Band 25, Heft 2

Metal matrix composites (MMCs) are the new-generation advanced materials that have excellent mechanical properties, such as high specific strength, strong hardness, and strong resistance to wear and corrosion. All these qualities make MMCs suitable material in the manufacture of automobiles and aircraft. The machining of these materials is still difficult due to the abrasive nature of the reinforced particles and hardness of MMCs. The conventional machining of MMCs results in high tool wear and slow removal of materials, thereby increasing the overall machining cost. The nonconventional machining of these materials, on the contrary, ensures much better performance. This paper reviews various research works on the development of MMCs and the subsequent hybrid composites and evaluates their performances. Further, it discusses the influence of the process parameters of conventional and nonconventional machining on the performance of MMCs. At the end, it identifies the research gaps and future scopes for further investigations in this field.

A genetic algorithm-based method is proposed to globally optimize the stacking sequence of multi-sandwich-panel composite structures for minimum weight with strength and buckling considerations. The prerequisites for the continuity between sandwich panels are first studied. To implement the summarized continuity rules in the evolutionary optimization, three newly constructed chromosomes are developed to encode the global stacking sequence with no additional repair. Genetic operators, including specialized mutation, swapping and crossover operators, are also developed to effectively explore the design space and keep the continuity rules followed. The Hashin criterion and maximum stress criterion are used to evaluate the strength of sandwich panels. A typical multi-sandwich-panel composite structure with identical and different core thicknesses is optimized to verify the validity and efficiency of the proposed method. It is found that much lighter solutions are obtained with an acceptable efficiency in all cases. It is also found that the weight of the multi-sandwich-panel composite structures can be further reduced when the core thicknesses are not identical.

An automated multiaxial cyclic loading pressure testing rig was developed as an alternative to the existing short-term test procedure specified by ISO 14692 and ASTM D2992. Conventionally, 14 months are required to estimate the residual properties at the end of expected life (20–50 years). The test periods and costs associated with this long-term test are high. To resolve this, a novel rig was developed based on the ultimate elastic wall stress (UEWS) algorithm, allowing five multiaxial stress ratios to be tested. The test involved the cyclic pressurizing of the pipe with 1-min of pressure and 1-min of zero pressure. The test rig was tested under five stress ratios using glass-epoxy composite pipes with winding angles of [±45°] 4 , [±55°] 4 and [±63°] 4 . The rig is capable of testing both static and cyclic pressure loading, thereby reducing the test period and related costs. The results provide a more realistic failure envelope.

The unmodified and nano-SiO 2 modified glass fiber reinforced polymer (GFRP) composites were prepared by the hot-compression molding process to investigate the effects of nano-SiO 2 on the mechanical and hygric properties of the GFRP composites. The results indicate that the nano-SiO 2 modification results in an increase of 9.7% and 7.9% in the tensile and flexural strength of the GFRP composites, and a decrease of 10.6% in the interlaminar shear strength (ILSS). The maximum swelling of the unmodified GFRP is 2.6 times as that of the nano-SiO 2 modified GFRP. The normalized-ILSS decrease of the nano-SiO 2 modified GFRP is only 12% after 138 days aging, while that of the GFRP reaches 31%. After 95-days hygric-aging, the decrease of the normalized flexural strength is 15.3% for the GFRP, while the normalized flexural strength of the nano-SiO 2 modified GFRP still maintains an increase of 5.0%. It is concluded that the nano-SiO 2 particle could improve the mechanical and hygric properties of the GFRP composites.

Homogeneous and functionally graded LM25 aluminium (Al) composites were fabricated by incorporating silicon nitride (10 wt%, 40 µm) particles through liquid metallurgy and centrifugal casting, respectively. The performance of these composites was compared with unreinforced alloy. The microstructural behaviour of the surfaces of unreinforced alloy, homogeneous composite and functionally graded composite (outer, middle and inner surfaces) were examined through optical microscopy. These surfaces were also evaluated for mechanical properties. An abrasive wear test was conducted on all these surfaces to determine their effect on wear rate. The microstructural results revealed a particle-rich region at the outer surface of the functionally graded composite material and uniform dispersion of reinforcement particles in the homogeneous composite. The outer region of the functionally graded composite showed greater hardness and the homogeneous composite displayed higher tensile strength. The abrasive wear rate increased with an increase in load and decreased with an increase in speed, and the particle-rich outer surface showed a lower wear rate. Scanning electron microscopy analysis revealed a particle-rich outer surface of functionally graded composite with fewer scratches. Therefore, higher wear resistance was observed at the outer periphery of functionally graded composites and this property can be well-utilised in automotive tribo-components such as in cylinder liners for improved performance.

Damages and economical losses due to problematic soils have caused researchers to conduct many studies for the stabilization of these soils within years. Especially, the use of fly ashes in soil stabilization provides great benefits in contributing to the economy, as well as decreasing the environmental pollution. In the present study, the stabilization characteristics of soil-fly ash mixtures were evaluated in terms of Atterberg limits, compaction characteristics, swell potential and unconfined compressive strength with curing effect. To determine these effects, Catalagzi and Soma fly ashes obtained from Turkey were used in different proportions by weight for stabilization of clay soil samples. It was found that the plasticity index of the soils decreased considerably with the addition of fly ashes, while the strength improved and swell potential decreased. The decreasing trend in the swell percentage and swell pressure values decelerated especially after 25% fly ash additive content and negligible changes occurred. Similar behavior was observed in strength tests. Experimental results show that swelling and strength properties of the soils could be improved by using fly ash and Soma fly ash is far more effective than Catalagzi fly ash.

Polyetheretherketone (PEEK)/Ni foam co-continuous composites were designed and prepared via the hot pressing technique, and their erosion-corrosion behaviors were evaluated using an impinging jet apparatus in 1% H 2 SO 4 and 5% silica sand with a flow rate of 30 m/s. Optical microscopy and scanning electron microscopy were used to describe the damage morphologies. A strong combination was shown between Ni foam and PEEK in the composites. PEEK was reinforced with Ni foam, and the erosion-corrosion resistance of the composites increased with the decreasing density and pore size of Ni foam. Volume loss under normal impact was higher than that under oblique impact.

Optimization design and manufacturing play an important role in obtaining successful composite structures with high efficiency and safe use of materials. In this paper, we first present the optimization design procedure for a composite box girder by ANSYS parametric design language (APDL) in the ANSYS software. The input parameters used in the simulation work were determined via fundamental experimental tests of composite specimens. Then we manufactured the designed composite box girder by mold-pressing prepreg technology according to the optimization results. The finial composite girder structure composed of arch top, web and bottom composite plate was obtained. The optimization procedure indicated that the use of stiffening plates in a girder could decrease the weight and increase the failure load. The location and ply mode of the stiffening plates in girder were suggested. The three-point-bending test was performed on the girder, and the test indicated that load-carrying capacity in unit mass of the optimized girder was as high as 107.8 N/g. Simulation and experimental results match well, and the maximum and minimum stresses in each layer were within the strength limitation of carbon material after optimized in the procedure.

Functionally graded materials (FGMs) are engineered materials that are inhomogeneous and can be purposefully processed to obtain discrete or continuously varying compositions/microstructures over a definable geometrical length. FGMs can be used in a number of applications, such as aircrafts, combustion nozzles, gas turbines, energy conversion cells, biomaterials, etc. The objective of this paper is to review the new developments in production processes and their prospects in the creation of next-generation FGMs. Traditionally, four potential methods were used for fabrications of FGMs, i.e. powder metallurgy, chemical vapor deposition, self-propagating high-temperature synthesis, and plasma spraying. Some of the recently developed methods are the cast-decant-cast process, friction stir processing, and laser-engineered net shaping, which are usually cost-effective and used to make a quiet change in properties. An effective production method for conversion of the concept of gradient into practice is still a challenge for the research community. In this paper, research works toward meeting these challenges will be highlighted, and the future scopes of investigation in this area will be explored.

Epoxy composites reinforced by Zirconium diboride (ZrB 2 ) particles were investigated by finite element models (FEMs). It helped to explore the relationship between the thermal conductivity of composites and the volume fraction, size, shape, orientation, and arrangement of the ZrB 2 particles. The results showed that the thermal conductivity performance of composites was improved effectively when filled with ZrB 2 particles. Specifically, epoxy composites filled with 50 vol% spherical ZrB 2 particles had 12.05 times the thermal conductivity of epoxy resin. At the same volume fraction, the number of ZrB 2 particles in the epoxy matrix has little influence on thermal conductivity due to the dimensionless models. At a high volume fraction, rectangular ZrB 2 particles improved thermal conductivity more effectively than spherical particles. In the comparison of thermal conductivities among composites reinforced by rectangular fillers, the thermal conductivities of composites were clearly affected by the length-width ratios of fillers, and this effect was monotonically increasing. The vertical orientations of particles could conduct heat most effectively compared with slant and parallel orientations. The agglomerate distribution of ZrB 2 particles has the negative effect of thermal diffusion in a certain direction compared with homogeneous distribution.

Cu-WS 2 -graphite-WS 2 nanotubes composite was fabricated by the powder metallurgy hot-pressed method. The effects of electrical current (5–15 A/cm 2 ) and sliding velocity (5–15 m/s) on the electrical wear behaviors of the composite were investigated using a block-on-slip ring wear tester rubbing against Cu-5 wt% Ag alloy ring under 2.5 N/cm 2 of applied load. The lubricating effect of WS 2 nanotubes and composition of tribo-film were analyzed. The results demonstrated that the contact resistance decreases but the wear rate increases as electrical current increases, because the adverse effects of electrical current soften the materials at “a-spots” and damage the tribo-film. Due to the adsorption of gaseous molecule film on the tangential direction of slip ring surface, with the rise of sliding velocity, the contact resistance increases while the wear rate reaches the minimum at a sliding velocity of 10 m/s. The reasonable addition of WS 2 nanotubes into the Cu-WS 2 -graphite composite to replace WS 2 powder can result in a reduction of both contact resistance and wear rate. X-ray photoelectron spectroscopy (XPS) analyses revealed that copper oxides, graphite, WS 2 and WS 2 nanotubes in the tribo-film play the main lubrication action at the tribo-interface.

We report the preparation and employability of carbon-coated Fe 3 O 4 (Fe 3 O 4 /C) microspheres functionalized with chloroacetic acid (CAA) for the removal of methylene blue (MB) in aqueous solution. The prepared magnetic microspheres (Fe 3 O 4 /C-CAA) were characterized by the following techniques: X-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectrometer, vibrating sample magnetometry, and Brunauer-Emmett-Teller. The characterization results showed that Fe 3 O 4 /C microspheres were modified by CAA without any phase change. Fe 3 O 4 /C-CAA microspheres have higher adsorption capacity for MB compared to Fe 3 O 4 /C microspheres. The Langmuir, Freundlich, and Temkin adsorption models were applied to describe the equilibrium isotherms, and the Langmuir adsorption model fitted well with the equilibrium data. The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetics data. However, the pseudo-second-order kinetic model fitted better with the adsorption kinetics data.

In the present study, the effect of fiber surface treatments (alkali and acrylic acid) on the thermal degradation behavior of coir fiber (CF)-low-density polyethylene (LDPE) composites with or without compatibilizer (maleic anhydride grafted LDPE, MA-g-LDPE) using thermogravimetric and derivative thermogravimetric analyses (TG/DTG) was analyzed and compared with those of untreated fiber composites. The TG/DTG results revealed that the thermal stability of the CF improved after the chemical treatments. However, the composite containing treated fiber showed lower thermal stability and started to degrade at a faster rate above 380°C in comparison to composites containing untreated fiber composites. Furthermore, the addition of MA-g-LDPE led to improvement in the thermal stability of both treated and untreated fiber composites in comparison to the same composite formulation without MA-g-LDPE. The composite containing untreated fiber and MA-g-LDPE demonstrated superior thermal stability among all the formulated composites, indicating strong fiber-matrix adhesion.

In this research work, the recycling of waste tea dust particles was done by preparing the injection moulded polypropylene (PP) composites using different (10–40 wt.%) loadings of tea dust particles as a filler. The tea dust particles were treated with maleic anhydride (MA) and its esterification effect was studied on physico-mechanical (morphology, mechanical, thermal and swelling) properties of tea dust:polypropylene (TD:PP) composites. Surface modification of tea dust particles was observed due to the MA treatment i.e. the esterification effect. The surface morphology of the composites showed better interfacial bonding between the maleated tea dust particles and PP than the untreated particles. The mechanical properties of the maleated TD:PP composites were found to be improved (200–300% higher tensile strength, 250% higher tensile modulus, 43% higher flexural strength and 10% higher hardness) as compared to untreated TD:PP composites. Crystallinity and thermal properties of the maleated TD:PP composites showed increasing trend with increase in filler content. Water absorption tests showed that maleated TD:PP composites absorb less water than that of untreated one. The increment in all these properties is due to the greater compatibility in tea dust particles and PP by MA treatment. Thus, tea dust particles can be suggested for preparation of composite materials.

The thermal conductivity of particulate composite models is well documented in the literature. This paper attempts to fit the experimental data for the thermal conductivity of polymer nanocomposites to a three-phase Krenchel model. The use of this model is applicable for structures that consist of a polymer matrix, a nanofiller, and an interfacial layer around the nanoparticles. The effect of Kapitza’s thermal resistance is implemented in the model along with the assumption that the nanofillers are cylindrical and well connected to each other; however, no parameters related to any type of dispersants or the dispersion techniques are stated in the model. The results of the three-phase Krenchel model were validated using the experimental data of thermal conductivity of multiwall carbon nanotubes embedded in polypropylene matrix nanocomposites. It was found that the model was in good agreement with the experimental thermal conductivity data. Moreover, the results from the model showed that the filler geometrical packing factor was 0.75; consequently, the carbon nanotubes formed bundles of several cylindrical tubes. The length of the interface between the nanotubes and the polymer matrix was around 1 Å. Finally, the thermal conductivity of the composite bundle cylinder was 21.63 W/(m K).

In this paper, a novel molecular dynamic model is presented to describe the growth mechanism of three-dimensional (3D) graphene-carbon nanotube (G-CNT) hybrid structure synthesized by catalytic chemical vapor deposition. For this purpose, first, the physisorption of a carbon atom on a graphene sheet (GS) is studied. Then the model is formulated by using kinetic theory and the longitudinal phonon oscillation of adsorbed carbon atoms on GS. Results show that the CNT grows on GS up to 0.3 mm. Also, there is an optimum temperature for growth of the 3D G-CNT hybrid structure, which can be calculated by the presented model. Finally, it is shown that increase of partial pressure leads to increase of length of growing CNT on GS.

The reinforcing abilities of cellulose microfibers and nanofibrillated cellulose (NFC) in poly(lactic acid) (PLA) were evaluated. NFC successfully prepared from regenerated cellulose fibers using high-speed blending for 60 min was introduced in a PLA matrix. The physical and mechanical properties of NFC-reinforced PLA composites were investigated in comparison with those of the composites with microfibers. NFC fibrils with diameters in the range of 100–500 nm were disintegrated from micron-sized regenerated fibers. A slight decrease in the degree of crystallinity and degradation temperature obtained for NFC after mechanical treatment was found compared with untreated microfibers. The introduction of NFC in the PLA effectively increased the tensile strength and Young’s modulus of the composites by 18% and 42%, respectively. The use of micron-sized fibers to reinforce PLA, on the other hand, showed a slight improvement in Young’s modulus (13%). The improvement in the mechanical properties of the composites reinforced with NFC was found because of the higher surface area of NFC and better interaction between the matrix and NFC fibrils. This allowed stress to transfer from the matrix to the reinforcement. NFC prepared using the high-speed blending could be an alternative to use as reinforcement in composites.

Porous recycled glass beds were produced for the potential use in water remediation. The present work discusses the structural and mechanical characteristics of filters made of commercially available powdered recycled glass. The study measured the porosity and percolation performance of the sintered glass beds as a function of the sintering parameters and the particle size of the original powdered glass. Moreover, because TiO 2 can serve as a photocatalyst to degrade organic pollutants, a TiO 2 /recycled glass composite was also studied. Optical microscopy helped measure the resulting porosity by quantitative image analysis. Finally, a performance map that specified the composite porosity, percolation, and compression characteristics was obtained as a function of sintering time, sintering temperature, glass particle size, and the percentage of TiO 2 added.

In this study, glass-fiber, grafted by epoxide-terminated hyperbranched polymer (GF-HBPE), was incorporated into epoxy resins for reinforcement purpose. The effects of GF-HBPE content on mechanical properties of the resulting epoxy-based composites, such as tensile strength, percentage elongation at break, flexural strength, and impact strength, were investigated. The experimental results revealed that GF-HBPE substantially outperformed impact resistance in both tensile and flexural tests. For instance, the tensile strength, percentage elongation at break, flexural strength, and impact strength of the epoxy composite with 1 wt% GF-HBPE increase by about 23.6%, 125%, 26%, and 74.5%, respectively, compared to the unmodified epoxy thermoset.