Theoretical and numerical study of lamellar eutectoid growth influenced by volume diffusion

We investigate the lamellar growth of pearlite at the expense of austenite during the eutectoid transformation in steel. To begin with, we extend the Jackson–Hunt-type calculation (previously used to analyze eutectic transformation) to eutectoid transformation by accounting for diffusion in all the phases. Our principal finding is that the growth rates in the presence of diffusion in all the phases are different compared to the case when diffusion in growing phases is absent. The difference in the dynamics is described by a factor ’ρ’ which comprises the ratio of the diffusivities of the bulk and the growing phases, along with the ratios of the slopes of the phase coexistence lines. Thereafter, we perform phase-field simulations, the results of which are in agreement with analytical predictions. The phase-field simulations also reveal that diffusion in austenite as well as ferrite leads to the formation of tapered cementite along with an overall increase in the transformation kinetics as compared to diffusion in austenite (only). Finally, it is worth noting that the aim of present work is not to consider the pearlitic transformation in totality; rather it is to isolate and thereby investigate the influence of diffusivity in the growing phases on the front velocity.     

A new approach to investigate tool condition using dummy tool holder and sensor setup

The industrial demand for automated machining systems to enhance process productivity and quality in machining aerospace components requires investigation of tool condition monitoring. The formation of chip and its removal have a remarkable effect on the state of the cutting tool during turning. This work presents a new technique using acoustic emission (AE) to monitor the tool condition by separating the chip formation frequencies from the rest of the signal which comes mostly from tool wear and plastic deformation of the work material. A dummy tool holder and sensor setup have been designed and integrated with the conventional tool holder system to capture the time-domain chip formation signals independently during turning. Several dry turning tests have been conducted at the speed ranging from 120 to 180?m/min, feed rate from 0.20 to 0.50?mm/rev, and depth of cut from 1 to 1.5?mm. The tool insert used was TiN-coated carbide while the work material was high-carbon steel. The signals from the dummy setup clearly differ from the AE signals of the conventional setup. It has been observed that time-domain signal and corresponding frequency response can predict the tool conditions. The rate of tool wear was found to decrease with chip breakage even at higher feed rate. The tool wear and plastic deformation were viewed to decrease with the increased radius of chip curvature and thinner chip thickness even at the highest cutting speed, and these have been verified by measuring tool wear. The chip formation frequency has been found to be within 97.7 to 640?kHz.     

Diffusivity of small molecules in polymers: Carboxylic acids in polystyrene

Gravimetry was used to study the diffusion of a homologous series of linear carboxylic acids (C_n, with n = 2, 6–16) in amorphous polystyrene at temperatures from 35 °C to 165 °C, that is, both below and above the polymer glass transition temperature of 100 °C. All the mass uptake results are well described by a simple Fickian model (for t < t_1/2) and were used to calculate the corresponding diffusion coefficients using the thin-film approximation. Acetic acid exhibits a peculiar diffusion rate: its diffusion coefficients in polystyrene do not follow the same trend of all the remaining acids, being smaller than those of hexanoic acid at the same temperatures. Polystyrene swells at a higher rate in hexanoic and octanoic acids than in acetic acid, at the same temperature. This peculiarity is confirmed using NMR spectroscopy for acetic and hexanoic acids. For all the carboxylic acids considered, the temperature dependence of the diffusion coefficients is non-Arrhenius in character. For each liquid penetrant, its log(D) increases linearly with the decrease in liquid viscosity associated with an increase in temperature. Plots of log(n²D) versus n suggest that higher-n carboxylic acids diffuse through a reptation-like mechanism at higher temperatures.     

Characterizing nutrient dynamics with relation to changes in partial pressure of CO2 in a tropical sewage‐fed aquaculture pond situated in a Ramsar wetland

The changes in nutrient dynamics (nitrate, ammonium, silicate, phosphate and iron concentration) vis‐à‐vis partial pressure of CO₂ in water [pCO₂(water)] from tropical sewage‐fed aquaculture ponds (East Kolkota Wetlands, India) were analysed by means of a microcosm. A significant relationship between these nutrient’s removal from the system and reduction in pCO₂(water) was observed (with few exceptions). These water bodies acted as significant sources of CO₂ in pre‐monsoon and monsoon seasons despite having substantial quantity of chlorophyll‐a to make it a net autotrophic system. The study revealed that if conditions favourable for optimum photosynthesis can be maintained in these ponds, the CO₂ source character of these ponds can be reversed. In the post‐monsoon season, when the pH of the water column was high, the system acted as sink for CO₂ which suggests the use of lime to prevent these systems from becoming hypereutrophic and carbon source at the same time.     

Application of acoustic emission technique for the detection of defects in rolling element bearings

The usefulness of acoustic emission (AE) measurements for the detection of defects in roller bearings has been investigated in the present study. Defects were simulated in the roller and inner race of the bearings by the spark erosion method. AE of bearings without defect and with defects of different sizes has been measured. For small defect sizes, ringdown counts of AE signal has been found to be a very good parameter for the detection of defects both in the inner race and roller of the bearings tested. However, the counts stopped increasing after a certain defect size. Distributions of events by ringdown counts and peak amplitudes are also found to be good indicators of bearing defect detection. With a defect on a bearing element, the distributions of events tend to be over a wider range of peak amplitudes and counts.     

Investigation into crater wear in drilling

This paper presents the effects of spindle rotational speed and feed rate on the crater wear along the lip of a drill. A theoretical model has been developed to correlate the cutting parameters with crater wear through the cutting forces. A series of experiments was conducted to study the performance of the drilling process in terms of drill wear and the effects of cutting parameters on it. The experiments were planned using the concept of a central composite rotatable design for three factors. An empirical relationship between crater wear and the cutting parameters at any point on the lip has been developed. The correlation coefficient between the experimentally measured and empirically calculated values of crater wear was found to be 0.9821. Crater wear has been recommended for acceptance as a performance index owing to the relative ease with which it can be measured and the fact that, at higher speeds, crater wear is more significant than flank wear. Close relationships between the experimental and theoretical results were found.     

Kinetics and performance evaluation of microbial fuel cell supplied with dairy wastewater with simultaneous power generation

Due to the growing demand for energy in the present-day world, it is obligatory to look for alternative sources of renewable energy. The derivation of power from microbial fuel cells (MFCs) has developed at the vanguard of the alternative source of renewable energy through the concomitant treatment of wastewater. Hence, the process development of MFC is obligatory for creating a sustainable source of renewable energy through the treatment of wastewater. To that end, an attempt was taken in the present study for sustainable power generation from single chamber microbial fuel cell (SCMFC) using Pseudomonas aeruginosa-MTCC-7814. The experiments were carried out in a batch process for 15 days with real dairy wastewater (RDW) having initial chemical oxygen demand (COD) of 8000 mg/L. The open-circuit voltage (OCV) found after 72 h of batch operation was 658 mV, which was maximum within the batch operation. The columbic efficiency (CE) of the batch process was found to be 46.59%. The maximum specific growth rate (μ_max) of Pseudomonas aeruginosa-MTCC-7814 was found to be 0.432 day^?1 during batch operation. However, saturation constant (Ks) and inhibition coefficient (K_i) were calculated as 608.74 mg/L, and 6582 mg/L, respectively. The maximum current density (I_max) and saturation constant (K_c) predicted from batch kinetics study were 132 mA/m² and 321 mg/L, respectively, which has resemblance with the data obtained from experiments. The maximum current density and power density from experiments were found to be 161 mA/m² and 34.82 mW/m², respectively. Results showed that a higher power density and current density values were obtained from the present study as compared to the earlier reports that utilized wastewater as the substrate for the MFC. Thus, the study suggests that Pseudomonas aeruginosa, (MTCC-7814) can be used as a promising biocatalyst in MFC for sustainable power generation through the utilization of wastewater treatment.     

Steady-state optimal controller with actuator noise variancelinearly related to actuator signal variance

The linear-quadratic-Gaussian (LQG) method assumes that the covariance matrix of the actuator noise is given before the design of the feedback matrix. However, in practice, the actuator-noise covariance matrix may depend on the actuator signal energy, which depends on the feedback. Consequently, the feedback from LQG theory degrades the system performance. The authors investigate the steady-state optimal controller when the noise variance of an actuator is linearly related to the variance of an actuator signal. This control system could be much more precise and/or spend much less control energy than the one obtained through the use of the ordinary LQG method