Low-velocity impact and static behaviors of high-resilience thermal-bonding inter/intra-ply hybrid composites

This study prepared inter/intra-ply hybrid composites reinforced with sandwich-structure recycled Kevlar nonwoven/glass woven compound fabric. Negative-depth needle punching and thermal bonding were applied to strengthen the structure with two compound cover plies and a fluffy cushioning center ply. The effects of center ply areal density, needle punching depth, and fiber blending ratio on the static and dynamic impact resistance behaviors of the composites were investigated. The results indicated that areal density significantly influenced the static and dynamic impact behaviors, which were both enhanced by the promotion of thermal-bonding points. As the needle punching deepened, the static and dynamic puncture resistances represented opposite tendencies because of different failure mechanisms. Static friction was the dominant factor for static puncture resistance, whereas kinetic friction was the dominant factor for dynamic puncture resistance. A similar phenomenon was observed when fiber blending ratio was varied. In terms of the non-penetrating dynamic cushioning test, areal density was the most distinct influence factor on cushioning behavior and the hybrid composites sample with an areal density of 700 g/m² could eliminate up to 66.5% of the incident force. Therefore, the inter/intra-ply hybrid composites showed high impact resistance and excellent dynamic cushioning property.     

A flexible conductive hybrid elastomer for high-precision stress/strain and humidity detection

Flexible and environment-responsive materials are essential for a large number of applications from artificial skin to wearable devices. The present study develops a flexible, ultra-low cost conductive hybrid elastomer(CHE), which possesses high responsive capabilities to stress/strain and humidity. CHE was composed of polydimethylsiloxane(PDMS) and starch hydrogel(SH), enabling great elasticity(56 kPa),high conductivity(10~(-2)S/m) and high sensitivity to external stimuli(gauge factor of CHE under stress and strain are 0.71 and 2.22, respectively, and sensitivity to humidity is 1.2 × 10~(-6)S/m per RH%). These properties render CHE a promising candidate for artificial skin and wearable electronics applications of continuously monitoring environmental information.     

Quasi-static and dynamic mechanical responses of hybrid laminated composites based on high-density flexible polyurethane foam

Hybrid laminated composites were fabricated based on high-density flexible polyurethane foam and reinforced with inter/intra-ply hybrid laminates. Transient responses of hybrid composites under quasi-static and dynamic loadings with various thicknesses and expansion factors were comparatively investigated. Experimental results revealed that foam cell collapse and hybrid laminates rupture were dominant mechanisms of energy absorption. Interlaminar stress and composite tensile strength determined the compressive potential energy and double-peak behavior. Quasi-static bursting and puncture resistances exhibited totally different relationships to various constructions and expansion factors. Energy dissipation capacity is influenced more significantly by the constant rate of transverse (CRT) puncture than dynamic puncture process. CRT puncture resistance is superior to the corresponding dynamic puncture resistance for all constructions. The hybrid laminated composites contributes to eliminate more than 95% of the incident force in the drop weight impact test. Compared with non-laminated panel, the hybrid laminated composites exhibited higher resistance to static and dynamic loadings.     

Glass fiber-reinforced polymer/steel hybrid honeycomb sandwich concept for bridge deck applications

Glass fiber-reinforced polymer (GFRP) bridge decks possess inherently high strength-to-weight ratios, but relatively low effective elastic moduli. As a result, serviceability issues govern GFRP bridge deck design. Therefore, the objective of this study was to increase the stiffness of a commercial GFRP honeycomb sandwich panel through the inclusion of steel within the cross section.     

Metal–polymer–metal sandwiches with local metal reinforcements: A study on formability by deep drawing and bending

The formability of metal–polymer–metal sandwich composites with embedded different solid and mesh steel inlays was investigated with the aim to gain information about their forming behaviour by shaping, especially deep drawing and bending. Therefore the geometry and the size of the local inlays have been varied. The reduction in thickness of these composites was quantified by photogrammetry. As a result the formability of sandwich composites with solid steel inlays is lower compared to non-reinforced ones. Sandwiches with mesh inlays showed a slightly increased thinning compared to sandwiches with circular solid inlays. Both variations revealed good formability. The results will be used for future tailoring of sandwich structures with particularly demanded properties.     

Synergy in hybrid polymer/nanocarbon composites. A review

The aim of this review article is to report the most recent developments in the understanding of and beliefs about the properties of polymer hybrid composites that are reinforced with various combinations of nanometer-sized carbon and mineral fillers. The discussions are primarily focused on an analysis and comparison of the electrical, thermal, and mechanical properties. It is shown that the introduction of a mixed (hybrid) system of filler nanoparticles into polymer matrices enhances the macro- and microproperties of the composites as a result of the synergistic interactions between the fillers and the simultaneous creation of a unique filler network in the polymer. The synergy of various types of carbon nanofillers and combinations of nanocarbon materials with inorganic fillers manifests itself as modifications of most of the properties of hybrid polymer composites relative to the properties of a polymer system containing a single filler. The reinforcing effect is related to the structure and particle geometry of the hybrid fillers, the interactions between the fillers, the concentrations and the processing methods.The existence of synergy between different types of carbon nanofillers, as well as with mineral fillers, shows great potential and could significantly increase applications of carbon-based nanomaterials.     

Behaviour of woven hybrid basalt-carbon/epoxy composites subjected to laser shock wave testing: Preliminary results

This study addresses the effect of basalt fibre hybridization on the damage tolerance of carbon/epoxy laminates subjected to laser shock wave tests. Interply hybrid specimens with two different stacking sequences (sandwich-like and intercalated) were tested at different laser intensities and residual post-shock properties of the different configurations have been characterized by quasi-static three point bending tests monitored by acoustic emission. Results indicate that the best compromise in terms of both quasi-static properties (2% reduction in flexural strength compared to all carbon laminates) and damage tolerance appears to be the sandwich-like structure with basalt fibre skins. In particular, this configuration exhibited the highest damage tolerance among the hybrids, with a percent decrease in flexural strength of about 5% compared to 15% in the case of all carbon laminates. Damage induced by laser shock testing in carbon-basalt woven fabric/epoxy composites is mainly inter-ply delamination. This study also highlights the tougher behaviour of basalt plies in response to a sudden application of load compared to carbon layers with a favourable hybridization effect.     

Metal–polymer–metal sandwiches with local metal reinforcements: A study on formability by deep drawing and bending

The formability of metal–polymer–metal sandwich composites with embedded different solid and mesh steel inlays was investigated with the aim to gain information about their forming behaviour by shaping, especially deep drawing and bending. Therefore the geometry and the size of the local inlays have been varied. The reduction in thickness of these composites was quantified by photogrammetry. As a result the formability of sandwich composites with solid steel inlays is lower compared to non-reinforced ones. Sandwiches with mesh inlays showed a slightly increased thinning compared to sandwiches with circular solid inlays. Both variations revealed good formability. The results will be used for future tailoring of sandwich structures with particularly demanded properties.     

Mode II fracture characterization of a hybrid cork/carbon-epoxy laminate

Fracture characterization under mode II loading of a hybrid laminate composed by a unidirectional carbon fiber-epoxy composite and cork was performed using the End Notched Flexure test. A data reduction scheme based on equivalent crack length concept, specimen compliance and Timoshenko beam theory was applied to evaluate fracture toughness under mode II loading of a composed beam (cork and carbon-epoxy composite). The adopted procedure depends exclusively on the data issuing from load–displacement (P–δ) curve and does not require crack length monitoring during the test which is a difficult task to be accomplished with the necessary accuracy in the ENF test. A numerical analysis using cohesive zone modeling and an inverse procedure was performed to assess the mode II cohesive law that simulates the material fracture under shear loading. It was concluded that hybridization is advantageous relative to monolithic carbon-epoxy laminate in which concerns the observed failure mode, which altered from typically brittle to very ductile thus contributing to avoid sudden shear failures in real applications.     

Shape memory and thermo-mechanical properties of shape memory polymer/carbon fiber composites

In this study, chopped carbon fiber reinforced trans-1, 4-polyisoprene (TPI) was developed via a proposed new manufacturing process with the aim of improving weak mechanical properties of bulk TPI bulk. Specimens of the developed shape memory polymer (SMP) composites were fabricated with carbon fiber weight fraction of 5%, 7%, 9%, 11% and 13%, respectively. Measured are the effects of chopped carbon fiber and temperature on: (a) shape recovery ratio and rate; (b) stress–strain relationship; (c) maximum tensile stress, strain and Young’s modulus; and (d) maximum stress and residual strain under a constant strain cyclic loading. In addition, SEM micrographs were also presented to illustrate the fracture surface. The present experimental results show that the SMP with 7% carbon fiber weight fraction appears to perform best in all the tests. This indicates that the 7% carbon fiber weight fraction could be the optimum value for the SMP developed using the proposed manufacturing process.     

Highly conductive graphene oxide/polyaniline hybrid polymer nanocomposites with simultaneously improved mechanical properties

Graphene oxide (GO) was added to a polymer composites system consisting of surfactant-wrapped/doped polyaniline (PANI) and divinylbenzene (DVB). The nanocomposites were fabricated by a simple blending, ultrasonic dispersion and curing process. The new composites show higher conductivity (0.02–9.8 S/cm) than the other reported polymer system filled with PANI (10⁻⁹–10⁻¹ S/cm). With only 0.45 wt% loading of GO, at least 29% enhancement in electric conductivity and 29.8% increase in bending modulus of the composites were gained. Besides, thermal stability of the composites was also improved. UV–Vis spectroscopy, X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) revealed that addition of GO improves the dispersion of PANI in the polymer composite, which is the key to realize high conductivity.     

Determination of fracture toughness and energy dissipation of SiO2-poly(methyl metacrylate) hybrid films by nanoindentation

In this paper we have applied different methods based on nanoindentation techniques to measure the toughness of SiO₂-poly methyl-methacrylate hybrid films on organic acrylic substrates. The hybrid films were deposited by the Sol-Gel method from precursor solutions containing tetraethyl-orthosilicate, methylmethacrylate and 3-trimethoxysilyl propyl methacrylate (TMSPM) as the coupling agent. The influence of TMSPM content in the hybrid precursor solution on the fracture behavior of the hybrid films was studied. The classical indentation crack length method was applied from nanoindentation tests to determine the stress intensity factor by direct measurement of crack length from atomic force microscopy images. A second method, based on the pop-in analysis allowed the separation of crack formation from film delamination from multiple pop-ins. Finally, a third method based on energy methods is also reported and discussed. The amount of TMSPM in the precursor solution showed a strong influence on the toughness of the hybrid films.     

Compressive mechanical properties of closed-cell aluminum foam–polymer composites

The compressive mechanical properties of two kinds of closed-cell aluminum foam–polymer composites (aluminum–epoxy, aluminum–polyurethane) were studied. The nonhomogeneous deformation features of the composites are presented based on the deformation distributions measured by the digital image correlation (DIC) method. The strain fluctuations rapidly grow with an increase in the compressive load. The uneven level of the deformation for the aluminum–polyurethane composite is lower than that for the aluminum–epoxy composite. The region of the preferentially fractured aluminum cell wall can be predicted by the strain distributions in two directions. The mechanical properties of the composites are investigated and compared to those of the aluminum foams. The enhancement effect of the epoxy resin on the Young’s modulus, the Poisson’s ratio and the compressive strength of the aluminum foams is greater than that of the polyurethane resin.     

Lightweight polyethylene non-woven felts for ballistic impact applications: Material characterization

The polyethylene non-woven felt, Dyneema Fraglight, has excellent capabilities to stop bomb fragments. According to the manufacturer, a felt with an areal density of 1.2 kg/m² stops a 17-grain projectile at 450 m/s. The research presented in this paper aims at improving our understanding of how non-woven felts work. Static tensile tests were performed at different strain rates and temperatures. The static tensile tests showed that there is an important size effect: the strength of the specimens decreases when increasing the size of the specimen, for lengths of 5 cm or less. This effect is expected since the felt is made by mixing, combing and needle punching of 5-cm-long fibers. The tests also showed that the felt is anisotropic and that at a temperature of 100 °C it loses a significant part of both its strength and strain to failure. Tensile tests at medium (1 s⁻¹) and high strain rates (1000 s⁻¹) did not show any evidence of strain rate dependence. Out-of-plane punching tests, designed to help with the modeling, were also performed and the results are presented.     

Development of a biocomposite based on green epoxy polymer and natural cellulose fabric (bark cloth) for automotive instrument panel applications

Natural fiber reinforced composites have attracted interest due to their numerous advantages such as biodegradability, dermal non-toxicity and with promising mechanical strength. The desire to mitigate climate change due to greenhouse gas emissions, biodegradable resins are explored as the best forms of polymers for composites apart from their synthetic counterparts which are non-renewable. In this study biodegradable bark cloth reinforced green epoxy composites are developed with view of application to automotive instrument panels. The optimum curing temperature of green epoxy was shown to be 120 °C. The static properties showed a tensile strength of 33 MPa and flexural strength of 207 MPa. The dynamic mechanical properties, frequency sweep showed excellent fiber-matrix bonding of the alkali treated fabric with the green epoxy polymer with glass transition temperature in the range of 160 °C–180 °C. Treatment of the fabric with alkali positively influenced the mechanical properties of the fabric reinforced biocomposites.     

Nano-indentation of hybrid silica coatings on surgical grade stainless steel

Hybrid silica-based coatings with tetraethoxysilane (TEOS), methyltrietoxysilane (MTES), hydroxyethyl-methacrylate (HEMA) and methacrylopropyl-trimethoxysilane (γMPS) as precursors, were employed to improve the performance of stainless steel used as orthopaedic material. Mechanical properties of the films, such as Young's modulus and hardness, were studied using the load and depth sensing indentation technique known as nano-indentation. The elastic/plastic and creep behaviours were also analyzed. Coatings with a high proportion of organic components (HEMA, γMPS) presented a more plastic response compared to the more vitreous coatings (containing only TEOS and MTES). They also showed the lowest Young's modulus and hardness. Therefore, the more vitreous coatings presented lower creep deformation that increased with the load applied.     

Improvement of formability and mechanical properties of magnesium alloys via pre-twinning: A review

Twinning can generate the change of texture and a large of twin boundaries, which can greatly influence the mechanical properties of magnesium alloys. Thus, pre-twinning can be considered to be a simple and feasible method to improve the mechanical properties of magnesium alloys. Recently, some studies have confirmed that pre-twinning can be an effective way to enhance the strength, formability and mechanical anisotropy of magnesium alloys. Based on these results, some aspects of the present research on the improvement of mechanical properties via pre-twinning are reviewed. The relevant mechanisms have been summarized. Finally, for this research field, a few critical scientific problems are also proposed.     

Evaluation of microstructure and mechanical properties of Al/Al2O3/SiC hybrid composite fabricated by accumulative roll bonding process

In this investigation, a new kind of metal matrix composites with a matrix of pure aluminum and hybrid reinforcement of Al₂O₃ and SiC particles was fabricated for the first time by anodizing followed by eight cycles accumulative roll bonding (ARB). The resulting microstructures and the corresponding mechanical properties of composites within different stages of ARB process were studied. It was found that with increasing the ARB cycles, alumina layers were fractured, resulting in homogenous distribution of Al₂O₃ particles in the aluminum matrix. Also, the distribution of SiC particles was improved and the porosity between particles and the matrix was decreased. It was observed that the tensile strength of composites improved by increasing the ARB passes, i.e. the tensile strength of the Al/1.6 vol.% Al₂O₃/1 vol.% SiC composite was measured to be about 3.1 times higher than as-received material. In addition, tensile strength of composites decreased by increasing volume fraction of SiC particles to more than 1 vol.%. Scanning electron microscopy (SEM) observation of fractured surfaces showed that the failure mechanism of broken hybrid composite was shear ductile rupture.     

Properties enhancement using oil palm shell nanoparticles of fibers reinforced polyester hybrid composites

Oil palm shell (OPS) nanoparticles were utilized as filler in fibers reinforced polyester hybrid composites. The OPS nanoparticles were successfully produced from the raw OPS using high-energy ball milling process. Fundamental properties including morphology, crystalline size, and particle size of the OPS nanoparticles were determined. Tri-layer natural fiber reinforcement (kenaf–coconut–kenaf fiber mat) polyester hybrid composites were prepared by hand lay-up techniques. The influences of the OPS nanoparticles loading in the natural fibers reinforced polyester hybrid composites were determined by analyzing physical, mechanical, morphological, and thermal properties of the composites. Results showed that the incorporation of the OPS nanoparticles into the hybrid composites enhanced the composite properties. Further, the natural fibers reinforced polyester hybrid composite had the highest physical, mechanical, morphological, and thermal characteristics at 3 wt.% OPS nanoparticles loading.