Prediction of hot tearing tendency for multicomponent aluminum alloys

It is of practical importance to be able to predict the hot tearing tendency for multicomponent aluminum alloys. Hot tearing is one of the most common and serious defects that occurs during the casting of commercial aluminum alloys, almost all of which are multicomponent systems. For many years, the main criterion applied to characterize the hot tearing tendency of an alloy system was based on the solidification interval. However, this criterion cannot explain the susceptibility-composition relation between the limits of the pure base metal and the eutectic composition. Clyne and Davies correlated the susceptibility-composition relationship in binary systems based on the concept of the existence of critical time periods during the solidification process when the structure is most vulnerable to cracking. The Scheil equation was used in their model using constant partition coefficient and constant liquidus slope estimated from the phase diagram. In the current study, the authors followed Clyne and Davies’ general idea, and directly coupled the Scheil solidification simulation with phase diagram calculation via PanEngine, a multicomponent phase equilibria calculation interface, and extended the model to higher order systems. The predicted hot tearing tendencies correlated very well with the experimental results of multicomponent aluminum alloys. This article is based on a presentation made in the John Campbell Symposium on Shape Casting, held during the TMS Annual Meeting, February 13–17, 2005, in San Francisco, CA.     

Influence of surface roughness on the calculation of optical constants of a metallic film by attenuated total reflection

The measured optical-constant errors that arise in the Kretschmann configuration from surface roughness have been analyzed. The broadening of the half-width and the change in the reflection minimum of the attenuated-total-reflection curve that are due to the surface roughness are described. Calculation of the correct optical constants and silver-film thickness is demonstrated.     

Alginate‐coated chitosan membrane for guided tissue regeneration

Chitosan membranes were first prepared by a thermally induced phase separation method and then alginate was coated on one side of the membranes by a modified dialysis apparatus to prepare alginate/chitosan membranes (A/C membranes). Electron spectroscopy for chemical analysis (ESCA), scanning electron microscope, and contact angle measurements were conducted to evaluate the surface characteristics. The mechanical strength, degradation behavior, and cell adhesion test were performed to evaluate the feasibility of using A/C membrane in guided tissue regeneration applications. The results revealed that alginates could effectively be coated onto the chitosan membrane. As observed in ESCA results, the N‐atomic emission peak was decreased from originally 6.2% on the untreated chitosan surface to 2% on the alginate‐treated surface. The contact angle decreased on the alginate‐modified side substantially, compared with the untreated side (from 88.4° to 34.2°). The A/C membrane had a higher water content of 71.8% in comparison to the chitosan membrane of 61.8%. Consequently, A/C membrane became stiffer and had a higher Young's modulus and strength. After a 30‐day in vitro shaking test, the weight of membranes was degraded to about 75% from the original. The 3T3 fibroblast cells showed less adhesion to alginate‐modified side as compared to the untreated chitosan‐side in cell adhesion test. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4528–4534, 2006     

General temperature rise solution for a moving plane heat source problem in surface grinding

In the present study, the general solutions for a transient state as well as for the temperature rise formed everywhere in the workpiece due to a rectangular-shaped moving plane heat source arising at the grinding zone are derived. The present analysis starts from a point heat source solution by applying the method of separation of variables to a three-dimensional heat conduction problem. Because the workpiece moving velocity is quite small, the convective term related to the workpiece velocity is first excluded from the heat conduction equation. This workpiece velocity effect will be included in the model by slightly modifying the coordinate variable in the sliding direction shown in the solution of the point heat source. Therefore, the general three-dimensional solution of the stationary temperature rise can be expressed in an integral form as a function of the product value of the unknown initial condition and the particular solution of temperature rise. The unknown initial temperature rise in the solution can be replaced by the point heat source due to frictional that multiplying the product of the Dirac delta functions defined for three directions. Using the definition of the Dirac delta function, the temperature rise solution for a point heat source can thus be obtained. This solution is further extended to obtain the moving and uniform heat sources arising in a rectangular grinding zone. A comparison among the experimental result and the theoretical results predicted by the present model and Jaeger’s model [Jaeger JC (1942) Proc Roy Soc, NSW 76:203–224.] show that the present model is quite accurate and is generally superior to Jaeger’s model; it can be applied to predict the three-dimensional temperature rise distributions in the workpiece.     

NOTCH EFFECT ON TWO-LEVEL CUMULATIVE LOW-CYCLE FATIGUE LIFE UNDER DIFFERENT BIAXIAL LOADING MODE SEQUENCES

Abstract Two-level cumulative low-cycle fatigue lives of AISI 316 stainless steel notched specimens with different biaxial loading mode sequences were experimentally analyzed in this paper. Forty-eight cases were conducted in the experimental program by considering the loading level sequence effect, the biaxiality of two levels and the cycle ratios. Results show that interlock effect caused by the characteristic fracture surfaces of the different biaxial states is beneficial to the cumulative fatigue lives. On the other hand, the tensile loading of the second level will accelerate the opening of cracks and decrease fatigue strength. Miner's rule predicts most fatigue lives within 30% error bands, and the loading level sequence effect was not found in this research involving complex fracture modes. Fractography of specimens in the cumulative fatigue tests is reported and discussed in this paper.     

The effect of mixing on reactor performance: an application of perturbation technique

The effect of local mixing on the performance of a reactor system is derived by the perturbation technique. It is found that the sign of the inner product of the adjoint vector λ and the acceleration vector ? is the only indicator as to whether or not local mixing at a certain point of a reaction path is desirable. A complex reaction system with competing side reactions of different order is treated as an example. The possibility of applying the results in this work to the selection of the optimal type of reactor is also discussed.     

Ultrasonic techniques for imaging and measurements in molten aluminum

In order to achieve net shape forming, processing of aluminum (Al) in the molten state is often necessary. However, few sensors and techniques have been reported in the literature due to difficulties associated with molten Al, such as high temperature, corrosiveness, and opaqueness. In this paper, development of ultrasonic techniques for imaging and measurements in molten Al using buffer rods operated at 10 MHz is presented. The probing end of the buffer rod, having a flat surface or an ultrasonic lens, was immersed into molten Al while the other end with an ultrasonic transducer was air-cooled to room temperature. An ultrasonic image of a character "N", engraved on a stainless steel plate immersed in molten Al, and its corrosion have been observed at 780 degrees C using the focused probe in ultrasonic pulse-echo mode. Because cleanliness of molten Al is crucial for part manufacturing and recycling in Al processing, inclusion detection experiments also were carried out using the nonfocused probe in pitch-catch and pulse-echo modes. Backscattered ultrasonic signals from manually added silicon carbide particles, with an average diameter of 50 microm, in molten Al have been successfully observed at 780 degrees C. For optimal image quality, the spatial resolution of the focused probe was crucial, and the high signal-to-noise ratio of the nonfocused probe was the prime factor responsible for the inclusion detection sensitivity using backscattered ultrasonic signals. In addition, it was found that ultrasound could provide an alternative method for evaluating the degree of wetting between a solid material and a molten metal. Our experimental results showed that there was no ultrasonic coupling at the interface between an alumina rod and molten Al up to 1000 degrees C; therefore, no wetting existed at this interface. Also because ultrasonic velocity in alumina is temperature dependent, this rod proved to be able to be used as an in-line temperature monitoring sensor under 1000 degrees C in molten Al.     

Hydrophobic Chromophores in Aqueous Micellar Solution Showing Large Two‐Photon Absorption Cross Sections

A series of new hydrophobic two‐photon absorbing (2PA) chromophores with varied electron‐donating groups in quasi‐linear and multibranched structures are synthesized to correlate their structure/photophysical property relationships. The feasibility of using these large two‐photon absorption cross‐sectional (δ, expressed in GM = 1 × 10^–50 cm⁴ s photon^–1 molecule^–1) materials in aqueous solution is also explored. All four hydrophobic 2PA materials can be encapsulated into micelles generated by dispersing an amphiphilic block copolymer, poly(methacrylic acid)‐block‐polystyrene (PMAA‐b‐PS), into water. The micellar nanostructures are characterized using dynamic light scattering, atomic force microscopy, and transmission electron microscopy. After these dyes are incorporated into micelles, they exhibit strong fluorescence in water. It is found that the quantum yield and δ values of these chromophores are strongly dependent on the diameters of the micelles, concentrations of the PMAA‐b‐PS, and molecular structures of the 2PA chromophores. One of the compounds that has a strong triarylamino donor and a multibranched structure exhibits a large δ value of 2790 GM and high quantum yield (0.56) in micelle‐containing water. Although this value is smaller than the original value of 5300 GM in toluene, it is still substantially larger than the values of most water‐soluble 2PA materials, which have δ values of less than 100 GM.     

Versioned linking of semantic enrichment of legal documents

Regulations affect every aspect of our lives. Compliance with the regulations impacts citizens and businesses similarly: they have to find their rights and obligations in the complex legal environment. The situation is more complex when languages and time versions of regulations should be considered. To propose a solution to these demands, we present a semantic enrichment approach which aims at (1) decreasing the ambiguousness of legal texts, (2) increasing the probability of finding the relevant legal materials, and (3) utilizing the application of legal reasoners. Our approach is also implemented both as a service for citizens and businesses and as a modeling environment for legal drafters. To evaluate the usefulness of the approach, a case study was carried out in a large organization and applied to corporate regulations and Hungarian laws. The results suggest this approach can support the previous aims.     

Evolution of microstructure and texture in an ultrafine-grained Al6082 alloy during severe plastic deformation

The evolution of microstructure and texture in Al6082 precipitation-hardened alloy during equal-channel angular pressing (ECAP) was studied. It was found that although the dislocation density and the subgrain size saturated after 1 pass, the size of grains bounded by high angle boundaries reached its minimum value only after 4 passes. Furthermore, the grain orientation distribution changes between 4 and 8 passes, indicating the development of grain boundary structure even after the saturation of the parameters of the microstructure. As a result of this evolution, the initial texture of the commercial alloy was diminished after 8 passes and the grain orientation distribution became to be close to random case.