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Synthetic mesophase pitches, extensively used as graphite precursors, manifest particular fluid-dynamic properties given their liquid crystal nature. Their recent use in infiltration processes to manufacture graphite-based monolithic and porous materials demands the study of their physical properties, mainly viscosity and contact angle, under dynamic conditions. In this work a new infiltration device was conceived and constructed to measure the infiltration kinetics of the AR24 naphthalene-based mesophase pitch and TiC nanoparticle-doped AR24 mesophase pitch into preforms of packed NaCl particles. The experiments allowed activation energies for viscosity to be obtained, along with pseudo-equilibrium and advancing contact angles. [ABSTRACT FROM AUTHOR]

A novel method of producing multilayered steels (MLS) with harmonically variable composition was developed by stacking the requisite number of layers, drilling uniform holes into the stacked assembly, inserting high strength rods of a suitable diameter into the holes, and hammering to interlock the multiple layers to finally form a multilayer preform. The preform was then subjected to severe plastic deformation processes, like cold forging, cold and/or hot rolling to obtain the final multi-layered product. High Carbon (H), Medium Carbon (M), Low Carbon (LC, L), Stainless steel (SS) sheets and Cr powder were chosen as the stacking materials and various stacking sequences were prepared. The interface between different layers showed strong diffusion bonding with very little or no presence of voids/pores suggesting excellent union. Compositional analysis showed alternate distribution of constituent elements across different layers of steels in different combination of multi-layered products. Flexure test of the SS-LC multilayer showed that the crack initiated due to early failure of SS layer was inhibited from growing due to the energy absorbing tendency of the LC steel on either side of the SS layer. Hardness and tensile properties of multi-layered steels depended on the different alternate combinations of various materials. [ABSTRACT FROM AUTHOR]

Chemical vapour infiltration (CVI) is widely used for fabricating carbon fibre-reinforced carbon materials for aircraft brake disks. This study aims at developing a numerical simulation method for predicting densification of the material during the CVI. Based on the multi-step reaction and deposition models, including the hydrogen inhibition model of pyrocarbon growth, transient 3D simulations of the CVI using methane as a precursor of the pyrocarbon were carried out via the finite element method coupling the mass transfer (by convection and diffusion) and the evolutive porous structure model with gas-phase and surface chemical reactions. The CVI of two different types of preforms was studied. The pore structure evolution models were derived not analytically but numerically with the aid of a computational tool for visualizing the fibre structures. An acceptable agreement was found between the predicted densification profiles and the experimental data obtained using a laboratory CVI reactor at a temperature of 1343 K, a methane pressure of 30 kPa and a total deposition time of 120 h. [ABSTRACT FROM AUTHOR]

Among the processing parameters of additive manufacturing, printing direction is of critical importance. While studies on effects of printing direction have so far mainly focused on mechanical properties of solid specimens, the present research is intended to demonstrate printing direction dependence of mechanical behavior of additively manufactured 3D preforms and their composites. Compressive behavior of additively manufactured 3D braid preforms and composites was investigated for three distinct printing directions (0°, 45° and Z-direction). Fused filament fabrication (FFF) of acrylonitrile-butadiene-styrene (ABS) filament and short carbon fiber/ABS (CF/ABS) filament was adopted. First, solid cube specimens were fabricated; the parts printed along 0° and 45° directions showed more fabrication-induced pores. Then, 3D braid preforms were fabricated and infused with silicone matrix. For preforms printed along 45° direction, inter-yarn adhesion was observed, which enhanced specimen initial modulus. On the other hand, Z-direction specimens showed higher structural ductility, due to inter-yarn slippage. [ABSTRACT FROM AUTHOR]

Concrete is the most extensively used construction material in the world, second to water. Increasing rate of urbanization and industrialization has lead to over exploitation of natural resources such as river sand and gravels, which is giving rise to sustainability issues. It has now become imperative to look for alternatives of constituent materials of concrete. Waste foundry sand, a by-product of ferrous and non ferrous metal casting industries is one such promising material which can be used as an alternative to natural sand in concrete. In last few decades, several studies have been conducted to investigate the effect of addition of waste foundry sand as partial and complete replacement of regular sand in concrete. It has been found suitable to be used as partial replacement of sand in structural grade concrete. A number of properties have been reviewed in the current paper, the results observed from the various studies depict that replacement of foundry sand to a certain extent enhance the durability as well as strength properties of the concrete but simultaneously decreases the slump value with the increase of replacement level of waste foundry sand. [ABSTRACT FROM AUTHOR]

Silicon-carbide particle (SiC p ) preforms with particle sizes of 20, 50, 100 and 150 μm were prepared by compression mold forming and heat treatment. A high resolution (~ 1.0 μm) three-dimensional (3D) X-ray micro-computed tomography (X-ray μ-CT) combined with 3D pore-network models were used to study the effect of particle size on 3D characteristics and spatial structures of pores in the preforms. The results demonstrated that as the particle size increased, the gap expansion caused by burning of starch reduced. When the particle size increased from 20 to 100 μm, the average areal porosity, homogeneity of pore distribution, connectivity, the numbers of small pores and throats, and average pore coordination number decreased; the average effective sizes of pores and throats increased. When the particle size further increased to 150 μm, the large gaps were filled by small particles resulted from the broken coarse particles, which decreased the homogeneity and connectivity of pores. As a result, the pore-network analysis shows that the numbers of small pores and throats and average pore coordination number increased. [ABSTRACT FROM AUTHOR]

In the injection molding of long fiber-reinforced resins, the breakage of fibers during the plastication process and while they are flowing past the check ring (CHR) is a common problem faced on manufacturing sites. However, no systematic research has been carried out. For the first time, the authors develop a heating cylinder with multiple ports on the wall for extracting the melted resin from the cylinder inside to perform in-process sampling of the resin. In this study, the new device was used to sample melted resin before and after CHR and to investigate the effects of the shape of the CHR on glass-fiber breakage. The experimental results clearly demonstrate that the breakage of fiber can be minimized to an extent where there is enough space for melted resin to gently flow and bypass the CHR. In addition, it was confirmed that the length of the CHR does not significantly affect glass-fiber breakage. [ABSTRACT FROM AUTHOR]

Abstract A356/316L interpenetrating phase composites were fabricated by infiltrating additively manufactured 316L lattices with molten A356. Measurements of the thermal conductivity of the composites showed an inverse rule-of-mixtures dependence on the 316L volume fraction. Compression tests revealed that the stress-strain response of the composites can be tailored by adjusting both the volume fraction and the topology of the 316L reinforcement. Tension tests on composites with 39 vol% 316L showed a strain to failure of 32%, representing an order of magnitude improvement over the strain to failure of monolithic A356. Inspection of the as-tested tensile specimens suggested that this exceptional damage tolerance is a result of the interpenetrating structure of the constituents. These results together demonstrate that this infiltration processing route avoids problems with intermetallic formation, cracking, and poor resolution that limit current fusion-based additive manufacturing techniques for printing metallic composites. [ABSTRACT FROM AUTHOR]

Surface treatment of optical glass fibers is an effective method to clean the impurities and remove the damage layer, such as scratches caused by the cold processing. Optical losses at the fiber core/cladding interface can thereby be decreased. Using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), we studied the surface composition and morphology of fluorophosphate (FP) glass after polishing and chemical etching. In addition, we investigated the etching mechanism and the optimal concentration of etching solution. Results show that the surface composition is very close to that of the bulk glass for some elements, and the root-mean-square (RMS) roughness is approximately 0.821 nm. A method including acid–alkali pretreatment and a second polishing step is a novel way to improve the smoothness of surface and to eliminate defects such as contaminants and scratches. [ABSTRACT FROM AUTHOR]

Carbon/carbon(C/C)–Zr–Ti–C composites were fabricated using chemical vapor infiltration and liquid metal infiltration processes. The residual thermal stress (RTS) distribution in the C/C–Zr–Ti–C composites was analyzed by Raman spectroscopy and finite element (FE) calculation. The mechanical behaviors of C/C–Zr–Ti–C composites with three types of carbon fiber preforms were tested. The results showed that there was very high compressive RTS in the fibers and high tensile RTS in the pyrocarbon (PyC) in the marginal region near the carbide. However, in the central region away from the carbide, relatively low compressive stress and tensile RTS were found in the fibers and PyC, respectively. The FE analysis showed that the introduction of carbide into the C/C composites caused a significant increase of the RTS in the PyC near the carbide, indicating that the carbide could change the RTS distribution in C/C composites. Moreover, the distribution of the RTS and its release combined with the carbide distribution and fiber architecture led to variations in the mechanical performance of composites with different preforms. [ABSTRACT FROM AUTHOR]

A new approach to optimize 3D preform shape in multi-step die forging based on Quasi-equipotential Field Method and Response Surface Method is proposed. Using the proposed method, the optimized preforging shape is determined in the hot forging of the pendulum mass. Based on the optimized preforging shape, the advisable blocking blank is constructed. The final perform design, including the advisable blocking blank and preforging shape, is completed. The desired pendulum mass forging without any defects and with smaller flash is obtained. [ABSTRACT FROM AUTHOR]

Highlights: [•] Gradually outline of the design process of a composite preform. [•] Detailed discussion on considerations, challenges and possible solutions. [•] Unique insight into a closed business community. [•] Composite preform design is a complicated, complex, and challenging task. [Copyright &y& Elsevier]

Abstract: We derive a mathematical model for an electromagnet inside a molding machine, and propose a novel loop-shaping method of the proportional–integral (PI) controller design for the system based on the generalized KYP (GKYP) lemma. The behavior of the molding machine is difficult to capture by using finite-dimensional models owing to eddy currents spatially distributed throughout the electromagnet. To analyze fundamental properties of the system both theoretically and experimentally, we first derive a mathematical model of the machine in terms of a partial differential equation (PDE). An analysis using the PDE model shows that a low-dimensional approximation performed by standard spatial discretization results in a spillover effect, which makes the behavior of the closed-loop system oscillatory. Then, to develop an easily tunable and implementable control system, we propose a novel loop-shaping method for PI control on the basis of the GKYP lemma. In this control system design, we use multiple low-dimensional models, which work simultaneously in specified finite frequency ranges. The proposed method successfully suppresses the spillover effect despite the use of low-dimensional approximants. Finally, we show the efficiency of the proposed control design method through numerical and experimental verification and discuss a performance limitation of the PI control. [Copyright &y& Elsevier]

Abstract: The thermal conductivity of SiC ceramics fabricated by liquid infiltrating molten Si into mesocarbon microbeads-based preform was investigated. The thermal conductivity of SiC ceramics decreased from 103 to 36W·m−1·K−1 at room temperature when the volume fractions of SiC, residual Si and unreacted C varied from 76.7 to 51.2vol.%, 11.2 to 0vol.% and 10.0 to 45.3vol.%, respectively. The microstructural investigation and Maxwell's model analysis revealed that the difference in thermal conductivity of the samples was mainly affected by the unreacted C and transition layer, which surrounding around the unreacted C, was composed of inhomogeneous and sparser SiC nanocrystalline. Since the volume of the transition layer was mainly determined by the outer area of the carbon particles, the unreacted C and transition layer, with relative low thermal conductivity, can make the thermal conductivity sharply decrease with the unreacted C content increasing. [Copyright &y& Elsevier]

Abstract: Coir fibre, an agricultural waste material of immense economic importance in Indian subcontinent, was used as a precursor to biomorphic SiC ceramics. Fibreboards made of coir fibres were converted to carbon templates by controlled thermal processing. Plant material precursors were characterised by analysis of molecular composition, by determination of bulk density and by scanning electron microscopy. Carbon templates were characterised by measurement of dimensional shrinkages, mass loss and bulk density and by scanning electron microscopy and XRD. The carbon templates were further subjected to infiltration with liquid Si at 1550 °C under vacuum, when spontaneous infiltration and reaction yielded composite ceramics preserving the morphology of native coir fibre derived precursors on macro and micro scale. The resulting material had a density of 2.59gcm−3 and, on a microstructural scale, contained SiC and Si in addition to carbon (trace) and porosity (2vol%). The end ceramics offered room temperature flexural strength of 116MPa and elastic modulus of 167GPa. Fractographic examination indicated brittle failure. The biomorphic SiC material derived from coir fibreboard precursor is likely to be suitable for use in advanced engineering applications as structural ceramics. [Copyright &y& Elsevier]

Abstract: The current paper analyzes the effect of outlet vent arrangements on the air traps and pressure distribution of a stacked-chip scale package (S-CSP) during encapsulation. A three-dimensional model of S-CSP is created using GAMBIT and analyzed using FLUENT code. In the molding process, the epoxy molding compound flow behavior calculated using the Castro–Macosko viscosity model by considering the curing effect, and the volume of fluid technique are applied for flow front tracking. The viscosity model is written in C language and compiled using User-Defined Function in FLUENT code. Three different types of outlet vent arrangement are considered in the analysis, namely, Type A, Type B, and Type C. Type A, which has the minimum outlet vent area, shows the minimum air trap and the highest average pressure distribution. The simulation results of the flow front profiles agree well with previous experimental results. [Copyright &y& Elsevier]

Abstract: Ethylene vinyl acetate (EVA) composites filled with zeolite (25 vol.%) were prepared using an internal mixer followed by compression molding machine. In order to enhance the thermal properties and fire retardancy of the composites, an intumescent flame retardant consisting of ammonium polyphosphate (APP)/pentaerythritol (PER) was incorporated into the composites. Two kinds of flame retardants were used which are untreated APP (APP1) and silane treated APP (APP2), where their effectiveness was evaluated by means of differential scanning calorimetry (DSC) and also thermogravimetric analysis (TGA). The results showed that both types of flame retardants have the ability to enhance the thermal stability of EVA/zeolite composites by producing charred layer which protects the underlying composites from the action of flame. Moreover, the incorporation of APP1 and APP2 has a significant effect on the composites degree of crystallinity. Meanwhile the results of tensile testing showed that the composites with APP2/PER exhibit better tensile properties compared to that with APP1/PER. This is expected since the application of silane-treated APP (APP2) could improve the dispersion of APP particles within EVA matrix. [Copyright &y& Elsevier]

Abstract: This paper highlights a method of using open-source CAD (Computer Aided Design) software and CAM (Computer Aided Manufacturing) in the manufacturing of building assembly systems. With the increase use of CAD/CAM technologies, and internet access on a global scale, we investigate open platforms to improve global production of modular systems and tackle fundamental building manufacturing systems for global application. This paper, examines a method of producing designs from conception to manufacture, using custom algorithms written in open-source CAD software. This system is geared primarily for the construction of buildings using moldable composite materials for housing developments in urban and rural regions in developing countries. The objective of this research is to create a system that is flexible for influencing and incorporating culture, design preference, and geographical innovation. A cradle molding device for manufacturing assembly systems was developed for producing block assemblies from moldable composites such as concrete, cob, and poured earth. [Copyright &y& Elsevier]

Abstract: The moulding properties of Igbokoda silica sand, bonded with Ijero–Ekiti clay, were investigated. American Foundrymen Society (AFS) standard cylindrical samples dimensioning Ø50 mm×50 mm in height were prepared from various sand–clay ratios with 5% tempering water, by applying three ramming blows of 6.666 g each from a height of 50 mm as required for foundry sands. The samples were subjected to various physical and mechanical tests. These include permeability, green compression strength, and dry compression strength tests. Green shear strength, dry shear strength, field mould strength, shattered index and refractoriness tests were also carried out on the samples. Samples containing 23–32% clay were found to possess adequate permeability, good strength and refractoriness suitable for casting of both ferrous and non-ferrous alloys. [Copyright &y& Elsevier]

Abstract: A new binder composed of α-starch, kaolin, sodium silicate, dextrin, phosphate and water in proportions 2.5–4.0%, 1.5–3.0%, 0.55%, 0.35%, 0.04% and 2.5–3.5% by weight percent respectively has been developed. The high-temperature resistant mechanism of the mold and core sand bonded with α-starch composite binder was studied by way of differential scanning calorimetry (DSC), X-ray diffraction (XRD), infrared (IR) spectra and scanning electron microscopy (SEM) analyses without sand or on a sand base. It is believed that the high-temperature strength of the sand mold or sand core is mainly dependent on the cohesive strength of the adhesive membrane between sand grains. When the binder was heated over 600°C, the kaolin in it reacted with the sodium silicate and phosphate separately, forming Al–O–Si three-dimensional skeleton and heat-resistant AlPO4, thus, the binder is provided with higher high-temperature resistant strength. This conclusion is also confirmed by the experimental research on the high-temperature mechanical properties of the binder bonded sand and the microstructure observation of the binding film. The research on the high-temperature resistant mechanism of the starch binder bonded sand is helpful to its high-temperature performance optimization and its application in the foundry industry. [Copyright &y& Elsevier]