Low cycle fatigue behaviour of dual-phase steel with different volume fractions of martensite

Completely reversed low cycle fatigue tests were carried out at a constant strain rate of 10^?2s^?1 on 3 mm thick sheet specimens of a dual-phase steel treated to give 1.5 to 28% martensite without changing the carbon content. Hysteresis loop shape, stress/strain response and plastic strain energy as a function of applied cycles are analysed for different microstructures. Strain/life and plastic strain energy per cycle ($\text{Δ}\text{W}\text{?}{}_{\mathrm{<mtext>p</mtext>}}$)/life (2N_f) plots are discussed in terms of microstructure. It is shown that during cycling the shape of the hysteresis loop continuously changes at lower volume fractions of martensite whereas it remains more or less constant for microstructures with a higher percentage of martensite. A Coffin-Manson type of plot between log ($\text{Δ}\text{W}\text{?}{}_{\mathrm{<mtext>p</mtext>}}$) and log (2N_f) is found to be applicable to test results of dual-phase steel with a wide range of martensite contents and is thus more versatile than the plot between log (Δ?_p/2) and log (2N_f) for predicting the fatigue life.     

Supercritical aerofoils: a survey

This paper gives a brief survey of the various developments that have taken place in transonic aerodynamics which have finally led to the realisation of supercritical aerofoils, which are not only shock-free under design conditions but also behave satisfactorily under off-design conditions. The paper explains how an initial high curvature around the sonic point, followed by a relatively flat surface of small curvature on the top side, which is typical of supercritical aerofoils, is needed to generate shock-free flow. Typical results presented for a conventional aerofoil and a supercritical aerofoil bring out the features which distinguish them. A brief account of the various methods available for analysis and design of supercritical aerofoils indicating their relative merits is also given. The first-order effects on the pressure distribution over such aerofoils due to viscous effects, particularly on shock location, are also briefly touched upon. Finally the benefits that accrue from the use of supercritical wings are dealt with.     

Contact damage initiation in silicon nitride in Hertzian indentation: role of microstructure

A bearing-grade silicon nitride with fine microstructure and a turbine-grade silicon nitride with coarse microstructure were studied with respect to the influence of their microstructures on (a) crack-growth-resistance behavior, (b) strength degradation due to Vickers indentation, and (c) crack initiation in quasi-static indentation with WC spheres. The turbine grade exhibited strong rising crack-growth resistance and less strength degradation due to Vickers indentation as compared to the bearing grade. Partial-ring or C cracks initiated in Hertzian indentation and the critical loads exhibited linear (Auerbach) variation with indenter radius above a critical value. For smaller radius, indentation plasticity preceded C-crack initiation. The bearing grade exhibited higher critical loads for C-crack initiation, but showed greater extension toward a ring crack than the turbine grade. These differences in crack initiation and growth were consistent with the differences in crack initiation and propagation toughness of the two grades. A ball-on-ball impact analysis was used to predict the critical velocities for initiating C cracks in the impact of silicon nitride surfaces with WC spheres.     

A feeder replenishment policy for a turret-head placement machine

In this paper, a feeder replenishment strategy for a turret-head placement machine is proposed. The proposed method decreases the production time in a high volume electronics-manufacturing environment by using multiple allocations of components to feeder slots. The related reduction in production time is achieved by reducing the total number of replenishments through feeder exhaust synchronization. In our approach, we first solve a 0–1 linear programming model to reduce the downtime due to the replenishments by utilizing the unused feeder slots for multiple assignments. Since any small variation in the reel sizes will disrupt the synchronization among feeder exhausts, we propose a procedure called ‘Fixed Replenishment Policy’ to reduce this effect. The approach has been tested with data obtained from a high-volume electronics manufacturer and the results are examined.     

EEG Based Biometric Framework for Automatic Identity Verification

The energy of brain potentials evoked during processing of visual stimuli is considered as a new biometric. In particular, we propose several advances in the feature extraction and classification stages. This is achieved by performing spatial data/sensor fusion, whereby the component relevance is investigated by selecting maximum informative (EEG) electrodes (channels) selected by Davies–Bouldin index. For convenience and ease of cognitive processing, in the experiments, simple black and white drawings of common objects are used as visual stimuli. In the classification stage, the Elman neural network is employed to classify the generated EEG energy features. Simulations are conducted by using the hold-out classification strategy on an ensemble of 1,600 raw EEG signals, and 35 maximum informative channels achieved the maximum recognition rate of 98.56 ± 1.87%. Overall, this study indicates the enormous potential of the EEG biometrics, especially due to its robustness against fraud.

Magnetic resonance imaging of water freezing in packed beds cooled from below

Full-field quantitative visualization of freezing interfaces requires the introduction of high resolution noninvasive methods. Magnetic resonance imaging (MRI) is a versatile tool for mapping the distribution of liquids (primarily water) in three-dimensional space, and is the only practical solution in systems that are strongly refracting or opaque to visible light. MRI is employed to visualize ice formation in water-saturated packed beds consisting of spherical beads packed in a cylindrical cavity and cooled from below. Imaging of the stagnant interstitial water is accomplished by exploiting the strong contrast in proton spin density signal between interstitial ice and liquid water. Our implementation of MRI allows fully three-dimensional reconstruction of the solidification front and adequate time resolution to quantify the freezing of pore water. The effect of pore space heterogeneity near the lateral walls of the cavity, as expressed by the ratio of bed to bead diameter, is examined with respect to the shape and propagation rate of the freezing interface. A modification of the test section also allows the study of freezing in pure water which is used for comparison. The present work demonstrates the kind of extra provisions in terms of design and choice of materials of the test section that are necessary in order to accommodate the special environment of the MRI scanner in heat transfer applications.     

Evaluation of thermal properties of food materials at high pressures using a dual-needle line-heat-source method

ABSTRACT:  Thermal properties of food systems at high pressure (HP) are important in the design and operation of HP processing equipment. Available techniques for thermal property evaluation under HP conditions are still very limited. In this study, a dual-needle line-heat-source (DNL) device was installed in an HP vessel to evaluate thermal conductivity ( k ), diffusivity (α), and volumetric heat capacity ( C _pV) of foods at high pressure. The DNL probe was calibrated using glycerin (0.1 MPa) and 2% (w/w) agar gel (0.1 to 350 MPa) at 5 and 25 °C. Calibration results showed a good correlation with the reference data of pure water: R ²= 0.966 for thermal conductivity and R ²= 0.837 for diffusivity, and a small standard deviation of relative error (3.18%) for the volumetric heat capacity. Fresh potato and cheddar cheese were used as test samples at 5 °C at selected pressure levels (0.1 to 350 MPa). The potato samples gave thermal properties very close to those of pure water, but much higher than those of the cheese. The k and α values of both potato and cheese increased with pressure and a 2nd-order polynomial well fitted their pressure dependency. The volumetric heat capacity data did not show a clear pressure-dependency trend. The experimental system worked well for the evaluation of thermal properties at pressures up to 350 MPa.     

Coupling exothermic and endothermic reactions in adiabatic reactors

The steady state and the dynamic behavior of coupling exothermic and endothermic reactions in directly coupled adiabatic packed bed reactors (DCAR) are analyzed using one-dimensional pseudo-homogeneous plug flow model. Two different configurations of DCAR (simultaneous DCAR—SIMDCAR and sequential DCAR—SEQDCAR) are investigated. In SIMDCAR, the catalyst bed favors both exothermic and endothermic reactions and both reactions occur simultaneously. SEQDCAR has alternating layers of catalyst beds for exothermic and endothermic reactions and hence the exothermic and endothermic reactions occur in a sequential fashion. The performance of both reactors, in terms of conversion achieved and manifested hot spot behavior, is compared with that of the co-current heat exchanger type reactor. Various possible operational regimes in SIMDCAR have been classified and the conditions for the existence of hot spots or cold spots in SIMDCAR are obtained analytically for the first order reactions with equal activation energies. The reactor behavior for the reactions with non-equal activation energies is also presented. The preliminary criteria for the selection of suitable reactor type and the general bounds on the reaction parameters to obtain the desired conversion for endothermic reaction with minimal temperature rise are proposed. The dynamic behavior of these reactors is important for control applications and we have reported some of the transient behavior.     

Ohmic Heating Behaviour of Cabbage and Daikon Radish

Shredded cabbage (50 % v/v) and Daikon radish cubes (57 % v/v) with different salt concentrations (0.15, 0.5, 1, 1.5, and 1.85 %) were heated from 30 to 70 °C in a static ohmic heating cell at different voltages (65, 80, 100, 120, and 135 V) and frequencies (60, 2070, 5030, 7990, and 10,000 Hz) to evaluate their ohmic heating behaviour. Radish heated under 1.5 % salt, 120 V and 7990 Hz or 1 % salt, 135 V and 5030 Hz conditions gave the shortest heating time of 6 min from 30 to 70 °C, and cabbage gave the longest time of 128 min at 0.15 % salt, 100 V, and 5030 Hz. Regression models of heating rate as a quadratic function of the sample temperature gave R² >0.98. The general trend observed was that the magnitude of the heating rate increased with frequency at high voltage but decreased at low voltage for cabbage, while the opposite trend was observed for radish. Heating was more efficient at higher salt concentration and applied voltage. Radish heated more rapidly than cabbage. A slight slope change was observed in all cases between 50 and 60 °C. The response surface models revealed linear, cross products and quadratic effects to be significant with R ² over 0.98.     

Ascorbic acid degradation in a model apple juice system and in apple juice during ultraviolet processing and storage

Ultraviolet radiation induced degradation of ascorbic acid in a model apple juice system and in apple juice was studied using a collimated beam batch UV reactor. In the model system, ascorbic acid degradation was more rapid at higher dose levels and the reaction accelerated with increasing exposure time. Ascorbic acid degradation significantly (P < 0.05) increased as the pH was raised from 2.4 to 5.5, although no difference was observed between 2.4 and 3.3. Increasing malic acid concentration between 0.1 and 1%, increased ascorbic acid degradation (P < 0.05) although there was no difference between 0.5 and 1.0%. Solution absorbance, varied by addition of tannic acid, decreased ascorbic acid degradation with increasing concentration due to absorption of UV radiation. Fructose at levels found in apple juice significantly increased ascorbic acid degradation while glucose and sucrose did not. Factors identified that accelerate ascorbic acid degradation may at least partially explain why ascorbic acid degradation occurred more rapidly in UV-treated apple juice than in the 0.5% malic acid model system. Ascorbic acid degradation continued after UV treatments during dark storage. Storage decreases were faster at higher initial UV dose levels and higher storage temperature. PRACTICAL APPLICATION: The present study shows the effect of UV processing on ascorbic acid, a key vitamin found in many fruit juices. Process developers and researchers can use this study as a model for designing experiments to identify factors that influence the stability of vitamin C and other bioactive compounds during UV processing.