Abstract: Carbon nanotubes (CNT)-reinforced magnesium alloy (AZ31) was fabricated using the technique of solidification processing followed by hot extrusion. Test specimens of both the composite and the unreinforced alloy were cyclically deformed at two different load ratios spanning tension-tension loading (R = 0.1) and fully-reversed tension-compression (R= -1) loading under total stress amplitude-control. A comparison of the CNT reinforced magnesium alloy with the unreinforced counterpart revealed well over two hundred percent improvement in cyclic fatigue life at load ratio of 0.1 and about two-hundred and fifty percent improvement in the high cycle fatigue life under conditions of fully-reversed loading [R= -1.0]. At all values of maximum stress, the high cycle fatigue response of both the reinforced and unreinforced magnesium alloy was found to degrade at the lower load ratio (-1.0). The synergistic and interactive influences of reinforcement and processing on microstructural development, cyclic fatigue life and kinetics governing fracture behavior are presented and briefly discussed.
Abstract: Because of their well known specific strength, stiffness and excellent durability properties, advanced composites are being considered for primary structures in launch vehicles, crew modules and various components for increased performance and cost reduction. Therefore, it is prudent and beneficial to review the engineering practices and lessons learned in connection with their use in related aeronautic and energy applications, where they are already replacing formerly used metallic materials. Examples of composite components will be shown for the reusable space shuttle orbiter where a number of different composite systems performed very satisfactorily. In addition, very large potential polymer composite designs for future launch vehicles will be discussed. Among them are payload shrouds, interstage structures and the typical intertank shell, wherein thrust booster rockets are often attached between the core stage propellant and oxidizer tanks. In addition, cryogenic propellant composite vessels of different sizes and shapes were fabricated with mostly excellent results, although some spectacular failures were also observed. High pressure composite overwrapped vessels, with and without metallic liners, will be described. Compared to widely used metallic materials, some special features of composites are listed. Relevant design allowables, depending on mission requirements, will be summarized and currently used design practice for aircraft and spacecraft in the US will be reviewed. The well-known “building - block” approach, which is often used to design military as well as civilian aircraft, will be summarized. Some of the most popular micromechanics and macromechanics computer programs used to analyze composite structures, especially with finite elements, will be listed. Although very high temperature composites like carbon/carbon, carbon/ceramic and ceramic/ceramic fiber/matrix systems are also selectively used, the focus in our discussion will be on advanced polymer matrix, carbon/glass fiber systems.
Abstract: This study demonstrated fiber-optic-based life cycle monitoring of an L-shaped carbon fiber reinforced plastic (CFRP) part. Fiber Bragg grating (FBG) sensors were embedded in the corner of the L-shaped specimen during the laminate lay-up process, and was then utilized to monitor the local strain change during the cure process, the demolding, the assembly, and a subsequent bending test. FBG spectral changes induced were comprehensively presented and discussed from the viewpoint of the mechanical and thermal deformation of the specimen. Internal state of the L-shaped part was successfully monitored throughout its life, confirming effectiveness of life cycle monitoring by embedded fiber-optic-based sensors for developing highly-reliable composite structures.
Abstract: Energy has always played a critical role in every country’s prosperity, environment and security. This critical topic has recently been pushed once again to the forefront of global attention due to several critical factors, among which include 1) unprecedented volatility of energy prices, 2) uncertainty of the long-term stability of traditional energy sources, and 3) mounting evidences of global climate change. The necessary transformational change in how we generate, supply, distribute and consume energy is an immense undertaking which requires concerted effort at the regional and global level.
Abstract: Natural fibres obtained from plant sources are attractive as a replacement for glass fibres in fibre reinforced plastic composites because of their environmental benefits. However, unlike synthetic fibres, natural plant fibres show considerable variability in their mechanical properties due to the effects of climate, soil quality, time of harvest, etc. Variability in properties of the fibres translates into variability in the properties of products made from natural fibre composites and this is a major obstacle to the more widespread use of these materials. One way to accommodate fibre variability would be to test the mechanical behaviour of samples from incoming batches of fibres and assign a grade to each batch, which could then be taken into account when the fibres are subsequently used to produce composite products. However, conventional methods of determining mechanical behaviour require test samples of constant cross-sectional area but, unfortunately, this is not the case for natural fibres which vary in shape, width and lumen size, from place to place along the fibre. Insight as to how to deal with such variability is provided from the textiles industry where strength is determined as a function of linear mass density rather than cross-sectional area. This paper examines the feasibility of using a similar approach for grading natural fibres for use in natural fibre composite products.
Abstract: Plant fibers are promising reinforcements for use in composite materials due to the low cost, high specific strength and modulus, easy availability, especially the renewability and environmental friendly characteristics. Natural fiber reinforced composites (NFRCs) have raised great attentions and interests from both the academic and industry in recent years.
Abstract: Stimulus-active polymers can change their shapes with respect to configuration or dimension upon exposure to a particular stimulus such as heat, electricity, light, magnetic, solvent and pH value. These unique characteristics enable stimulus-active polymers to be used in a myriad of fields, including clothing manufacturing, automobile engineering, medical treatment, and aerospace engineering. Stimulus-active polymers can be applied in smart textiles and apparels, intelligent medical instruments and auxiliaries, artificial muscles, biomimetic devices, heat shrinkable materials for electronics packaging, micro-electro-mechanical systems, self-deployable sun sails in spacecrafts, miniature manipulator, actuators and sensors, and many more. This paper presents some recent progress of soft smart materials and their applications. Special emphasis is focused upon shape memory polymer (SMP), electro-active polymer (EAP) for aerospace engineering such as space deployable structures and morphing aircraft, which has highlighted the need for development of these materials. A detailed overview of development in these smart soft materials, of which the undergoing and future applications are used in adaptive structures and active control, is presented. The paper concludes with a short discussion for multi-functional soft smart materials and their composites that are expected to extend the range of development and applications available to the related researches and engineers.
Abstract: The motivation for the need of small-scale devices has made thin films technologically important in the recent years. They have found applications in broad fields, such as microelectronic integrated circuits, magnetic information storage systems, optical coatings and wear resistant coatings. However, the mechanical performance of these materials tends to depend on fabrication and post-processing parameters. With the intent of improving the mechanical properties of the films, a relatively novel concept of sandwich composite films has been tried in this research. Poly-methyl methacrylate (PMMA) and Graphene Oxide (GO) have been used to manufacture the sandwich films, where PMMA films have served as the facings and electrospun PMMA/GO nanofibre mat forms the sandwich core. Dimethylformamide (DMF) and Tetrahydrofuran (THF) solvents are used in suitable proportions to dissolve PMMA, and then GO is added to this solution to obtain a uniform suspension of PMMA/GO for electrospinning. The mechanical and functional properties depend on the fibre quality and their distributions in the mat, which in turn depends on the concentration of the solution. Therefore, design of experiments based on mixture analysis was used to identify the solution concentration for obtaining uniform fibre diameters and their distribution throughout the electrospun core. The analysis suggested 23% PMMA and 2% GO concentrations in the solution would give uniform fibre diameters and dispersion throughout the mat.
Abstract: Now, over 90% of energy is produced by fossil fuel including coal, oil and natural gas, etc. With the time go on and the same consumption rate of energy, the energy status of world will be more serious. So human being should be finding other cleanness energy in order to meet their need. The solar energy is a promising energy which can be realized in the future most experts believe. Firstly, the concept of SSPS is brought forward in this paper. Additionally, the status of energy consumption and the studying trend of space solar power system (SSPS) are described which comprise the key technologies of SSPS in need. Then the key materials of development of SSPS and some suggestions are presented.