Weldability Evaluation and Microstructure Analysis of Resistance‐Spot‐Welded High‐Mn Steel in Automotive Application

In this paper, resistance spot weldability of high‐Mn steels were investigated in order to get high reliability in welded joints of automotive components. Microstructural characterizations, cross‐tensile test (CTT), microhardness tests of spot welded parts were conducted. The effects of weld current on the microstructural characteristics, mechanical properties, and fracture modes were investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The hardness in the weld nugget was observed to be lower than that in the base metal (BM). In CTT, the failure initiation was observed to occur at the boundary of the weld nugget. Also welding imperfections of welded parts were investigated. Liquation cracking in heat affected zone (HAZ), porosity, and shrinkage cavity were found most common welding defects in welded parts. Furthermore, the effects of welding imperfections on weld quality and failure criteria were identified and discussed.     

Correlating mechanical properties of sinter phases with their chemistry and its effect on sinter quality

In this study, pot sinter tests were carried out to study the sintering properties of iron ores of different alumina (2–4–6%) level. It was observed that the 6% alumina level ores have a higher RDI values and decreased tumbler index (TI) compared to its other two counterparts. It was observed that an increase in composite fracture toughness (CFT) of sinter improves the Tumbler as well as RDI of the sinter. Beyond 4 CFT there is remarkable improvement in TI, RDI and RI values. The mechanical strength parameters of sinter phases were further correlated and analysed with respect to the chemistry of sinter and mineralogy of sinter phases. There is strong evidence which suggests that the Al₂O₃ deteriorates the strength of the phases by making them hard and thus generating cracks in them. Unlike alumina, CaO and SiO₂ tend to stabilise and improve the strength of the phase.     

Evaluating mangroves of Krishna Wildlife Sanctuary in relation to the general status of mangroves in Andhra Pradesh,India

The present study was carried out to check whether there is a decline in mangrove cover of Andhra Pradesh state, India, as cited by a few studies. The research analysed mangrove dynamics of Krishna Wildlife Sanctuary of Andhra Pradesh state, using temporal satellite data of six periods. Analysis of these data showed major changes in the mangrove areas of the sanctuary. In 1972, the mangrove cover was 82.76 km², which then decreased to 80.47 km² in 1981, and then further dropped to 69.52 km² in 1990. Comparatively an area of 13.22 km² was lost from 1972 to 1990. The area recorded in 2000 was 101.98 km² and the positive trend of increase in mangrove areas was observed in both 2009 (138.36 km²) and in 2014 (158.16 km²). Overall, an increase of 88.64 km² mangrove area was observed from 1990 to 2014. The study confirms the increase in mangrove cover in the state, disagreeing with the observations of decrease in mangrove cover made by other studies previously.     

Fracture Mechanics Based Model for Fatigue Remaining Life Prediction of RC beams Considering Corrosion Effects

This paper presents methodologies for crack growth study and fatigue remaining life prediction of reinforced concrete structural components accounting for the corrosion effects. Stress intensity factor (SIF) has been computed by using the principle of superposition. At each incremental crack length, net SIF has been computed as the difference of SIF of plain concrete and reinforcement. The behaviour of reinforcement has been considered as elasto-plastic. Uniform corrosion rate has been assumed in the modeling. Corrosion effect has been accounted in the form of reduction in the diameter and modulus of elasticity of steel. Numerical studies have been carried out to validate the methodologies. It is observed that the predicted remaining life for RC beam without corrosion effects is significantly larger compared to plain beams. The predicted remaining life decreases with increase in percentage of corrosion.     

Anaerobic Biodegradation of Polyhydroxybutyrate in Municipal Sewage Sludge

Anaerobic biodegradation in sewage sludge of polyhydroxybutyrate (PHB) was investigated. Evolved gaseous carbon was measured to assess biodegradability according to ASTM D5210. Mass-loss experiments were performed to determine degradation kinetics. Changes in the polymer properties were investigated. The impact of a natural plasticizer [tributyl citrate (TBC)] on biodegradation was determined. Polylactic acid was also biodegraded for comparison. Melt-pressed plates of PHB (with thicknesses of 0.24, 0.5, 1.2, 3.5, and 5.0 mm) were biodegraded to investigate the relationship between initial mass:initial surface area ratios and decay rates. Scanning electron microscopy micrographs of degraded specimens were recorded for visual illustration of the degradation process. A relationship between initial mass:initial surface area and degradation rates indicates that the thickness and surface area of the material affect its degradation. The degradation rates were impacted by the sewage sludge activity. TBC additive hindered PHB’s rate of degradation. Thermal properties, molecular bonding, and molecular weight measured by differential scanning calorimetry, Fourier transform infrared, and size exclusion chromatography, respectively, were only slightly affected by biodegradation, indicating that recycling PHB will not affect its performance.     

Thermal stability of high-k Er-silicate gate dielectric formed by interfacial reaction between Er and SiO2 films

We fabricated a high-k Er-silicate gate dielectric using interfacial reaction between Er and SiO₂ films and investigated its thermal stability. The reduced capacitance with increasing annealing temperature is associated with the chemical bonding change of Er-silicate from Er-rich to Si-rich, induced by a reaction between Er-silicate and Si during thermal treatment. Further an increase in the annealing temperature (>500 °C) causes the formation of Si dangling bonds, which is responsible for an increased interface trap density.     

Cell Docking in Double Grooves in a Microfluidic Channel

Microstructures that generate shear‐protected regions in microchannels can rapidly immobilize cells for cell‐based biosensing and drug screening. Here, a two‐step fabrication method is used to generate double microgrooves with various depth ratios to achieve controlled double‐level cell patterning while still providing shear protection. Six microgroove geometries are fabricated with different groove widths and depth ratios. Two modes of cell docking are observed: cells docked upstream in sufficiently deep and narrow grooves, and downstream in shallow, wide grooves. Computational flow simulations link the groove geometry and bottom shear stress to the experimental cell docking patterns. Analysis of the experimental cell retention in the double grooves demonstrates its linear dependence on inlet flow speed, with slope inversely proportional to the sheltering provided by the groove geometry. Thus, double‐grooved microstructures in microfluidic channels provide shear‐protected regions for cell docking and immobilization and appear promising for cell‐based biosensing and drug discovery.