Ali Reza Sabet

The aim of this study was to evaluate the influence of organo‐montmorillonite (OMMT) content on rheology, crystalline structure, and also hardness and tensile properties of uncured and lightly cured acrylonitrile‐butadiene rubber (NBR)/poly(ethylene‐co‐vinyl acetate) (EVA)/OMMT nanocomposites. The nanocomposites containing 0 to 7 wt% OMMT was prepared and then cured with 0.3 wt% dicumyl peroxide. The low‐angle X‐ray diffraction results revealed that curing clearly improved the degree of exfoliation in the materials having high OMMT content. It was found from the hardness and tensile tests that the values of hardness, tensile strength, modulus, and energy at break were higher for the cured nanocomposites than those of the uncured materials in the range of OMMT examined. The results obtained from the Casson plot revealed that the nanofiller played a more effective role in increasing the yield stress of the uncured materials than that of the cured counterparts at a constant OMMT content. The characteristic relaxation time was also progressively increased with OMMT content for the uncured materials; however, the value was higher for the cured materials and it was much less sensitive to the nanofiller content. The I₁₁₀/I₂₀₀ peak intensity ratio of EVA calculated from the wide‐angle X‐ray diffraction patterns decreased with increasing in OMMT content for the uncured and cured materials; however, the value was always higher for the cured counterparts.

The mixture design method was used to model the physical and mechanical properties of ethylene-octene copolymer (EOC) nanocomposite containing organically modified montmorillonite (OMT) which were cross-linked dynamically by various amounts of dicumyl peroxide (DCP). A mixture design technique with three components was employed to assess the correlations between the selected properties of the nanocomposites and the component values. For this purpose, EOC, OMT and DCP content were selected as the components. The influences of these components were studied on the tensile strength, modulus at 100% strain, strain at break, x-ray peak intensity and the initial slope of the logarithm of storage modulus versus the logarithm of angular frequency of the nanocomposites prepared. The regression equations of the models as well as contour plots were generated for the properties studied. Good agreements were found between the experimental results and those predicted by the models. The contour plots of each property were overlaid within the applied constraints to discover the combination of factor ranges that provided the nanocomposite with optimal performance.

This study experimentally investigates the high-velocity impact response of long glass fiber-reinforced polypropylenes with different fiber lengths. The study considers three long fiber thermoplastic composites, i.e. 5, 10, and 20 mm prepared via a combination of extrusion and pultrusion processes and a crosshead die. An internal mixer was used to obtain an isotropic compound. The dispersion quality of each compound was confirmed using burn off test. A gas gun with a spherical projectile was employed to conduct high-velocity impact tests at three velocities of 144, 205, and 240 m/s. Internal mixer operation resulted in extensive fiber length reduction for all three long fiber thermoplastic lengths. Results from mechanical tests (Tensile and Izod impact) revealed an increasing value with increase in long fiber thermoplastic length, i.e. fiber length. High-velocity impact results showed higher impact performance for 20 mm long fiber thermoplastic compound compared to 5 and 10 mm long fiber thermoplastic containing specimens. Rate of increase in energy absorption from neat polypropylene to 5 and 10 mm long fiber thermoplastic compounds is much higher than from 10 to 20 mm long fiber thermoplastics. High-velocity impact tests indicated that there may be a threshold value for fiber length beyond which the fiber length plays a lesser role. Scanning electron microscopic analysis showed more fiber breakage at the impact point at a higher impact velocity than the lower end of high-velocity impact.

This study investigates high velocity impact performance of glass-reinforced plastic (GRP) laminates struck by sharp nose conical projectiles and compares the experimental results with some available predicting models. Five models were selected for assessment. Close correlation was obtained between predicted ballistic limit velocities from the models, which incorporated projectile nose geometry with that of experimental results. Considerable scatter was observed for the other models. Projectile deviation from normal impact during perforation was the reason for this discrepancy. Successful modification was made to one of the models using residual velocity results from a high velocity impact test instead of quasi-static results.

This study investigates high velocity impact performance of nanoclay reinforced polyurethane foam core composite sandwich panels. The sandwich structure consists of composite facings made from glass fiber woven roving reinforced unsaturated polyester resin and rigid polyurethane foam core with density of 49 kg/m³. High velocity impact tests in the range of 100–140 m/s were conducted with 10.7 g semispherical tip steel projectile. The amounts of nanoclay incorporated in the foam core were 0.25, 0.5, 1, and 3 wt%. Small angle x-ray scattering showed the sample containing 0.5 wt% nanoclay has better clay dispersion. Results showed specimen containing 0.5 wt% nanoclay has the highest impact performance and energy absorption as well as lowest projectile residual velocity for the plates that experienced full perforation. The specimen containing 3 wt% nanoclay showed lowest ballistic performance. The presence of nanoclay in the foam structure resulted in an increase in the number of cells per unit volume and reduced cell size.