Active,passive and transpassive dissolution of a nickel base super alloy in concentrated acid mixture solution

The electrochemical and corrosion behaviour of a nickel base super alloy (C-263) has been investigated in the deaerated binary and ternary solution mixture of concentrated phosphoric acid, acetic acid, sulphuric acid, nitric acid or water using potentiostatic technique at 35°C. The possibilities of electropolishing of this alloy in these solution mixtures have been also explored. The alloy showed distinct active, passive and transpassive behaviour in the experimental solutions. The alloy remained active and turned passive in the negative potential region. Transpassive dissolution of the alloy is observed and electropolishing is achieved in this region. The best electropolishing is obtained in 50% H₃PO₄ + 40% CH₃COOH + 10% H₂SO₄. Higher content of water in the electrolytic solution is not useful for electropolishing of the alloy The experimental results also suggest that a current plateau in the transpassive potential region is not a sufficient condition to achieve electropolishing.     

Flexure control using piezostack actuators: design and implementation

In this paper, the application of high control authority piezostack actuators (PSAs) for active vibration control of large-scale flexible structures is studied. The idea is to add PSAs at appropriate locations of a flexible structure in order to strengthen its stiffness characteristics. In this regard, a flexible link of a macro-micro manipulator system actuated with PSAs is considered. The design of a mechanism for converting the force produced by a PSA to a bending moment is presented and a model for a system consisting of a flexible beam and a PSA is obtained. To this end, the solution of the governing partial differential equation with nonhomogeneous boundary conditions is obtained. Using singular value decomposition of the controllability Grammian of the system, optimum values for actuator parameters are obtained. The experimental results confirm that the suggested method can open up new possibilities in active vibration control of large-scale structures that require a large amount of control authority.     

A demonstration of melt rate control during VAR of “Cracked” electrodes

A particularly challenging problem associated with vacuum arc remelting occurs when trying to maintain accurate control of electrode melt rate as the melt zone passes through a transverse crack in the electrode. As the melt zone approaches the crack, poor heat conduction across the crack drives the local temperature in the electrode tip above its steady-state value, causing the controller to cut back on melting current in response to an increase in melting efficiency. The difficulty arises when the melt zone passes through the crack and encounters the relatively cold metal on the other side, giving rise to an abrupt drop in melt rate. This extremely dynamic melting situation is very difficult to handle using standard load-cell based melt rate control, resulting in large melt rate excursions. We have designed and tested a new generation melt rate controller that is capable of controlling melt rate through crack events. The controller is designed around an accurate dynamic melting model that uses four process variables: electrode tip thermal boundary layer, electrode gap, electrode mass and melting efficiency. Tests, jointly sponsored by the Specialty Metals Processing Consortium and Sandia National Laboratories, were performed at Carpenter Technology Corporation wherein two 0.43 m diameter Pyromet® 718 electrodes were melted into 0.51 m diameter ingots. Each electrode was cut approximately halfway through its diameter with an abrasive saw to simulate an electrode crack. Relatively accurate melt rate control through the cuts was demonstrated despite the observation of severe arc disturbances and loss of electrode gap control. Subsequent to remelting, one ingot was sectioned in the “as cast” condition, whereas the other was forged to 0.20 m diameter billet. Macrostructural characterization showed solidification white spots in regions affected by the cut in the electrode.     

Evaluation of Laminated Circular Elastomeric Bearings

This paper evaluates the behavior and performance of laminated circular elastomeric bearings and compares them to those of square and rectangular bearings. The study included an experimental evaluation and a nationwide survey of state Department of Transportations on the use and performance of circular bearings and bearings in general in their states. The experimental investigation studied the bearings' behavior in compression, compression and rotation, and compression and shear. Results from this limited study showed that the three bearings have similar stress-strain behavior in compression and they are in agreement with the AASHTO LRFD guide stress–strain curves. In compression and rotation, the AASHTO LRFD substructure moments are slightly less than the measured values for circular bearings and rectangular bearings rotated about their strong axis for a compressive stress of 10.3?MPa (1.5?ksi) and slightly higher than those of rectangular bearings rotated about their weak axis. In compression and shear, the shear stiffness of circular and square bearings is in agreement with theoretical values within the range of design displacements. Results from the survey showed that many states are using circular bearings and more states would consider using them, however no maintenance or monitoring data were available on their short-term and long-term performance.     

Are large firms internationalizing the generation of technology?Some new evidence

Internationalization of technology remains a subject of considerable interest to analysts and policy makers in the 1990s. This paper is a modest attempt at providing some new empirical observations for debate and discussion on one dimension of the subject, namely, the nature and extent of the production of technology undertaken by large firms outside their home base. The evidence, based on the US patenting activities of the world's largest 539 firms (based in 13 countries and covering 16 product groups), shows that for an overwhelming majority of them technology production remains close to the home base. It also shows that firms devoting a large proportion of their resources to technology are amongst the least internationalized. When these firms do go abroad, there is no systematic relationship between their relative presence in a technical field and the relative strength of the host country. The analysis points to the dangers of generalizing on the basis of anecdotal evidence from a small sample of firms from a particular country or sector     

Instron texture profile of buffalo milk cheddar cheese as influenced by composition and ripening changes

Buffalo milk Cheddar cheese samples of different ages were analysed for compositional attributes (CA), ripening indices (RI) and Instron Textural Profile (ITP). All samples were compositionally alike, except for pH and salt-in-moisture (SM) contents. RI showed significant variations. CA and RI showed highly significant correlations within themselves and with each other, except for moisture with pH, SM with moisture, MNFS, Fat and FDM and Fat with MNFS. The ITPs of cheeses showed significant variations and had highly significant intercorrelations indicating their interdependence. CA (except moisture and MNFS) and RI showed a highly significant correlationship with ITPs. Moisture content showed a highly significant correlationship with all ITPs, except cohesiveness and springiness, where it was significant. MNFS content showed significant correlations only with hardness and brittleness. Stepwise regression analysis revealed that MI was the most predominant factor influencing cheese texture, followed by pH, SM, FDM and TVFA. Knowing Ca and RI, the textural properties of cheeses can be forecast through mathematical equations. Similarly the age of cheese can also be predicted if RI and/or textural properties are known.     

Durability of hygrothermally aged graphite/epoxy woven composite under combined hygrothermal conditions

The objective of this study was to examine the effects of hygrothermal aging on the durability of a graphite/epoxy woven composite material system. The study was part of a larger project in which the objective was to evaluate and model the effects of moisture, temperature, and combined hygrothermal conditions on the strength and life of a graphite/epoxy woven composite material system. The results presented here represent an extension of the work by Patel and Case (Int. J. Fatigue 22 (2000) 809).

The hygrothermal aging consisted of cyclical temperature and moisture variations which were meant to simulate mission conditions for an advanced subsonic aircraft. Durability studies were carried out on the aged material system in the form of fatigue and residual strength testing under humid and elevated temperature environments. Damage mechanisms and failure modes were determined through fatigue testing, residual strength testing, and nondestructive evaluation.

Changes in physical appearance, thermal analysis results, fracture surfaces, and moisture diffusion behavior all supported the idea that the material was affected by the aging process. However, experimental testing also showed that the initial and residual tensile properties of the aged material were virtually unaffected by the imposed environmental aging (as compared to unaged material testing results), except when tested at elevated temperature. At elevated temperature, both the dynamic stiffness and residual strength were noticeably reduced from that at room temperature.