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The printing conditions in Fused Deposition Modelling (FDM) affect the amount of induced residual stresses within the printed part and its dimensional accuracy. Among the thermoplastic feedstock for FDM, semi-crystalline polymers are more prone to part distortion due to crystallisation. Therefore, this study aims to numerically investigate the behaviour of semi-crystalline polymer under various FDM printing conditions (namely print speed and ambient temperature) and the resultant residual stress and warpage in the printed parts. For this, the coefficient of thermal expansion (CTE) and the thermo-mechanical properties of the polymer under study (polypropylene), and the crystallisation kinetics are coupled with the evolving temperature and time during printing. The values of residual stress and warpage are calculated and compared for the bottom and top layers of the samples. From the results, it was observed that increasing the nozzle speed from 30 mm/s to 60 mm/s resulted in the bottom and top layers exhibiting a 15% and 13% decrease in residual stress, respectively. Similarly, a drop in warpage (~30%) was observed for both layers. The reduction in residual stress and warpage with increased printing speed is attributed to the improved heat transfer between the deposited roads and the reduced cooling rate. Increasing the ambient temperature from 25 °C to 75 °C resulted in a 2% and 3% decrease in residual stress in the bottom and top layers, respectively. In terms of warpage, an insignificant increase (~1%) was observed in both top and bottom layers. This is explained by the counter effects of reduced thermal gradients (i.e., lower cooling rate) and increased crystallisation on the overall amount of residual stress and warpage. 3D scanning of experimentally printed samples was used for verification of the simulation results, and good agreement between these is reported.

Residual stresses and warpage adversely affect the dimensional accuracy and performance of 3D-printed semi-crystalline polymers in Fused Deposition Modelling (FDM). One of the main challenges in FDM is to understand and relate the impact of printing conditions on part distortion for optimizing the 3D-printing process to achieve good print quality. Hence, the effect of various printing parameters, particularly print bed temperature, layer bonding, layer thickness and raster pattern, on built-up residual stresses and warpage is simulated in this work, by building a relationship between the crystallisation kinetics, viscoelastic and thermo-mechanical properties of the polymer in relation to changes in temperature during FDM using element activation in COMSOL. To the best of our knowledge, this is a novel approach for quantitative prediction of part distortion in FDM of semi-crystalline polymers under various printing conditions. Based on the simulation results, it is observed that a decrease in layer thickness from 0.5 mm to 0.1 mm results in an 89% drop in warpage and a reduction in residual stress of 24%. Applying a line raster pattern reduces warpage and residual stresses by 16% and 36%, respectively in comparison with a zigzag raster pattern. Very good agreement is observed between simulation and experimental results for warpage under various printing conditions. The results of this study can be used to predict and/or minimise part distortion in a semi-crystalline, 3D-printed polymer by simulating the effect of printing parameters on residual stresses during FDM.

Variations in mould shrinkage when using organic and inorganic pigments in semicrystalline polymers is a well-known phenomenon within industry. These differences in mould shrinkage are thought to be caused by the presence of the pigments acting as nucleating agents, altering the crystallisation of semicrystalline polymers. These shrinkage variations can give rise to problems in obtaining the correct interference fit between parts and can cause issues in automated equipment such as filling lines. It has been previously reported that the onset temperature of crystallisation measured via DSC (differential scanning calorimetry) can be used to predict shrinkage when a variety of neat pigments are added to un-nucleated PP (polypropylene). However, the shrinkage and crystallisation behaviour of masterbatch pigments, which are widely used industrially is poorly understood. To better understand the influence of masterbatch pigments on crystallisation and shrinkage behaviour, injection moulded samples were prepared using variety of reds, whites, and purple commercial-masterbatch pigments with PP. The crystallisation kinetics and crystallinity were studied using DSC, LPOM (Linkam hot stage polarising optical microscopy), XRD (X-ray diffraction), and FTIR (Fourier transform infrared spectroscopy). The morphology was investigated via LPOM and SEM (scanning electron microscopy). A clear correlation was observed between the crystallisation onset temperature measured using DSC and the recorded shrinkage. A strong relationship was also observed between the percentage crystallinity measured using FTIR and shrinkage. Quinacridone and pyrrole based red and purple pigments were found to act as strong nucleating agents, with the pyrrole based red pigment also acting as β nucleator in PP. The white pigments were found to have less influence on the nucleation behaviour. For the pigments which induced the largest variation in shrinkage, a higher rate of nucleation and proportionally smaller spherulitic diameter was observed by DSC, SEM, and LPOM.

In this study, high-performance flexible strain sensors based on carbon nanotube (CNT) and graphene nanoplatelet (GNP) filled thermoplastic polyurethane (TPU) composites were fabricated via Fused Filament Fabrication (FFF) 3D printing. The introduction of GNPs generated a more complete conductive network of the composites due to the improved nanofiller dispersion. Due to the synergy of CNTs and GNPs, the printed CNT/GNP(3:1)/TPU sensor shows higher sensitivity (GF = 136327.4 at 250% strain), larger detectable range (0–250% strain), and better stability (3000 cycles) compared with the CNT/TPU and GNP/TPU sensors with a nanofiller content of 2 wt%. Furthermore, the printed sensors can accurately detect strains at different frequencies (0.01–1 Hz). A modelling study based on tunneling theory was conducted to analysis the strain sensing mechanism, and the theoretical results agreed well with the experimental data. The capability of the sensors in monitoring physiological activities and speech recognition has also been demonstrated.

Semi-crystalline polymers develop higher amounts of residual stress and part distortion (warpage) compared to amorphous polymers due to their crystalline nature. Additionally, the FDM processing parameters such as ambient temperature play an important role in the resulting residual stresses and part distortion of the printed part. Hence, in this study, the effect of ambient temperature on the in-built residual stresses and warpage of amorphous acrylonitrile-butadiene-styrene (ABS) and semi-crystalline polypropylene (PP) polymers was investigated. From the results, it was observed that increasing the ambient temperature from 50 °C to 75 °C and further to 120 °C resulted in 0.22-KPa and 0.37-KPa decreases in residual stress of ABS, but no significant change in the amount of warpage. For PP, increasing ambient temperature from 50 °C to 75 °C led to a more considerable decrease in residual stress (0.5 MPa) and about 3% increase in warpage. Further increasing to 120 °C resulted in a noticeable 2 MPa decrease in residual stress and a 3.4% increase in warpage. Reduction in residual stress in both ABS and PP as a result of increasing ambient temperature was due to the reduced thermal gradients. The enhanced warpage in PP with increase in ambient temperature, despite the reduction in residual stress, was ascribed to crystallization and shrinkage.

Tufting has been shown to improve the mechanical properties of composites. Unlike other published works which rely on commercially available materials, for this study, continuous polymer yarns with diameters ranging from 160 μm to 720 μm of unfilled PPSU and PPSU nanocomposites with 1 wt.% of carbon nanotubes (CNT) were prepared using a twin-screw extruder. The tensile properties of these yarns generally improved with the addition of CNT at higher values of ‘screw speed to haul-off’ ratio. This effect is correlated with the yarn draw down ratio and attributed to the nanofiller orientation induced in the thermoplastic matrix. The fibres exhibited as much as a 23% increase in Ultimate Tensile Strength (UTS) for the same parameter set when loaded with CNT. Depending on filler and processing parameters set, yarns varied in UTS from 96.4 MPa to 206.2 MPa for unfilled PPSU and PPSU-CNT, respectively.

In this study, PEEK nanocomposites with 0, 0.5, 1, and 2wt% IF-WS2 were manufactured by injection moulding and Fused Deposition Modelling (FDM). To compare the impact of the two processing methods and the incorporated nanoparticles on the morphology, crystallization and final mechanical properties of the nanocomposites, SEM, DSC and tensile testing were performed. In general, a good distribution of nanoparticles was observed in PEEK, although larger agglomerates were visible at 2 wt% IF-WS2. The crystallization degree of PEEK increased with increasing loading of IF-WS2 nanoparticles up to 1wt% and then declined at 2 wt%, due to lower level of particle dispersion in this sample. The 3D printed samples showed slightly higher crystallinity at each IF-WS2 loading in relation to the injection moulded samples and extruded filaments, because of multiple reheating effect from subsequent layer deposition during FDM, causing recrystallization. In general, incorporation of IF-WS2 nanoparticles increased the mechanical properties of pure PEEK in both 3D printed and injection moulded samples. However, this increment was more noticeable in the 3D-printed nanocomposite samples, resulting in smaller gap between the mechanical properties of the 3D-printed samples and the injection moulded counterparts, in respect to pure PEEK, particularly at 1 wt% IF-WS2. This effect is ascribed to the increased inter-layer bonding of PEEK in the presence of IF-WS2 nanoparticles in FDM. In general, the lower mechanical properties of the 3D printed samples compared with the injection moulded ones are ascribed to poor interlayer bonding between the deposited layers and the presence of voids. However, addition of just 1 wt% of IF-WS2 nanoparticles into PEEK increased the tensile strength and Young’s modulus of the FDM PEEK materials to similar levels to those achieved for unfilled injection moulded PEEK. Therefore, incorporation of IF-WS2 nanoparticles into PEEK is a useful strategy to improve the mechanical performance of FDM PEEK.

Through-thickness stitching, in the form of tufting, has been shown to be a potentially successful method of improving resistance to delamination. Tufting is a single-sided stitching technique that involves the insertion of a yarn through a fabric, in the z-direction. However, further research into the development of a tailored tufting yarn could yield a greater improvement in the mechanical properties of the overall composite. Unlike other published works which rely on commercially available materials, for this study four thermoplastic yarns were produced from polyetheretherketone, polysulfone, polyethersulfone and polyphenylsulfone. Their ability to be tufted into a composite was examined along with their influence on the overall mechanical properties of the composite.

This paper extends the applications of a novel and fully automated multi-scale computational homogenisation framework, originally proposed by the authors (Ullah et al. (2017)) for unidirectional and 2D-textile composites, to 3D-textile composites. 3D-textile composites offer many advantages over 2D-textile composites but their highly complicated and unpredictable post-cured geometries make their design very challenging. Accurate computational models are therefore essential to the development of these materials. The computational framework described in this paper possesses a variety of novel features which have never been tried for this class of composites and can potentially help to fully automatise and improve their design process. A unified approach is used to impose the representative volume element boundary conditions, which allows convenient switching between linear displacement, uniform traction and periodic boundary conditions. The computational framework is implemented using hierarchic basis functions of arbitrary polynomial order, which allows one to increase the order of approximation without changing the finite element mesh. The yarns' principal directions, required for the transversely isotropic material model are calculated using a potential flow analysis along these yarns. This feature is very useful for 3D-textile composites and can accurately determine fibres’ directions even in the case of very deformed yarns. A numerical example from literature consisting of a 3D-orthogonal woven composite is used to demonstrate the correct implementation and performance of the developed computational framework. Also, the developed computational framework is used to perform a comparative study of the homogenised mechanical properties of five 3D-textile composites with different yarn architectures.

The alternately-organized poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) multilayer materials were prepared through layer-multiplying coextrusion. With the multiplication of layers, the thickness of each layer was reduced in proportion and the layer interfaces were enriched generating a broader and more continuous thermal transition temperature (Ttrans) from PVDF to PMMA layers as mapped by in-situ thermal analysis. The low-Ttrans side originated from the glass transition of PMMA, whereas the high-Ttrans side was dominated by the melting of PVDF crystals based on the heating curves of DMA and DSC. The dielectric spectroscopy and 2D-SAXS were performed and demonstrated that the compositional diffusion not only broadened the relaxation distribution of amorphous chains, but also strengthened the interaction between amorphous and crystalline domains. Therefore, a unique multilayer network, where the crystals in PVDF layers acting as physical networks connected the neighboring amorphous layers, was fabricated and its potential application in obtaining multi-shape memory effect (MSME) was disclosed for the first time. The results exhibited that the 1024-layer specimen owned a better triple- and quadruple-shape memory capacity than conventional blend which possessed the same compositions and a similar Ttrans range. The latter one even failed to successively memorize more than two temporary shapes. A possible mechanism was proposed through polarized IR and creeping-recovery measurements. Higher phase continuity which benefited for the stress transfer was revealed to play a significant role in strengthening the shape-fixing and -recovering ability during each shape-memory progress. Accordingly, a new physically-compounding strategy was addressed to achieve outstanding MSME for meeting complex demands in smart applications.

Multi-walled carbon nanotube (MWCNTs) and graphene nanoplatelet (GNPs) filled high-density polyethylene (HDPE) composites with randomly dispersed (DCN) and segregated (SCN) conductive network structures were fabricated by a solution-assisted mixing method. The damage self-sensing behavior of the resulting composites was investigated via in situ electrical-mechanical measurements. The results show that nanofiller type and conductive network structure significantly influence the damage self-sensing behavior of the composites. The relative resistance change (RRC) of HDPE/MWCNT composites during tensile deformation can be divided into three stages. Compared to HDPE/MWCNT composites with DCN structures, more robust conductive networks are formed in SCN structures, resulting in smaller RRC. The self-damage sensing behavior of all HDPE/GNP composites follows a similar trend, starting with a quasi-linear increase in RRC followed by a sudden rise induced by brittle fracture of the material. Nanofiller content was also found to affect the damage self-sensing behavior of the composites with a higher nanofiller loading corresponding to a lower damage sensing sensitivity. A modeling study based on tunneling theory was also conducted to further analyze the mechanism. In addition, the tensile properties of the composites were measured. This study provides some important information for development of smart structural materials.

Polyetheretherketone (PEEK) is a biocompatible polymer widely used for biomedical applications. Because it is biologically inert, bioactive phases, such as nano-hydroxyapatite (HA), have been added to PEEK in order to improve its bioactivity. 3D printing (3DP) technologies are being increasingly used today to manufacture patient specific devices and implants. However, processing of PEEK is challenging due to its high melting point which is above 340 °C. In this study, PEEK-based filaments containing 10 wt% of pure nano-HA, strontium (Sr)- doped nano-HA and Zinc (Zn)-doped nano-HA were produced via hot-melt extrusion and subsequently 3D printed via fused deposition modelling (FDM), following an initial optimization process. The raw materials, extruded filaments and 3D printed samples were characterized in terms of physicochemical, thermal and morphological analysis. Moreover, the mechanical performance of 3D printed specimens was assessed via tensile tensing. Although an increase in the melting point and a reduction in crystallization temperature was observed with the addition of HA and doped HA to pure PEEK, there was no noticeable increase in the degree of crystallinity. Regarding the mechanical behavior, no significant differences were detected following the addition of the inorganic phases to the polymeric matrix, although a small reduction in the ultimate tensile strength (~14%) and Young's modulus (~5%) in PEEK/HA was observed in comparison to pure PEEK. Moreover, in vitro bioactivity of 3D printed samples was evaluated via a simulated body fluid immersion test for up to 28 days; the formation of apatite was observed on the surfaces of sample surfaces containing HA, SrHA and ZnHA. These results indicate the potential to produce bioactive, 3DP PEEK composites for challenging applications such as in craniofacial bone repair.

Although 3D woven composites have exceptional out-of-plane properties, there is a lack of understanding for these materials in crash application in automotive and aerospace industries. To encourage the use of 3D wovens in crashworthy automotive structures, knowledge must be gained so that designers can adjust the highly flexible weave parameters to create tailor-made performance materials. Here we show that fabric pick density causes large changes in progressive failure modes and associated energy absorption, particularly in the dynamic regime, where the quasi-static to dynamic energy absorption loss typical of composites is completely removed. Compression and flexure properties, which are known to be linked to crash performance in composites, are also investigated for these 3D woven layer-to-layer interlock carbon-epoxy composite structures. 3D fabric preforms are manufactured in three different pick densities: 4, 10 & 16 wefts/cm. With a constant warp density of 12 warps/cm from carbon fibres. Increasing the pick density improved specific energy absorption (SEA) even in relatively inefficient progressive failure modes like folding, which has not previously observed in composite materials. SEA values up to 104 J/g (quasi-static) and 93 J/g (dynamic) are recorded. This work shows that minor weft direction (transverse) weave changes can lead to sizeable improvements in warp direction (axial) energy absorption without fundamentally redesigning the weave architecture.

Fused deposition modelling (FDM), one of the most popular additive manufacturing (AM) technique, was used to investigate the elastic properties of 3D printed polyamide-based polymer composites structures. The aim of this work is to study the mechanical properties of continuous carbon fibre reinforced polyamide polymer composite samples using tensile and flexural testing by varying the fibre volume contents with applying pressure, temperature and holding the samples for 60 minutes in the platen press. The results show that the strength and stiffness increase with the increase in fibre volume content (fraction). Hot pressed samples exhibit the increase in tensile strength by about 27 % and elastic modulus by 11 % because of increasing the fibre volume fraction from 29 % to 35%. Synergetic effect of both short and continuous carbon fibre was also studied, and it was observed that the tensile properties were higher for the samples reinforced with short and continuous fibre than only continuous fibre polymer composites. Effects of voids on 3D printed continuous carbon fibre-reinforced polymer composites were quantified. A microstructure study of the 3D printed polymer composites was carried out using scanning electron microscope (SEM). Following SEM analysis on the tested specimens, it was observed that there is a strong correlation between the mechanical properties and the microstructure. Fibre volume fraction was measured using ASTM D-3171 using acid digestion method to determine the amount of fibre contents before and after hot pressing (compaction). From Micro- Computed Tomography (µCT) it was confirmed that hot pressing reduces the void content which in return increases the strength and modulus.

3D woven composites show significantly improved out-of-plane properties over traditional 2D laminates. This high through-thickness reinforcement is desirable in crashworthiness applications where crushing energy can be increased by composites’ improved interlaminar toughness. However, their use in practical applications is stunted by the poor understanding of how small variations in weave parameters, whether intended or not, affect the performance of these materials. Here, we demonstrate that small changes in textile properties, in this case pick density and float length have a knock-on effect that can greatly improve or diminish the crush performance of a 3D woven layer-to-layer structural fabric. Quasi-static and dynamic energy absorption values up to approximately 95J/g and 92J/g respectively are achieved. Crush performance is investigated on omega-shaped coupons, under both quasi-static and dynamic loading conditions with crush rates between 2mm/min and 8.5m/s. The failure mechanisms present during progressive crush under quasi-static loading transitions between more expected brittle dominated failure and ductile dominated failure, which is more typical of metals under similar loading conditions. Whereas when dynamic loading is considered, the materials present a more typical splaying failure event. As a result, additional exploration of the three-point bending response of these varied architectures is presented as a means of further explaining the interplay between lamina bending and progressive folding/micro-buckling in these materials. The effect of the weave’s architectural alterations on physical composite properties such as weight, density and conformability to shape is also investigated.

Diglycidyl ethers of bisphenol-A (DGEBA)/methyl tetrahydrophthalic anhydride/polyethersulphone (PES) blends are prepared as matrix resins for thermally conductive composites using graphite nanoplatelets (GNPs) as the conductive component. The epoxy/PES blends form a network structure via reaction-induced phase separation (RIPS) during the curing process, and the GNPs are selectively localized in the PES phase and at the interface leading to a three-dimensional continuous filler network. With this unique structure, the thermal conductivity of the epoxy/PES/10 wt% GNPs composite is increased to 0.709 W m−1 K−1, which is nearly 3.5 times that of the pure epoxy or a 52% increase compared to the epoxy/GNP composite without PES. In addition, it is found that the impact strength of the composite relative to the unfilled material is also improved.

The gas-barrier properties of semicrystalline polymers can be significantly adjusted by tailoring the arrangement of their impermeable crystalline lamellae. In particular, the highest barrier efficiency is achieved when the arrangement of the lamellae stacks is perpendicular to the direction of gas diffusion. The work reported on in this paper provides a strategy to achieve such a lamellar arrangement with the aid of a self-assembly nucleator and a two-dimensional (2D) interface. PT (PLA + TMC-300) and PTG (PLA + TMC-300 + graphene) were coextruded to form alternating PT/PTG multilayers with different layer numbers. During isothermal treatment at 140 °C, the dissolved TMC-300 first self-assembles into solid-state fibrils that are perpendicular to the 2D PT/PTG-layered interface due to the induced effects of the graphene. Subsequently, these TMC-300 fibrils induce the epitaxial growth of PLA lamellae with a normal parallel to the fibrillar direction of the TMC-300. In this way, a designed arrangement where...

In this paper, reduced graphene oxide (rGO), decorated with immobilized carbon nanotubes (CNTs), was introduced into a thermoplastic polyurethane (TPU) matrix to obtain a conductive nanocomposite with 2 wt% nanofillers content. Hot-pressed composite sheets were then biaxially stretched into films to efficiently fabricate flexible strain sensors. The biaxial stretching process was shown to promote secondary dispersion and parallel alignment of the nanofillers, resulting in the sensors exhibited significantly higher sensitivity (GF = 150 for the rGO/TPU4×4 sensor with a stretching ratio of 4 × 4 relative to GF = 3.5 for the rGO/TPU1×1 sensor at 30% strain). Furthermore, due to the synergy of the CNTs and rGO nanoparticles, the rGO/CNT/TPU4×4 sensor had a lower resistivity (5.62 × 104 Ω·m), wider monitoring range (0.3 ∼ 400% strain), and higher stability compared with the rGO/TPU4×4 sensor. The ability of the sensor to recognize body movements and physiological activities was also shown.

In this study, multi-walled carbon nanotube (MWCNTs) and graphene nanoplatelet (GNPs) filled high density polyethylene (HDPE) composites with dispersed and segregated network structures were prepared by solution-assisted mixing. Simultaneous DC conductivity and differential scanning calorimetry (DSC) was used to measure electrical conductivity during the composite thermal phase transitions. It was found that the conductive network is deformed during melting and rebuilt again during annealing due to the re-agglomeration of nanofillers. The re-building of the structure is significantly affected by the original network structure and by the shape and loading of the nanofillers. Both deformation and reorganisation of the network lead to a drastic changes in the conductivity of composites. The crystallization process also affects the conductive network to some extent and the subsequent volume shrinkage of the polymeric matrix after crystallization results in a further decrease in the resistivity of HDPE/GNP composites. Classical electrical percolation theory combined with a kinetic equation is used to describe the conductivity recovery of composites during annealing, and the results are found to be in good agreement with the experimental data.

Different dimensional carbon nanofillers, such as carbon nanotubes (CNTs), graphene nanoplatelets (GNPs) and carbon black (CB), are often incorporated into polymers in a hybrid form to fabricate multifunctional nanocomposites. In this paper, biaxial stretching of binary carbon nanofiller reinforced high density polyethylene (HDPE) nanocomposites was carried out at various stretching ratios in order to investigate the influence of carbon nanofillers on material deformation behaviour and the influence of biaxial deformation on the structure and properties of the deformed material. It is shown that the strain hardening behaviour of nanocomposites upon biaxial stretching is gradually enhanced with increasing aspect ratios of the nanofillers. The deagglomeration and reorientation of nanofillers in the polymer matrix can be observed during deformation. Furthermore, biaxial stretching significantly affects the final tensile, electrical and barrier properties of the deformed nanocomposites, depending on the components of carbon nanofillers introduced. The stretched HDPE/GNP/CNT and HDPE/GNP/CB nanocomposites exhibit greatly improved tensile and barrier properties.

Improvement of the mechanical properties of FFF 3D printed CF/PEEK composites was achieved by printing under favorable crystallization conditions. It was possible to improve the layer-layer tensile strength more than fivefold from 6.96 MPa to 36.28 MPa by printing in a specially customised, low cost printer operated with a heated print chamber at 230℃. The influence of the chamber temperature on the mechanical and crystalline structure was investigated to determine the best conditions. A maximum flexural modulus of 14 946 MPa and flexural stress at break of 248.9 MPa were achieved. A proof of concept study involved the 3DP of a CF/PEEK mould tooling insert for injection moulding. This insert replaced a costly traditional metal insert to print short production runs of ABS and HIPS polymers. This work offers a low cost and rapid means to produce effective tooling inserts for the injection moulding industry.

This paper shows modifying binder float-length, an easily adjustable parameter, there is significant influence on impact energy absorption, impact resistance and damage tolerance in 3D-woven layer-to-layer carbon/epoxy composites. Binder float-length was changed by modifying textile design without changing loom set-up. Three float lengths (1/2, 2/2 and 3/2) in consistent architecture were woven using constant warp density. Out-of-plane drop-weight impact was performed at 32 J&42 J energy and showed increases in float-length decreased energy absorption by 49% and 32% respectively in warp direction with no significant changes in weft. Conversely, in axial impact tests, higher float length showed higher crush force efficiency and specific energy absorption. This study has also concluded, in both out-of-plane and axial impact scenarios, higher float lengths increase damage tolerance. This work has expanded how minor changes in preform parameters can significantly change both out-of-plane and in-plane impact performance of 3D-woven composites without increased manufacturing cost, time or complexity.

Sewing has attracted a great deal of attention as a method to improve the delamination performance of carbon fibre laminate composites. A critical factor in the commercial exploitation of the technology is the development of a suitable sewing yarn, with other researchers looking at a variety of commercial fibres such as Kevlar. It would appear from the literature that fundamental research into what properties a suitable yarn should have has not been carried out. In this work, a commercial fibre designed for sewing applications was sourced from Toho Tenax (Germany) and used as a control. Unlike in published works, rather than relying on yarns which could be purchased commercially, selection criteria were drawn up and promising polymers identified and then extruded as a yarn. Based on the selection criteria, thermoplastic yarns were extruded using polysulfone, polyethersulfone, polyphenylsulfone and polyetheretherketone. It was found that despite the fact that the commercial fibre had much better mechanical properties as a straight fibre, when it was knotted or looped (to try and simulate the effects of sewing), there was a dramatic decrease in the mechanical properties (the ultimate tensile strength dropped by 88% due to a single knot). There was no significant change in the mechanical properties of the thermoplastic yarns. As a result, it is concluded the thermoplastic fibres created could potentially be better suited for sewing applications compared to commercial fibres such as Kevlar and further work is planned to sew the yarns and test the delamination performance.

A comparative study of unary and binary carbon nanofiller reinforced high density polyethylene (HDPE) composites with 4 wt.% nanofillers was carried out in order to assess the reinforcement effect and synergy of carbon nanofillers with different dimensions. Rheology and resistivity tests indicate that the relative effectiveness of generating rheological and conductive networks is as follows: multi-walled carbon nanotubes (MWCNTs) > carbon black (CB) > graphene nanoplatelets (GNPs), while the reinforcement effect in modulus is: GNPs > MWCNTs > CB, at the same loading. The resistivity of all the HDPE/CB/MWCNT composites is quite close to the that of HDPE/MWCNT composites, indicating CB may be a good replacement for MWCNTs considering the relatively low cost of CB. A synergistic effect in modulus is observed in the HDPE/GNP/MWCNT and HDPE/CB/MWCNT composites due to the formation of nanofiller–polymer–nanofiller network structures.

In this article, a comparative study of biaxial stretching at different stretching ratios for melt mixed high-density polyethylene (HDPE)/carbon nanofiller composites containing 4 wt% multiwalled carbon nanotubes (MWCNTs), graphene nanoplatelets (GNPs) or carbon black (CB) was conducted in order to investigate the influence of the carbon nanofillers on the processability of the material and on its final properties after processing. It is shown that the addition of carbon nanofillers results in a significant strain hardening behavior upon biaxial stretching, greatly improving the deformation stability and thus processability of the material. The reinforcement effectiveness of the nanofillers in strain hardening behavior is CB

Processing conditions can significantly influence the structure and properties of polymer nanocomposites. In the present study, melt mixed high density polyethylene (HDPE)/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared via twin-screw extrusion and then compression molded (CM). The effect of heating temperature, pressing time and cooling rate on the structure, electrical and mechanical properties of the CM nanocomposites was systematically investigated. Volume resistivity tests indicate that the nanocomposite with 2 wt.-% MWCNTs, which is in the region of the electrical percolation threshold, is very sensitive to the CM parameters such that heating temperature > pressing time > cooling rate. Generally, the resistivity of nanocomposites decreases with increasing heating temperature and pressing time. Interestingly, the electrical resistivity of the rapidly cooled nanocomposite with 2 wt.-% MWCNTs is about 2 orders lower than that of the slowly cooled nanocomposite which is attributed to the lower crystallinity and smaller crystallites presenting less of an obstacle to the formation of conductive pathways. The tensile properties of the nanocomposite with 2 wt.-% MWCNTs are also influenced by the compression molding parameters to some extent, while those of the nanocomposites with higher MWCNT loading are insensitive to the changes in processing conditions. The modulus of the nanocomposites increases by about 25 to 50 % and 110 to 130 %, respectively, with the incorporation of 2 and 4 wt.-% MWCNTs, which agrees well with the theoretical values predicted from Halpin-Tsai and Mori-Tanaka models. This work has important implications for both process control and the tailoring of electrical and mechanical properties in the commercial manufacture of conductive HDPE/MWCNT nanocomposites.

Due to the complex structure of 3D woven fabrics, their mechanical properties and failure modes tend to deviate from that of conventional equivalent 2D woven and unidirectional fabric composites . A lack of in-depth understanding of the relationships between the weave parameters and mechanical properties of 3D woven composite materials has inspired this investigation. This paper presents a comprehensive experimental study of the effect of pick density on the mechanical properties such as tension, compression, short beam shear and Izod impact energy in 3D layer-to-layer glass/epoxy woven composite structures. The 3D woven fabrics are manufactured in two different pick density extremes: 4 and 14 picks/cm with a constant end density of 12 ends/cm from Hybon 2002 E glass fibres. The mechanical properties were improved by the decrease in waviness and misalignment of the load carrying fibres. An interesting observation which has never been seen before was made in lower pick density specimens under tensile loading. Severe diagonal crack propagation because of strain-induced shear failure was observed and attributed to influence of the movement of misaligned yarns with increasing tensile strain . This study has helped in deriving a relationship between the weave parameters and the in-plane mechanical properties and expected failure in this 3D woven layer-to-layer warp interlock glass fabric.

Yarn diameters ranging from 160 µm to 720 µm of unfilled PPSU and PPSU nanocomposites with 1 wt.% of either carbon nanotubes (CNT) or carbon nanofibers (CNF) were prepared using a twin screw compounder. The tensile properties of these yarns generally improve with the addition of CNT or CNF at higher values of screw speed-to-haul off ratio. This effect is correlated with the yarn draw down ratio and attributed to nanofiller orientation and crystallinity induced in thermoplastic matrix. The fibres have as much as a 23% increase in Ultimate Tensile Strength (UTS) for the same parameter set when loaded with CNT, while the greatest increase observed for larger particle size fillers CNF is just 3.77%. Depending on filler and processing parameters set, yarns varied in UTS from 24.84MPa to 206.23MPa for unfilled PPSU and PPSU-CNT, respectively.

In this study in-plane mechanical properties of continuous carbon fibre reinforced thermoplastic polyamide composite manufactured using a Markforged Two 3D printing system was evaluated and compared against predicted values from classical laminated-plate theory. Strength, stiffness and Poisson’s ratio of the composite specimens were measured using tensile testing both in longitudinal and transverse direction and the shear properties were also measured. The influence of fibre orientation on mechanical properties was investigated and were compared with that of non-reinforced nylon samples and known material property values from literature. It was determined that the modulus of elasticity and tensile strength values were significantly improved to 603.43 MPa and 85 GPa respectively as compare to unreinforced nylon specimens. Furthermore, cross-sectional micrographs of specimens are analysed to observe the microstructure and fracture mechanism of the 3D printed composite. Experimentally determined values were used to predict the behaviour of the materials in different orientation using classical laminated-plate theory on the commercially available LAP (Laminated Analysis programme) software. The model developed will allow the designers to predict the elastic (mechanical) properties of 3D printed parts reinforced with fibre for components which require specific mechanical properties.

This paper reports experimental investigations of 3D woven carbon/epoxy composites on quasi-static and dynamic tensile properties in the longitudinal (warp) and transverse (weft) directions. Firstly, quasi-static tests were conducted to determine a baseline tensile strength and to find out the adequate specimen geometry required for dynamic testing. Secondly, dynamic tensile properties at intermediate strain rates (nominal strain rates from 0.1 to 200 s-1) were investigated alongside the corresponding failure mechanisms. Detailed information on failure patterns is obtained with strain field measurements from Digital Image Correlation (DIC) and CT scans. The results show that 3D woven composites are strain rate insensitive and the crack initiation is located near weft yarns and binding interlacement points due to the presence of resin rich areas.