Science and Technology of Materials最新文献

Recent times, metal matrix composites (MMC) are considered as candidate materials for numerous applications such as aerospace, automotive and military industries due to improved properties over the conventional metals and alloys. Out of the different categories of metal matrix composites, discontinuous particulate reinforced composites are preferred for industrial applications due to low manufacturing cost. High fracture toughness, improved ductility and machinability characteristics support the selection of metal matrix nanocomposites (MMnC) over conventional composites for different applications. The majority of nanocomposites are produced through liquid state processing due to faster processing time and economy. However, the conventional liquid processing method leads to poor wetting of reinforced nanoparticles by molten metal that degrades the quality of the fabricated nanocomposite. This paper reviews some of the advanced liquid state processing techniques adopted for the improved wettable characteristics of nanoparticles and their uniform distribution in the metal matrix.

Metal matrix composites based on aluminum alloy AA7050 reinforced with graphene nanoparticles are fabricated using stir casting and squeeze casting techniques. Mechanical characteristics studies were performed on both the stir cast and squeeze cast composite specimen. Taguchi's L27 orthogonal array was used for the design of experiments. Certain parameters like melting temperature (775, 800 and 825 °C), stirring speed (300, 400 and 500 rpm) and graphene content (0.3, 0.5 and 0.7 wt%) with three levels were considered for the experiments. Based on the experimental results, analysis of variance (ANOVA) was conducted to determine the level of influence of the parameters on the tensile strength of the specimens. The microstructural result shows that graphene particles are uniformly distributed in the aluminum matrix only in the composites with 0.3 wt % graphene irrespective of the process followed for the fabrication of composite samples. It is being found that the tensile properties of both stir cast and squeeze cast samples have been enhanced for 0.3 wt% of graphene in the AA7050 composites. Increasing the graphene content beyond 0.3 wt% results in cluster formation.

The bamboo fiber has been studied as composite reinforcement for offering lightness and more resistance to the material. Alkalization and acetylation are superficial chemical treatments based on alkaline solution and on a solution based in acid and acetic anhydride, respectively, which modify the fibers composition, introducing functional groups acetyl, turning it hydrophobic. In this project, it was aimed the application of the alkalinization and acetylation treatments, attempting to improve the fibers adhesion to the polymers when in a composite. The fibers were evaluated by moisture content, water absorption tests by immersion, density, infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, tensile tests, and morphological analysis. When acetylated, the bamboo fiber presented lower water absorption (62.98%), gained thermal stability of approximately 50 °C, presented lower crystallinity (62.47%) and, according to SEM images, the fibers has shown an increase of surface roughness, facts that contribute to the best fiber/matrix adhesion in composites. The acetylation decreased the mechanical strength of the fiber, supporting 19,820 MPa, against 27,670 MPa from the natural and 31,730 MPa from the alkaline.

Naturally available filaments have recently become attractive to researchers, engineers, and scientists because of suitability as an alternative reinforcement for fiber reinforced polymer composites. Low cost, fairly good mechanical properties, non-abrasive and bio-degradability attributes, abused as a swap for the regular fiber. The tractable properties of normal fiber reinforced composites are mainly influenced by the interfacial adhesion between the matrix and the fibers. In this article survey on biosoftening, adhesion, the effect of fiber length, the effect of chemical treatments of long areca fibers, Influence of mercerization on the tensile strength of long & short areca fibers, areca husk have been discussed.

Calcium metastannate CaSnO₃ with orthorhombic crystal system has been synthesized at low temperature by molten salt method using KCl-LiCl as a reaction medium and equimolar of SnO₂ and CaCO₃ as precursors. The process parameters including the reaction temperature, salt type, and salt to precursor weight ratio were investigated. Rietveld refinements on X-ray powder diffraction patterns were performed using X'Pert HighScore Plus software to calculate phase percent of each phase present in the obtained powder. The results of these calculations were followed in order to choose the salt system that requires the least reaction temperature to produce the highest CaSnO₃ percent. The as-prepared compound was characterized by various techniques such as X-Ray diffraction (XRD), energy dispersive X-Ray spectrometry (EDX), Fourier transform infrared spectrometry (FTIR), and field emission scanning electron microscope (FE-SEM). The experimental results showed that highly crystalline phase pure CaSnO₃ laminar plates could be prepared at 1000 °C for short period of time without any other detectable secondary phases.

In creep-strength-enhanced ferritic steels, hydrogen-induced cold cracking of weldments is a serious issue. In the present research work, the effect of cooling medium on tensile properties and microstructure evolution of P91 steel weldments has been studied. For water-cooling condition, the diffusible hydrogen metal in deposited metal was measured by the mercury method. The microstructure of weldments in different cooling condition was characterized by using the field-emission scanning electron microscope (FE-SEM) and optical microscope. The fractured tensile test samples were characterized using the FE-SEM. The maximum tensile strength was measured to be 624 MPa for air-cooling medium (very low level of diffusible hydrogen).

Using selective laser melting (SLM) is possible to manufacture molds with cellular internal structures with different porosity degree. Furthermore, internal geometry design can be improved as a function of the desired structural and thermal stress solicitations. In this work two types of cellular internal structures – hexagonal and cub-octahedral – were developed and manufactured using the SLM process. These topologies were generated with the purpose of creating a high degree of internal porosity and getting satisfactory results in terms of thermal and mechanical behavior when compared with similar dimensional bulk structures. The mechanical and thermal behaviors of each cellular topology were evaluated numerically and experimentally through compression and thermal tests. From numeric and experimental results, it can be concluded that hexagonal cellular internal topology provides a higher mechanical strength when compared to the cub-octahedral cellular structure while the thermal analysis shows that cub-octahedral topology is more efficient for heat dissipation. Both cellular topologies have demonstrated, however, to be appropriate for use in injection mold structures. In addition, the use of these cellular topologies provides light weight structuring with an approximate 58% weight reduction, which represents a considerable saving of material total cost to manufacturing of an injection mold.

This work focuses on finding methodologies to describe the effective elastic properties of metal foams. For this purpose, numerical methods and analytical models, were used. Kelvin cells and Weaire–Phelan structures were modelled to represent both open and closed-cell representative unit-cells. These unit-cells were then subjected to different homogenization methods: (i) Far field methods with single freedom constraints, where it was used two different approaches based on the load case. (ii) Asymptotic Expansion Homogenization (AEH) with periodic boundary conditions. The analytical, numerical and experimental results were then compared. The results indicate that the far field methods gave more precise predictions. However, AEH provides more information on the behaviour of the unit-cells. Using this detailed information, it was possible to perform an anisotropy analysis. Furthermore, contrary to the closed-cells, the open-cell numerical methods and analytical models are within the experimental results range.

Bone is a heterogeneous material in which structural levels can be identified, from the microscale to macroscale. Multiscale models enable to model the material using homogenization techniques. In this work, an innovative homogenization technique for trabecular bone tissue is proposed. The technique combines the fabric tensor concept and a bone phenomenological material law, linking the apparent density with the trabecular bone mechanical properties. The proposed methodology efficiently homogenizes the trabecular bone highly heterogeneous medium, allowing to define its homogenized microscale mechanical properties and to reduce the analysis computational cost (when compared with classical homogenization techniques). In order to verify the efficiency of the technique several examples were solved using a confined square patch of trabecular bone under compression. In the end, the results obtained with a classic homogenization technique and the proposed methodology were compared.

This Special Issue contains a small collection of the papers presented during the second edition of the joint conference on Cellular Materials, together with the International Conference on Dynamic Behaviour of Cellular Materials, and held at the Department of Mechanical Engineering, University of Aveiro, Portugal (September 25 to 27, 2017). Within three days, experts from different countries (Brazil, Colombia, Croatia, France, Germany, Italy, Mexico, Poland, Portugal, Russia, Slovenia and Turkey) presented about 50 lectures (both in oral and poster sessions), including five plenary lectures given by renowned international experts.