Key Engineering Materials Vols. 334-335

Abstract: The response of Carbon/epoxy composites under high velocity impact was investigated experimentally. The strain rate dependent behavior of T300 Carbon/epoxy matrix composite in tension is studied experimentally by split Hopkinson bar technique. Dynamic stress-strain plot was obtained and compared with the quasi-static tensile test results. The results of the study indicate that Carbon/epoxy composites are strain rate dependent materials. Stacking sequence has a significant effect on the material response. Tensile strength of the composites all increased with increasing strain rate. And failure strain decreased when strain rate increased.

Abstract: The use of alternative materials from agriculture and plantation bio-mass has widely been researched especially for use in bio-composites. These bio-mass have been used in flour form as fillers, in fibre form as reinforcements and in both flour and fibre forms as bulking agents. These bio-mass not only enhanced the composites but also help to reduce the burden on natural fibres from the forests. Furthermore, these bio-mass fibres can be used as an alternative or supplementary raw material in composites such as fibre glass-polymer composites by replacing part of the synthetic fibres, if not all, depending on the final application of the finished composites. Combining one material with other materials provides a strategy for producing advanced composite materials that take advantage of the properties especially bending strength of both types of resources. It allows the researcher to design materials based on end-use requirements within a framework of cost, availability, recyclability, energy use, and environmental considerations. This paper reports on the bending strength of MDF from kenaf, oil palm EFB, and from admixtures of EFB and kenaf in different ratios. Production of composite material from these diversified resources will not only help to reduce the pressure on natural forests, it is also an alternative to overcome waste disposal problems in palm oil industries. The results indicate that kenaf and EFB could be mixed to produce MDF. The panel produced can be used for furniture components such as table tops and shelves, wall partitions and door panels.

Abstract: In the textile industry, recently, it is urgent to develop the recycling system of the polyester fiber waste which results from the manufacturing process of sythetic fabric. However, most of the fiber wastes are destroyed by fire or buried underground. In this paper, the insulating composites which consist of polyester fiber wastes and PLA films are molded by compression molding method. In the process of preforming, the polyester fiber wastes are arrayed in uni-direction, and PLA films are inserted among layers of the polyester fiber wastes as binder. Namely, the polyester fiber wastes layers and PLA films are laminated alternately. In this paper, pitch (distance among the fiber wastes) and number of layers of polyester fiber wastes are varied, and the effect of pitch and number of layers of polyester fiber wastes on mechanical property and thermal insulating propertiy of the composites are discussed. As the result, it is concluded here that the melted state and the thickness of layers of PLA affect largely on the thermal conductivity and the bending strength of the boards.

Abstract: Despite a large number of technical papers on vibration of composite shallow shells, all the previous papers have dealt with shallow shells with uniform curvature to avoid difficulty in the analysis. Recent composite products, however, require various surface designs of thin panels from the viewpoint of industrial design, for example, in the fender and door panel designs of commercial vehicles. The present study proposes an analytical method to deal with vibration of shallow shells with non-uniform curvature. An interpolating function is introduced to represent the required surface shape and the corresponding curvature is derived as a function of the position (x,y). The obtained curvature is substituted into the total potential energy of the shell, and the procedure is shown to derive a frequency equation in the Ritz method. Numerical examples clarifies the effects of non-
uniform curvature on the natural frequencies and mode shapes.

Abstract: Structural plate elements in composite structures are typically fabricated by stacking orthotropic layers, each of which is composed of reinforcing fibers and matrix materials. In this work, three optimum design approaches are compared to clarify the advantages and disadvantages for optimizing the buckling performance of laminated composite plates. The first approach is developed recently by the authors, where the buckling load is maximized with respect to the lamination parameters by a gradient method and then the optimum lay-up design is determined by minimizing the errors between the optimum parameters and parameters for all possible discrete lay-ups. The second approach is the layerwise optimization (LO) approach where the fiber orientation angle in each layer is optimized step-by-step by repeating one dimensional search. The third one is a direct application of a simple genetic algorithm (SGA). In numerical examples, three sets of results are compared to discuss on the methodology for buckling optimization.

Abstract: Composite materials are frequently used in automobile and other moving vehicle structures. External and internal sounds sometimes cause unpleasant effects on the users and environment, and reduction of such sound is one of the key engineering problems. This study presents an acoustic radiation analysis from forced vibration of laminated rectangular plates and proposes a design approach to reduce the sound pressure from the plates. In the analysis the sound pressure at an arbitrary point over the plate is derived and is used as an object function in the optimization. A set of the fiber orientation angles is used as the design variable, and is optimized to minimize the sound pressure at the designated point. It is shown in numerical examples that the optimum design for sound pressure reduction is possible by the present approach.

Abstract: Steel reinforcement concrete is one of the most widely used composite materials in architectural and civil engineering. The alkaline of concrete makes steel passive state, so the steel bars in conrete are kept in anti-corroded phase. Carbon dioxide in atmosphere, however, chemically reacts to the alkaline components in long term, and the passive state of steel is missing. Steel corrosion in concrete is not visible but it may cause decaying buildings or civil construction. The author developed the electrochemical measurement method of monitoring steel corrosion rate in concrete. With the measurement method, the author measured the variety of corrosion rates of steel reinforcement in several atmospheres, such as indoors, outdoors, in-water, underground, and so on. In this paper, found and analyzed mechanisms of steel corrosion in those atmospheres are mainly shown. For an interesting result, the most corroded sample is not the sample exposed outdoor, nor exposed in water, but the sample exposed in wet room. This may cause the diffusion balance of oxygen and water in concrete.

Abstract: The size dependent miscibility of binary polymer blend films of polystyrene (PS) and tetramethylbisphenol-A polycarbonate (TMPC) is studied by the molecular dynamics (MD) simulation in the way of computing Flory-Huggins interaction parameter, χ, of the blend films, which determines the blend films compatibility. It is found that the miscibility of the two polymers decreases as the film thickness D decreases. After that, the size dependent glass transition temperature Tg(w,D) of the two polymers blend films in miscible ranges are determined by computer simulation and the Fox equation where w is the weight fraction of the second component.

Abstract: Under the assumption that the artificial viscosity coefficient at the propagating crack tip is in inverse proportion to power law of the plastic strain rate, a rate-sensitive constitutive relationship is derived for perfect elastic-plastic material. With the adoption of the rate-sensitive constitutive relationship, it is asymptotically investigated the propagating tip fields of plane strain mode II. And the quasi-static equations are obtained separately governing the stress and strain fields at the crack-tip by means of Airy stress function. Numerical calculations of governing equations are carried out by double parameters shooting, with selections of appropriate values of each characteristic parameter by combinations of boundary, and the fully continuous stress-strain fields are obtained at the crack-tip. The analytical and computational results indicate that viscosity effect is an important factor in crack-tip fields.