Anisotropic threshold stress intensity factor, KIH and crack growth rate in delayed hydride cracking of Zr-2.5Nb pressure tubes

The objectives of this study are to systematically investigate the delayed hydride cracking (DHC) velocity and the threshold-stress intensity factor, K _IH , of a Zr-2.5Nb pressure tube as a function of orientation and elucidate the cause of this anistropic DHC behavior. The DHC velocity as a function of orientation was determined using flattened cantilever beam specimens with 60 ppm H while the threshold-stress intensity factor K _IH , was evaluated as a function of orientation on the curved compact-tension (CT) and cantilever-beam (CB) specimens charged with hydrogen to 200 ppm H. To infer a difference in a stress gradient ahead of the crack tip as a function of orientation, tensile tests were conducted at temperatures ranging from room temperature (RT) to 560 °C using small tensile specimens of 2-mm-gage length taken from three directions of the tube. A textural change was investigated by comparing the inverse pole figures before and after DHC while the {10 7} pole figures were constructed to find out the growth pattern of the DHC crack as a function of orientation. Faster DHC velocity and lower K _IH were obtained over temperatures of 170 °C to 270 °C, when the DHC crack grew in the longitudinal direction of the Zr-2.5Nb pressure tube. The strain hardening after yielding and the extent of the textural change accompanied by DHC were higher in the longitudinal direction of the tube, suggesting a higher stress gradient ahead of the crack tip. Thus, the anisotropic DHC behavior of a Zr-2.5Nb pressure tube is discussed based on the stress gradient ahead of the crack tip governed by strain-hardening rate after yielding and a change in texture accompanied by DHC, and the distribution of the {10 7} hydride habit planes. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

A microfluidic gel valve device using reversible sol–gel transition of methyl cellulose for biomedical application

We have fabricated a microfluidic gel valve device that used reversible sol–gel transition of methyl cellulose (MC). A microheater and a microtemperature sensor were implemented in each microchannel in the gel valve device. Before evaluating the performance of the gel valve device, various properties of the MC solution were investigated using viscometer, spectrophotometer, and NMR. Gelation temperature was increased as the MC concentration was increased. Clear gel, an intermediate state between clear sol and turbid gel, was found at the temperature range from 30–40°C to 50–60°C. Temperature at each microchannel of the device was measured and the effect of the temperature difference on the valve operation was elucidated. In order to have normal operation of the gel valve, it was important to keep the temperature of the heated microchannel around 60°C while keeping the temperature of the flowing microchannel below 35°C. The temperature difference between two microchannels was about 23 K when fan forced cooling (FFC) method was used. For normal performance of the gel valve device, a temporary pause of fluid flow for at least 5 s was required to complete the local gelation in the microchannel. Stable gel valve performance was obtained at the flow rates larger than 5 μl/min. The gel valve device showed no leakage up to 2.07×10⁴ Pa.     

Cavity formation from inclusions in ductile fracture

The previously proposed conditions for cavity formation from equiaxed inclusions in ductile fracture have been examined. Critical local elastic energy conditions are found to be necessary but not sufficient for cavity formation. The interfacial strength must also be reached on part of the boundary. For inclusions larger than about 100Å the energy condition is always satisfied when the interfacial strength is reached and cavities form by a critical interfacial stress condition. For smaller cavities the stored elastic energy is insufficient to open up interfacial cavities spontaneously. Approximate continuum analyses for extreme idealizations of matrix behavior furnish relatively close limits for the interfacial stress concentration for strain hardening matrices flowing around rigid non-yielding equiaxed inclusions. Such analyses give that in pure shear loading the maximum interfacial stress is very nearly equal to the equivalent flow stress in tension for the given state of plastic strain. Previously proposed models based on a local dissipation of deformation incompatibilities by the punching of dislocation loops lead to rather similar results for interfacial stress concentration when local plastic relaxation is allowed inside the loops. At very small volume fractions of second phase the inclusions do not interact for very substantial amounts of plastic strain. In this regime the interfacial stress is independent of inclusion size. At larger volume fractions of second phase, inclusions begin to interact after moderate amounts of plastic strain, and the interfacial stress concentration becomes dependent on second phase volume fraction. Some of the many reported instances of inclusion size effect in cavity formation can thus be satisfactorily explained by variations of volume fraction of second phase from point to point.     

100‐MHz CMOS circuits directly fabricated on plastic using sequential laterally solidified silicon

Abstract— CMOS TFT circuits were fabricated on plastic using sequential laterally solidified silicon combined with a low‐temperature CMOS process. The unity‐gain frequencies of the best of NMOS TFTs are greater than 250 MHz, and the CMOS ring oscillators operate at 100 MHz. To the best of the authors' knowledge, these are the highest‐frequency circuits ever fabricated directly on plastic. This high‐performance CMOS‐on‐plastic process can be applied to the fabrication of AMLCD integrated drivers and AMOLED pixels on plastic substrates.     

Optimizing the binary discriminant function in change detection applications

Binary discriminant functions are often used to identify changed area through time in remote sensing change detection studies. Traditionally, a single change-enhanced image has been used to optimize the binary discriminant function with a few (e.g., 5-10) discrete thresholds using a trial-and-error method. Im et al. [Im, J., Rhee, J., Jensen, J. R., & Hodgson, M. E. (2007). An automated binary change detection model using a calibration approach. Remote Sensing of Environment, 106, 89-105] developed an automated calibration model for optimizing the binary discriminant function by autonomously testing thousands of thresholds. However, the automated model may be time-consuming especially when multiple change-enhanced images are used as inputs together since the model is based on an exhaustive search technique. This paper describes the development of a computationally efficient search technique for identifying optimum threshold(s) in a remote sensing spectral search space. The new algorithm is based on “systematic searching.” Two additional heuristic optimization algorithms (i.e., hill climbing, simulated annealing) were examined for comparison. A case study using QuickBird and IKONOS satellite imagery was performed to evaluate the effectiveness of the proposed algorithm. The proposed systematic search technique reduced the processing time required to identify the optimum binary discriminate function without decreasing accuracy. The other two optimizing search algorithms also reduced the processing time but failed to detect a global maxima for some spectral features.     

Numerical studies of transient opposed-flow flames using adaptive time integration

Numerical simulations of unsteady opposed-flow flames are performed using an adaptive time integration method designed for differential-algebraic systems. The compressibility effect is considered in deriving the system of equations, such that the numerical difficulties associated with a high-index system are alleviated. The numerical method is implemented for systems with detailed chemical mechanisms and transport properties by utilizing the Chemkin software. Two test simulations are performeds hydrogen/air diffusion flames with an oscillatory strain rate and transient ignition of methane against heated air. Both results show that the rapid transient behavior is successfully captured by the numerical method.     

Transcrystalline morphology and mechanical properties in polypropylene composites containing cellulose treated with sodium hydroxide and cellulase

To evaluate the transcrystalline effects caused by various fibers, which were untreated, or treated with sodium hydroxide and cellulase, isothermal crystallization was performed. It was observed that the untreated and cellulase-treated cellulose fibers (cellulose I) had a nucleating ability to transcrystallize at PP matrix. Especially, cellulose fibers treated with Sodium hydroxide (cellulose II) transcystallized at PP matrix. This result was different from other's. Cellulose fibers also transcrystallized at PP/MAH-PP matrix irrespective of the type of cellulose crystalline structure. In PP/MAH-PP/CELL system, MAH-PP was located around the fiber surface at initial crystallization time, but was gradually expelled from that with the increase of crystallization time, and existed at outer boundaries of transcrstalline region at the final crystallization time. These phenomena were confirmed by IR-IRS spectra. The tensile strength of PP/CELL and PP/MAH-PP/CELL composites decreased with the increase of isothermal crystallization time. Therefore, it is thought that transcrystallinity gives rise to negative effect of tensile strength.     

Menopausal transition of Korean immigrant women: a literature review

The menopausal transition needs to be understood in terms of the multiple mediating factors within the context in which women experience it. For immigrant women especially, the menopausal experience is complicated by multiple transitions and social marginality, so it cannot be adequately explained without considering this complexity. In this paper we review the literature on the menopausal transition of a group of vulnerable immigrant women in two ways: describing the transitions themselves (menopause, immigration, and housewife to employee), and describing factors that mediate the menopausal transition experience (family norms, meaning of menopause and women's work, and health practices). We emphasize the context and suggest areas of needed research.     

Optimal design of composite hood with reinforcing ribs through stiffness analysis

Fiber glass reinforced composites like sheet molding compounds (SMC) have recently been widely used in the fabrication of two-piece automobile hoods for passenger cars. In the present investigation, a one-piece composite hood with reinforcing ribs was optimally designed and manufactured by resin transfer molding in order to reduce manufacturing cost. In order to obtain the optimal design, stiffness analyses for deflections due to self-weight, oil canning, and torsion test conditions were carried out by applying the ABAQUS/Standard program. Based on these analyses, the thickness dimension of the composite hood required to maintain a stiffness comparable to a conventional steel hood was determined. For optimization studies of the weight reduction of the currently proposed one-piece composite hood with reinforcing ribs, IDESIGN program was employed. Based on a recursive quadratic programming technique, the thickness dimensions of the reinforcing ribs were optimized. The deflection ratios between fiber glass reinforced composite and conventional steel hoods were minimized in the optimization studies. From the present studies, it was found that the weight saving effect obtained by introducing the optimally designed one-piece composite hood was 37% compared to the conventional steel hood. This ranged approximately from 30 to 40% for composite hoods manufactured by resin transfer molding, depending on the composite materials used. Through these studies, it was confirmed that the one-piece composite hood was a preferable design and manufacture, compared to currently used composite hood made in two pieces, in terms of weight reductions and manufacturing cost without losing the stiffness required.