Band 23, Heft 2

Biocomposites (natural fiber composites) from local and renewable resources offer significant sustainability; industrial ecology, eco-efficiency, and green chemistry are guiding the development of the next generation of materials, products, and processes. Considerable growth has been seen in the use of biocomposites in the domestic sector, building materials, aerospace industry, circuit boards, and automotive applications over the past decade, but application in other sectors until now has been limited. Nevertheless, with suitable development, the potential exists for biocomposites to enter new markets and thus stimulate an increase in demand. Many types of natural fibers have been investigated with polymer matrices to produce composite materials that are competitive with synthetic fiber composites which require special attention. The agricultural wastes can be used to prepare fiber-reinforced polymer composites for commercial use and have marketing appeal. The growing global environmental and social concern, high percentage of exhaustion of petroleum resources, and new environmental regulations have forced the search for new composites, compatible with the environment. Many references to the current status of research work on the applications of biocomposites are cited in this review.

Electrical properties of plastic products can be adjusted by adding a certain amount of carbon nanotubes (CNT) in the injection molding process. However, injection molding parameters should be arranged carefully due to their influence on electrical properties of CNT-reinforced plastic composites. In this study, polycarbonate/CNT nanocomposites, having three different CNT concentrations (1, 3 and 5 wt%), were produced and injection molded by using three different injection temperatures and speeds to investigate their influence on electrical resistivity. It was found that the electrical resistivity was influenced greatly by the injection temperature when 1 wt% amount of CNT was used in the nanocomposite. However, the effect of injection speed was negligible.

This work presents the multiobjective optimization of machining parameters during the electrical discharge machining (EDM) of aluminum (Al)-silicon carbide (SiC) metal matrix composites (MMC). The process parameters considered were current, pulse on-time, dielectric flushing pressure, and SiC particles. A copper rod was used as an electrode. An Al-SiC MMC with Al 6061 as matrix and SiC particles having three different sizes (i.e., 15, 25, and 40 μm) were used as workpieces. The experiments were planned using design of experiments through response surface methodology (RSM). The mathematical models were developed to predict the better performance measures such as the material removal rate (MRR), electrode wear rate (EWR), surface roughness (SR), and cylindricity (CY). The desirability approach in RSM was performed for optimization. It was found that the MRR increases with increasing peak current, pulse on-time, flushing pressure, and particle size. The EDM parameters are to be analyzed for the MRR, EWR, SR, and CY. The best one is proposed for validation.

This study is aimed at investigating the production and wear properties of a functionally graded (FG) silicon carbide (SiC)-reinforced composite material, which was produced by stir casting followed by centrifugal casting. SiC powder (5 wt.%) was added into liquid aluminum at 750°C via stir casting, at which temperature a centrifugal force was applied to the mixture to drive the SiC particles toward the outer region of the mold. The results showed that two distinct regions formed in the cast samples after the centrifugation process. The outer region showed approximately 25% SiC particles resulting in almost SiC particle-free area in the internal region of the FG SiC-reinforced composite material. The test results showed that higher hardness and higher wear resistance could be obtained at the SiC-rich periphery of the cast FG composite material.

Within the scope of the experiments, the initial and final fracture behaviors in glass roving and glass cloth composites were investigated. After the production of two types of composite panels with the hand lay-up method, tensile and three-point bending tests on composites were conducted. Acoustic emission (AE) and optical microscopy (cross-sectional observation) analyses based on the various strain rates in bending tests were performed to see the fracture initiation and propagation in composites. The initial fractures were transverse cracks in the glass roving composites; these were delaminations in glass cloth composites. The final fractures were transverse cracks, delaminations, and fiber breakages in glass roving and glass cloth composites. In this study, the fracture process and mechanisms of glass roving and glass cloth composites were successfully identified by AE characteristics and cross-sectional observations.

Imitating the structure of steel-reinforced concrete, a composite coupling good damping capacity and mechanical property was fabricated by pressure infiltration progress. The aluminum (Al) matrix composite was hybrid reinforced by 20% volume fraction of SiC particle (SiC p ) and 20% volume fraction of TiNi fiber (TiNi f ). The damping capacity of the composite in the temperature range from 30°C to 290°C was studied using a dynamic mechanical analyzer (DMA). Due to the B19′→B 2 reverse martensitic transformation in TiNi f , a damping peak showed up in the heating process. Furthermore, both the hysteretic effect of the martensite/variants interfaces in TiNi f and the weak bonding interface between SiC p and TiNi f were attributed to the high damping capacity of the composite. After tension deformation, a compressive stress was formed in the composite in the heating process. With the help of compressive stress, the value of the damping peak was much higher than before, since the movement of dislocation in the Al matrix was easier.

In this paper, thermal buckling analysis of composite laminated beams resting on a two-parameter elastic foundation is carried out by means of the variational iteration method (VIM). The solution procedure is based on the first-order shear deformation beam theory of Timoshenko combined with the von Karman type of geometrical non-linearity. Both edges of the beam are assumed to be axially restrained while may possess various out-of-plane boundary conditions. The elastic foundation is modelled via the two-parameter Pasternak medium which takes into account the vertical interaction of the elements. The governing equilibrium equations are obtained by means of the virtual displacement principle. Stability equations are then obtained by means of the adjacent equilibrium criterion. These equations are uncoupled to extract individual equations in terms of lateral displacement. The resulted differential equations are solved via the VIM. The study examines the VIM in obtaining the closed-form analytical solutions for thermal buckling of composite laminated beams. Furthermore, it is shown that for some special materials with negative thermal expansion coefficient, buckling may occur under cooling rather than heating or it may not occur at all.

Considering the desired characteristics of functionally gradient materials (FGM), such as good thermal and wear resistance, this paper investigates the mechanical behavior of FGM microgripper under DC voltage and temperature variation. It is assumed that the two microbeams of the FGM microgripper are mounted symmetrically against each other, and the volume of ceramic varies exponentially with microbeam thickness. The nonlinear equations governing the static and dynamic deflection of microbeams due to the application of DC voltage and temperature variation are derived and solved using the step-by-step linearization method and the Galerkin method. In previous studies, the mechanical behavior of a microgripper with homogenous and the same material has been investigated; in this paper, the response and stability of the FGM microgripper against DC voltage and temperature variation are investigated. Also, the effect of geometrical dimensions, ceramic volume, and its variations with microbeam thickness on the mechanical behavior and system stability is studied.

Concrete is one of the materials in which polymer wastes are utilized. Generally, these wastes are added at specific rates in scientific studies but an important problem of waste polymers is size irregularity. Even when consistent dosage rates are used, variations in polymer size can lead to variability in the physical and mechanical properties of the concrete produced. The aim of this study is to determine physical and mechanical properties of polyvinyl chloride (PVC)-containing concretes. In order to produce normal and high strength concretes, 10%, 20%, and 30% replacement ratios of PVC powder and granules by volume of aggregate are used. Slump, fresh and hardened densities, compressive strength, capillary water absorption, and abrasion were tested on all concrete types. As the PVC ratio increases, important changes are seen in all physical and mechanical concrete properties. The unit weights of the 10%, 20%, and 30% replacement PVC powder concretes are lower by ∼4%, 8%, and 13%, respectively, as compared to the reference mixtures, and the replacement PVC granule concretes are lower by ∼2%, 4%, and 7%. Compressive strength test results showed similar trends. As PVC replacement increases, the capillary water absorption decreases between 10% and 50%, and abrasion decreases between 27% and 77%.

This study focused on the dry sliding wear behavior of the natural fiber called borassus fruit fiber (Palmyra fruit fiber) reinforced polyester composite. Composites are molded with different fiber weight fractions. Composites are fabricated by using both the untreated and the mercerized fibers. Mercerizations of the fibers are done with 1 N solution. The structural properties like tensile, flexural, and impact strengths are experimented as per ASTM and reported. The dry sliding wear study was done using the Pin-on-Disc apparatus as per ASTM G99. In particular, more emphasis has been devoted for wear behaviors at different velocity conditions and loads. Based on the experimental data, the optimum sliding velocity and the corresponding load were suggested.

Lignin is a coproduct of biofuel and paper industries, which exhibits binding qualities when mixed with water. Lignin is an ideal candidate for a sustainable stabilization of unpaved roads. To this end, an experimental program was devised and carried out to quantify effects of lignin on compaction and early age shear strength behaviors of sand. Samples were prepared by mixing a particular type of coproduct called calcium lignosulfonate (CaL) with sand and water. Based on the extensive analyses of six series of strength tests, it was found that a normalized cohesion increased with an increasing normalized areas ratio. Normalizations were carried out by dividing the cohesion and area ratio by gravimetric CaL content whereby the area ratio was obtained by dividing the portion of the cross-sectional area occupied with lignosulfonate-water (CaL-W) paste by the total cross-sectional area. While the increase in the normalized cohesion eventually leveled out, the cohesion peaked at 6% of CaL. Thus, sand-CaL-water (S-CaL-W) mixes sustained larger shear stresses than dry sand for a range of normal stresses below the limiting normal stress. Consequently, the early age behavior indicates that adding CaL-W to sand is clearly beneficial in the near-surface applications in dry sand.

This study shows the optimization method for a new complex structural model: laminated carbon fiber-reinforced plastic (CFRP) deck plates with polystyrene foam (EPS) inner core. The structure is designed for both minimal cost and minimal weight, taking into consideration the design constraints as follows: maximum deflection of the total structure, stress in the composite plates, stress in the polystyrene foam, eigenfrequency of the structure, thermal insulation of the structure, and size constraints for the design variables.