Microstructure and mechanical properties of an Al–TiC metal matrix composite obtained by reactive synthesis

A metal matrix composite has been obtained by a novel synthesis route, reacting Al₃Ti and graphite at 1000 °C for about 1 min after ball-milling and compaction. The resulting composite is made of an aluminium matrix reinforced by nanometer sized TiC particles (average diameter 70 nm). The average TiC/Al ratio is 34.6 wt.% (22.3 vol.%). The microstructure consists of an intimate mixture of two domains, an unreinforced domain made of the Al solid solution with a low TiC reinforcement content, and a reinforced domain. This composite exhibits uncommon mechanical properties with regard to previous micrometer sized Al–TiC composites and to its high reinforcement volume fraction, with a Young’s modulus of ∼110 GPa, an ultimate tensile strength of about 500 MPa and a maximum elongation of 6%.     

Tribological behavior of PTFE nanocomposite films reinforced with carbon nanoparticles

Carbon-based nanoparticles synthesized by heat treatment of nanodiamond in the temperature range of 1000–1900 °C were added to PTFE film to investigate the structural effect of the carbon particles on the tribological properties of PTFE composite film. Carbon-based nanoparticles were prepared by milling with micron sized beads in chemically treated water before their addition to PTFE film. The wear and frictional properties of PTFE nanocomposite film were measured by the ball on plate type wear test. The wear resistance of PTFE film was found to be enhanced by the addition of 2 wt% of carbon nanoparticles. The wear coefficient of PTFE film was decreased from 16.2 to 3.5 × 10⁻⁶ mm³/N m by the addition of carbon-based nanoparticles heat-treated at 1000 °C. Increasing the heating temperature of the nanodiamonds caused the extent of aggregation and particle size to increase. The wear resistance of PTFE nanocomposite film was enhanced by the addition of nanodiamonds heat-treated at 1000 °C, but decreased when the heat treatment temperature of carbon nanoparticles was further increased. Tribological behavior of PTFE nanocomposite films depending on the types of carbon nanoparticles were explained based on the structural, physical and chemical modification of carbon nanoparticles.     

Analytical modeling and experimental study of tensile strength of asphalt concrete composite at low temperatures

In this study, analytical modeling of the tensile strength of hot-mix asphalt (HMA) mixtures at low temperatures was developed. To do this, HMA mixtures were treated as a two-phase composite material with aggregates (coarse and fine) dispersed in an asphalt mastic matrix. A two-phase composite model, which was similar to Papanicolaou and Bakos's [J. Reinforced Plast. Compos. 11 (1992) 104] model with a particle embedded in an infinite matrix, was proposed. Unlike Papanicolaou and Bakos's model, an axial stress was introduced to the fiber end to consider the load transferred from the asphalt mastic the aggregate. Efforts were also made to consider the effect of aggregate gradation, asphalt mastic degradation, and interfacial damage between the aggregates and asphalt mastic matrix on the tensile strength of the HMA mixtures. Experimental investigations were conducted to validate the developed theoretical relations. A reasonable agreement was found between the predicted tensile strength and the experimental results at low temperatures. Parameters affecting the tensile strength of asphalt mixtures were discussed based on the calculated results.     

Self-healing property of epoxy/nanoclay nanocomposite using poly(ethylene-co-methacrylic acid) agent

This paper investigates the self-healing repair of cracks in an epoxy/nanoclay nanocomposite using mendable poly[ethylene-co-methacrylic acid] (EMAA) particles. The effects of two different concentrations of EMAA agent on the self-healing efficiency were measured using single edge notch bar (SENB) testing. Inclusion of EMAA particles into the nanocomposite results an increase in the fracture strength and strain of the SENB specimens. Damaged SENBs were healed at 150 °C for 30 min to achieve up to 63% recovery in critical stress intensity and over 85% recovery in sustainable peak load. Also, X-ray diffraction (XRD) analysis and tensile test used in order to examine the nanocomposite structure and investigate the effects of EMAA inclusion on the nanocomposite mechanical properties. The pressure delivery mechanism of the healing agent is shown by scanning electron microscopy (SEM) images. It seems EMAA can be used as an effective self-healing agent for epoxy/nanoclay nanocomposites.     

Numerical study of the effects of reinforcement/matrix interphase on stress-strain behavior of YAl2 particle reinforced MgLiAl composites

For the potential influence produced by the reinforcement/matrix interphase in particle reinforced metal matrix composites (PMMCs), a unit cell model with transition interphase was proposed. Uniaxial tensile loading was simulated and the stress/strain behavior was predicted. The results show that a transition interphase with both appropriate strength and thickness could affect the failure mode, reduce the stress concentration, and enhance the maximum strain value of the composite.     

Fatigue behaviour of nanoclay reinforced epoxy resin composites

Nanoparticle filling is a feasible way to increase the mechanical properties of polymer matrices. Abundant research work has been published in the last number of years concerning the enhancement of the mechanical properties of nanoparticle filled polymers, but only a reduced number of studies have been done focusing on the fatigue behaviour. This work analyses the influence of nanoclay reinforcement and water presence on the fatigue behaviour of epoxy matrices. The nanoparticles were dispersed into the epoxy resin using a direct mixing method. The dispersion and exfoliation of nanoparticles was characterised by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Fatigue strength decreased with the nanoclay incorporation into the matrix. Fatigue life of nanoclay filled composites was significantly reduced by the notch effect and by the immersion in water.     

Strength analysis of particulate polymers

Impregnating polymeric matrix with stiff particles may significantly improve structural response of a composite material. Such improvements have to be weighed against the effects of the stress concentration at the particle–matrix interface that influence local strength and toughness. In the present paper we elaborate on the issue of local stresses and strength in particulate polymer matrix composites considering polyurethane matrix impregnated with alumina particles in numerical examples. The parametric analysis presented in the paper is concerned with the effects of the particle volume fraction and the particle-to-matrix stiffness ratio on the local stresses and initial damage. We also discuss the resilience of the impregnated polyurethane, i.e. the density of energy necessary to produce initial damage. The approach to the analysis of fracture in the composite with initial damage is discussed accounting for available experimental observations. Three scales of fracture corresponding to different phases of the development and propagation of the crack are identified, including microfracture at the particle–matrix interface and mesofracture limited to the matrix surrounding the particle. While these scales of fracture should be analyzed by numerical methods, macrofracture that occurs after the crack “emerged” from the representative unit cell where it originated can be considered using available analytical techniques. The methodology of the stress analysis of a particulate material consisting of an incompressible hyperelastic matrix and much stiffer elastic particles is also proposed in the paper.     

Fatigue and Izod impact performance of carbon plain weave textile reinforced epoxy modified with cellulose microfibrils and rubber nanoparticles

This work details an experimental investigation on understanding the effects of hybrid epoxy resins, filled with micro-fibrillated cellulose (MFC) and carboxylated nitrile-butadiene rubber nanoparticles (XNBR), on the tensile–tensile fatigue performance of carbon plain weave textile reinforced composites. Twelve combinations of MFC and XNBR weight contents in the epoxy resin (from 0% to 0.5% MFC and from 0% to 3% XNBR) were considered for preliminary quasi-static tests and five of them were selected to study the fatigue behaviour considering different loading levels. Moreover, the effect of the twelve fillers contents was observed on the Izod impact strength. The investigation finds that the best fatigue performance, for the considered weight contents of fillers, is of the composite enhanced with the maximum content of MFC. The SEM observations of the fracture surfaces indicate the extensive “plastic” deformation of the matrix and the improved fibre and matrix adhesion.     

Glass fibers with clay nanocomposite coating: Improved barrier resistance in alkaline environment

Coatings made from neat vinyl ester and nanoclay reinforced vinyl ester composites are applied onto individual glass fibers as well as rovings to evaluate their barrier resistance against alkali and moisture attack. The fibers coated with clay nanocomposites present a significantly less damage caused by the diffusing alkali ions, giving rise to a much higher residual tensile strength after aging than the fibers without coating or those with a neat polymer coating. The static fatigue test performed on individual fibers verifies the advantage of using nanoclay composite to retard the corrosion process under the combined stress and alkaline environment. Similar beneficial effects of incorporating nanoclay on residual strength are identified for impregnated fiber bundles. The above observations confirm the excellent barrier characteristics of intercalated/exfoliated nanoclay in polymer that are applied in composite structures on both the microscopic and macroscopic scales.     

Cure path dependency of mode I fracture toughness in thermoplastic particle interleaf toughened prepreg laminates

The effect of cure cycle on fracture behaviour of a commercial thermoplastic particle interleaved prepreg system was investigated. Laminates were manufactured at 700 kPa in an autoclave using eight different thermal cycles that included both raising the cure temperature above the standard 180 °C cure cycle and incorporating an intermediate dwell stage between 150 and 170 °C prior to reaching the 180 °C cure temperature. Double cantilever beam tests were conducted on specimens from the cured laminates. The stick–slip crack behaviour, observed in samples manufactured using the standard cure cycle, changed to stable crack growth when processing deviated by 10 °C. The mode I fracture toughness values were reduced by 11–22% when incorporating an intermediate dwell stage before the final cure temperature. Scanning electron microscopy inspection of the fracture surfaces showed differences between samples made by standard cure cycles and those made using process deviations.