Effect of W-addition on low cycle fatigue behavior of high Cr ferritic steels

A study was done to investigate the effect of tungsten (W) addition on the microstructure, tensile properties and low cycle fatigue (LCF) properties of 9Cr-lMo steels at 298K and 873K. Four steels containing different amounts of W (0W, 1.2W, 1.8W and 2.7W) were normalized at 1323K for 1 hour and tempered at 1023K for 1 hour. Microstructural analysis revealed that no significant differences wete observed in their tempered martensitic microstructure of 0W, 1.2W and 1.8W alloys, but d-ferrite was observed to form at the prior austenite grain boundaries of the 2.7W alloy. With the increase in W content, yield and tensile strength increased at both temperatures. Low cycle fatigue life also increased with the W content up to 1.8%, but decreased in the 2.7W alloy, which was primarily due to the presence of soft d-ferrite acting as the crack initiation site. The fatigue life at 873K was reduced compared to that at 298K, due not only to the decrease in strength at high temperature but also to the formation of oxide layers along the slip bands, which increases slip irre-versibility during cyclic deformation. This article based on a presentation made in the symposium “The 1^st Korea—Japan Structural Dynamic Symposium”, held at Sunchon National University, Sunchon, Korea, August 5–8, 1999 under the auspices of The Korean Insitute of Metals and Materials and Research and Development Center for Automobile Parts and Materials.     

Optimization of the influential factors for the improvement of CO2 utilization efficiency and CO2 mass transfer rate

Microalgae fix CO₂ as energy source and afford biomass and high valued products such as carotenoids, pigments, proteins, and vitamins that can be used for the production of nutraceuticals, pharmaceuticals, animal feed additives, cosmetics, etc. Carbon dioxide is the sole source of carbon and it is supplied continuously for the microalgal cultivation. But undissolved CO₂ is lost by outgassing and sufficient dissolved CO₂ should be provided to avoid carbon limitation. The effect of CO₂ mass transfer with different CO₂ concentrations, aeration rate of gas, bubble size, baffle type and baffle number on the growth of Chlorella sp. AG10002 was investigated and the optimized conditions for the enhancement of biomass productivity were determined. We confirm that these results can be provided as basic data to improve the CO₂ mass transfer ability for the high density culture of Chlorella sp. and some microalgae having commercial value.     

Modeling of a non-Newtonian flow between parallel plates in a flip chip encapsulation

The viscosity of the underfill encapsulant may be different under the conditions of different shear rate, filler content, and temperature. Most of the encapsulant is epoxy containing silica fillers. It exhibits non-Newtonian behavior in the underfill flow. The effect of the viscosity variations on the underfill filling flow was investigated in this study. An analytical model of the filling flow is proposed to accomplish the shear-rate depending viscosity. Due to the addition of fillers in the encapsulant, the viscosity may exhibit both shear thinning and thickening behaviors depending on the temperature and filler content. This study proposes a model of the viscosity considering both effects. In the situations demonstrated in the results, the shear thinning and thickening effects may have major influence on the velocity profile and the filling speed.     

Durable antimicrobial finish of cotton fabrics

Cotton fabrics were treated with Biopag, which does not have any functional groups that are reactive toward cellulose, using crosslinking agents or a binder, for the purpose of imparting a durable antimicrobial finish. In this respect, it was found that the crosslinking agents were more effective than the binder. It was confirmed by FT‐IR that the characteristic split peaks of Biopag were still seen even after repeated launderings. The crosslinking agents deteriorated the whiteness and tensile strength of the Biopag‐treated cotton fabrics, while the wrinkle recovery angles (WRAs) were significantly improved. The one‐step padding of Biopag and the crosslinking agent was found to be superior to the two‐step padding method in which Biopag padding was followed by padding of crosslinking agent in respect of WRA, whereas the whiteness and tensile strength were vice versa. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

A methodology for systemic‐structural analysis and design of manual‐based manufacturing operations

The main objective of this study was to develop a method for systemic‐structural analysis and design of manufacturing assembly operations based on the activity theory. The “activity” was defined as behavior distinctively specific to workers, associated with mobilizations and realization of conscious manufacturing goals. The fundamental units of analysis of activity are actions that are both motor and mental. Activity is considered as a complicated structure of actions that are logically ordered in space and time. Each action is comprised of different operations. The building blocks of motor actions are motions. The building blocks of cognitive actions are mental operations. Activity integrates not merely cognitive and behavioral components, but the energy components as well. The proposed methodology is illustrated using an example of two manufacturing assembly operations. © 2001 John Wiley and Sons, Inc.     

Direct Physical Imaging and Chemical Probing of LiFePO4 for Lithium‐Ion Batteries

The control of unexpectedly rapid Li intercalation reactions without structural instability in olivine‐type LiFePO₄ nanocrystals is one of the notable scientific advances and new findings attained in materials physics and chemistry during the past decade. A variety of scientific studies and technological investigations have been carried out with LiFePO₄ to elucidate the origins of many peculiar physical aspects as well as to develop more effective synthetic processing techniques for better electrochemical performances. Among the several features of LiFePO₄ that have attracted much interest, in this article we address four important issues—regarding doping of aliovalent cations, distribution of Fe‐rich secondary metallic phases, nanoparticle formation during crystallization, and antisite Li/Fe partitioning—by means of straightforward atomic‐scale imaging and chemical probing. The direct observations in the present study provide significant insight into alternative efficient approaches to obtain conductive LiFePO₄ nanocrystals with controlled defect structures.     

Sliding mode control of a shear-mode type ER engine mount

This paper presents feedback control characteristics of a shear-mode type electro-rheological (ER) engine mount. The field-dependent yield stress of an arabic gum-based ER fluid is obtained using a couette type electroviscometer, and it is incorporated into the governing equation of motion of the ER engine mount, which is derived from a bond graph model. A sliding mode controller which directly represents the field-dependent damping force is formulated by taking into account the stiffness and damping properties of the systems as parameter uncertainties. The controller is then experimentally realized by imposing a semi-active actuating condition. The effectiveness of the proposed ER engine mount is demonstrated showing capabilities of isolating the vibrations due to sinusoidal and random excitations.     

Strain hardening behavior during manufacturing of tube shapes by hydroforming

Safe and robust process design relies on knowledge of the evolution of the mechanical properties in a tube during hydroforming. The manufacturing of tubular shapes generally consists of three main stages: bending, preforming, and expansion. The latter is usually called hydroforming. As a result of these three steps, the final product’s strain hardening history is nonlinear. In the present study, the strain hardening behavior during hydroforming was experimentally investigated. The variation of local flow stress and/or local hardness was used as an index of the strain hardening during the various steps and the local flow stress and/or local hardness were used with respective correlations to determine the effective strain. The strain hardening behavior during hydroforming after preforming has been successfully analyzed by using the relationships between hardness, flow stress, and effective strain for variable pre-strains prior to hydroforming. The comparison of predicted hardness with measured hardness confirms that the methodology used in this study is feasible, and that the strain hardening behavior can be quantitatively estimated with good accuracy.