Journal of Composite Materials

Hydrothermally synthesized undoped and Sr-doped hydroxyapatite-dispersed polyether ether ketone composites has been fabricated by using hot isostatic pressing technique with 5, 10, 15, and 20 wt.% as the dispersoids content. The detailed structural investigation of the fabricated composites has been performed by scanning electron microscope, high-resolution transmission electron microscope, and X-ray diffraction technique that confirmed the uniform dispersion of the dispersoids with the polyether ether ketone matrix. The microindentation measurements show that the mechanical properties of the polyether ether ketone matrix improved remarkably with incorporation of the hydroxyapatite (HAp) particles. The nondestructively evaluated elastic modulus so obtained for the matrix and composites were further validated through finite element analysis. Moreover, the in vitro cytotoxic of the fabricated nanocomposites were also evaluated to assess its potential as a bioactive material.

In this work, the correlation between electrical conductivity and uniaxial deformation of a material with highly segregated distribution of conductive filler is studied. Multi-walled carbon nanotubes are used as a model filler. A numerical model that can be used to predict changes in conductive microstructure made of multi-walled carbon nanotubes in response to uniaxial deformation of material is proposed. The model takes into account the ability of nanotubes to assume various conformations and orientations during deformation. Numerical simulations are conducted for uniformly distributed multi-walled carbon nanotubes providing confinement of the filler in a two-dimensional film structure with high volume fraction of the filler. The embedded element method to conduct realistic and computationally efficient simulation of multi-walled carbon nanotube behavior during deformation of the composite material is implemented. Finally, the results of numerical simulations of changes in electrical conductivity of composite during deformation are compared with the experimental data to prove the correctness of assumptions used in the model.

The effect of out-of-plane stitching and the addition of multiwalled carbon nanotubes on the short-beam shear properties of carbon/epoxy composites were investigated. Stitching influenced the short-beam strength of carbon satin and twill fabric composites, where the stitched satin carbon/epoxy composites showed improved short-beam properties compared with the unstitched satin carbon/epoxy composites. In general, stitching and MWCNTs addition enhanced the short-beam strength of the composite. The fracture of the composites generally exhibited as a combination of lateral total matrix cracking, warp fiber breakage and interlayer opening. In addition, all the structures experienced angularly sheared catastrophic through-the-thickness layer breakage. It was also shown that delamination was largely restricted in stitched and nano-added composites when compared to the unstitched samples. It can be concluded that nanostitching could be considered for improving short-beam strength properties of the composite.

The present study aims to investigate the influence of modified zinc oxide nanoparticles content on the physico-chemical properties of sawdust/epoxy composite specimens. The results show an improvement in the mechanical properties in terms of flexural strength, impact strength, and hardness with increasing the modified zinc oxide nanoparticles content up to 5%, while the physical properties such as water absorption and thickness swelling percentages are decreased directly with increasing the content of modified zinc oxide. In addition, the behavior of irradiated composite specimens containing 5% modified zinc oxide nanoparticles at different gamma-irradiation doses, 10, 30, and 50 kGy, has been studied. The results indicate that the irradiated composite specimens at 10 kGy have better physico-chemical properties as compared to the unirradiated specimens. Furthermore, the antimicrobial properties of composite specimens containing 5% modified zinc oxide at 0 kGy and 10 kGy against different plant pathogenic fungi and bacteria are also discussed. The results demonstrate that the growth activity of fungi and bacteria on the composite specimens are reduced to a great extent as compared to the control composite specimens (0% of zinc oxide nanoparticles). Thermal behavior and morphology of the prepared specimens are detected using thermogravimetric analysis and scanning electron microscopy technique.

This study describes the changes in some properties of two series of nylon 612/TiO₂ composites by varying filler type (untreated and treated) and content (up 8.0 wt.%). The samples preparation by simultaneous anionic copolymerization-molding process ensures a good dispersion of the filler in matrix. Differential scanning calorimetry, thermogravimetrical analysis, static mechanical testing, dynamic mechanical analysis and scanning electron microscopy allowed to investigate the effects of filler loading on the mechanical, thermal and morphological characteristics of the samples and revealed the importance of filler treatment on the composites behaviour. The semicrystalline character has been proved by differential scanning calorimetry (only a single melting peak is present) and wide-angle X-ray diffraction (two reflexion plane with d-spacing of 0.4311 and 0.3817 nm appear). At the same filler content, the difference ΔH_m1–ΔH_c was higher for the samples with treated filler. The lower T_m,α(2) in comparison with T_m,α(1) revealed a modification of the nucleation process during crystallization. The main mass loss of the samples occurred between 277 and 550℃. The addition of the filler leads to the improvement of flexural strength and flexural modulus in comparison with neat copolymer. Incorporating 8.0 wt.% treated filler, the T_g value increases by about 11.0%, reaching 61.0℃.

In this study, the diameter of polyvinyl butyral nanofibers was modeled using response surface method based on three variables, at three levels of central composite design and particle swarm optimization-least squares support vector machine. Under optimal conditions, the measured mean diameter of the nanofibers was 175 nm. Sensitivity analysis in both models showed that polyvinyl butyral concentration in the solution was found to be the most effective parameter on the nanofiber diameter. The voltage is placed in the next. Fracture toughness under Mode I condition shows that the use of electrospun nanowebs as an interlayer in the structure of multi-layers composite has a positive effect on the G_Ic which values for the oriented and random nanofibers modified samples increased by 60% and 55%, respectively. According to SEM images, the main mechanism of fracture toughness in these samples was crack deflection and nanofibers crack bridging.

As far as the tensile properties of natural fibres as reinforcements for composites are concerned, flax fibres will stay at the top-end. However, an efficient conversion of fibre properties into their corresponding composite properties has been a challenge, due to the fibre damages through the conventional textile methods utilised to process flax. These techniques impart disadvantageous features onto fibres at both micro- and meso-scale level, which in turn degrade the mechanical performances of flax fibre-reinforced composites (FFRC). Undulation of fibre is one of those detrimental features, which occurs during traditional fibre extraction from plant and fabric manufacturing routes. The undulation or waviness causes micro-compressive defects or ‘kink-bands’ in elementary flax fibres, which significantly undermines the performances of FFRC. Manufacturing flax fabric with minimal undulation could diminish the micro-compressive defects up to a substantial extent. In this research, nonwoven flax tapes of highly aligned flax fibres, blended with a small proportion of polylactic acid have been manufactured deploying a novel technique. Composites reinforced from those nonwoven tapes have been compared with composites reinforced with woven Hopsack fabrics and warp knitted unidirectional fabrics from flax, comprising undulating fibres. The composites reinforced with the highly aligned tapes have shown 33% higher fibre-bundle strength, and 57% higher fibre-bundle stiffness in comparison with the composites reinforced with Hopsack fabric. The results have been discussed in the light of fibre undulation, elementary fibre individualisation, homogeneity of fibre distribution, extent of resin rich areas and impregnation of the fibre lumens.

The high cost of mineral-based fillers and their processing difficulties have necessitated the search for alternative and cheaper filler materials, usually agro-waste materials such as coconut shells. The coconut shells were carbonized, pulverized, and sieved into four particles sizes, namely; 63 μm, 150 μm, 300 μm, and 425 μm. The carbonized coconut shell particles of each particle size were used as fillers in the preparation of polypropylene-filled composites at filler loadings of 0, 10, 20, 30, and 40 wt. %. The control was the neat polypropylene of 0% filler addition. The polypropylene/carbonized coconut shell particles composites were prepared via melt blending of polypropylene and the filler in an injection molding machine to obtain composite sheets. The influence of filler loading on the mechanical properties was evaluated. The addition of fillers was found to improve the yield strength, tensile strength, tensile modulus, flexural strength, flexural modulus, and hardness of polypropylene as these mechanical properties increased with increase in filler loading. The elongation at break and modulus of resilience of the prepared polypropylene/carbonized coconut shell particles composites were, however, observed to decline with an increase in the filler loading. Compared with the neat polypropylene, the filler showed enhanced mechanical properties in the prepared composites. SEM revealed good filler–matrix interaction because of good interfacial adhesion. The incorporation of more filler resulted in the formation of more spherulite-producing nuclei, reduction of pore sizes, and enhanced particle size distribution with improved mechanical properties. Experimental data modeling showed the addition of more than 48% carbonized coconut shell particles to polypropylene would compromise property enhancement.

Natural fiber composites have the potential to be widely applied as an alternative to or in combination with glass fiber composites in sustainable energy-absorbing structures. This study investigates the behavior of hemp fiber-reinforced vinylester composites when subjected to low-velocity impact loading by using an instrumented falling weight impact equipment. Different stacking sequences are tested, including a hybrid pattern resulting from a combination of natural and traditional glass fibers. Both penetration and indentation tests are performed. In the light of an increase in safety of green composite components and systems subjected to low-velocity impacts, next to the numerical models, the development of theoretical models is also useful and low time-consuming. Therefore, analytical models, available in the literature for traditional fiber-reinforced plastics and aimed at predicting the critical load of delamination onset, the indentation as a function of absorbed energy, as well as the approximation of the load–displacement curve, are used and implemented in this work. Good agreement was found between the theoretical predictions and experimental results.

Tuning the electromechanical performance in piezoresistive composite strain sensors is primarily attained through appropriately employing the materials system and the fabrication process. High sensitivity along with flexibility in the strain sensing devices needs to be met according to the application (e.g. human motion detection, health and sports monitoring). In this paper, a highly stretchable and sensitive strain sensor with a low-cost fabrication is proposed which is acquired by embedding the chopped carbon fibers sandwiched in between silicone rubber layers. The electrical and mechanical features of the sensor were characterized through stretch/release loading tests where a considerably high sensitivity (the gauge factor about 100) was observed with very low hysteresis. This implies high strain reversibility (i.e. full recovery in each cycle) over 700 loading cycles. Moreover, the sensors exhibited ultra-high stretchability (up to ∼300% elongation) in addition to a low stiffness meaning minimal mechanical effects induced by the sensor for sensitive human motion monitoring applications including large and small deformations. The results suggest the promising capability of the present sensor in reflecting the human body motion detection.