CRACK GROWTH BEHAVIOUR OF FATIGUE MICROCRACKS IN LOW CARBON STEELS

The behaviour of low carbon steels has been studied, in particular the initiation and growth of the major crack which led to final fracture of smooth specimens, via surface replica and photomicrograph techniques. From this study, the fracture process and fatigue life prediction characterized by the growth of surface microcracks have been analysed by a new approach unifying the conventional approaches based on the final fracture of materials with the fracture mechanics approach. Knowledge of fracture parameters is critical for non-destructive inspection during service life and the application of fracture mechanics to life prediction and assessment.     

Synthesis of new pH-sensitive polyurethane gels using polyethylene glycol modified urethane acrylate and urethane acrylate anionomer

New type of amphiphilic pH-sensitive polyurethane networks, derived from the mixture of polyethylene glycol-modified urethane acrylates (PMUA) and urethane acrylate anionomer (UAA), were prepared and their swelling behaviors were evaluated. Three kinds of polymerization methods were employed in the synthesis of polyurethane networks. Polyurethane networks prepared by a process similar to that of soap-free emulsion polymerization (UAHG) showed the highest swelling ratio and pH-sensitivity. Additionally, four kinds of UAHG gels were prepared at different composition of UAA. As the composition ratio of UAA to PMUA increased, swelling of UAHG gels in alkali pH buffer solution and their pH-sensitivity greatly increased. Additionally, swelling of UAHG gels changed reversibly with the change of pH. Received: 18 November 1996/Revised: 10 January 1997/Accepted: 14 January 1997     

Erosive Wear Mechanism of New SiC/SiC Composites by Solid Particles

A solid-particle erosive wear test by impinging silicon carbide (SiC) powders was carried out at room temperature over a range of median particle sizes of 425–600 μm, speed of 100 m/s and impact angle of 90° and assessed by wear measurements and scanning electron microscopy. Erosive wear behaviour was examined on newly fabricated nano-powder infiltration and transient eutectoid (NITE) SiC/SiC composites and two commercial composites by the chemical vapour infiltration (CVI) and NITE fabrication route. Microstructural observation was performed to examine the correlation between erosive wear behaviours and fabrication impurities. Conspicuous defects were observed in the prototype materials as the forms of porosity, fibre deformation, residual oxide, pyrolytic carbon (PyC) deformation, PyC cleavage, among others. Erosive wear behaviour was rather serious in the prototype of fabricated composites, which employ pre-SiC fibre and phenolic resin. Two dominant erosive wear mechanisms were observed: delamination of constituents, mainly caused by erosive crack propagation, and fragmentation and detachment of constituents, which usually resulted from erosive impact. A unit size of delamination was the most decisive factor affecting wear volume. The bonding strength of each constituent was mostly affected by various forms of porosities. Therefore, the fundamental cause and subsequent results must be carefully elucidated. The correlation of microstructural defect and wear behaviour was investigated with the aim of reducing dominant wear by improving fabrication conditions. The final product of the cost-effective composite had a 2.5-fold higher resistance than the commercial CVI composite. Consequently, by controlling fabrication impurities, we have been successful in developing and improving a new fabrication technique; consequently, the known defects are rarely observed in final product. A schematic wear model of erosive wear mechanisms is proposed for the newly fabricated SiC/SiC composites under particle erosion.     

Capillarity-induced patterning of thin polymer films and related regular dewetting structures

When a thin polymer film is spin-coated on a solid substrate and heated above its glass transition temperature (T_g) while in conformal contact with a patterned polydimethylsiloxane (PDMS) mold, capillarity forces the polymer melt to fill up the void space of the mold, thereby forming a negative replica of the polymer after mold removal. In this study, particular emphasis is given to the nodal dewetting phenomenon in a thin, laterally confined polymer film that sticks to a substrate. When heated above the glass transition temperature, the film dewets from the substrate through the generation of nodal waves, with the PDMS wall acting as a node. Various superposed waves were observed depending on the intrinsic period of dewetting and the confining width of the cavity.     

Effects of myosin light chain kinase inhibitors on carbachol-activated nonselective cationic current in guinea-pig gastric myocytes

The effects of myosin light chain kinase inhibitors on muscarinic stimulation-activated nonselective cationic current (ICCh) in guinea-pig gastric antral myocytes were studied using the whole-cell patch-clamp technique. ICCh was induced by carbachol (CCh, 50 microM) at a holding potential of -30 mV or -60 mV. ML-7, a chemical inhibitor of myosin light chain kinase (MLCK), inhibited ICCh concentration dependently in a reversible manner (53 +/- 8.6% at 1 microM, mean +/- SE, n = 11). In addition, amplitudes of ICCh were only 37 +/- 2.7% of the daily control values following the addition of a peptide inhibitor of MLCK to the pipette solution. On the other hand, ML-7 had an inhibitory effect on voltage-operated Ca2+ channel current. The peak value of Ba2+ current at 0 mV was reduced to 35 +/- 7.4% (n = 9) by 3 microM of ML-7. As ICCh is known to have an intracellular Ca2+ dependence, we tried to exclude the possibility that ML-7 inhibited ICCh indirectly via suppression of Ca2+ current and the similar inhibitory effects of ML-7 on ICCh were confirmed under the following conditions: (1) clamp of membrane potential at -60 mV; (2) clamp of intracellular [Ca2+] to 1 microM by 10 mM BAPTA; (3) pre-inhibition of Ca2+ channel by verapamil. Different from the effects on ICCh, ML-7 barely inhibited the same cationic current induced by guanosine 5'-O-(3-thiotriphosphate) (GTP[gammaS], 0.2 mM) in the pipette solution. These results suggest that a Ca2+/calmodulin-MLCK-dependent pathway can modulate the activation of ICCh in guinea-pig gastric antral myocytes.     

Effects of filter additives on cake filtration performance

Effects of various additives, such as diatomaceous earth, inorganic adsorbent, and polymeric flocculant, on cake filtration performance were evaluated. By performing the standard vacuum filtration experiments under a constant pressure condition, we quantified their ability to reduce cake compressibility and to remove fine particulate matters. From the flux decline curves obtained, we used modified Ruth equation to determine the cake compressibility index. The filtrate clarity was quantified by measuring its turbidity spectrophotometrically. Diatomaceous earth filter aid was very effective in reducing the compressibility thereby improving filtrate flux. Calcium phosphate adsorbent was more effective in clarity improvement than in flux enhancement, whereas an anionic flocculant was effective in both aspects. When these additives were used together, the expected additive, synergic effect was not realized. However, about 3.5 times higher initial flux and 6-fold improved clarity were obtained as compared to the control experiment. Experimentally obtained flux decline curves were perfectly fitted into one of the Hermia’s blocking filtration law equations. Also, it was experimentally observed that the compressibility reduction improved filtrate clarity in a linear fashion. This type of approach is useful to quantitatively determine each additive’s characteristics and thus to maximize the performance of cake filtration operations.     

Pulse width modulation for analog fiber-optic communications

The pulse width modulation (PWM) technique has been revisited and analyzed to evaluate its merits for application to analog signal transmission in fiber-optic links. Fourier analysis of the PWM signal reveals that it can be used as a vehicle to launch an analog signal onto optical fiber when a symmetrical natural sampling process is used. The SNR of the modulated signal depends on the timing jitter of the carrier pulses and a wide-band (45 MHz) SNR of 45 dB has been obtained with a commercially available multimode laser transmitter. A linear dynamic range of over 50 dB has been experimentally demonstrated. The full fiber bandwidth can be utilized by using a very high pulse carrier frequency, while a more popular pulse frequency modulation technique provides about a 10-MHz analog signal bandwidth when 1 km of multimode fiber is used in conjunction with a short wavelength (0.87 μm) LED transmitter. Analog transmission capability was experimentally demonstrated by constructing a simple video link using common laboratory equipment. The performance of the video link supports the PWM modulation theory developed here and elsewhere. The experimental results indicated that PWM is potentially very attractive for low-cost broad-band local area network (LAN) application, including future highly interactive offices, hospitals, and automated factory floors.     

Solution phase synthesis of amyloid-cleaving catalysts, two [1,3,5]triazine based compounds

Solution phase synthetic method for amyloid-cleaving catalysts was developed, which bears triazine core, scaffold with bulky and that have various solubility properties; Co(III) complex of cyclen (1,4,7,10-tetraazacyclododecane) for catalytic group, and two imaging agents for binding group. This synthetic method was identified by H-NMR, C-NMR for intermediates and MS for the last products. The yields by this method surpassed solid phase synthesis and took much lower labor, expense, and time. The products which were synthesized by solution phase synthetic method showed good catalytic activities.     

Synthesis and characterization of fluorene-carbazole and fluorene-phenothiazine copolymers with carbazole and oxadiazole pendants for organic light emitting diodes

We report the synthesis and characterization of new series of the fluorene based polymers with carbazole and oxadiazole pendants for the generation of the white emission out of the EL device. In the fluorene backbone, hole transporting units such as carbazole or phenothiazine were incorporated to improve the EL brightness and efficiency. The PFCzOxd-co-PCzs and PFCzOxd-co-PPTZs in EL spectra showed maximum peaks at around 430 nm and additional large peaks at around 530 and 500 nm, respectively. In case of PFCzOxd-alt-PCz and PFCzCzPCz-co-PFOxdOxdPCz, the EL spectra of the polymers showed two distinct peaks comprising the maximum at 427 nm, which corresponds to the EL spectra of the conjugated backbone, and additional broad peaks at around 540 and 530 nm, respectively. The CIE coordinates of the devices from PFCzOxd-alt-PCz and PFCzCzPCz-co-PFOxdOxdPCz were (0.28, 0.33) and (0.25, 0.32), respectively, approaching the value of the standard white of National Television System Committee (NTSC) (0.33, 0.33).