 3JD, UK
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 May 2016 Received in revised form 15 July 2016 Accepted 17 August 2016 Available online 20 August 2016
Hybrid composites with carbon and natural ﬁbres offer high modulus and strength combined with low cost and the ability to damp vibration. This study investigates carbon (CFRP), jute (NFRP) and hybrid (HFRP) ﬁbre reinforced polymers manufactured using the resin transfer moulding process. Tensile strength reduced with increasing injection pressure for NFRP (72.7 MPa at 4 bar, 45.5 MPa at 8 bar) and HFRP (98.4 MPa at 4 bar, 92.4 MPa at 8 bar). The tensile modulus for HFRP (15.1 GPa) was almost double that for NFRP (8.2 GPa) and one third of CFRP (44.2 GPa). Loss factor reduced at small strains (104) with increasing pressure for NFRP (0.0123 at 4 bar, 0.0112 at 8 bar) and HFRP (0.0048 at 4 bar, 0.0038 at 8 bar) but all were greater than CFRP (0.0024). Increased injection pressure improved the surface properties and prevented read through of the weave pattern, NFRP (Ra ¼ 2.15 mm at 4 bar, 1.51 mm at 8 bar) and HFRP (Ra ¼ 1.80 mm at 4 bar, 1.42 mm at 8 bar). Hybridisation of low cost, sustainable jute with carbon ﬁbre offers a more sustainable and economic alternative to CFRPs with excellent damping properties. © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Keywords: Hybrid Internal friction/damping Mechanical testing Resin transfer moulding
1. Introduction Fibre reinforced polymer composites are now applied widely in industry where it is desirable to reduce mass by taking advantage of their high speciﬁc strength and stiffness. Carbon ﬁbres are energy intensive to manufacture making them expensive ﬁnancially and environmentally . An alternative approach is to use natural ﬁbres which are renewable, have low embodied energy, low cost and low density . However, they have poor mechanical properties, high variation, sensitivity to moisture and poor adhesion between ﬁbre and matrix . Recycling of carbon ﬁbre reinforced polymers (CFRPs) at their end of life is the subject of intense research focused on extracting value from both ﬁbres and matrix [4e7]. Natural ﬁbre reinforced polymers (NFRPs) are either composted or burnt for energy recovery at their end of life with the primary advantage of being carbon neutral . Hybrid ﬁbre reinforced polymers (HFRPs) use two or more reinforcements with a single matrix giving rise to a more favourable balance between advantages and disadvantages of the core components [9,10]. The combination of a high strength ﬁbre such as
* Corresponding author. E-mail address: [email protected]
ﬁeld.ac.uk (J. Meredith).
glass or carbon with natural ﬁbres can lead to a desirable mix of performance, cost and environmental attributes. Glass ﬁbre epoxy composites have been hybridised with jute , kenaf , sisal  and bamboo . Carbon-ﬂax HFRPs have demonstrated enhanced mechanical properties versus NFRPs and improved damping [15,16]. NFRPs rely on mechanical interaction between ﬁbre and matrix versus chemical bonding with synthetic ﬁbres making them better able to damp vibrations . Damping in NFRPs is via the properties of plant ﬁbres including entanglement, voids in the lumen, heterogeneity of the cell wall and reversible hydrogen bonding in the cell wall [18e20]. Damping in NFRPs can also be tailored by using ﬁbre twist and crimp . CFRPs have poor damping characteristics and are highly resonant . This is beneﬁcial for applications such as musical instruments, however when applied in structures subject to vibration the lack of damping can cause resonant vibration. CFRPs have high speciﬁc stiffness and low levels of damping with loss factors typically below 0.002 compared with NFRPs with loss factors of 0.01 or higher . A heavy structure with high inherent damping (i.e. high capacity for dissipate vibration energy) is less likely to suffer from vibration problems. Resin transfer moulding (RTM) is popular in the automotive and aerospace industries since it is a clean and eco-friendly closed
http://dx.doi.org/10.1016/j.compositesb.2016.08.019 1359-8368/© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
S. Ashworth et al. / Composites Part B 105 (2016) 60e66
mould process. RTM requires placement of a ﬁbre preform into a closed mould followed by injection of liquid resin under pressure to inﬁltrate and wet the ﬁbres and prevent void formation . It is a process able to deliver high quality components at the required volume and cost to make them practical for aerospace and when used with high pressure for a short cycle time, the automotive industry . Studies have shown that it can improve inter laminar shear strength, save weight, reduce manufacturing time, improve surface ﬁnish and reduce cost . Process parameters inﬂuence the way a composite is formed during moulding through events such as air entrapment and wetting which can lead to excessive voidage, also known as porosity within the composite . The tensile properties, ﬂexural strength, fatigue resistance, susceptibility to weathering and consistency of strength are all affected by an increase in void content . Irrespective of the type of matrix, the type of dry ﬁbre, or the moulding process used, the interlaminar shear strength of the composite decreases by approximately 7% for every 1% increase in void content although this does not apply to 3D woven or discontinuous ﬁbre composites . Process parameters including resin injection rate, resin injection pressure and temperature are widely known to affect void formation. Understanding how each parameter affects void formation is critical in the design of an optimum resin transfer moulding process . This study focuses on a family of natural ﬁbres known as ‘bast’ ﬁbres; they are collected from the skin or inner bark on the stem of certain plants, mainly dicotyledonous. The speciﬁc type of ﬁbre being investigated is jute. In terms of usage, production and global consumption it is second only to cotton, it is signiﬁcantly less energy intensive to manufacture than carbon ﬁbre and low cost at less than £500 per tonne compared with £770e7500 per tonne for carbon [29,30]. This work examines the performance of natural, hybrid and carbon epoxy composites manufactured via RTM at two different pressures. Property evaluation includes the sensitivity of the ﬂexural modulus and loss factor to the dynamic strain, behaviour which has not been reported elsewhere for natural and hybrid composites. 2. Experimental procedure
(n), fabric areal weight (Aw), ﬁbre density and laminate thickness (d). Fibre density for a T300 ﬁbre is 1.76 g/cm3 (Torayca) and 1.46 g/ cm3 for jute .
nAw rf d
Once mixed the resin was drawn into the injector under vacuum and left to degas for 5 min. The mould was then evacuated and the resin injected into the RTM tool at a constant pressure as set on the Hyperject. After 5e10 min the resin had passed through the ﬁbre stack and was visible in the vacuum line. The vacuum line was then clamped off and pressure on the resin feed maintained for 1 min before also being clamped off. The resin ﬁlled mould was then left to cure for 12 h at room temperature. In this work the resin and RTM variables were set to deliver a quality panel rather than a fast process. After cure the panel was ejected and post cured with the following cycle: 40 C for 2 h, 60 C for 2 h, 80 C for 2 h, 100 C for 2 h and 120 C for 12 h and then cooled slowly to room temperature. All ramp rates were set to 2 C per minute. 3. Analysis 3.1. Dimensional study Each panel was cut along its centre line and its thickness measured at 10 evenly spaced points using a Vernier calliper. 3.2. Tensile testing Ultimate tensile strength and tensile modulus were determined according to the American Society for Testing and Materials (ASTM) D3039/DB3039M. A minimum of ﬁve samples were cut from each panel with dimensions 250 25 mm. Glass ﬁbre reinforced end tabs were bonded onto each sample with epoxy resin (Araldite Rapid, Huntsman Advanced Materials, UK) leaving a gauge length of 150 mm. Tests were carried out on a Mayes DH50 servo hydraulic test machine with a calibrated 100 kN load cell. Tensile modulus was calculated between 0.001 and 0.003 strain according to the standard.
2.1. Materials 3.3. Dynamic testing A 199 gsm 2 2 twill 3K-T300 carbon ﬁbre fabric (Sigmatex, UK) and a 550 gsm 2 2 twill jute fabric (Biotex, UK) were used throughout this work. The fabrics were cut into 28 cm 28 cm plies before being inserted into the mould cavity with all plies laid at 0 . A low viscosity epoxy resin suitable for RTM was used, DR2188 (Delta Resins, UK) with hardener HY2188 (Delta Resins, UK) and mixed at a ratio of 100 parts by mass of epoxy with 32 parts by mass of hardener. 2.2. Manufacture A steel RTM tool was designed to manufacture a panel 300 300 3 mm. It had a gating system which utilised convergent ﬂow from all sides and a vacuum port in the centre of the panel (Fig. 1). Resin was injected via a Hypaject (Magnum Venus Products, UK). Before moulding ﬁve coats of release agent (227CEE, Marbocoat, UK) were added to the mould surfaces. An initial study was undertaken to establish the level of ﬁbre compression required to prevent ﬁbre wash and the ﬁnal layups for each panel are shown in Table 1. The thickness of the ﬁbre pack was measured using a Vernier calliper. For each material one panel was manufactured at 4 bar and another at 8 bar injection pressure. Fibre volume fraction (FVF) was calculated using the formula below using number of plies
The loss factor (h) and ﬂexural modulus (Ef) of the materials were determined from free vibration tests on cantilever beam specimens. Test specimens were cut parallel to the 0 ﬁbre alignment axis with dimensions 250 12.5 mm. End tabs, 50 mm in length, were created from E-glass/epoxy composite and bonded to the surface of one end of the specimens using epoxy resin (Araldite Rapid, Huntsman Advanced Materials, UK). Tests on each specimen involved measurement of the free response following a manual deﬂection of the tip. The specimen was set up as a cantilever beam by clamping the end tab into a heavy block. After manual deﬂection of the tip, the response of the beam at a location 58 mm from the clamp, was measured using a 1605-10 laser displacement probe (Micro-Epsilon, UK). To minimise noise in the signal, an opaque sticker was placed on the specimen to prevent the laser beam passing through the material. The response was captured digitally using a sampling rate of 2560 Hz using a SigLab2 data acquisition system. The voltage induced in the laser probe was converted to displacement using a conversion of 10 mm/ V stated by the probe manufacturer. The damping ratio z and the natural frequency un were determined from the free response data using Matlab software. As the damping was assumed to be light, but with some nonlinearity, a
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Fig. 1. Exploded view of RTM tool for manufacture of composite panels.
Table 1 Layup details for each panel type. Material type
Ply composition Thickness of the dry ﬁbre pack (mm) Calculated FVF
3 plies jute 4.2 26.9%
1 carbon e 3 jute e 1 carbon 4.7 28.9%
14 carbon 3.5 45.2%
modiﬁcation to the standard logarithmic decrement approach was used. The times and amplitudes of the peaks and troughs over the desired part of the response were ﬁrst identiﬁed and the natural frequency obtained from the mean period between individual points. An example is given from the 4 bar NFRP sample in Fig. 2. If damping is linear viscous, a plot of the logarithm of successive peak (or trough) amplitudes against time yields a straight line. Assuming nonlinearity in damping, low-order polynomials were ﬁtted to the measured data points. This was done separately for peaks and troughs and the average taken to eliminate the effects of static bias caused, for example, by slow realignment of the equilibrium point in viscoelastic specimens. Results of a 3rd order polynomial ﬁt for the 4 bar NFRP sample are shown in Fig. 3. The instantaneous logarithmic decrement at any time was then
obtained from the gradient of the mean line using:
where is g is the gradient of the natural logarithm of amplitude with respect to time and un is the natural frequency in Hz. Note that the natural frequency did not change appreciably with amplitude for any of the specimens. The damping ratio z was then calculated using:
z ¼ sﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ ﬃ 2
As the damping levels were low, the undamped and damped
Fig. 2. Free vibration response demonstrating selected peak and trough points for 4 barb NFRP.
Fig. 3. Polynomial curve ﬁt to test data.
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natural frequencies were more or less identical and therefore assumed to be the same. The ﬂexural modulus Ef was then obtained from:
48p2 ru2n L4
b4 t 2
where r is the density, L is the length of the beam outside the clamp, t is the thickness and b ¼ 1.875104 is a constant that accounts for the mode shape. As measurements were taken at the natural frequency, the loss factor h in each case was obtained from:
h ¼ 2z For each test, the spread of peak and trough data points from the ﬁtted polynomial had a standard deviation of less than 4%. Eight responses were recorded for each material and values of loss factor and ﬂexural modulus were averaged across this range. The tests showed a high level of repeatability with standard deviations for modulus and loss factor being less than 0.5% and 5% respectively. It was considered more useful to relate loss factor to peak strain rather than time or deﬂection levels as it is more general. The peak strain was estimated assuming the deformation of the composite beam was similar to that of a homogeneous Euler-Bernoulli beam. The result from the 4 bar NFRP sample is provided in Fig. 4 and shows the extent of the scatter from different tests. 3.4. Optical microscopy The corner of each panel was removed with a cut at 45 to the ﬁbre direction. Each sample was mounted in EpoFix (Struers, UK) with EpoDye (Struers, UK), and polished using an Isomet (Buehler, UK) with the following procedure: P1200 abrasive, 9 mm diamond polish, 6 mm diamond polish and 0.05 mm polish. Samples were examined using a Fusion vision system (Qioptiq, UK) with a 5 mega pixel camera (Paxcam, USA). Six images of each sample were taken at 8 objective and analysed with Pax-it software (Paxcam, USA) to determine the void content and ﬁbre volume fraction (FVF). 3.5. Surface analysis The surface of each sample was assessed for roughness and surface texture using an InﬁniteFocusSL (Alicona Imaging GmbH, Austria) with 10 optical magniﬁcation. A 5 5 mm area in the centre of panel was measured using a vertical resolution of 100 nm and a lateral resolution of 1 mm. For surface roughness calculations, a ﬁlter value of lc ¼ 0.8 mm was chosen. Practically this value determines the intersection
between roughness and waviness components. Form removal was completed for all scans to ensure that the roughness proﬁles were centred about a zero point to account for any surface tilting. The image was analysed using three, 4 mm long, 10 mm wide proﬁles drawn across the measured area in both 0 and 90 ﬁbre directions for all specimens in order to meet ISO 4288 requirements. The images collected for the surface roughness measurements were also used for surface texture processing. As before, a lc ﬁlter value of 0.8 mm was applied to the image before textural parameters were collected from the software according to ISO 25178. 4. Results and discussion All panels were manufactured successfully except for the 4 bar carbon panel. The pressure proved inadequate to wet the fabric fully and so this has been excluded from the results. All results are presented in Table 2 below. In the case of NFRP and HFRP samples an increase in pressure from 4 to 8 bar gave a small increase in average panel thickness of 0.14e0.15 mm most likely as a result of mould deﬂection due to pressure. 4.1. Results of tensile testing Results for the tensile strength of all samples are shown in Fig. 5. Mean values are plotted with error bars set at one standard deviation. The NFRP and HFRP panels produced at 8 bar had a lower tensile strength than those produced at 4 bar. This was most noticeable for the NFRP samples where tensile strength dropped by approximately 38% versus 6% for HFRP. Previous research has demonstrated variation in mechanical properties due to resin injection pressure. It was observed that doubling the injection pressure into a mould containing E-glass ﬁbre produced parts with an 11% reduction in tensile strength . This was explained by an increase in void content at the higher pressure. An investigation of glass epoxy composites via RTM using 3e5 bar found higher pressure had little effect on interlaminar shear strength but it reduced ﬂexural strength and increased storage modulus . Another study investigated void formation and tensile strength of glass vinylester composites made via RTM and found that impregnation velocity was critical to optimise these properties . In the present study higher injection pressure has had a marked effect on the tensile strength of NFRP which cannot be explained by increased void content or decreased FVF. It is possible that the higher pressure is introducing damage into the natural ﬁbres within the composite. The inclusion of carbon plies for the HFRP panel has given a useful increase in tensile strength but more signiﬁcantly the tensile modulus has almost doubled. In addition, the tensile modulus for both NFRP and HFRP have shown a small increase with injection pressure. The CFRP panel demonstrated signiﬁcantly higher tensile strength and modulus than NFRP and HFRP panels and had a tensile strength comparable with previous work with 2 2 twill T300 epoxy composite at a similar FVF (584 versus 535.2 MPa) demonstrating valid results . It is of note that while the CFRP has a speciﬁc strength of 361.6 versus 115 for a 6061 T6 aluminium both the HFRP and NFRP panels fall below this. As such careful consideration should be used if they are being applied purely for weight saving applications. 4.2. Results for vibration testing
Fig. 4. Damping ratio for different peak strain levels for 4 bar NFRP material.
The vibration testing results are summarised in Table 2. Fig. 6 highlights the average loss factor for all materials, it can be seen that in each case, damping gradually increases with strain amplitude although this is slight. The natural ﬁbre specimens have
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Table 2 Results for thickness, FVF, tensile strength and modulus, damping ratio, ﬂexural modulus, density and surface roughness. Material type
4 bar NFRP
8 bar NFRP
4 bar HFRP
8 bar HFRP
8 bar CFRP
Mean thickness (mm) Calculated FVF Tensile strength (MPa) Tensile modulus (GPa) Loss factor, εmax ¼ 104 Loss factor, εmax ¼ 103 Flexural modulus (GPa) Fibre volume fraction (%) (overall FVF of particular phase for HFRP) Density (g/cm3) Speciﬁc strength (tensile strength/density) Surface quality, Sa (mm) Surface roughness, Ra (mm)
3.12 36.2% 72.7 8.2 0.0123 0.0155 8.46 45.8%
3.27 34.6% 45.5 8.7 0.0112 0.0145 12.4 50.9% 1.22 37.3 1.89 1.51
3.29 41.2% 92.4 15.5 0.0038 0.0087 33.7 CF 77.8% (10.8%) NF 45.6% (39.3%) 1.27 72.7 1.82 1.42
3.19 49.6% 535.2 44.2 0.0024 0.0050 50.5 56.8%
1.22 59.6 2.89 2.15
3.15 43.1% 98.2 15.1 0.0048 0.0072 32.3 CF 69.2% (10.0%) NF 42.6% (36.4%) 1.27 77.3 3.02 1.80
Fig. 5. Graph of tensile strength and modulus for each material.
1.48 361.6 1.10 0.94
Fig. 7. Loss factor comparison at different strain levels.
Fig. 6. Average loss factors for all material.
considerably more damping than the carbon ﬁbre ones while the results for the hybrid specimens lie between them. It is also noticeable that the NFRP and HFRP specimens produced at high pressure have lower damping at low strain levels than those produced at low pressure. This difference reduces as the strain level increases. Fig. 7 shows the loss factor at different strain levels and Fig. 8 the ﬂexural modulus. The results demonstrate that ﬂexural modulus increases somewhat with injection pressure for both NFRP and HFRP. More signiﬁcantly the ﬂexural modulus of HFRP is approximately three times that for the NFRP, a major improvement and closer to the value of the CFRP panel (33.7 versus 50.5 GPa). In Fig. 7, the signiﬁcant contribution that natural ﬁbres make to
Fig. 8. Graph of ﬂexural modulus for each sample.
damping levels can be seen: compared with CFRP, the NFRP has more than four times the damping while the hybrid has twice as much. This is important for potential applications as an increase in damping results in a proportional decrease in resonant vibration amplitudes. It is also apparent that damping increases at higher strain levels. Some of this increase may be attributed to clamp friction and aerodynamic effects which are more signiﬁcant at higher vibration amplitude (and hence higher dynamic strains). However, sensitivity of the strain dependence to material type
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indicates the inﬂuence of other factors. For example, increasing pressure during manufacture consistently reduces damping at low strains but at higher strains, the trends in NFRP and HFRP differ. Previous studies [16,18,19,21] that have reported damping levels for natural ﬁbre and hybrid composites have provided results for tests where the peak strain was signiﬁcantly less than 400 mε and have not considered amplitude dependence. The mechanism causing sensitivity of the strain dependence to manufacturing pressure is therefore uncertain. One explanation may be the state of the interface between the ﬁbre and matrix. At higher dynamic strains, some slip may occur which provides additional friction damping. However, as the overall stiffness does not change appreciably, this effect may be relatively minor. An alternative reason may be that the higher pressure cure alters the properties of the natural ﬁbre itself such that it provides less damping at low strains. It is instructive to note that the strain dependence curve for carbon ﬁbre, whose properties are relatively stable, is a different shape, being almost linear. The vibration test results suggest that HFRPs could be a viable alternative to CFRPs in structural applications that require the composite to perform well in ﬂexure but at lower cost than a pure carbon panel. The HFRP considered contained only 2 plies of carbon ﬁbre as opposed to 14 plies in the CFRP making it signiﬁcantly cheaper. The location of carbon ﬁbre within the ﬁbre pack has a small effect on tensile properties but considerable effect on ﬂexural modulus. 4.3. Results from optical microscopy Images from optical microscopy are shown in Fig. 9, and results for ﬁbre volume fraction analysis in Table 2. All samples were free of measurable voids. The six images used for analysis were selected at random although a thorough search of all samples using microscopy revealed no areas with voids. This is a reﬂection of the wellcontrolled RTM process which was scrupulously checked for vacuum leaks before each panel was manufactured. FVF for NFRP varied from 45.8 to 50.9% which is reasonable given the heavy jute fabric and relatively coarse weave pattern. FVF for the HFRP panel was measured separately in the carbon and natural ﬁbre regions. FVF in the natural ﬁbre region was 42.6e45.6% and in the carbon region 69.2e77.8%. This may be because it was measured with a 1200 200 pixel box in the carbon region generally dominated by ﬁbre. The CFRP panel had an FVF of 56.8% which is high for a woven composite via RTM. The results demonstrate that a higher injection pressure leads to a small increase in FVF for the natural ﬁbre sections of both the NFRP (45.8e50.9%) and HFRP (42.6e45.6%). This may be counterintuitive given the small increase in thickness at high pressure although previous work has demonstrated that pressure has a signiﬁcant effect on FVF . It is likely that the compression of the ﬁbre stack via the mould and convergent design of the mould driving the ﬁbre stack towards the centre are responsible for a measured FVF which is higher than the calculated value for all samples.
4.4. Results from surface analysis After post cure the samples had visibly different surfaces, in particular the 4 bar samples demonstrated greater roughness. The results for surface quality (Sa e average height of selected area) and surface roughness (Ra e average roughness of proﬁle) are graphed in Fig. 10. The 8 bar CFRP sample had the best surface quality and reﬂected the ground surface of the steel tool. For both the NFRP and HFRP there was a signiﬁcant improvement in surface quality and roughness with an increase in pressure. It was evident that the resin rich regions of the layup had not shrunk away from the surface and in both cases the 8 bar samples got close to the 8 bar CFRP sample. 5. Conclusions Tensile strength reduced with increasing injection pressure for NFRP (72.7 MPa at 4 bar, 45.5 MPa at 8 bar) and HFRP (98.4 MPa at 4 bar, 92.4 MPa at 8 bar). This could not be explained by measured FVF which actually increased with pressure or voidage which remained at 0%. It is most likely as result of pressure induced damage to the jute ﬁbres. The HFRP samples demonstrated a useful increase in tensile strength over NFRP at both pressures although strength was well short of CFRP (535.2 MPa). The tensile modulus for HFRP (15.1 GPa) was almost double that for NFRP (8.2 GPa) and one third of CFRP (44.2 GPa). There was a signiﬁcant increase in damping for NFRP and HFRP versus CFRP. Higher pressures appear to reduce the damping ratio but also change the strain dependence. This may be due to alterations in the ﬁbre-matrix bond. The loss factor at small strains (104) reduced slightly with increasing pressure for NFRP (0.0123 at 4 bar, 0.0112 at 8 bar) and HFRP (0.0048 at 4 bar, 0.0038 at 8 bar) but all values were greater than CFRP (0.0024). At high strains
Fig. 10. Surface quality (Sa) and roughness (Ra)for all samples.
Fig. 9. Typical ﬁbre volume fraction optical microscopy images for a) 4 bar NFRP, b) 8 bar NFRP, c) 4 bar HFRP, d) 8 bar HFRP, e) 8 bar CFRP.
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(103) the loss factor decreases for NFRP (0.0155e0.0145) and increases for the HFRP (0.0072e0.0087) with increasing pressure. The ﬂexural modulus of the HFRP (32.3 GPa at 4 bar and 33.7 GPa at 8 bar) was signiﬁcantly greater than NFRP (8.5 GPa at 4 bar and 12.4 GPa at 8 bar) and approaching CFRP (50.5 GPa). In ﬂexure, the increase in damping from using HFRP is proportionally greater than the reduction in modulus so resonant vibrations would be lower for the same applied forcing. NFRP had a low density of 1.22 g/cm3 compared with HFRP (1.27 g/cm3) and CFRP (1.48 g/cm3) which did not change with pressure. However, pressure had a marked effect on surface roughness and quality. For NFRP (Ra ¼ 2.15 mm at 4 bar, 1.51 mm at 8 bar) and HFRP (Ra ¼ 1.80 mm at 4 bar, 1.42 mm at 8 bar) an increase in pressure improved the surface properties and prevented read through of the weave pattern. Neither the NFRP (Ra ¼ 1.51 mm) or HFRP (Ra ¼ 1.42 mm) samples were able to match the CFRP (Ra ¼ 0.94 mm). Hybridisation of low cost, sustainable jute with carbon ﬁbre offers a more sustainable and economic alternative to CFRPs with excellent damping properties. Acknowledgements The authors would like to acknowledge Innovate UK (101798) for contributing to this work. References  Howarth J, Mareddy SS, Mativenga PT. Energy intensity and environmental analysis of mechanical recycling of carbon ﬁbre composite. J Clean Prod 2014;81:46e50.  Meredith J, Coles SR, Powe R, Collings E, Cozien-Cazuc S, Weager B, et al. On the static and dynamic properties of ﬂax and Cordenka epoxy composites. Compos Sci Technol 2013;80(0):31e8.  Saheb DN, Jog J. Natural ﬁber polymer composites: a review. Adv Polym Technol 1999;18(4):351e63.  Pimenta S, Pinho ST. Recycling carbon ﬁbre reinforced polymers for structural applications: technology review and market outlook. Waste Manag 2011;31(2):378e92.  Meredith J, Cozien-Cazuc S, Collings E, Carter S, Alsop S, Lever J, et al. Recycled carbon ﬁbre for high performance energy absorption. Compos Sci Technol 2012;72(6):688e95.  Li X, Bai R, McKechnie J. Environmental and ﬁnancial performance of mechanical recycling of carbon ﬁbre reinforced polymers and comparison with conventional disposal routes. J Clean Prod 2016;127:451e60.  Turner TA, Pickering SJ, Warrior NA. Development of recycled carbon ﬁbre moulding compounds e preparation of waste composites. Compos Part B Eng 2011;42(3):517e25.  Faruk, O., A.K. Bledzki, H.-P. Fink, M. Sain,Biocomposites reinforced with natural ﬁbers: 2000e2010. Progress in Polymer Science. 37(11): p. 1552e1596.  Jawaid M, Abdul Khalil HPS. Cellulosic/synthetic ﬁbre reinforced polymer hybrid composites: a review. Carbohydr Polym 2011;86(1):1e18.  Dhakal HN, Zhang ZY, Guthrie R, MacMullen J, Bennett N. Development of ﬂax/carbon ﬁbre hybrid composites for enhanced properties. Carbohydr Polym 2013;96(1):1e8.  Patel VA, Vasoya PJ, Bhuva BD, Parsania PH. Preparation and physicochemical study of hybrid glass-jute (treated and untreated) bisphenol-C-based mixed epoxy phenolic resin composites. Polymer-Plastics Technol Eng 2008;47(8):
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