Key Engineering Materials Vols. 334-335

Abstract: Elastic wave transmission characteristics through a fiber-reinforced composite layer are studied by the two-dimensional steady-state finite element analysis. To this purpose, boundary conditions are formulated which account for the connection of the model domain to the semi-infinite regions as well as a certain periodicity of the fiber arrangement. The transmission characteristics through a composite layer are computed for the longitudinal and transverse wave incidence, assuming a finite number of fiber alignments in a square array. The analysis delineates the existence of clear stop bands in the case of transverse wave incidence, even with a few lines of fibers aligned normal to the propagation direction. These stop bands are discussed on the basis of the interference effects of neighboring fiber alignments as well as neighboring fibers in each alignment.

Abstract: Nowadays, researches for replacing material systems for cryogenic propellant tanks by composites have been being performed for the purpose of light weight of a launch vehicle. In this paper, a type III propellant tank, which is composed of the composite developed for cryogenic use and an aluminum liner, was fabricated and tested considering actual operating environment, that is, cryogenic temperature and pressure. For this aim, liquid nitrogen (LN2) was injected into the fabricated tank and in turn, gaseous nitrogen (GN2) was used for pressurization. During this test procedure, strains and temperatures on the tank surface were measured. ESG (electric strain gage) and thermocouple were used for the measurement of strain and temperature, respectively. Delamination between hoop layer and helical one, was detected during the experiment. Finally, Tsai-Wu criterion for the tank and microscopy for the composite/aluminum ring specimen were carried out to investigate the reason why delamination had happened.

Abstract: The composite, based on a polymer matrix such as Bisphenol A glycol dimethacrylate (Bis-GMA), urethane dimethacrylate (UDMA), and triethyleneglycoldimethacrylate (TEGDMA) and a reinforced-ceramic filler has been used in dental restorative materials. The light curing composite consists of Bis-GMA, TEGDMA, UDMA, Bis-GMA/TEGDMA, Bis-GMA/UDMA, or UDMA/TEGDMA polymer systems and a fumed silica filler with 35 weight ratio loading was synthesized using camphorquinone (CQ) and 2-(dimet6hyloamino)ethyl methacrylate (DMAEMA) as an initiator system. FTIR spectroscopy was used to determine the degree of conversion (DC) of the composites. Polymerization shrinkage and physical properties such as hardness strength and flexural strength were correlated with the composites containing different polymer systems.

Abstract: Laminated composite plates have lower interlaminar strength making it difficult to apply interference-fit rivet joining. In this paper, a three-dimensional finite element model has been developed in order to simulate the riveting process on composite plates. The finite element model is based on continuum elements and accounts for some important mechanisms involved in a whole riveting process. The stresses around the rivet hole and the deformed shapes of the rivet are presented together with the effects of the interference fit and the geometry of the washer when the rivet joints are subjected to the compressive load. The numerical results show the applicability of an interference-fit riveting in composite laminates.

Abstract: Ankle Foot Orthosis (A.F.O) should endure the uncountable repeating impact and fatigue loadings due to the gait characteristics. This study investigated the impact deflection and relationship between the absorbed energy and the residual strength rate using the cross ply GFRP (glass/epoxy) and the woven AFRP (aramid/epoxy) for the leaf spring in A.F.O. In conclusion, the equation was suggested to evaluate the absorbed energy and the residual strength rate by the different impact velocities. When the cross ply GFRP and the woven AFRP was selected for the leaf spring in A.F.O, it was reasonable to use the cross ply GFRP for the parts subject to the large impact and the woven AFRP for the parts to require the high elastic energy such as the large deformation.

Abstract: The applicable bending moment equation of LIPCA is necessary even though the fiber layer ply orientation is changed. The aim of this research is to evaluate the relationship between the total effective moment (ME) and Bernoulli-Euler bending moment (M) when the ply orientations of unidirectional CFRP, which is one of the various laminate configurations in LIPCA, are changed. Since the related previous equation between the performance stroke range (h) and the radius of curvature (ρ) was just applicable to the CFRP ply orientation [0], it will be modified using these results. The related modified equation, which has nothing to do with the various CFRP ply orientation, is also suggested and compared with the previous equation.

Abstract: Nature has developed many novel solutions and extracting these design solutions from nature is known as biomimetics. Cancellous bone contains trabecular bone (solid) and marrow (fluid), plays an important role for load transfer of the knee joint. The objective of this research is to mimick the solid-liquid composition of the cancellous bone and to develop the material that has the excellent load dispersion ability. In the previous research, the solid-liquid composition of the cancellous bone has been modeled as solid-air composites that was made with Al honeycomb and silicon films. Air pressure in cells affected the load dispersion characteristic under static loading condition. In this study, to investigate the influence of the compression speed, impact tests were carried out. We investigated the influence of directions of holes to cell walls, foil thickness, hole diameter and the number of holes on the load dispersion ability. Presence of silicon film and air in cells affected the load dispersion characteristic under dynamic loading condition. Solid - air composition and relaxing local deformation by optimal design improve load dispersion ability.

Abstract: Sulphoaluminate-alite cement (SAAC) was successfully prepared from high alumina fly ash. XRD analysis indicated that the optimal mineralogical phase of cement clinker was obtained under condition of MG=1.05, MS =0.95 at 1300oC, and C4A3 S reached the strongest intensity and is 58.73% in the phase of calcined clinckers. SEM observation showed that C4A3 S are well developed into regular diamond/hexagon-shaped crystal with the size of 1~3.5 μm in the clinker. Hydrated clinker exhibited its new formed dominant phases in AFt, C-S-H and Afm. Pillar shaped AFt and sheet shaped AFm coexisted among the colloidal C-S-H substrate. It is demonstrated that the prepared cement shows a compressive strength of 27 MPa (1d), 36 MPa (3d), 49 MPa (28d), and flexural strength of 5.9 MPa (1d), 5.9 MPa (3d), 6.1 MPa (28d), indicated that the hydration product owned a good mechanical strength at early ages and increased steadily in the later stages.

Abstract: TiCp/ZA-12 composites have been fabricated by XDTM method and stirring-casting techniques. The behavior of TiC particle in the solidification interface has been studied through conventional and directional solidification techniques. The results demonstrate that under conventional solidification conditions, the particles with lower content mainly distribute in eutectic phases; while when at a larger content of TiC particles, they exist both in eutectic phases and in primary phases. Under directional solidification, due to the repulsion of primary phases of alloy on TiC particles, the particles congregate and form band structure, and extent of the congregation in band structure relates to TiC particles content. With the increasing of TiC particles content, their congregation in band structure decreases, and the band structure disappears when the content of TiC particles exceeds 6%. The tests for mechanical properties reveal that the tensile strength and yield strength increase with increasing fraction of TiC particles. When the fraction of TiC particles increase up to 10%, the tensile strength and yield strength are 390MPa and 340MPa, respectively and they increase by 11% and 17% than that of matrix respectively.

Abstract: A novel retrofitting method using extremely prestressed carbon fiber sheets, MLML (Multi-Layer Multi-Tensioning) method, was proposed for improving the flexural strength of reinforced concrete structures. The experimental results suggested that the crack initiation strength and the energy absorbing capacity of RC beams could be largely improved by the MLMT method. However, the advantage of the MLMT method was not so clear on the rebars yielding strength and the ultimate flexural strength of RC beams, compared with the conventional methods.