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D. K. Bhattacharya ¹, S. Dasgupta ²

Affiliations
1 Department of Geology, Ranchi University, Ranchi - 834 008, IN
2 Department of Mines and Geology, Ranchi - 834 002, IN

Abstract

Apatite mineralisation occurs in the host rock chlorite phyllite which grades into chlorite schist and is granitised. Discontinuous veins of apatite within apatite-magnetite rock exhibit many morphological types. The apatites also contain tantalum, niobium, titanium, molybdenum and vanadium. Studies reveal that apatite mineralisation is controlled by both structure and lithology.

Keywords

Apatite Mineralisation, Purulia Dist, West Bengal.

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Anal Kumar Sinha ¹, D. K. Bhattacharya ²

Affiliations
1 Mineral Exploration Corporation Ltd., Ashok Nagar, Ranchi - 834 002, IN
2 Dept. of Geology, Ranchi University, Ranchi - 834 008, IN

Abstract

No Abstract.

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D. K. Bhattacharya ¹, D. Mukherjee ², V. C. Barla ³

Affiliations
1 Post Graduate Department of Geology, Ranchi University, Ranchi - 834 008, IN
2 202, Manna Surti Complex, Lohianagar, Kankarbagh, Patna - 800 020, IN
3 P.G. Department of Geology, Vinoba Bhave University, Hazaribag - 821 305, IN

Abstract

Komatiite near Semra village, southwest of Daltonganj in Palamau District of Jharkhand, occurs within tremolite actinolite schist of ultramafic parentage. The fragmented olivine phenocrysts show mutually parallel as well as angular alignment, representing relict spinifex texture. Mineralogically the Semra ultramafic is lehrzolite in composition. The cumulates lack visible deformation suggesting original magmatic crystallization of these ultramafic rocks. The present occurrence of Spinifex Textured Peridotitic Komatiite (STPK) in Chhotanagpur Gneissic Complex (CGC) at northwestern part of Eastern Indian Shield is of great significance as it opens up a possibility of the presence of Archaean rock in CGC, which is yet to be established.

These ultramafics are geochemically characterised by distinctive high MgO, Ni, Cr and poor in alkali, TiO₂, Ba, Cs, Rb, Nb, Hf and Y contents. It has low abundance of incompatible elements and is LREE depleted [(La/Yb)_n=0.74 - 1.07] with enriched flat HREE profile, representing chondrite like composition. This shows diagnostic convex upward REE profile. All these together with relict but distinct spinifex texture confirm the komatiitic character of Semra ultramafic. The chemical data plots for ultramafics confine to komatiite field in discriminate diagrams. The Mg# (>74) of the Semra ultramafics are comparable to primitive upper mantle Mg# (89.8) and high enough for rocks derived from ultramagnesian liquid of the mantle derived source. Considerably high Zr concentration in Semra ultramafic is attributed to Zr-enriched mantle source. Geochemically Semra ultramafics is comparable with "Al-undepleted" Munro type komatiites. Depleted incompatible trace elements also point towards Al-undepleted nature for the investigated ultramafics, which are characterised by distinctive low SiO₂ content in comparison to many well known komatiites of the world. The low K₂O content indicate plume related magmatism for its generation. Tectonic setting of this STPK with distinctive cumulus nature is suggestive of its emplacement in an extensional tectonic regime.

Keywords

Komatiite, Plume Magmatism, Extensional Regime, Chhotanagpur Gneissic Complex, Semra, Palamau, Jharkhand.

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P. Palanichamy ¹, A. Joseph ¹, Sanjai Rai ¹, T. Jayakumar ¹, D. K. Bhattacharya ¹, K. V. Kasiviswanathan ¹

Affiliations
1 Indira Gandhi Centre for Atomic Research, Kalpakkam, IN

Abstract

The knowledge of the nature and magnitudes of residual stress (RS.) in a weld joint is important for avoiding distortions and premature failures. Both analytical and experimental techniques are used for getting information on RS distributions.

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P. Palanichamy ¹, A. Joseph ¹, K. V. Kasiviswanathan ¹, D. K. Bhattacharya ¹, Baldev Raj ¹

Affiliations
1 Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, IN

Abstract

This paper discusses the results of measurement of residual stress pattern across butt weld joints by ultrasonic velocity measurements in 15 mm and 47 mm thick AISI type 304 stainless steel plates. These are supplemented by results obtained from hole drilling strain gauge measurements. Pulse echo overlap technique was used to measure the through thickness longitudinal ultrasonic velocities. Acoustoelastic constant was determined to convert the change in ultrasonic velocities to residual stress values. The residual stress pattren obtained by the two techniques showed similar trends. Brief overview of various other residual stress measurement methods, and various techniques for ultrasonic velocity measurements are included in the paper.

Keywords

Residual Stress, Austenitic Stainless Steel, Weld Joint, Ultrasonic Velocity, Acoustoelastic Constant, Strain Guage Technique.

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V. C. Padaki ¹, P. Barat ¹, Baldev Raj ¹, D. K. Bhattacharya ¹

Affiliations
1 Radiometallurgy Laboratory, Reactor Research Centre, Kalpakkam—603 102, IN

Abstract

Austenitic steel welded structures are widely used in power stations, petrochemical industries and nuclear industries. These welded structures pose unique problems for ultrasonic testing not experienced with ferritic steel welds. Since X radiography cannot be used in many cases (like inservice inspection, thick welds, planar defects, etc.), it becomes imperative that ultrasonic testing be used. To do this, the problems encountered during examination of austenitic steel weldments must be understood and solved.

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Jugnu Prasad ¹, D. K. Bhattacharya ¹

Affiliations
1 Department of Geology, Ranchi University, Ranchi-834008, IN

Abstract

In the northwestern fringe of Chotanagpur Gneissic Terrain (CGT) number of occurrences of high MgO ultramafic cumulates are recorded emplaced adjacent to Gondwana basin. The ultramafics occur as veins, lenses and tongue like bodies in metaultramafites and exhibit close spatial association with amphibolites. Mineralogically they are composed of olivine, clinopyroxene, orthopyroxene, magnetite±Cr spinel±phogopite±sphene and are lehrzolitic in composition. Chemically they are characterized by high MgO, Ni,Cr and low TiO₂,alkalies and silica and exhibit komatiitic signature. Major oxide, Trace element and Rare Earth Element ratios suggest their similarity with Al-undepleted Munro type komatiite. Al-undepleted nature together with flat HREE distribution pattern and different elemental ratios suggest absence of garnet in the melting residue. Depth of magma generation estimated on the basis of major oxide ratios suggests melting depth of 150 km at pressure 6-7 Gpa for komatiite magma. They are postulated to be derived from a plume tail or from the innermost part of a plume head.

Keywords

Chotanagpur Gneissic Terrain, High Mgo, Cumulates, AL-Undepleted Munro Type Komatiite, Plume.

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G. Das ¹, N. K. Mukhopadhyay ¹, S. Ghosh Chowdhury ¹, D. K. Bhattacharya ¹

Affiliations
1 Material Characterization Division, National Metallurgical Laboratory, Jamshedpur-831 007, IN

Abstract

The present study was aimed at analysing the failure of a weld repaired turbine casing after 30 years of total service including 5 years after weld repair. The casing vvas weld repaired by a high alloyed weld metal (24Cr-32Ni-4Mn-Fe). The base metal consisting of ferrite-pearlite microstructure did not show any appreciable degradation during service. δ ferrite was observed at the interface of weldment and HAZ as predicted by the Schaeffler diagram. The δ- ferrite phase appeared to transform to alloy carbides and a-phase during high temperature service.

The difference between thermal expansion coefficients of ferritic and austenitic stainless steel led to the generation of stress in addition to the usual thermal stress. The resultant stress was estimated to be near to the yield stress indicating that the weld zone experienced a typical condition of low cycle fatigue. The presence of striations on the fracture surface confirmed thermal fatigue as the failure mode. Crack growth took place along the grain boundaries embrittled by a-phase and led to failure. The correct choice of the filler metal should have been a high Nibase alloy having similar coefficient of thermal expansion as the ferritic steel base metal.

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