Plastic Optical Fiber Displacement Sensor Based on Dual Cycling Bending

In this study, a high sensitivity and easy fabricated plastic optical fiber (POF) displacement sensor is proposed. A POF specimen subjected to dual cyclic bending is used to improve the sensitivity of the POF displacement sensor. The effects of interval between rollers, relative displacement and number of rollers on the sensitivity of the displacement sensor are analyzed both experimentally and numerically. A good agreement between the experimental measurements and numerical calculations is obtained. The results show that the interval between rollers affects sensitivity most significantly than the other design parameters. Based on the experimental data, a linear equation is derived to estimate the relationship between the power loss and the relative displacement. The difference between the estimated results and the experimental results is found to be less than 8%. The results also show that the proposed POF displacement sensor based on dual cyclic bending can be used to detect displacement accurately

Time-aging time-stress superposition in soft glass under tensile deformation field

We have studied the tensile deformation behaviour of thin films of aging aqueous suspension of Laponite, a model soft glassy material, when subjected to a creep flow field generated by a constant engineering normal stress. Aqueous suspension of Laponite demonstrates aging behaviour wherein it undergoes time dependent enhancement of its elastic modulus as well as its characteristic relaxation time. However, under application of the normal stress, the rate of aging decreases and in the limit of high stress, the aging stops with the suspension now undergoing a plastic deformation. Overall, it is observed that the aging that occurs over short creep times at small normal stresses is same as the aging that occurs over long creep times at large normal stresses. This observation allows us to suggest an aging time - process time - normal stress superposition principle, which can predict rheological behaviour at longer times by carrying out short time tests.Comment: 26 pages, 7 figures, To appear in Rheologica Act

gamma-irradiated poly(tetrafluoroethylene) particle-filled low-density polyethylene. II. UV stability of LDPE in the presence of 2 degrees-PTFE powder and silane coupling agents

Ultraviolet (UV) stability of gamma-irradiated poly(tetrafluoroethylene), 2 degrees-PTFE, powder-filled low-density polyethylene (LDPE) was studied in this work. The mechanical and thermal properties of 2 degrees-PTFE powder-filled LDPE were discussed in our previous work (Akinay and Tincer, 1999). It already has been shown that silane coupling agents (SCAs) result in improvements in mechanical properties. The UV stability of these samples was followed by a comparision between strain at break measured after UV irradiation and the initial strain at break, in terms of their ratio defined as residual elongation. The development of carbonyl index was also determined by infrared measurements. To get further UV stability, a hindered amine light stabilizer (HALS) was also used. Whereas addition of 2 degrees-PTFE slightly enhanced the UV stability of LDPE, mercapto type silane (A-189) treatment appeared to increase the UV stability compared with the other types of silane treatments. HALS highly improved the UV stability of untreated and silane-treated 2 degrees-PTFE-filled LDPE at given UV irradiation time. Although we observed some fluctuations in the experimental data of HALS and SCA treated 2 degrees-PTFE-filled LDPE, the coaddition of HALS and SCAs showed synergetics effects in the UV stability compared with the separate additions. (C) 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 877-888, 1999

Preparation and characterization of ultrahigh molecular weight polyethylene and polyisoprene solvent-cast blend films

This study covers the preparation of noncrosslinked and crosslinked solvent-cast blend films of ultrahigh molecular weight polyethylene (UHMWPE) and polyisoprene rubber (PIR) and their mechanical, thermal, IR spectroscopic, and morphological characterizations. Solvent-cast films of polymer blends with 0, 10, 20, 35, 50, and 65% PIR composition were prepared by vigorous stirring from a hot decalin solution. The films were crosslinked chemically by using acetophenone as a crosslinking agent under UV radiation. The mechanical properties, measured as ultimate properties and tensile modulus, were found to decrease with PIR content but crosslinking was found to enhance the ultimate strength and tensile modulus. DSC results revealed that melting point of UHMWPE remains almost constant in blends. However, upon crosslinking, the melting point of UHMWPE is depressed almost 5 degrees C. We observed a similar trend in the enthalpy change of the melting of UHMWPE and the variation of percent crystallinity in UHMWPE. Scanning electron microscopy (SEM) studies on the fractured surfaces of the blends showed that the fibrillar texture is present in both crosslinked and noncrosslinked blends. The crosslinking appeared to be through oxygen linkages, which are preferentially conjugated to double bonds, in addition to the possible carbon-carbon crosslinks. (C) 1998 John Wiley & Sons, Inc

Radiation grafting of vinyl monomers onto poly(tetrafluoroethylene) powder produced by gamma irradiation and properties of grafted poly(tetrafluoroethylene) filled low density polyethylene

Scrap poly(tetrafluoroethylene) (PTFE) was gamma irradiated under an ambient atmosphere in order to produce extensive chain scission and oxidative degradation. After irradiation the PTFE was ground into a fine powder (2 degrees -PTFE) and graft;ed with styrene (St), vinyl acetate (VAc), and 4-vinylpyridine (4-VP) by using the direct irradiation technique. The grafted PTFE were then blended with low density polyethylene (LDPE). The study covered the characterization of irradiated PTFE and grafted 2 degrees -PTFE powder with various methods. Mechanical grinding was found to reduce trapped radicals formed during the irradiation process faster than the annealing process. Grafting on 2 degrees -PTFE was followed by gravimetric analysis, TGA, and the change in the particle size of the samples. Although we reached almost 20% grafting by weight in the St and 4-VP monomers, VAc grafting was found to be maximum at around 8% by weight at the maximum absorbed dose. The addition of VAc grafted 2 degrees -PTFE into LDPE produced better final mechanical properties with a fine dispersion. However, as may be expected, the incorporation of the other two 2 degrees -PTFEs into LDPE showed low film quality and poor mechanical properties. (C) 2000 John Wiley & Sons, Inc

Bond strength and failure analysis of lining materials to denture resin

Objectives: This study was conducted to investigate the bonding properties of five lining materials to a denture base resin. Two hard (chemical-cured resin: Kooliner "Coe Labs, USA" and light-cured VLC resin: Triad "Dentsply, USA") and three soft (chemical-cured resin: Express "Alcos,-USA", heat-temperature vulcanized 'HTV' silicone material: Molloplast-B "Regneri GmbH, Germany" and room-temperature vulcanized 'RTV' silicone material:Ufi Gel-P "Voco,Germany") liners were used