Applied Mechanics and Materials Vols. 182-183

Abstract: Organo-montmorillonite (OMMT)/nature rubber (NR) nanocomposites were prepared by mixing method. The microstructure of these composites was characterized by SEM and XRD. The effect of OMMT on mechanical properties and thermal conductivity of the nanocomposites was investigated in detail. SEM and XRD confirmed the intercalated structure of OMMT/NR nanocomposites. The introduction of a small amount of OMMT greatly improved the mechanical properties and thermal conductivity behavior, which was attributed to the nanometer scale dispersion and stronger interactions between OMMT and NR chains.

Abstract: Pure Bi₁₂SiO₂₀ powder was successfully prepared by a molten salt method using Bi₂O₃ and SiO₂ as raw materials and using KCl-K₂CO₃ as flux at 635°C with the heating rate of 5°Cmin^-1. The phase composition and microstructure of these products were analyzed by X-ray diffraction and scanning electron microscopy, and the effects of the processing parameters, such as the ratio of Bi₂O₃/SiO₂, calciniation temperature, isothermal time and relative amount of salt, on the composition and particle size were investigated. The results indicated that regardless of changing the ratio of Bi₂O₃/SiO₂, calciniation temperature, isothermal time or relative amount of salt the reaction only yielded Bi₁₂SiO₂₀ without Bi₂SiO₅ and Bi₄Si₃O₁₂. Henceforth, KCl-K₂CO₃ molten salts may be considered as an ideal reaction medium to synthesize pure phase of Bi₁₂SiO₂₀. The particle size of Bi₁₂SiO₂₀ phase can be determined by changing the temperature, isothermal time and relative amount of salt.

Abstract: Damage behavior of foam core sandwich composites subjected to quasi-static indentation testing was investigated detailedly. Force-displacement curves and the cross-sections of damaged sandwich panels were analyzed. Effects of core thickness, face-sheet thickness and toughness of face-sheet materials were discussed by comparison with different specimens subjected to quasi-static indentation testing. Results showed that damage behavior of sandwich composites had identical feature. Collapse of foam core initially appeared, and then foam core generated crack. Delamination and fiber breakage of upper face-sheet occurred. Finally, the foam core and the face-sheet were disengaged. For the specimens with thick foam cores, the foam crack extended in longitudinal direction was caused. However, for the specimens with thin foam cores, the foam cracked in transverse direction. After face-sheets were toughened with PAEK, the damage resistance and the maximum force of the sandwich panels increased. Also, the shear angle of foam crack changed to be lager. Compared with the penetrated damage behavior of sandwich panels with thin face-sheets, the upper face-sheets of the former the specimens with thick face-sheets bulged partially and could not be penetrated.

Abstract: In this paper, two carbon fiber/bismaleimide resin composites were prepared via ex-situ toughening technique. The damage resistance and damage tolerance of these two fiber-reinforced polymer composites were then studied in terms of low-velocity impact test and compression strength after impact (CAI). The results indicated that the T300 carbon fiber-reinforced composites had better damage resistance response and higher damage tolerance, and the visual observation of damage was also achieved. However, the T700 carbon fiber-reinforced composites had higher breaking elongation, and therefore the composite was not sensitive to the low-velocity impact. In addition, the CAI strength of this composite was still low.

Abstract: Based on two novel organic materials coded as EB515 and EB 47 for fabricating a flexible OLED device, we, herewith, propose a noval testing experiment to demonstrate the electrical, optical, and lifespan performances of a flexible OLED by continuously bending it mechanically. The testing model is designed as the following: continuously cyclic bending 5000 times on a flexible OLED. After foregoing test, the findings show that the leakage current increased in the beginning of bending, then decreased; also the luminance of OLED reduced first, then recoverd. We, therefore, conclude that the reduction of leakage current and luminance may stem from the OLED surface microcracks in the process of bending. Also, after further examination to the surface of substrate by lift-offing the organic layer, we found the organic layer has been impaired and damaged, but the ITO layer remained in good condition.

Abstract: In this paper, carbon fiber reinforced resin matrix composites were produced by stacking eight pieces of carbon fiber woven plain fabric and subjected to accelerated ageing. Accelerated ageing was carried out in oven at 180°C for three different time intervals (60 hours, 120 hours and 180 hours). The influence of different ageing time intervals at 180°C on tensile properties of laminated composites was examined, compared with the composites without aging. The appearance and damage forms of these laminated composites were investigated. The results revealed that the tensile strength of the laminates declined significantly after long term accelerated aging at 180°C. The average tensile strengths of composite samples aged 60 hours, 120 hours, and 180 hours period of time at 180°C are 80.36%, 79.82%, 76.57% of average tensile strength of composite samples without aging, respectively. The high temperature accelerated aging makes the resin macromolecular structure in the composites changed, and then the adhesive force between fiber bundles and resin declines rapidly which result in the tensile strength of composites aged decrease. This research provides a useful reference for long term durability of laminated/epoxy resin composites.

Abstract: The paper investigats the polarization properties and mechanical behavior of new piezoelectric polymer material plates by experimental procedures and finite element analysis. In this study, the PVDF materials are used to produce the piezoelectric polymer layer and the coating film, we have provided nice procedures for manufacturing piezoelectric polymer plates (PVDF). In order to find the proper proportion of the PVDF to achieve the best material properties, the mechanical behavior of displacements and stresses for the electrets is investigated by experimental measurement and finite element analysis (with ANSYS). It is investigated whether the thicknesses of specimens will affect the polarization. The paper is presented modal analysis techniques for piezoelectric thin plates.

Abstract: A study on dynamic mechanical properties of carbon fiber plain woven fabric (with fiber orientation of 0°/90°) / epoxy resin laminated composites with different fiber volume fraction was carried out. The test method is single input single output free vibration of cantilever beam hammering modal analysis method. The effect of different fiber volume fraction on the modal parameters of laminated composites was analyzed. The experimental results show that with the fiber volume fraction increasing, the natural frequency of laminated composites becomes larger and damping ratio becomes smaller. The fiber volume fraction is greater, the peak value of natural frequency becomes higher and the attenuating degree of acceleration’ amplitude becomes slower.

Abstract: In this paper, a kind of composite laminates whose reinforcement is four-layer biaxial weft knitted (FBWK)fabric made of carbon fiber as inserted yarns has been made. The composite laminates have been impregnated with epoxy resin via resin transfer molding (RTM) technique. The samples of the experiments have been made from the composite laminates. The bending properties of the FBWK fabric reinforced composite materials with different fiber volume fraction have been investigated. The results show that the bending strength of this kind of composites increases with the fiber volume fraction increasing. The bending strength of FBWK reinforced composites with fiber volume fraction of 52% can reach 695.86 MPa. And the relationship between bending load and deflection is obviously linear.

Abstract: Shape memory epoxy polymer (SMEP-1) was modified by introducing flexible epoxy into existing resin system. The thermal transition temperature (Ttrans) of shape memory polymer was tailored from 100°C to 76°C with the increase of the weight fraction of the flexible epoxy. The toughness of the polymer was also measured at the same time. The results show that the toughness of the polymer was improved especially at ultralow temperature. The addition of the flexible epoxy didn’t affect the excellent shape memory properties of the polymers.