Dielectric Contrast Imaging using Apertureless Scanning Near-field Optical Microscopy in the Reflection Mode

Debdulal Roy,M. E. Welland,S. H. Leong 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.1

A reflection-mode, apertureless (scattering type) scanning near-field optical icroscope (SSNOM) in reflection geometry with a tip focus monitoring facility has been developed and used for imaging dielectric contrast at the nanoscale in both direct-detection and heterodyne interferometric mode. The approach curves (plot of near-field signal with tip-sample separation) were obtained and these were used to predict extent of near-field signal collection. The quality of the images obtained by adopting the heterodyne interferometric technique has been compared with those obtained by direct detection. For the former, independent phase imaging was also possible and performed.

Implications of bi-directional interaction on seismic fragilities of structures

Pramanik, Debdulal,Banerjee, Abhik Kumar,Roy, Rana Techno-Press 2016 Coupled systems mechanics Vol.5 No.2

Seismic structural fragility constitutes an important step for performance based seismic design. Lateral load-resisting structural members are often analyzed under one component base excitation, while the effect of bi-directional shaking is accounted per simplified rules. Fragility curves are constructed herein under real bi-directional excitation by a simple extension of the conventional Incremental Dynamic Analysis (IDA) under uni-directional shaking. Simple SODF systems, parametrically adjusted to different periods, are examined under a set of near-fault and far-fault excitations. Consideration of bi-directional interaction appears important for stiff systems. Further, the study indicates that the peak ground accelertaion, velocity and displacement (PGA, PGV and PGD) of accelerogram are relatively stable and efficient intensity measures for short, medium and long period systems respectively. '30%' combination rule seems to reasonably predict the fragility under bi-directional shaking at least for first mode dominated systems dealt herein up to a limit state of damage control.

Notes : Optimization of Tannase Production by Aureobasidium pullulans DBS66

( Banerjee ),( Debdulal ),( Bikas R. Pati ) 한국미생물 · 생명공학회 2007 Journal of microbiology and biotechnology Vol.17 No.6

Multi Tribo-Performance Optimization of AA7075–Al2O3 Composites by Grey Based Response Surface Methodology

Santanu Sardar,Debdulal Das 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6

Any engineering surface, even a highly polished one, is prone to abrasion which incurs most of the wear related expenses. Two-body abrasion causes severe material and dimensional losses and is affected by a variety of extrinsic and intrinsic variables. Furthermore, tribo-responses like wear resistance (WR), coefficient of friction (COF) and abraded surface roughness(ASR) are three distinct characteristics in nature, and therefore, multi-objective optimization is necessary for design andselection of engineering systems. In the present article, tribo-performances of stir-cast alumina reinforced Al–Zn–Mg–Cumatrix composites in terms of WR, COF and ASR were evaluated under two-body abrasion with varying abrasive size, loadand sliding distance. Irrespective of abrasion conditions, the developed composites exhibited superior WR ability with substantiallylower COF but much greater ASR than alloy. All three tribo-responses were first converted into a single responseof grey relational grade (GRG); afterwards, response surface based central composite design was adopted to improve triboperformancesof the composites through optimal factor setting by which WR would become the greatest, and COF and ASRwould be the lowest. Abrasive size followed by reinforcement quantity was evaluated as the preeminent one among all thefactors on GRG. The role of different control factors on observed tribo-characteristics was explained via identification ofvarious micro-mechanisms of abrasion.

Influence of Artificial Aging on Mechanical Properties and High Stress Abrasive Wear Behaviour of Al–Mg–Si Alloy

Aluru Praveen Sekhar,Debdulal Das 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.2

The present study evaluated hardness, tensile properties and two-body abrasive wear behaviour of Al–Mg–Si alloy specimensartificially aged at 448 K for different durations ranging from 0.5 to 504 h. In addition to the measurements of Vickers hardnessand tensile properties, wear tests of differently aged alloys were conducted against SiC abrasive paper of 220 grit sizeunder normal load of 9.81 N with the help of a pin-on-disc tribometer. Abrasive wear characteristics were assessed in termsof measurements of specific wear rate and roughness of the abraded surfaces. These were substantiated via examinations ofworn surfaces, collected wear debris and subsurfaces of worn specimens to comprehend the micro-mechanisms of abrasion. The abrasive wear performance varied significantly with the duration of artificial aging and the lowest specific wear rate aswell as roughness of the abraded surfaces corresponded to the peak-aged condition. An attempt was also made to correlatemechanical properties and tribological performance. It was found that the specific wear rate exhibited direct linear relationwith the strain hardening exponent, and inverse linear relationships with hardness, yield strength and strength coefficient. Microplowing, microcutting and microcracking were identified as mechanisms of abrasion; the extents of these processeswere found to be governed by the state of aging that determined the mechanical properties.

Development of Commercial Trace Moisture Sensor: A Detailed Comparative Study on Microstructural and Impedance Measurements of Two Phases of Alumina

Manju Pandey,Prabhash Mishra,Debdulal Saha,K. Sengupta,S. S. Islam 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.2

Porous alumina thin film has been investigated in order to find its sensitivity in the trace moisture level. Alumina, with two different phases were obtained using sol-gel process and fired between 400°C to 1000°C. FESEM, BET, AFM and XRD techniques were employed for microstructural characterization of the sintered thin film in two phases. A detailed analysis is done to assess the superiority of gamma (γ) - over alpha (α) phase using impedance spectroscopy. It was observed that gamma phase is more sensitive towards trace level moisture sensing.

Low Cycle Fatigue Performance and Failure Analysis of Reinforcing Bar

Md Abu Bakkar,Rajib Saha,Debdulal Das 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12

Low cycle fatigue (LCF) behaviour and associated failure mechanisms of a thermo-mechanically treated Fe 500D steel rebarhave been experimentally evaluated with a view to assess its performance under seismic condition. The total axial straincontrolledLCF tests have been performed at five different strain amplitudes (± 0.30 to ± 1.00%) at ambient temperature untilfailure maintaining a constant true strain rate of 1 × 10− 3 s− 1 and a fixed strain ratio of − 1. Fatigue data have been analysedfollowing both strain–life and plastic strain energy–life relationships; while, macro as well as micro features of the failedspecimens, have been critically examined. These are supplemented by microstructural characterizations in addition to tensileand hardness measurements. Significant reduction of yield strength is recorded under dynamic loading which is responsiblefor considerable cyclic softening of rebar till failure in all strain amplitudes indicating the deterioration of seismic resistanceproperty. Both strain–life and plastic strain energy–life relationships are found to accurately predict the cyclic plasticbehaviour of the selected rebar. A near Masing behaviour is established by three different analytical approaches. The fatiguecrack is always found to initiate at the transverse rib root and primarily propagates alongside the rim region.

Plastic Behavior of Ferrite–Pearlite, Ferrite–Bainite and Ferrite–Martensite Steels: Experiments and Micromechanical Modelling

Saroj Kumar Basantia,Ankita Bhattacharya,Niloy Khutia,Debdulal Das 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5

In this work, low carbon low alloy steel specimens were subjected to suitable heat treatment schedules to develop ferrite–pearlite (FP), ferrite–bainite (FB) and ferrite–martensite (FM) microstructures with nearly equal volume fraction of hardsecond phase or phase mixture. The role of pearlite, bainite and martensite on mechanical properties and flow behaviour wereinvestigated through experiments and finite element simulations considering representative volume elements (RVE) basedon real microstructures. For micromechanical simulation, dislocation based model was implemented to formulate the flowbehaviour of individual phases. The optimum RVE size was identified for accurate estimation of stress–strain characteristicsof all three duplex microstructures. Both experimental and simulation results established that FM structure exhibited superiorstrength and FP structure demonstrated better elongation while FB structure yielded moderate strength and ductility.The von Mises stress and plastic strain distribution of the individual phase was predicted at different stages of deformationand subsequent statistical analyses indicated that hard phases experienced maximum stress whereas, maximum strainingoccurred in soft ferrite phase for all three structures. Micromechanical simulation further revealed that strain accumulationoccurred at the F–P and F–B interfaces while the same was observed within the martensite particles apart from the F–Minterfaces for FM. These observations were further substantiated through the identification of void and crack initiation sitesvia subsurface examinations of failed tensile specimens.

Influence of Ageing on the Intergranular Corrosion of an Al–Mg–Si Alloy

Aluru Praveen Sekhar,Arijit Samaddar,Ashim Bikash Mandal,Debdulal Das 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12

This report investigates the influence of ageing on the susceptibility to intergranular corrosion (IGC) of an Al–Mg–Si alloy. The selected AA6063 Al-alloy has been exposed to ageing treatments at a predetermine temperature of 423 K for durationsof 1 to 168 h to achieve the wide range of ageing states covering under- to peak- to over-aged. The ageing behaviour of theselected alloy has been determined based on the results of hardness and tensile properties. The susceptibility to IGC has beenevaluated following the British standard (BS ISO-11846) method B and assessed based on the average and maximum corrosiondepths apart from in-depth surface and sub-surface characterizations of corroded specimens. It has been observed thatthe depths of corrosion increase monotonically with increase in ageing time. With progress of artificial ageing, the dominantmode of corrosion gradually changes in the order of minor pitting, moderate pitting, pitting plus localized IGC, localizedIGC and uniform IGC. The phenomenon of preferential dissolution of Mg from the β″ (Mg5Si6) and β (Mg2Si) precipitatesas well as the existence of Fe-rich intermetallic particles at the grain boundaries cause the pitting and intergranular corrosionbecause of the formation of local galvanic cells between the lower corrosion potential of Mg-depleted precipitates orprecipitate free zones and to the adjacent anodic grain boundary precipitates.