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In recent years, the synthetic cores of sandwich panels have experienced an increase in demand to be replaced by environmentally friendly materials. Furthermore, with the stringent fire protocols introduced in the building codes due to recent fire incidents around the world, it is imperative to conduct fire performance studies for all structural materials. The mechanical performances of the different core structures in sandwich panels have been extensively studied and documented in the literature, although the influence of those core structures on the fire reaction properties has not yet been fully understood. The aim of this work is to experimentally investigate, for the first time, the effects of the core structures, namely, corrugated and honeycomb cores manufactured from flax reinforced polymeric composites and radiata pine plywood, on their flammability. A bench-scale cone calorimeter has been employed to measure the fire reaction properties of the two types of materials along with the subsequent effects of the core structures. The orientations of the cores were observed to significantly impact the performances of the samples under fire. The honeycomb cores, with the open cells exposed to the heat flux, generally had better fire performance compared to those of the corrugated cores with higher time to ignition (10 s or more) and time to peak heat release (65 s or more), having almost similar initial masses and peak heat release rates. Furthermore, among the two material systems, the plywood cores outperformed the flax-FRPP cores, specifically in ignition time, smoke production, total heat release and peak heat release rate. The results helped in confirming that the honeycomb cores have overall better fire performance and the use of plywood as the core material is viable even when fire is involved.

The demand for stretchable, soft and wearable multifunctional devices based on conductive polymer composites is rapidly growing because of their compelling applications, including physical and physiological measurements on the human body. This paper reports a simple and cost-effective technique to fabricate electrically conductive flexible films with graphite (GRP) flakes and an elastomer, silicone rubber (SR). The mechanical, thermal, electromechanical and electrothermal characterisations of the composites were conducted. While the dynamic electromechanical response of the composites demonstrated their potential applications as wearable sensors, the electrothermal characteristics of the devices showed their suitability to be used as flexible protective circuits and flexible temperature sensors. The synergistic effect of GRP flakes with carbon black (CB) particles was also studied. GRP-SR composites showed a thermal conductivity (TC) of 1.08 W m−1 K−1 and were thermally stable up to up to 300 °C. The good TC and thermal stability along with their deformability, make them suitable to be used as thermal interface devices in arbitrarily shaped surfaces.

To minimize the surface roughness and delamination problems during the end milling of natural fiber reinforced composites (NFRCs), it is essential to understand the effects of the machining paramet...

The present work focuses on creating a better understanding of the possibility of forming specific geometric structures from plywood and subsequently develops an improved equation for representing ...

Fabrication of electrically conductive yarns (glass, flax and polypropylene fibers) coated with graphene nanoparticles (GNP) were characterized for their mechanical properties and compared with their electrical properties. The composites were produced with the use of polymeric binders (epoxy resin and thermoplastic starch) and two different dip-coating methodologies were developed to create the coating layers. Technique-1 involved coating of binder and then GNP layer whereas Technique-2 had a mixture of binder and GNP in the predetermined ratio, which was coated on the yarns. The mechanism of adhesion varies or influences on a number of factors such as the nature of the fiber surface, coating method and effective binder. Tensile properties of the yarns were measured by an appropriate standard, and the highest tensile strength was noticed with epoxy-based glass fiber samples as 222 MPa followed by flax fiber samples as 206 MPa. The composites of starch-based showed poor mechanical performance compared to those of epoxy ones. This was due to poor adhesion between the surface and starch layer (interphase) where the Van der Wall’s force was quite low. Electrical conductivity, glass fiber yarns with epoxy binder were identified to have the highest electrical conductivity of 0.1 S.cm−1 among other samples.

In this work, the fire reaction properties of flax-polypropylene (PP) composites were investigated at multiple sample angles both experimentally and numerically under two different heat flux conditions (35 and 50 kW/m2) in the cone calorimeter environment. An innovative testing setup which can accommodate a wide range of angles between 0° and 90° for the sample angle frame was developed to perform cone calorimeter tests at different sample angles. An advanced numerical predictive model based on the finite volume method was developed using the fire dynamics simulator (FDS) to quantify the dependency of ignition and combustion properties with sample angles. The numerical model was validated against experimental data from the cone calorimeter tests. The experimental and numerical analyses were conducted to quantify the effects of sample orientation on the different fire reaction properties i.e., ignition time, ignition temperature, burn time, heat release rate (HRR), critical heat flux, etc. The numerical method was utilised to analyse the mechanisms controlling the effect of heat convection and radiation blockage on the heating process. The study establishes that the sample orientation (with respect to the heat flux normal) has a significant influence on the fire reaction properties of natural fibre composites.

The integration of intumescent flame-retardant (IFR) additives in natural fiber-based polymer composites enhances the fire-retardant properties, but it generally has a detrimental effect on the mechanical properties, such as tensile and flexural strengths. In this work, the feasibility of graphene as a reinforcement additive and as an effective synergist for IFR-based flax-polypropylene (PP) composites was investigated. Noticeable improvements in tensile and flexural properties were achieved with the addition of graphene nanoplatelets (GNP) in the composites. Furthermore, better char-forming ability of GNP in combination with IFR was observed, suppressing HRR curves and thus, lowering the total heat release (THR). Thermogravimetric analysis (TGA) detected a reduction in the decomposition rate due to strong interfacial bonding between GNP and PP, whereas the maximum decomposition rate was observed to occur at a higher temperature. The saturation point for the IFR additive along with GNP has also been highlighted in this study. A safe and effective method of graphene encapsulation within PP using the fume-hood set-up was achieved. Finally, the effect of flame retardant on the flax–PP composite has been simulated using Fire Dynamics Simulator.

We have developed a method of converting chicken feather to high-performance flame retardant through a solution-based chemical treatment. The synergistic effect of the chicken feather fiber and loa...

A series of Fe-3 to 18 at.% Cr binary ferritic alloys were neutron irradiated side by side, in the Advanced Test Reactor (ATR) at a temperature of ∼320 °C to a dose of ∼1.8 dpa. Three types of features that form under irradiation are relevant: (i) solute clusters; (ii) α′ precipitates; and, (iii) dislocation loops. The size and number density of the precipitates and loops were measured by transmission electron microscopy (TEM) and compared to previous atom probe tomography (APT) observations. The loop density systematically decreases with increasing Cr, while the number of α′ precipitates increase at 9Cr and above. A major objective of this work is to estimate the dispersed barrier obstacle strength factors (αj) for loops, clusters and α′ precipitates, based on the combined microstructural observations and corresponding irradiation hardening measurements. Standard dispersed barrier-hardening models and computationally derived superposition rules were least square fit to determine the αj. The optimized hardening predictions are in very good agreement with experiment if mixed linear sum and root square sum superposition rules are used. Five increments of 168 h isochronal anneals of the 6Cr alloy between 300 and 400 °C coarsened the loops, while 300 h anneals of the 18Cr at 500 and 600 °C coarsened and dissolved the α′ precipitates, respectively, consistent with the Fe-Cr phase diagram.

In this research, two nano-clays, halloysite nano-tube (HNT) and layered double hydroxide (LDH), were employed to compare fire and mechanical properties of epoxy composites based on ammonium polyphosphate (APP) and each of the two nano-clays. The results showed that the combination of APP and nano-clay achieved a significant reduction (approx. 87%) in peak heat release rate of epoxy resin. The comparative analysis also demonstrated that the total heat release of the composite including HNT was approx. 18% lower than that of the LDH based composite. Moreover, HNT generated higher tensile properties in the composite. Overall, the HNT (∼1.5 USD/kg) is a more cost-effective nano-clay than LDH (∼180 USD/kg) to effectively improve the fire resistance and maintain the mechanical properties of epoxy composites.

Wearable strain sensors for various applications, such as human motion detection, soft robotics, and healthcare have recently received extensive attention. Although a number of strain sensors based on various active materials have been proposed, a simple and practical method to obtain both high stretchable and sensitive strain sensors remains challenging. This paper presents a simple, scalable and environment-friendly fabrication method for wearable strain sensors, based on wool yarns, as abundant, lightweight, and stretchable natural materials. A simple coating technique was used to achieve highly conductive wool yarns using a conductive ink. Different types of strain sensors were then fabricated by changing the shape of the active material within the elastomer to tune their sensitivity. In detail, the conductive yarns were sandwiched within the Ecoflex in the form of a straight line (CWY-1 strain sensors) or serpenoid curves (CWY-2 and CWY-3 strain sensors). The strain sensors were fully characterized up to 200% of applied tensile strain. Gauge factors of 5 and 7.75 were found within the percentage stretch ranges of 0–127 and 127–200 %, respectively, for the CWY-1 strain sensors. We have also demonstrated the ability of the strain sensors to monitor human muscle and joints movements.

In this study, the authors have applied the “Oblique Cross Section” or OCS method, for the determination of the hardness changes in ion irradiated 316 stainless steel. The steel sample was irradiated with 1, 2 and 3 MeV He2+ ions. The samples were then polished at an angle of ∼15° from the ion irradiated surface, and the hardness on the cross-section was tested using nanoindentation in non-continuous stiffness measurement mode (non-CSM) at various distances from the ion irradiated surface. A profile of the hardness versus depth from the irradiated surface was thus obtained. It is shown that this method is quite suitable for single energy ion irradiation, when the energy is relatively high (≥1 MeV He in stainless steel), as it gives a better match between the damage peak and hardness peak locations than the “Top-down” method. The hardness profiles can be divided into two broad regions, viz. the pre-damage-peak plateau, and the peak hardness region. The results are contrasted with finite element (FE) models. The FE modelling shows formation of a secondary plastic zone in the unirradiated material beyond the irradiated layer, which was verified by cross-sectional transmission electron microscopy (TEM). Other aspects of the deformation below the nanoindents were also studied and illuminated by cross-sectional TEM. Thus, both experimental techniques and theoretical methods are employed here to elucidate the deformation processes and hardness measurement results, thereby establishing a more profound understanding of this relatively uncommon, but potentially powerful method for testing the mechanical property changes in ion irradiated materials, and of thin-layered materials in general.

Self-healing polymer composites are part of a class of materials which have the capability to repair themselves when damaged. They are often tested by inflicting damage onto them and then performing a mechanical test to initiate and measure self-healing. Self-healing efficiency is commonly defined as the ratio of a recovered property value to its original value. Applying this in practice can be challenging as most self-healing experiments are idealized scenarios. In this work, microcapsules containing epoxy and mercaptan self-healing agents were incorporated into ±45° composite weaves that were subjected to cyclic tensile loading and unloading. A damage mechanics theory was applied to quantify the change in stiffness and determine self-healing effectiveness. As this method did not enable a direct comparison between the damaged and healed states of the material, a new methodology was developed to take into account the energy levels of the material in order to quantify self-healing performance.

In this paper, a coupled fire-structure model combining the finite volume and finite element methods, which captures the essential physics of the problem has been developed. The model is based on a multi-physics framework where the essential physics pertaining to the combustion process of the fire and resultant thermo-mechanical response of the structure, in particular, of natural fibre reinforced composites, has been incorporated. In addition, a relatively new concept of adiabatic surface temperature has been introduced as a practical means to transfer data between fire and thermal/structural models at the gas-solid interface. The model predicts the temperature, stress distribution and deformation behaviour of composite beams under combined thermal and mechanical loads.

This paper focuses on developing hybrid composites of conductive polymers with graphene which have been shown to form a synergistic relationship between the components by lowering the percolation threshold and therefore achieving significant electrical conductivity at relatively low filler loadings. A variety of analytical techniques have been used to determine the factors contributing towards the electrical conductivity performance in these composites and the results of which have been used to construct a production method based on the solution casting process. The key factors identified have included the polarity of the primary polymer, the level of homogeneity of the dispersion of the conductive filler materials and the crystallinity of the resulting composite which in this case is increased by the addition of sucrose. Optimising for these factors the production method has been able to manufacture samples with an electrical conductivity of up to 14.2 S.cm−1 at a filler loading of 10 wt.% graphene and 10 wt.% conductive polymer in the base polymethyl methacrylate matrix. These have been investigated for application in 3D printing as an alternative to wiring or expensive printable conductive inks, and successful samples have been produced with an electrical conductivity of 11.3 S.cm−1.

In this paper, microtensile testing is demonstrated to be a viable technique for measuring irradiation hardening and reduction of ductility of ion irradiated hot isostatic pressed SA508 ferritic/bainitic steel. Ion irradiation with He2+ was used as a surrogate for neutron irradiation to reach a damage level of 0.6 dpa (Kinchin-Pease). The mechanical properties of four unirradiated microtensile steel specimens were measured and compared to the bulk properties: when averaged the 0.2% proof stress was 501.6 ± 56.0 MPa, in good agreement with the macrotensile 0.2% proof stress of 456.2 ± 1.7 MPa. On the basis of the agreement between microtensile and standard tensile 0.2% proof stress in the unirradiated material, it was possible to directly measure irradiation induced hardening from ion irradiation performed with He2+ ions to a dose of 0.6 dpa. Microtensile testing of the ion irradiated steel revealed an increase in 0.2% proof stress of approximately 730 MPa. The irradiation hardening measured by nanoindentation was 3.22 ± 0.29 GPa. Irradiation hardening was higher than that previously observed in neutron irradiated low alloy steels exposed to similar doses at low temperatures (

Wearable electronics have generated a strong demand for stretchable, skin-mountable and flexible sensors. This paper provides an effective technique for fabricating conductive networks using graphene-based polymer composites. Graphene-carbon black-silicone rubber (G-CB-SR) composites were cast in a mould, and a film was fabricated to make a composite strain sensor. Here we investigate how the remarkably different geometry affects the effective conductivity and piezoresistive properties of the composites. The electromechanical response of the G-CB-SR composites showed highly reversible and durable behaviour. It was stretchable up to 300%, and the gauge factor (GF) depended on the composition of the composites. The large strain sensors made of high-quality G-CB-SR film was achieved by solution intercalation with low-cost production and easy scalability.

An intumescent flame retardant working with various combinations of acid source, blowing agent, and char former promises high performance and low toxicity. However, the research for more potent functional constituents and their best combination is still extremely important. Here we report on a novel way to use keratinous fibers as the host material for creating an effective flame retardant. A simple solution-based treatment to implant amine phosphate and phosphoric acid in the fiber through sequential monomer infiltration is found to be significantly effective for applying flame retardancy and reducing the flammability of polymeric materials. After the flame-retardant fiber modification, polypropylene (PP) shows significantly improved flame retardancy to achieve V-0 grade and >70% reduced peak heat release rate in vertical burning and cone-calorimeter tests, respectively. We expect this strategy of converting the low-grade keratinous fiber to valuable flame-retardant material to become a novel and attract...

The demand for flexible and wearable devices based on novel nanomaterials is rapidly growing due to their applications in human motion detection, soft robotics, human-machine interface and similar applications. Herein, we report a systematic study on the fabrication of electrically conductive yarns made of natural fiber yarns coated with graphene nanoplatelets (GNPs) and carbon black (CB). The highly conductive yarns are then utilized to fabricate wearable, stretchable, and durable strain sensors. Our strain sensors demonstrate a good sensitivity with gauge factors (GFs) in the range of 1.46 to 5.62, depending on the magnitude of the applied strain and displacement rate. The strain sensors show reliable electromechanical response to strains as large as 60%, suggesting their potential application in human motion detection. They can successfully detect a range of human movements, such as finger, wrist, and knee joint movements, pronunciation, breathing, and swallowing. Finally, we propose a flexible grid structured pressure sensor to detect finger touch that could be utilized as flexible touch panels. Keywords: Flexible strain sensor, Wearable sensor, Conductive natural fiber yarns, Graphene nanoplatelets, Human motion detection

Several studies have been done on physiochemical properties of thin films of graphene materials, but less on their mechanical properties. The mechanical properties such as tensile and storage modulus of films of graphene oxide (GO), different reduced graphene oxides (rGO), functionalised reduced graphene oxide (frGO) and a few layers graphene (graphene) were analysed in this study. During syntheses processes, a range of variations occurs due to different reducing agents and functionalising components used; this affects or changes the mechanical properties of the materials. In addition, it has become vital to comprehend the mechanical properties of these films as the potential applications such as sensor and electrodes demand extended life cycles or lifetime. It has been found that the ultimate tensile strength (UTS), tensile modulus, and storage modulus vary across all the samples that highly depend on nature/efficiency of reducing agent used, amount of impurities such as oxygen functional groups and defect density such as discrepancies/holes in the aromatic structure. The highest UTS and modulus have been identified with a few layers graphene and with hydroiodic acid reduced GO among the rGOs. The frGO shows almost similar properties to that of graphene.

Profiled hollow core sandwich panels (SPs) and their components (outer layers and core) were manufactured with ponderosa and lodgepole pine wood strands to determine the effects of low-velocity impact forces and to observe their energy absorption (EA) capacities and failure modes. An instrumented drop weight impact system was applied and the tests were performed by releasing the impact head from 500 mm for all the specimens while the impactors (IMPs) were equipped with hemispherical and flat head cylindrical heads. SPs with cavities filled with a rigid foam insulation material (SPfoam) were also tested to understand the change in EA behavior and failure mode. Failure modes induced by both IMPs to SPs were found to be splitting, perforating, penetrating, core crushing and debonding between the core and the outer layers. SPfoams absorbed 26% more energy than unfilled SPs. SPfoams with urethane foam suffer less severe failure modes than SPs. SPs in a ridge-loading configuration absorbed more impact energy than those in a valley-loading configuration, especially when impacted by a hemispherical IMP. Based on the results, it is evident that sandwich structure is more efficient than a solid panel concerning impact energy absorption, primarily due to a larger elastic section modulus of the core’s corrugated geometry.

Susceptibility to damage from heat and flame is one of the major issues for utilisation of natural fibre reinforced polymeric composites in practical applications. Thus, the knowledge of thermal decomposition and flammability of the bio-based fibres, polymers and their composites is highly required for the materials selection and the development of composite products. Moreover, suitable flame retardant treatments on these composites have shown to effectively enhance their thermal stability and fire resistance. This article provides a review of research on thermal behaviour and flammability of natural fibres, such as cellulose and protein based fibres, and polymers along with composites filled with these materials. Furthermore, eco-friendly flame retardant treatments to overcome the environmental impact of conventional flame retardants are introduced with the combined effects of natural fibres on composites' fire performance. In addition, a review of studies on the predictive models regarding thermal response and structural damages of composites in fire is also included with their advantages and limitations.

The effect of crystal orientation and strain rate on the deformation behaviour of high-purity Ni single crystals is investigated using in-situ micro-tensile techniques. Ni foils, 12 μm thick, were fashioned into micro-tensile samples. The samples were pulled in tension along and directions at nominal displacement rates of 5 nm/s and 500 nm/s. These orientations were chosen because of the expectation of multiple slip on different numbers of slip systems. Analysis of stress-strain plots in conjunction with orientation imaging revealed that the oriented samples featured a lower yield stress, higher elongation and more complex deformation behaviour than the oriented sample. In fact, the samples with orientation showed two peaks in the engineering stress-strain curves, a unique behaviour hitherto unobserved. The higher strain rate increased the flow strength for both orientations, the results being in broad agreement with macroscopic tests. These results are analysed using plasticity theory, and it is shown that the results obtained from microscopic tests in single crystal Ni are largely consistent with macro-scale behaviour in polycrystalline samples if the appropriate theoretical adjustments are made for size and orientation effects, using Hall-Petch and Taylor theories.

Electron backscatter diffraction (EBSD) has been used to obtain orientation maps across a multi-pass slot weld in austenitic stainless steel plate. Spatially-resolved intragranular misorientation analyses have been performed, and a relationship between lattice misorientation and accumulated plastic strain has been used to quantify welding-induced plasticity. Qualitative features are captured across multiple length scales. Quantitative accuracy is demonstrated by comparing the misorientation-based analysis to complementary hardness-based measurements, as well as numerical predictions obtained using computational weld mechanics. The shortcomings of the present misorientation analysis and the underlying assumptions made are discussed.

The demand for stretchable, flexible, and wearable multifunctional devices based on conductive nanomaterials is rapidly increasing considering their interesting applications including human motion detection, robotics, and human-machine interface. There still exists a great challenge to manufacture stretchable, flexible, and wearable devices through a scalable and cost-effective fabrication method. Herein, we report a simple method for the mass production of electrically conductive textiles, made of cotton and wool, by hybridization of graphene nanoplatelets and carbon black particles. Conductive textiles incorporated into a highly elastic elastomer are utilized as highly stretchable and wearable strain sensors and heaters. The electromechanical characterizations of our multifunctional devices establish their excellent performance as wearable strain sensors to monitor various human motions, such as finger, wrist, and knee joint movements, and to recognize sound with high durability. Furthermore, the electrothermal behavior of our devices shows their potential application as stretchable and wearable heaters working at a maximum temperature of 103 °C powered with 20 V.

Herein, electrically conductive natural and synthetic yarns through electrophoretic deposition (EPD) technique were fabricated. A parametric study on the conductivity enhancement of the yarns is carried out by Taguchi method. Using this method, the desirable conditions are determined by studying the effects of important parameters on the electrical conductivity of the yarns in the EPD coating process. Based on the L18 design of experiments table, the preferred combination of factors to obtain the highest electrical conductivity of the yarns is found by Taguchi analysis. In addition, the Pareto ANOVA analysis is conducted to identify the major contributing factors on the electrical conductivity of the yarns. Characterisation techniques, such as scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR) in attenuated total reflectance (ATR) mode, and thermogravimetric analysis (TGA) are utilised for better understanding the microstructure and physical properties. When powered by only 3 V, the maximum temperature of a Joule heated conductive sample based on natural fibre yarns reached 102°C in less than 25 s.

Influence of wool fibres (WF) in improving the flame retardant and mechanical properties of polypropylene/kenaf fibre/intumescent ammonium polyphosphate (PP/KF/APP) composites is described. Flammability of PP/KF/APP/WF composite was evaluated using cone calorimetry, UL 94-V vertical burning tests and thermo-gravimetric analysis, and compared to results of similar composites which contained an ultraviolet ray stabiliser and colourant combination (PP/KF/APP/UVC). Tensile, bending and impact test analyses were also conducted on both sets of composites. PP/KF/APP/WF system had stable residual char at elevated temperatures, significantly improving fire protection. High degree of cross-linked stable char formation and residual char in PP/KF/APP/WF composite provided sufficient evidence of synergistic effect of wool. WF increased the tensile modulus of the composite by approximately 16%, while UVC (together with APP) improved the composite's flexural stiffness by 21%.

The knowledge of impact behaviour of heat exposed composites is very limited, even though this could be one of the critical issues for many practical applications. Therefore, the current study was conducted to investigate the effect of preheating on the impact performance of glass and flax fibre reinforced composite laminates by a comprehensive set of experiments. The composite laminates were partially damaged by heat convection (using a fan assisted furnace) and their impact properties, such as force and energy absorption, were measured under a low velocity (1.85 m/s) impact loading situation. The impact test results showed that the heat exposure at 300 °C increased the energy absorption of the glass fibre composites but reduced those of the flax fibre composites. Furthermore, an addition of ammonium polyphosphate, as a flame retardant, also incremented the absorbed energy of the heat exposed composites and significantly reduced the heat release rate, resulting in an acceptable vertical burning behaviour, that meets the aviation standard requirements.

Recent advancements in stretchable, flexible and wearable strain sensors, based on natural materials, show their interesting potential for use in human motion detection, soft robotics and human–machine interactions. However, a grand challenge still exists: finding an effective strain-sensing mechanism to obtain both high stretchability and high sensitivity through a facile manufacturing technique. In this paper, a simple, environmentally friendly, and scalable process to develop such strain sensors based on cotton fabric, which is an abundant, cost-effective and lightweight natural material, is discussed. An effective coating technique is proposed to achieve highly conductive cotton fabric with the aid of a conductive ink that is a hybrid of graphene nanoplatelets and carbon black particles. The sandwich-structured wearable strain sensors can work within a wide strain range of up to 400%, with an ultrahigh maximum gauge factor of 102 351, caused by the formation of controlled intentional cracks within the fabric after rupture training. The strain sensors show great performance at very low strain levels (less than 2%). Their excellent response in detecting a full range of human movement is also demonstrated.

Although the effectiveness of organic–inorganic combination on the flammability reduction in polymeric materials has been proved by the multi-layer coating method on fabric and foam, the technique has not been intensively investigated for bulk polymers. In order to impart the excellence of the combination to bulk polymers, the thermal barrier resulted from the hybrid has to be triggered in the entire region of the polymer during combustion. In this work, phosphate loaded chicken feather fibers (CFF) with layered silicate outer coatings are developed into an efficient intumescent flame retardant (IFR) material system for polypropylene (PP). The organic–inorganic hybrid material, designed for silicate reinforced composite char formation during combustion, allows the modified PP composite to achieve significantly improved flame retardancy compared to that of the composite modified by the only phosphate. A small silicate content (0.4 wt%) leads to 27 wt% reduction in phosphate to achieve the same level of flame retardancy for PP. Furthermore, the efficiency of loaded phosphate, measured by a cone calorimeter, is 14% higher than that of a commercial IFR, ammonium polyphosphate (APP). Thermal gravimetric analysis and cone calorimeter tests demonstrate a suppressed decomposition of phosphorus and CFF at a higher temperature due to robust char formation. The characterization of the char residue using SEM-assisted elemental analysis confirms the silicate reinforced char. Flame retardant mechanism and mechanical performance have also been investigated to aid a better understanding and furthering its performance improvement.

Sustainable green manufacturing forms a critical aspect in the current times, where environmentally clean and renewable material, such as plywood, can be used not only for decorative purpose but also for producing particular profile sections. The goal of the present work is to minimise or eliminate the shape distortion through the spring-back or spring-forward (negative spring-back) phenomenon experienced by plywood during profile forming. Commercially acquired 3-ply laminates were used initially to investigate the influence of forming temperature and in-situ curing time while producing U-sections. Statistical analyses using Taguchi and full Factorial methods were employed for the design of experiments to find the ideal combination of the parameters providing minimal spring-back. Considering the structural integrity and the aesthetic aspect, the ideal values parameters were obtained as the forming temperature being 250 °C and the in-situ curing time being 80 s, giving a spring-back of 2.93°. The results were then applied to achieve sections with multiple 90° bends (top-hat sections) through a chemical-free process, giving an error of about 6% from the statistical study. They were also observed to experience significant spring-forward after curing. These led to the development of a modified forming technique where the top-hat profiles had negligible spring-back or spring-forward ( ≤ 1 0 ) .

This article focuses on the optimisation of electrical and mechanical properties of hybrid blends of polyoxymethylene (POM) as primary thermoplastic matrix, polypyrrole (PPY) as secondary conducting polymer and graphene (G) as reinforcement. An initial Taguchi analysis was performed with a focus on improving electrical conductivity (σ) and tensile strength. A mixture analysis using ‘simplex’ statistical design was applied to develop an experimental subset that identified an optimal combination in weight-percentage. Both electrical and mechanical properties were improved by the addition of PPY and graphene particles due to hybridisation mechanism as well as double percolation threshold. The maximum electrical conductivity of 0.95 S cm−1 was achieved with POM reinforced with 3 wt.% of G and 2.5 wt.% of PPY loading. The mechanical properties were found to be increased with increase in addition of both G and PPY.

A titanium aluminide (TiAl) alloy 45XD has been irradiated by a He ion beam with an energy of 5 MeV on a tandem accelerator at the Australian Nuclear Science and Technology Organization (ANSTO). The total fluence of He ions was 5 × 1017 ion cm−2. A 17 μm uniform damage region from the material surface with a helium concentration of about 5000 appm was achieved by using an energy degrading wheel in front of the TiAl target. The micro-size test specimens from the damage layer were fabricated using a focused ion beam & scanning electron microscope (FIB-SEM) system. The in situ SEM micromechanical compressive testing was carried out inside an SEM and the results indicated irradiation embrittlement in the helium affected region. Electron back scatter diffraction (EBSD) analysis has been applied to reveal the orientation of the lamellae in the TiAl specimens, and used to understand the deformation processes in the sample. The irradiation damage of gallium ion beam from FIB on the surface of TiAl sample was also investigated.

Pre-impregnated flax and thermoplastic poly(amide) composite tapes have been produced using a novel process. The manufacturing method uses an impregnation unit with a siphon system to impregnate continuous flax yarns with the polymer in the form of a slurry. After water evaporation, the powder is sintered and the coated yarns are compressed by passing them through a pair of heated rollers. Using a parametric study of the process, tape quality has been assured using the key outcome criteria of tensile strength/stiffness, surface roughness, fibre weight fraction, width and thickness. The temperature of the air heater placed before the roller has the biggest influence on tape quality. A heating model was developed using finite element software LS-DYNA. The research novelty comes from producing composite tapes with good tensile properties and surface finish using aligned natural fibres; the feasibility of automated tape placement and winding has also been demonstrated.

Biochar based wood/polypropylene (PP) composites were manufactured with two flame retardants (FRs): ammonium polyphosphate/APP and magnesium hydroxide/Mg(OH)2. The amounts of wood and biochar were alternated for accommodating the FRs in each blend. Flammability and mechanical characterisation for both the batches containing different FRs were done. Having higher proportion of biochar and less wood is beneficial to reduce flammability. The thermally stable biochar contributes to formation of effective char to restrict O2 transfer into PP. The higher weight ratio of biochar than wood in the composites compromised the tensile and flexural strengths to some extent as the APP and Mg(OH)2 particles were trapped inside biochar pores consequently reducing the effectiveness of biochar pore infiltration by PP. In general, addition of biochar with a woody biomass (with FRs) to neat PP significantly impedes its flammability while enhancing certain mechanical properties, such as flexural strength and tensile/flexural moduli and preserving the tensile strength.

Graphene has received significant attention in recent years due to its outstanding electronic, mechanical, chemical and physical properties. Graphene materials can potentially be used in a variety of applications, such as functional nanocomposites, electrodes, flexible transparent devices and thin conductive films. This article focuses on the analysis of structural evolution and development of different of reduced graphene oxides (rGOs), and the results are compared with structural features of functionalised reduced graphene oxide and graphene. The aromatic disorder and irregularity of these materials influence their own properties; particularly, their electrical conductivity aspects were studied indirectly through Raman spectroscopy. The quantification of their Raman spectra and microstructural analysis were examined to assess the relationship between aromatic structures and electrical conduction mechanism. The results showed that aromaticity of GO changes under different chemical reduction treatments and hydroiodic acid reduction gave an electrical conductivity of 103.3 S cm−1 as highest amongst a number of rGOs produced. Moreover, the integrity of aromatic structure through different reduced graphene oxides changed quite significantly and the Raman results were able to correlate the electrical conductivity with their structural regularity.

Novel sandwiched structures of cellulose nanowhiskers (CNWs) were found for the first time at the cross section of fractured starch/CNWs composite films. CNWs were obtained by hydrolysing bleached flax yarns through heating in a concentrated sulfuric acid (60 wt. %) aqueous solution at 55 °C for 60 min. Starch and starch/CNWs composite films were prepared by casting starch and mixtures of starch/CNWs homogenous aqueous suspensions, which was followed by drying at atmosphere. The CNWs’ layers are sandwiched within starch matrices in a parallel direction to nanocomposite film surfaces. The layer thickness increases with an increase in the content of CNWs. The discovery of novel sandwiched structures demonstrates that both the interaction and evaporation rate of the solvent can affect the dispersion and thus play important roles in the nanoparticle dispersion. Such nanocomposite films in the presence of self-assembled multi-layer structures may further improve mechanical and gas barrier properties as a promising material candidate for food packaging applications.

The combined effects of ammonium polyphosphate and talc on the fire and mechanical behaviour of epoxy/glass fabric composite systems and neat epoxy resin were investigated. Recorded data from cone calorimeter and UL-94 vertical burning experiments reveal that the incorporation of additives can enhance the flame retardancy of both epoxy resin and glass fabric reinforced composites. TGA results demonstrate that the introduction of additives improve the thermal stability of epoxy resin at high temperatures. Moreover, the addition of flame retardants to epoxy resin increases the tensile and flexural moduli. However, due to the incompatibility of the additives with epoxy, the strengths are compromised. Then again, the epoxy/glass fabric composites with flame retardant additives have improved the fire properties without significantly affecting the mechanical performance.

The use of biomaterial scaffolds has been an enormous field of research in tissue engineering, where the aim is to use graft materials for assisting the human body in recovering lost functions. Currently, there are many ways biomaterial scaffolds can be fabricated; however, many of these techniques involve the use of toxic organic solvents during the process. As biocompatibility is one of the mandatory requirements in designing a successful scaffold, there is an interest in fabricating scaffolds that are completely organic solvent-free. This paper describes the development and characterization of novel micro-/nano-fibrillar composites (MFC/NFC) that can produce scaffolds which are completely free from organic solvents. In this research, the cytocompatibility of these materials have been tested in vitro using mouse osteoblast-like cells and primary rat tenocytes, where cell numbers increase over the culture period, demonstrating the material viability. Gene expression analysis of primary rat tenocytes on MFC/NFC scaffolds demonstrate tenocytic behavior, and histology studies show an increase in cell formation on NFC scaffolds. This study establishes the potential of using the MFC/NFC technique to produce completely organic solvent-free scaffolds capable of hosting musculoskeletal cells, in the hope of providing a graft material for non-union skeletal fractures and rotator cuff repairs. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1393-1404, 2017.

Due to the realisation of the reinforcement potential of waste based biochar and wool in polymeric composites, in the recent past, their individual flammability, thermal and mechanical properties were determined. Composites were manufactured with biochar and with both biochar and wool in conjunction with the halogen free flame retardant, which was followed by their characterisation through cone calorimeter, limiting oxygen index (LOI), thermogravimetry, tension/flexural tests, and scanning electron microscopy (SEM). Biochar exhibited a high resistance to heat without being ignited and possessed very low heat release and smoke production rates. Wool, although, had relatively high peak heat release rate (PHRR), its advantageous charring ability enabled a gradual reduction in heat release until flameout. The hardness and modulus of biochar were 4.3 GPa and 26 GPa, respectively. The tensile strength and modulus of wool were 160 MPa and 4.8 GPa, respectively. Composites containing biochar and wool significantly reduced the PHRR, smoke production, and elevated the mass loss rate (compared to neat polypropylene/PP). Hybridisation with wool proved to be beneficial for enhancing the LOI. Certain mechanical properties, such as flexural strength and tensile/flexural moduli, were preserved and enhanced, respectively, due to biochar pore infiltration by PP as seen in SEM.

Biocomposites were manufactured with biochar and polypropylene at five loading levels (0, 15, 25, 30, and 35 wt%) by compounding and injection moulding. Biocomposites were tested by tension, bending, cone calorimeter, thermogravimetry, differential scanning calorimetry, X–ray diffraction, and infrared spectroscopy. Incorporation of increasing amount of biochar to neat polypropylene continuously improved its tensile modulus and flexural strength/modulus. The peak heat release rate and smoke production of the biocomposites were significantly reduced as a result of biochar addition. The high surface area of biochar allowed polypropylene to flow in creating a mechanical interlocking and improving the mechanical properties. The thermally stable biochar provided a compact char structure during combustion which prevented the heat and mass transfer between the polypropylene and the ambient O2. Thermal stability of polypropylene was increased as a result of biochar inclusion, as observed in thermogravimetry.

A sample of oxide dispersion strengthened (ODS) MA957 steel was irradiated with 5 MeV He2+ ions in the STAR accelerator and its mechanical property changes were tested by nanoindentation and also in tension using an in situ micro-mechanical testing device inside a scanning electron microscope. The ion irradiation process was accomplished using an Al degrader wheel to obtain a relatively uniform damage profile compared to single energy irradiation, with an average dose of ~1.5 displacements per atom (dpa) up to a depth of ~ 10 μm. The small grain size (0.25 – 1.7 μm) of the material enabled the micro-tensile samples (~ 5 × 5 × 17 μm) to be treated essentially as polycrystalline specimens. The results of the tensile tests before and after the radiation are analysed with the aid of strain measurement through a digital correlation method. These results are then compared with nanoindentation hardness measurements. Transmission electron microscopy images reveal a high density of fine (1 nm diameter) bubbles, along with a relatively low density of dislocation loops. An estimation of strengthening due to these sources using the dispersed barrier hardness model shows that a root sum square superposition law predicts the increase in strength to a good degree of accuracy. It is apparent that a major fraction of the increase in strength due to ion irradiation could be attributed to He bubbles, and only a relatively small proportion of the hardening to dislocation loops and black dot damage.

This study aims to give an understanding on the effects of diverse natural fibers on the mechanical properties and wear behavior of high-speed steel tool when machining polypropylene (PP) based natural fiber-reinforced composites (NFRCs). Rice husk (RH), jute and kenaf of 30 wt% each with notable differences in silicon content, hardness and aspect ratio values are used as reinforcements. The influence of worn-out tool on surface finish, machining force and work-tool interface temperature has also been elucidated. The microscopic analysis has enabled us to identify the distinct tool lives and wear mechanisms for the machined NFRCs demonstrating: (i) rigorous mechanical abrasion with strip chipping, cracks, galling and large nose deformation for RH/PP; (ii) less severe abrasion combined with adhesion and attrition wears for jute/PP; and (iii) mild abrasion/scratch marks with attrition wear and formation of protective/transfer layer for kenaf/PP composites. A remarkable difference has been observed in the flank wear values, such as VB = 0.25 mm after 55 min of machining for kenaf/PP composites whereas VB = 0.3 mm within 6 min for RH/PP. The machined surface textures generated by the worn tools reveal a plowing mechanism for RH/PP and jute/PP composites while shearing type for kenaf/PP composites. Overall, kenaf/PP composites prove to have superior mechanical and machinability characteristics in comparison to RH/PP composites, which reveal inferior outcomes. For the first time, a modified Taylor’s tool life equation, including silicon content and reinforcement aspect ratio has been derived with an error

In this work, the authors apply the “top-down” nanoindentation testing method to assess the mechanical property changes in ion-irradiated metallic alloys for three different ion energies in order to understand the relationship between ion energy, damage peak depth and hardness peak depth. The samples were irradiated with He +2 ions having 1, 2 and 3 MeV beam energies respectively. The curves for ΔH (radiation induced hardness) have been obtained by calculating the difference of the irradiated and unirradiated hardness curves after these were corrected for indentation size effect. Three-dimensional analytical and numerical models have been developed to obtain greater insight into the mechanisms involved in the nanoindentation processes, the nature of the plastic zone, and how these affect the hardness results, including the full hardness profiles with respect to depth. This is particularly valuable in situations where the damage profile is non-uniform, as in the present case, and provides the means to predict expected hardness peak positions and values for a given irradiation dose.

This article focuses on the influence of surface topography (roughness), surface chemistry (carbon and oxygen functional groups) and physical (film thickness) parameters on the electrical conductivity of graphene oxide (GO) and reduced graphene oxide (rGO) films. This study was carried out to understand how changes in chemistry, roughness and film thickness, arising from the reduction process, alter the electrical properties of the films. Improved understanding is needed to control and optimise these parameters in graphene/rGO films for future applications where targeted property performance is needed. Films with smooth surfaces, measured using confocal imaging, and lower thicknesses have been shown to possess higher electrical conductivity. X-ray diffraction patterns shows minor changes in d-spacing, though improvements in crystal perfection, orientation and crystallinity could be concluded. X-ray photoelectron spectroscopy shows a significant decrease in the oxygen present at the surface as the films are exfoliated to reduce their thickness. Conductivity improves as the materials become increasingly defect-free, achieved by careful control of reduction and post-processing techniques. Ideal practical conductivity is achieved for films of 4 μm thickness: beyond this point, no practical gains are made (about 25 exfoliation trials from the bulk cast film).

Wool, as a naturally fire resistant fibre, has been incorporated with other additives, such as ammonium polyphosphate (APP), talc and maleic anhydride grafted polypropylene (MAPP), to manufacture polypropylene (PP) based composites. A single-screw extruder, attached with a flat die, has been used to successfully produce continuous wool-PP composite sheets. Furthermore, the significant roles of nitrogen content of APP and the talc in forming the effective char to increase the composites' fire retardancy have been identified through cone calorimeter tests. In particular, it is highly interesting to note that a reduction of APP content from 20 to 15 wt% was possible to achieve a direct self-extinguishment (V-0 rating) of the composite. The decrease in APP amount has also led to the reduction of material cost due to APP's relatively high price (USD 13–14/kg) and limit the possibility of deteriorating mechanical properties due to APP addition. The MAPP has enhanced thermal stability and mechanical properties compared to those without the additive, which could be attributed to the improved interfacial adhesion between wool and PP. A computational fluid dynamics model has also been developed by Fire Dynamics Simulator to mimic the cone calorimeter tests, which agreed reasonably well with the experiments. Keywords: Wool, Ammonium polyphosphate, Flammability, Mechanical properties, Fire Dynamics Simulator