Two experimental methods to determining stress–strain behavior of work-hardened surface layers of metallic components

Two experimental methods to characterize the mechanical behavior of work-hardened surface layers of metallic materials, induced by mechanical surface treatments, are described and discussed. The study was conducted using two steels with different mechanical properties, subjected to a similar shot-peening treatment. To characterize the elastic–plastic behavior of the surface layers affected by shot-peening, the X-ray diffraction assisted four-point bending method (XRDABM) and the normalized hardness variation method (NHVM) were applied. The results were compared and discussed taking into account the advantages and disadvantages of both methods. Similar yield strength values of the treated surfaces were found by both proposed methods. Taking into account their measuring characteristics, these can be considered complementary methods.     

Evaluation of Phase Equilibria Involving the Liquid Phase in the Hf-Si System

Metal-silicon-boron (Me-Si-B) alloys have been extensively studied due to their potential to develop high temperature structural materials. In this sense, information from accurate phase diagram becomes important. This work presents results of detailed microstructural characterization of as-cast hafnium-silicon alloys to assess the liquid composition associated to the invariant reactions of this system. The alloys were prepared by arc melting from high purity hafnium and silicon under argon atmosphere. The phases present in the alloys were identified by scanning electron microscopy and x-ray diffraction. Important discrepancies were found between the data obtained in this work and those of the most recent phase diagrams, especially the composition of the liquid phase in the following reactions: L + Hf₅Si₃ ? Hf₂Si, 32.5 at.% Si instead of 21 at.% Si, L + Hf₃Si₂ ? Hf₅Si₃, 37.0 at.% Si instead of 30.3 at.% Si and L + Hf₅Si₄ ? HfSi, 52.5 at.% Si instead of 58.3 at.% Si.     

Thermodynamic Evaluation of the Phase Stability and Microstructural Characterization of a Cast B1914 Superalloy

The boron-carbon superalloys (BC alloys) were developed to reduce the carbon content of the alloys to less than 0.02 wt.% and increase the boron content to 0.1 wt.% in some Ni-based superalloys. In this study, we have used characterization techniques, such as DTA, XRD, SEM coupling, and thermodynamic calculation using Thermo-Calc software, to obtain information about the phase transformation reaction temperatures and the elemental compositions of the microstructural constituents encountered in the B1914 superalloy. The microstructure of the B1914 superalloy was composed of a gamma (γ) phase with a dendritic structure and gamma prime (γ′) phase with a cuboidal shape. Precipitates of γ′ and a lamellar eutectic, composed of γ/(Mo,Cr,Ni)₃B₂, were identified in the interdendritic region. The thermodynamic calculation results have shown to be a valuable tool for predicting the transformation temperature, such as liquidus, γ’ solvus, and incipient melting point. These transformations are important parameters used in casting simulation software for determining the heat treatment and welding repair conditions for parts made from this alloy.     

Salivary Amylase Induction by Tannin-Enriched Diets as a Possible Countermeasure Against Tannins

Tannins are characterized by protein-binding affinity. They have astringent/bitter properties that act as deterrents, affecting diet selection. Two groups of salivary proteins, proline-rich proteins and histatins, are effective precipitators of tannin, decreasing levels of available tannins. The possibility of other salivary proteins having a co-adjuvant role on host defense mechanisms against tannins is unknown. In this work, we characterized and compared the protein profile of mice whole saliva from animals fed on three experimental diets: tannin-free diet, diet with the incorporation of 5% hydrolyzable tannins (tannic acid), or diet with 5% condensed tannins (quebracho). Protein analysis was performed by one-dimensional gel electrophoresis combined with Matrix-Assisted Laser Desorption Ionization-Time of Flight mass spectrometry to allow the dynamic study of interactions between diet and saliva. Since abundant salivary proteins obscure the purification and identification of medium and low expressed salivary proteins, we used centrifugation to obtain saliva samples free from proteins that precipitate after tannin binding. Data from Peptide Mass Fingerprinting allowed us to identify ten different proteins, some of them showing more than one isoform. Tannin-enriched diets were observed to change the salivary protein profile. One isoform of α-amylase was overexpressed with both types of tannins. Aldehyde reductase was only identified in saliva of the quebracho group. Additionally, a hypertrophy of parotid salivary gland acini was observed by histology, along with a decrease in body mass in the first 4 days of the experimental period. G. da Costa and E. Lamy have contributed equally to this work.     

Structural analysis and optimisation of press brakes

A model of the bending process in Press Brakes is established using Timoshenko beam theory. Expressions for the workpiece bending error are derived that explicitly consider the influence of shape, dimensions and initial deformation of the machine structural components on its bending accuracy. The minimization of the bending error is formulated in terms of optimisation problems that are solved numerically using a genetic algorithm. The methodology presented in this paper permits the analysis of existing Press Brake design solutions, the optimisation of their performance and the development of new solutions.     

Analysis of microstructure and wear strength of hard facing used by the sugar and alcohol industry

The sugar and alcohol sector has seen huge growth in recent years in Brazil; however, maintenance in this industry comes at a high cost due to loss of metal from the equipment via wear mechanisms. The objective of this work is to evaluate the abrasive wear resistance and the microstructure of hard claddings deposited in a single layer. Four types of consumables are used in the sugar and alcohol industry: a clad electrode of FeCrC alloy, 4.0 mm of diameter and three self-shielded tubular wires, all 1.6 mm in diameter, of FeCrC, FeCrCNb and FeCrCTiMo alloys. The base metal used was SAE1020 steel. The welds with the tubular wires were produced in short circuit transfer mode, with the same welding current and voltage values. For the wear test a rubber wheel was used, in accordance with ASTM standard G65-91. The wear test pieces were removed from the central region of the test plates, and from the same region two groups of samples were removed for microstructural analysis (under an optical microscope). The results of the tests with the rubber wheel showed that the FeCrCNb alloy had the highest wear resistance, followed by the clad electrode, and the FeCrCMoTi alloy and FeCrC alloy had the worst performance. The FeCrC alloy (for both the clad electrode and for the tubular wire) showed a microstructure formed by M7C3 primary carbonates distributed in a matrix of lower hardness; the alloy containing Nb showed a similar microstructure as well as the presence of NbC carbonates; in turn, the alloy with Ti and Mo added revealed the presence of large primary titanium carbonates.     

Identification of temperature and moisture content fields using a combined neural network and clustering method approach

Studies on the dynamics of temperature and moisture content distributions in porous soils have provided important insight on their effect on the building hygrothermal behavior, where the interaction between both building and soil can contribute to reduce building thermal gains or looses. Hygrothermal aspects can be related to many attributes such as energy consumption, occupants' thermal comfort and health, and material deterioration. Recently, a great variety of mathematical models to predict thermal and moisture content profiles in porous media have been presented in the literature. Most of those models are based on analysis of multilayer measurements or on Fourier analysis. The development and validation of such mathematical models facilitate the understanding of heat and moisture flows at different soil depths. In this research, a radial basis function neural network (RBF-NN) approach, combined with Gath–Geva clustering method in order to predict the temperature and moisture content profiles in soils, has been presented. A set of data obtained from the computation of the coupled heat and moisture transfer in porous soils for the Curitiba city (Paraná State, Brazil) weather data file has been used by the RBF-NN modeling method. Simulation results indicate the potentialities of the RBF-NNs to learn, for the one step ahead identification, the behavior of temperature and moisture content profiles in the media at various depths.     

Eating behavior in response to food-cue exposure: Examining the cue-reactivity and counteractive-control models.

Many studies have demonstrated that those high in weight-related concerns eat more after food-cue exposure, which is consistent with predictions of the cue-reactivity model. However, the counteractive-control model predicts that exposure to fattening foods activates dieting-related goals and behavior in weight-concerned individuals. Although these models seem incongruous, the authors hypothesized that the salience of the cue could represent a critical factor in determining which model is activated. The authors predicted that attending to salient food cues would result in increased intake (cue reactivity) in individuals with high weight-related concerns, whereas incidental food-cue exposure would result in decreased intake (counteractive control), relative to control exposure. The authors employed a 3 (attended vs. incidental vs. control cue) × 2 (low vs. high weight-related concerns) design. As expected, participants with high weight-related concerns who attended to a food cue ate more than did both those with high weight-related concerns in the control condition and those with low weight-related concerns in the attended-cue condition; however, intake of individuals with high weight-related concerns who were exposed to the incidental cue did not differ from that of those in the control condition. The manner of food-cue presentation may be a critical factor in determining eating behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)