Influence of cast versus wrought microstructure on the processing map for hot working of stainless steel type AISI 304

Processing maps for hot working of as-cast and wrought stainless steels of type AISI 304 have been developed in the temperature range 600 to 1250°C and strain rate range 0.001 to 100 s−1. The domain of dynamic recrystallization (DRX) in as-cast material occurs at higher temperatures (1250°C) and lower strain rates (0.001 s−1) than in the wrought steel (1100°C and 0.01 s−1). The effect is explained in terms of enhanced nucleation rate of DRX due to the carbide, ferrite particles, stable oxides/nitrides and second-phase intermetallics in the as-cast microstructure. The DRX domain is wider in the wrought material although the peak efficiency is less (32%) than in the as-cast case (40%). The flow instability regime is not significantly affected by the initial microstructure

Influence of state of stress on the processing map for hot working of stainless steel type AISI 304L: compression vs. torsion

Processing maps for hot working of stainless steel of type AISI 304L have been developed on the basis of the flow stress data generated by compression and torsion in the temperature range 600–1200 °C and strain rate range 0.1–100 s−1. The efficiency of power dissipation given by 2m/(m+1) where m is the strain rate sensitivity is plotted as a function of temperature and strain rate to obtain a processing map, which is interpreted on the basis of the Dynamic Materials Model. The maps obtained by compression as well as torsion exhibited a domain of dynamic recrystallization with its peak efficiency occurring at 1200 °C and 0.1 s−1. These are the optimum hot-working parameters which may be obtained by either of the test techniques. The peak efficiency for the dynamic recrystallization is apparently higher (64%) than that obtained in constant-true-strain-rate compression (41%) and the difference in explained on the basis of strain rate variations occurring across the section of solid torsion bar. A region of flow instability has occurred at lower temperatures (below 1000 °C) and higher strain rates (above 1 s−1) and is wider in torsion than in compression. To achieve complete microstructure control in a component, the state of stress will have to be considered.

Processing map for hot working of as cast magnesium

The constitutive flow behaviour in hot working of as cast magnesium has been studied with the help of a processing map developed in the temperature range 300-550°C and strain rate range 0·001-100 s−1. The map, interpreted using the dynamic materials model, revealed that the material undergoes dynamic recrystallisation at 425°C and 0·3 s−1, which are the optimum parameters for hot working. Ai temperatures higher than 450°C and strain rates lower than about 0·1 s−1, wedge cracking occurs in as cast magnesium. The wedge cracking domain has a high efficiency of power dissipation (60%), whereas the dynamic recrystallisation domain has a value of 34%. At temperatures below 450°C and strain rates above 10 s−1, the material exhibits flow instability in the form of mechanical twinning. At higher temperatures and strain rates, instability is manifested by flow localisation.

Processing map for hot working of stainless steel type AISI 316L

Processing and instability maps using a dynamic materials model have been developed for stainless steel type AISI 316L in the temperature range 600-1250-degrees-C and strain rate range 0.001-100 s-1 with a view to optimising its hot workability. Stainless steel type AISI 316L undergoes dynamic recrystallisation, with a peak efficiency of 35% at 1250-degrees-C and 0.05 s-1, which are the optimum parameters for hot working this material. The material undergoes dynamic recovery at 900-degrees-C and 0.001 s-1. The increase in the dynamic recrystallisation and dynamic recovery temperatures in comparison with stainless steel type AISI 304L is attributed to the presence of a backstress caused by the molybdenum additions. These results are in general agreement with those reported elsewhere on stainless steel type 316 deformed in hot extrusion and hot torsion. At temperatures < 850-degrees-C and strain rates > 10 s-1, the material exhibits flow localisation owing to adiabatic shear band formation, whereas at higher temperatures (> 850-degrees-C) and strain rates (> 10 s-1) mechanical twinning and wavy slip bands are observed. (C) 1993 The Institute of Materials.

Dietary habits and obesity: the role of emotional and cognitive factors

In post-industrialised societies, food is more plentiful, accessible and palatable than ever before and technological development has reduced the need for physical activity. Consequently, the prevalence of obesity is increasing, which is problematic as obesity is related to a number of diseases. Various psychological and social factors have an important influence on dietary habits and the development of obesity in the current food-rich and sedentary environments. The present study concentrates on the associations of emotional and cognitive factors with dietary intake and obesity as well as on the role these factors play in socioeconomic disparities in diet. Many people cognitively restrict their food intake to prevent weight gain or to lose weight, but research on whether restrained eating is a useful weight control strategy has produced conflicting findings. With respect to emotional factors, the evidence is accumulating that depressive symptoms are related to less healthy dietary intake and obesity, but the mechanisms explaining these associations remain unclear. Furthermore, it is not fully understood why socioeconomically disadvantaged individuals tend to have unhealthier dietary habits and the motives underlying food choices (e.g., price and health) could be relevant in this respect. The specific aims of the study were to examine 1) whether obesity status and dieting history moderate the associations of restrained eating with overeating tendencies, self-control and obesity indicators; 2) whether the associations of depressive symptoms with unhealthier dietary intake and obesity are attributable to a tendency for emotional eating and a low level of physical activity self-efficacy; and 3) whether the absolute or relative importance of food choice motives (health, pleasure, convenience, price, familiarity and ethicality) contribute to the socioeconomic disparities in dietary habits. The study was based on a large population-based sample of Finnish adults: the participants were men (N=2325) and women (N=2699) aged 25-74 who took part in the DILGOM (Dietary, Lifestyle and Genetic Determinants of Obesity and Metabolic Syndrome) sub-study of the National FINRISK Study 2007. The participants weight, height, waist circumference and body fat percentage were measured in a health examination. Psychological eating styles (the Three-Factor Eating Questionnaire-R18), food choice motives (a shortened version of the Food Choice Questionnaire), depressive symptoms (the Center for Epidemiological Studies Depression Scale) and self-control (the Brief Self-Control Scale) were measured with pre-existing questionnaires. A validated food frequency questionnaire was used to assess the average consumption of sweet and non-sweet energy-dense foods and vegetables/fruit. Self-reported total years of education and gross household income were used as indicators of socioeconomic position. The results indicated that 1) restrained eating was related to a lower body mass index, waist circumference, emotional eating and uncontrolled eating, and to a higher self-control in obese participants and current/past dieters. In contrast, the associations were the opposite in normal weight individuals and those who had never dieted. Thus, restrained eating may be related to better weight control among obese individuals and those with dieting experiences, while among others it may function as an indicator of problems with eating and an attempt to solve them. 2) Emotional eating and depressive symptoms were both related to less healthy dietary intake, and the greater consumption of energy-dense sweet foods among participants with elevated depressive symptoms was attributable to the susceptibility for emotional eating. In addition, emotional eating and physical activity self-efficacy were both important in explaining the positive association between depressive symptoms and obesity. 3) The lower vegetable/fruit intake and higher energy-dense food intake among individuals with a low socioeconomic position were partly explained by the higher priority they placed on price and familiarity and the lower priority they gave to health motives in their daily food choices. In conclusion, although policy interventions to change the obesogenic nature of the current environment are definitely needed, knowledge of the factors that hinder or facilitate people s ability to cope with the food-rich environment is also necessary. This study implies that more emphasis should be placed on various psychological and social factors in weight control programmes and interventions.

Characteristics of superplasticity domain in the processing map for hot working of an Al alloy 2014---20vol.%Al2O3 metal matrix composite

The processing map for hot working of Al alloy 2014-20vol.%Al2O3 particulate-reinforced cast-plus-extruded composite material has been generated covering the temperature range 300-500 degrees C and the strain rate range 0.001-10 s(-1) based on the dynamic materials model. The efficiency eta of power dissipation given by 2m/(m + 1), where m is the strain rate sensitivity, is plotted as a function of temperature and strain rate to obtain a processing map. A domain of superplasticity has been identified, with a peak efficiency of 62% occurring at 500 degrees C and 0.001 s(-1). The characteristics of this domain have been studied with the help of microstructural evaluation and hot-ductility measurements. Microstructural instability is predicted at higher strain rates above (ls(-1)) and lower temperatures (less than 350 degrees C).

Bayesian Decentralized Spectrum Sensing in Cognitive Radio Networks

This paper considers the problem of spectrum sensing, i.e., the detection of whether or not a primary user is transmitting data by a cognitive radio. The Bayesian framework is adopted, with the performance measure being the probability of detection error. A decentralized setup, where N sensors use M observations each to arrive at individual decisions that are combined at a fusion center to form the overall decision is considered. The unknown fading channel between the primary sensor and the cognitive radios makes the individual decision rule computationally complex, hence, a generalized likelihood ratio test (GLRT)-based approach is adopted. Analysis of the probabilities of false alarm and miss detection of the proposed method reveals that the error exponent with respect to M is zero. Also, the fusion of N individual decisions offers a diversity advantage, similar to diversity reception in communication systems, and a tight bound on the error exponent is presented. Through an analysis in the low power regime, the number of observations needed as a function of received power, to achieve a given probability of error is determined. Monte-Carlo simulations confirm the accuracy of the analysis.

Formation and propagation of bands in jerky flow:a coupled lattice map description

There has been revival of interest in Jerky flow from the point of view of dynamical systems. The earliest attempt in this direction was from our group. One of the predictions of the theory is that Jerky flow could be chaotic. This has been recently verified by us. We have recently extended the earlier model to account for the spatial aspect as well. Both these models are in the form of coupled set of nonlinear differential equations and hence, they are complicated in their structure. For this reason we wish to devise a model based on the results of these two theories in the form of coupled lattice map for the description of the formation and propagation of dislocation bands. We report here one such model and its results.

Microstructural control in hot working of IN-718 superalloy using processing map

The hot-working characteristics of IN-718 are studied in the temperature range 900 °C to 1200 °C and strain rate range 0.001 to 100 s−1 using hot compression tests. Processing maps for hot working are developed on the basis of the strain-rate sensitivity variations with temperature and strain rate and interpreted using a dynamic materials model. The map exhibits two domains of dynamic recrystallization (DRX): one occurring at 950 °C and 0.001 s−1 with an efficiency of power dissipation of 37 pct and the other at 1200 °C and 0.1 s−1 with an efficiency of 40 pct. Dynamic recrystallization in the former domain is nucleated by the δ(Ni3Nb) precipitates and results in fine-grained microstructure. In the high-temperature DRX domain, carbides dissolve in the matrix and make interstitial carbon atoms available for increasing the rate of dislocation generation for DRX nucleation. It is recommended that IN-718 may be hot-forged initially at 1200 °C and 0.1 s−1 and finish-forged at 950 °C and 0.001 s−1 so that fine-grained structure may be achieved. The available forging practice validates these results from processing maps. At temperatures lower than 1000 °C and strain rates higher than 1 s−1 the material exhibits adiabatic shear bands. Also, at temperatures higher than 1150°C and strain rates more than 1s−1, IN-718 exhibits intercrystalline cracking. Both these regimes may be avoided in hotworking IN-718.

Hot deformation characteristics of INCONEL alloy MA 754 and development of a processing map

The characteristics of hot deformation of INCONEL alloy MA 754 have been studied processing maps obtained on the basis of flow stress data generated in compression in the temperature range 700-degrees-C to 1150-degrees-C and strain rate range 0.001 to 100 s-1. The map exhibited three domains. (1) A domain of dynamic recovery occurs in the temperature range 800-degrees-C to 1075-degrees-C and strain rate range 0.02 to 2 s-1, with a peak efficiency of 18 pct occurring at 950-degrees-C and 0.1 s-1. Transmission electron microscope (TEM) micrographs revealed stable subgrain structure in this domain with the subgrain size increasing exponentially with an increase in temperature. (2) A domain exhibiting grain boundary cracking occurs at temperatures lower than 800-degrees-C and strain rates lower than 0.01 s-1. (3) A domain exhibiting intense grain boundary cavitation occurs at temperatures higher than 1075-degrees-C. The material did not exhibit a dynamic recrystallization (DRX) domain, unlike other superalloys. At strain rates higher than about 1 s-1, the material exhibits flow instabilities manifesting as kinking of the elongated grains and adiabatic shear bands. The material may be safely worked in the domain of dynamic recovery but can only be statically recrystallized.

Microstructural control in hot working of IN-718 superalloy using processing map

The hot-working characteristics of IN-718 are studied in the temperature range 900 degrees C to 1200 degrees C and strain rate range 0.001 to 100 s(-1) using hot compression tests. Processing maps for hot working are developed on the basis of the strain-rate sensitivity variations with temperature and strain rate and interpreted using a dynamic materials model. The map exhibits two domains of dynamic recrystallization (DRX): one occurring at 950 degrees C and 0.001 s(-1) with an efficiency of power dissipation of 37 pct and the other at 1200 degrees C and 0.1 s(-1) with an efficiency of 40 pct. Dynamic recrystallization in the former domain is nucleated by the delta(Ni3Nb) precipitates and results in fine-grained microstructure. In the high-temperature DRX domain, carbides dissolve in the matrix and make interstitial carbon atoms available for increasing the rate of dislocation generation for DRX nucleation. It is recommended that IN-718 may be hot-forged initially at 1200 degrees C and 0.1 s(-1) and finish-forged at 950 degrees C and 0.001 s(-1) so that fine-grained structure may be achieved. The available forging practice validates these results from processing maps. At temperatures lower than 1000 degrees C and strain rates higher than 1 s(-1), the material exhibits adiabatic shear bands. Also, at temperatures higher than 1150 degrees C and strain rates more than 1 s(-1), IN-718 exhibits intercrystalline cracking. Both these regimes may be avoided in hot-working IN-718.

Processing map for hot working of Ni–16Cr–8Fe alloy (IN 600)

The hot deformation characteristics of IN 600 nickel alloy are studied using hot compression testing in the temperature range 850-1200-degrees-C and strain rate range 0.001-100 s-1. A processing map for hot working is developed on the basis of the data obtained, using the principles of dynamic materials modelling. The map exhibits a single domain with a peak efficiency of power dissipation of 48% occurring at 1200-degrees-C and 0.2 s-1, at which the material undergoes dynamic recrystallisation (DRX). These are the optimum conditions for hot working of IN 600. At strain rates higher than 1 s-1, the material exhibits flow localisation and its microstructure consists of localised bands of fine recrystallised grains. The presence of iron in the Ni-Cr alloy narrows the DRX domain owing to a higher temperature required for carbide dissolution, which is essential for the occurrence of DRX. The efficiency of DRX in Ni-Cr is, however, enhanced by iron addition.

Spectral Sensing of Adaptive Frequency Hopping Signal for Cognitive Radio

The issue of dynamic spectrum scene analysis in any cognitive radio network becomes extremely complex when low probability of intercept, spread spectrum systems are present in environment. The detection and estimation become more complex if frequency hopping spread spectrum is adaptive in nature. In this paper, we propose two phase approach for detection and estimation of frequency hoping signals. Polyphase filter bank has been proposed as the architecture of choice for detection phase to efficiently detect the presence of frequency hopping signal. Based on the modeling of frequency hopping signal it can be shown that parametric methods of line spectral analysis are well suited for estimation of frequency hopping signals if the issues of order estimation and time localization are resolved. An algorithm using line spectra parameter estimation and wavelet based transient detection has been proposed which resolves above issues in computationally efficient manner suitable for implementation in cognitive radio. The simulations show promising results proving that adaptive frequency hopping signals can be detected and demodulated in a non cooperative context, even at a very low signal to noise ratio in real time.