DAMAGE ASSESSMENT USING NDE TECHNIQUES: CURRENT · PDF fileDAMAGE ASSESSMENT USING NDE...

DAMAGE ASSESSMENT USING NDE TECHNIQUES:CURRENT SCENARIO AND DIRECTIONS

Baldev Raj, T. Jayakumar and C.K. MukhopadhyayMetallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India

E-mail : [email protected]

(Received 1 October 2003 ; in revised form 29 July 2004)

ABSTRACT

A number of non-destructive evaluation (NDE) techniques such as ultrasonic, micro-magnetic, eddy current,acoustic emission, infrared thermography, laser interferometry, positron annihilation, X-Ray diffraction, smallangle neutron scattering and in-situ metallography are employed for assessing creep and fatigue damage inmaterials. In this paper, an assessment on the current scenario and directions for damage assessment usingvarious NDE techniques is given.

OVERVIEWTrans. Indian Inst. Met.

Vol.58, Nos. 2-3, April-June 2005, pp. 141-157

STRAIN CONTROLLED LOW CYCLE FATIGUE ANDCREEP-FATIGUE INTERACTION BEHAVIOUR OF

MODIFIED 9Cr-1Mo FERRITIC STEEL

S.L. Mannan, K. Bhanu Sankara Rao, M. Valsan and A. NageshaMaterials Development Group

Indira Gandhi Centre for Atomic ResearchKalpakkam 603 102, Tamil Nadu, India


(Received 23 September 2003 ; in revised form 12 March 2004)

ABSTRACT

Influence of temperature, strain rate and hold time on the low cycle fatigue (LCF) behaviour of a modified9Cr-1Mo ferritic steel in the normalized and tempered condition is reported. Total axial strain controlled LCFtests were conducted at strain rates in the range 3!10-4 s-1 to 3!10-2 s-1 at different strain amplitudes varyingfrom ±0.25 to ±1.0% and hold times up to 30 min. in peak tension over temperatures in the range 300 to873 K. The cyclic stress response behaviour, in general, showed an initial brief hardening for the first fewcycles, followed by a gradual and continuous softening regime. The fatigue failure at high strain amplitudesand high strain rates of testing was marked by extensive crack branching and formation of secondary cracks.Oxidation-assisted crack initiation and propagation contributed to life reduction at high temperatures and lowstrain rates. Fatigue life was found to decrease with increase in the duration of hold time in tension. The datagenerated is compared with that from the literature and also with the best-fit and design curves from the RCC-MR code.



CAVITATION AND GRAIN GROWTH DURINGSUPERPLASTIC DEFORMATION AND THEIRCORRELATION WITH FLOW BEHAVIOUR

B.P. Kashyap, S.P. Toppo and A. GargDepartment of Metallurgical Engineering and Materials ScienceIndian Institute of Technology, Bombay, Mumbai 400 076, India


(Received 7 October 2003 ; in revised form 13 March 2004)

ABSTRACT

Grain growth, cavitation and flow stress data, which are available together for limited materials duringsuperplastic deformation, were collected and analyzed to explore the interdependence in microstructural changesand its impact on flow properties. The grain size (dg) varies with strain (") as dg ∝#$

c, c being strain exponent,whereas cavity volume (Cv) follows Cv = A$2 +B$ + C type polynomial relationship, where A, B and Care coefficients. The interrelationship between Cv and dg can be expressed by: Cv ∝ exp(dg). While flowhardening is attributed to grain growth in the early part of deformation, the occurrence of cavitation is foundto cause flow softening at later stage of deformation.



OVERVIEW

GRAIN BOUNDARY CHEMISTRY ANDHIGH TEMPERATURE PLASTIC FLOW IN

POLYCRYSTALLINE ALUMINA

Hidehiro YoshidaDepartment of Advanced Materials Science, Graduate School of Frontier Science, The University of Tokyo

Bldg. of Engineering #4, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 JapanE-mail : [email protected]


ABSTRACT

Most commercial ceramics are fabricated by an addition of sintering aids, which often yield amorphous phasein grain boundaries at sintering temperatures. The composition of grain boundary phase is of primary importancein fabrication of ceramics. However, high-temperature plastic flow is rate-controlled by grain boundarydiffusion even in oxide ceramics without grain boundary amorphous phase because of sluggish lattice diffusion.In such cases, grain boundary diffusivity in oxide ceramics at high temperatures is affected seriously bypresence of doped cation segregated in the vicinity of grain boundaries. Typical example of a small dopanteffect on the high-temperature creep in polycrystalline Al2O3 is briefly introduced in this paper. A firstprinciple molecular orbital calculation based on simple cluster models indicates that ionic bond strength inAl2O3 is enhanced by presence of zirconium or lanthanoid cation at the grain boundaries. The high-temperaturecreep resistance in Al2O3 can be controlled by enhancement of the ionic bonding strength at the grainboundaries. Local quantum structure analysis seems to be a powerful way to understand the small dopant effecton various properties in oxide ceramics.

Trans. Indian Inst. Met.


FATIGUE FAILURE OF ENGINEERING STRUCTURES

S.K. Bhaumik, M. Sujata and R.V. KrishnanMaterials Science Division

National Aerospace Laboratories, Bangalore-560 017, INDIAE-mail : [email protected]

(Received 24 September 2003 ; in revised form 27 April 2004)

ABSTRACT

Majority of service failures in engineering structures occur by fatigue and it amounts to about 60% of the totalfailures. A number of factors influence the fatigue life of a component in service, viz., (i) complex stresscycles, (ii) engineering and design, (iii) manufacturing and inspection, (iv) service conditions and environmentand (v) material of construction. Present paper discusses the fatigue failures of engineering components withexamples drawn from case histories.



OVERVIEW

THERMOMECHANICAL FATIGUE BEHAVIOUR OFMETALLIC HIGH TEMPERATURE MATERIALS

H.-J. Christ1, H.J. Maier2 and R. Teteruk3

1Institut für Werkstofftechnik, Universität Siegen, D-57068 Siegen, Germany2Lehrstuhl für Werkstoffkunde, Universität Paderborn, D-33098 Paderborn, Germany

3Siemens Power Generation, D-45473 Mülheim a. d. Ruhr, GermanyE-mail: [email protected]

(Received 2 October 2003 ; in revised form 5 August 2004)

ABSTRACT

In the present study, three widely used life models were modified to allow for life prediction underthermomechanical fatigue (TMF) loading conditions. Two of these models are based on the accumulation ofcreep as the main damaging effect, while the third model assumes that the energy expenditure can be used asmeasure of damage. A new model is introduced which comprises both fatigue and time-dependent effects (creepand oxidation) and does not require fit parameters. In order to assess the predictive capabilities of the models,life prediction results, which were calculated solely on isothermal data, were compared with TMF data obtainedon a stainless steel and a SiC particulate reinforced aluminium alloy. The analysis of the data obtaineddemonstrated that TMF tests are not sufficient per se to evaluate a life model. Rather TMF tests chosen forvalidation of life models should be conducted under loading conditions such that coupling effects betweenvarious damage mechanisms become apparent.



QUALIFICATION OF CREEP, FATIGUE ANDFRACTURE DESIGN OF PFBR COMPONENTS BASED

ON TESTS

P.Chellapandi, A.Biswas, R.Srinivasan, S.C.Chetal and S.B.BhojeIndira Gandhi Centre for Atomic Research, Kalpakkam 603 102, INDIA.


(Received 3 October 2003 ; in revised form 26 April 2004)

ABSTRACT

In 500 MWe Prototype Fast Breeder Reactor, the critical out-of-core components are main vessel (MV),control plug, inner vessel, intermediate heat exchangers, steam generators (SG) and hot pipelines. The salientstructural mechanics features are large size thin walled shell structures, relatively low operating pressure (<1 MPa, except SG which operates at 17 MPa), high operating temperatures (820 K for hot pool) and largethermal gradients (%T of 150 K between hot and cold pool). These components are designed by analysis(employing numerical techniques such as FEM) to meet the requirements of French Design Code RCC-MRfor the design life of 40 y.

In order to ensure that the design, analysis, indigenous material and indigenous manufacturing technologycomply with the design and construction code rules, tests are carried out on a few important full scalecomponents and mockups having component features such as welds, multiaxiality and stress concentrationeffects under simulated loading conditions. Particularly in the domain of creep, fatigue and fracture design,a series of tests were conducted in Structural Mechanics Laboratory (SML) with the objectives of qualifyingthe performance of components in the reactor and the fracture assessment procedure for the FBR applicationand for demonstrating leak before break (LBB) argument for MV, sodium piping and SG.

This paper highlights the summary of theoretical analyses that have been carried out on creep, fatigue andfracture design of critical components. Subsequently, the paper deals with a few of the experimental investigationsthat have been carried out essentially to qualify the creep-relaxation behaviour of IHX tube to tubesheet joint,creep rupture strength of SG tubes, fatigue and fracture assessment of SG tube bends and LBB justificationof a typical full scale Tee of secondary sodium circuit.



STRUCTURAL INTEGRITY ASSESSMENTOF COMPONENTS OPERATING AT

HIGH TEMPERATURE

H.S. Kushwaha, B.K. Dutta and M.K. SamalReactor Safety Division, Bhabha Atomic Research Centre

Trombay, Mumbai-400085, IndiaE-mail : [email protected]

(Received 26 September 2003 ; in revised form 9 August 2004)

ABSTRACT

For the remaining life assessment of components in a plant that operates in the creep range under cyclicloading, creep-fatigue interaction phenomena is one of the most important considerations. Hence a predictionmethod for the accumulation of damage due to creep and fatigue during the operating life of the componentis necessary. The objective of this paper is to describe the conventional and fracture mechanics based methodsfor creep and fatigue damage assessment of high temperature components. A number of codes existingworldwide for such an assessment have been reviewed. As a case study, the hot reheat pipe bend (elbow) ofa thermal power plant was selected. The operating temperature for the elbow is 813 K and it is subjected to3.5 MPa of internal pressure for full power operation. The moments and forces acting on the elbow arecalculated by taking into account all piping loads due to thermal and dead loads. Circumferential and longitudinalpart-throughwall semi-elliptical cracks (internal and external) at intrados and crown are postulated. The nominalstresses of the elbow are calculated using BARC in-house FEM code MADAM. The stress intensity factorsand limit loads of the corresponding cases are calculated using the RCC-MR AI6 and API procedures. Thedamage due to creep is evaluated using reference stress method of R5 and API codes. The crack growth ratesfor various crack configurations were compared. It was observed that the stress intensity factors and crackgrowth rates are higher for longitudinal part-through cracks and R5 provides a conservative estimate ofremaining life of the component compared to API.



DESIGN AND MATERIAL ISSUES FOR ELEVATEDTEMPERATURE SERVICE COMPONENTS DESIGNED

AS PER ASME SECTION VIII DIVISION 1

S.C.Chetal and R.SrinivasanIndira Gandhi Centre for Atomic Research, Kalpakkam 603 102, INDIA



ABSTRACT

The ASME Code Section VIII Division 1 is a popular design code in many countries and provides rules fordesign of pressure vessels, which operate at temperatures that are in the creep regime of the materials ofconstruction. However, the code does not directly address some design, materials and fabrication issues thatbecome relevant for pressure vessels that operate at high temperature. Further, the code does not provide rulesfor design of pressure vessels beyond 1089 K and multiple design conditions including short time excursion.The design rules imply a design life of 105 h less and thus providing no guidance for life shorter or longerthan 105 h. Less knowledgeable users may end up either in increased capital cost in merely following the codeor increased risk of premature pressure vessel failure in certain cases. The paper attempts to bring out the gapsin ASME Section VIII Division 1 code for design of vessels for elevated temperature service and therecommendations to bridge the same.



REVIEW

EFFECT OF ALLOYING ON DUCTILITY AND LOWCYCLE FATIGUE BEHAVIOUR OF Ti, Ni AND Fe

BASED ALUMINIDES

K.V.U. Praveen and Vakil SinghCentre of Advance Study, Department of Metallurgical Engineering

Institute of Technology, Banaras Hindu University, Varanasi-221 005, India.E-mail : [email protected]


ABSTRACT

Aluminides of Ti, Ni and Fe are ordered intermetallics and possess many attractive properties for hightemperature application. Aluminides with high Al content like TiAl, NiAl and FeAl have relatively lowerdensity, better oxidation resistance and superior mechanical properties than their counterparts with lower Alcontent (Ti3Al, Ni3Al and Fe3Al). However, in general, aluminides display poor ductility at ambient temperatureand even upto their order/disorder transformation temperature. Various attempts have been made to improveductility of both M3Al and MAl type aluminides through different routes. As compared to tensile and creepproperties, less attention has been paid on the LCF behavior of these aluminides particularly of Ni and Fe basedones. LCF behavior of different types of aluminides is discussed.



REINFORCED POLYMER GEAR : FATIGUE ANDFAILURE ANALYSIS

S. Senthilvelan and R. GnanamoorthyDepartment of Mechanical EngineeringIndian Institute of Technology Madras

Chennai - 600 036, INDIA.E-mail : [email protected]

(Received 26 September 2003 ; in revised form 14 February 2004)

ABSTRACT

Gears made of advanced polymers and polymer reinforced composites find increasing application in home,office and industrial equipments. Increasing use of polymer and reinforced polymers is mainly due to economicaland technical advantages compared to metals. Polymer reinforced gears are light in weight and can beeconomically produced using injection molding techniques. However, the low mechanical strength and temperatureresistance limits the application of polymer gears for load bearing applications. This paper describes thedevelopment and performance of Nylon 6 and Nylon 6 Glass Filled polymer gears manufactured using injectionmolding process. Gears with a module of 2 mm and 20° pressure angle were developed in the laboratory. Apower absorption type polymer gear test rig has been used for evaluating the gear fatigue performance. Polymergears were tested against metallic gears at different torque levels. Number of cycles to failure at differentcontact stress levels were generated. Glass filled nylon gears performed well compared to nylon gears at highstress levels. At higher stress levels, significant tooth shape distortion and crazing followed by cracking wasdominant for unfilled and glass filled polymers, respectively.

TP 1928Trans. Indian Inst. Met.


PREDICTION OF LONG-TERM CREEP RUPTURESTRENGTH FOR MODIFIED 9Cr-1Mo FERRITIC

STEEL

V.S. Srinivasan, K. Laha, K. Bhanu Sankara Rao, S.L. Mannan and Baldev RajMaterials Development Group

Indira Gandhi Centre for Atomic Research, Kalpakkam-603 102, INDIAE-mail : [email protected]

(Received 2 October 2003 ; in revised form 27 February 2004)

ABSTRACT

Creep rupture stresses at temperatures between 723-923 K have been estimated at a rupture life of 2.63!105 hfor mod. 9Cr-1Mo steel, using short-term tests data. Larson-Miller Parameter (LMP) and artificial neuralnetwork (ANN) approaches have been employed for extrapolation. The results are compared with extrapolatedRCC-MR code data.



ARTIFICIAL NEURAL NETWORK APPROACH TOLOW CYCLE FATIGUE AND CREEP-FATIGUE

INTERACTION LIFE PREDICTION OF MODIFIED9Cr-1Mo FERRITIC STEEL

V.S. Srinivasan, A. Nagesha, M.Valsan, K. Bhanu Sankara Rao,S.L. Mannan and Baldev Raj

Materials Development Group, Indira Gandhi Centre for Atomic Research (IGCAR)Kalpakkam-603 102 Tamil Nadu, INDIA.



ABSTRACT

Low cycle fatigue (LCF) behaviour of normalized and tempered modified 9Cr-1Mo steel has been studied atvarious temperatures, strain amplitudes, strain rates and hold-times. The alloy in general showed a reductionin fatigue life with increase in temperature, increase in strain amplitude, decrease in strain rate and with anincrease in the duration of hold time in tension. The capability of artificial neural network (ANN) approachto life prediction under LCF and creep-fatigue interaction conditions has been assessed by using the data fromNational Institute for Materials Science, Japan and that generated in our laboratory. It is demonstrated that thepredictions are well within a factor of two.



TP 1931

CREEP STRENGTHENING OF TYPE 316 STAINLESSSTEEL WELD METAL BY NITROGEN

M.D. Mathew, S. Latha, K. Bhanu Sankara Rao and S.L. MannanIndira Gandhi Centre for Atomic Research

Kalpakkam, 603 102 INDIAE-mail : [email protected]


ABSTRACT

Creep properties of type 316 stainless steel weld metal were studied using nitrogen-free and 0.07 wt% nitrogen-bearing electrodes. Creep tests were carried out in the temperature range 823 - 923 K and rupture lives upto20,000 hours. Nitrogen-alloyed weld metal showed lower steady state creep rate, higher rupture life and lowerrupture ductility as compared to nitrogen-free weld metal. Increase in creep resistance of the nitrogen-alloyedweld metal has been attributed to strengthening of the austenite matrix by nitrogen through solid solutionstrengthening and decrease in stacking fault energy. Decrease in rupture ductility is mainly attributed totransformation of delta-ferrite into intermetallic phases. The role of nitrogen on creep deformation, fracture,and delta-ferrite phase transformation behaviour are rationalised on the basis of the microstructural observations.



TP 1932

CREEP DEFORMATION AND FRACTURE BEHAVIOROF TYPE 316L(N) STAINLESS STEEL

C. Girish Shastry, M.D. Mathew, K. Bhanu Sankara Rao and S.L.MannanMaterials Development Group, Indira Gandhi Centre for Atomic Research, Kalpakkam-603 102 INDIA



ABSTRACT

Nitrogen-alloyed, low carbon grade of type 316 stainless steel has been developed indigenously in collaborationwith Alloy Steel Plant (ASP), Durgapur for the nuclear steam supply system components of Prototype FastBreeder Reactor. Creep properties of this material have been determined at 873 and 923 K at various stresslevels and compared with the creep properties of imported steel of similar chemical composition. Materialdeveloped at ASP was found to be comparable to the imported steel with respect to its creep properties at 873and 923 K.



ON THE CREEP, TENSILE AND IMPACTPROPERTIES OF A 120,000 h SERVICE-EXPOSED

2.25Cr-1Mo STEEL

C. Girish Shastry, M.D. Mathew, P.R. Sreenivasan, K. Bhanu Sankara Rao,G. Bandyopadhyay* and S.L.Mannan

Materials Development Group, Indira Gandhi Centre for Atomic Research, Kalpakkam-603 102, INDIA.* R&D Centre, NTPC, Noida-201 301, INDIA.



ABSTRACT

Residual life analysis of thermal power plant components is important because of the need to avoid costlyforced outages, catastrophic failures and premature retirement of components fit for service even after completionof the original design life. Such components include boiler tubes, superheater outlet headers, reheater headers,steam pipes, steam turbine casings and steam chests. Creep, tensile and fracture toughness are importantconsiderations in the design of these components. Thus, extension of life depends on extent of degradation inthese properties due to service exposure. This paper presents the creep, tensile and impact properties of a2.25Cr-1Mo ferritic steel reheater header pipe after being in service for 120,000 hours at 813 K under a steampressure of 2.4 MPa. Creep tests were carried out in the temperature range 813-913 K. Tensile tests werecarried out between 813 and 913 K at four strain rates between 2.9 ! 10-5 and 2.9 ! 10-3 s-1. Tensile andcreep properties did not show any appreciable degradation due to service exposure. Charpy impact propertieswere determined from instrumented impact tests. The Charpy indices like upper-shelf energy and fractureappearance transition temperature did not exhibit any significant change as compared to the properties of virginmaterial.



TP 1934

MATHEMATICAL MODELLING OF STEADY STATECREEP IN METAL MATRIX COMPOSITES

Prem E. J. Babu, U.T.S. Pillai, S. Savithri # and B.C. PaiMetal Processing Division, # Computational Modelling and Simulation SectionRegional Research Laboratory (CSIR), Thiruvananthapuram – 695 019, India



ABSTRACT

A novel micromechanical approach has been developed for predicting the steady state creep behavior of metalmatrix composites (MMCs). The developed micromechanical model is an analytical formulation based on straincompatibility. Further, the theory embodies the non-linear and rate-dependent nature of the ductile matrix, aswell as the elasticity of both the matrix and the fiber. The proposed formulation presented in a generalizedmanner can be appliied to a large class of MMC systems. The predicted creep rate for the composite usingthe present model is compared with the available results in the literature.



FATIGUE LIFE ESTIMATION OF WELDED JOINTS –A TWO STAGE PROPAGATION APPROACH

P.Johan Singh*, S.L.Mannan* and D.R.G.Achar**

*Indira Gandhi Centre for Atomic Research, Kalpakkam-603 102, India.**Indian Institute of Technology, Chennai-600 036, India.



ABSTRACT

The fatigue life of flawed materials such as cruciform joints with lack of penetration (LOP) defects may beseparated into two portions: that fraction of the life in which flaws sharpen to become active fatigue cracks(initiation), and that fraction in which the sharpened cracks steadily enlarge until fracture occurs (propagation).A two-stage propagation model for life prediction based on fracture mechanics approach incorporating near-threshold crack growth data has been offered. The experimental part consists of fatigue tests for cruciformjoints of AISI 304L stainless steel. Constant amplitude fatigue tests with stress ratio, R = 0 have been carriedout with a frequency of 30 Hz. This study suggests that the life prediction using the proposed two-stagepropagation model was simple, accurate and requires limited and known parameters



CREEP RUPTURE PROPERTIES OF INDIGENOUSELYDEVELOPED MODIFIED 9Cr-1Mo STEAM

GENERATOR TUBE STEEL

E. Isaac Samuel, B.K. Choudhary, K. Bhanu Sankara Rao and S.L. MannanMaterials Development Group

Indira Gandhi Centre for Atomic Research, Kalpakkam – 603 102 INDIAE-mail : [email protected]


ABSTRACT

The results of the creep tests performed on the modified 9Cr-1Mo steel specimens, machined from steamgenerator (SG) tubes of 17.2 mm outer diameter and 2.3 mm wall thickness, in the temperature range 823-873 K indicated that the creep deformation is characterised by a small amount of instantaneous strain followedby a decreasing creep rate (primary), a minimum creep rate (secondary) and an accelerating creep rate (tertiary)regimes. At all temperatures, stress dependence of minimum creep rate obeyed Norton’s power law andexhibited a high value of stress exponent. The stress exponent decreased from 13.3 at 823 K to 12.3 at873 K. Rupture life decreased with increasing temperature and stress. The SG tube exhibited high creepductility and loss of creep ductility was not observed with increasing rupture life. The fracture mode remainedtransgranular characterised by dimples resulting from micro-void coalescence. The creep-rupture strength ofSG tube material was found to be higher than the average creep strength values specified for the steel in FrenchNuclear Design Code, RCC-MR.



THE EFFECT OF PRIOR MICROSTRUCTURE ON THELOW CYCLE FATIGUE BEHAVIOUR OF A 15Cr-15Ni,

Ti MODIFIED AUSTENITIC STAINLESS STEEL

R. Sandhya, K. Bhanu Sankara Rao and S.L. MannanMaterials Development Group

Indira Gandhi Centre for Atomic ResearchKalpakkam-603102, India



ABSTRACT

Fully austenitic 15Cr-15Ni titanium modified austenitic stainless steel (Alloy D9) is being used as fuel cladand wrapper material in fast breeder reactors. As part of a larger programme of characterising the Low CycleFatigue (LCF) and Creep-Fatigue Interaction behaviour of this alloy as a function of Ti/C ratio, the alloy witha Ti/C ratio of 8 has been tested in three microstuctural conditions:(a) solution annealed (b) 20 % cold workedand (c) aged at 1023 K / 2h. LCF tests have been carried out at 823 and 923 K employing strain amplitudesin the range ±0.25% to ±1.0% at a strain rate of 3 x 10 –3 s –1. At both the temperatures tested the solutionannealed material exhibited cyclic hardening, while the cold worked material exhibited cyclic softening. Theaged material showed hardening for the first few cycles, followed by cyclic softening. While the solutionannealed material exhibited superior LCF lives in terms of plastic strain resistance, the cold worked and agedmaterials exhibited better LCF resistance in terms of total strain resistance especially at lower strain amplitudes.The deformation substructure developed during fatigue deformation has been characterized and correlatedwith the cyclic stress response and LCF life



INFLUENCE OF PROCESSING ROUTE AND SECTIONTHICKNESS ON THE CREEP RUPTURE PROPERTIES

OF 9Cr-1Mo STEEL

B.K. Choudhary, E. Isaac Samuel, K. Bhanu Sankara Rao and S. L. MannanMaterials Development Group

Indira Gandhi Centre for Atomic Research, Kalpakkam – 603 102, INDIAE-mail : [email protected]


ABSTRACT

The paper presents the influence of processing method and section thickness on creep-rupture properties of 9Cr-1Mo ferritic steel. Creep tests were performed on specimens machined from tube plate forging (1000 mmdiameter and 300 mm thickness) and plate (20 mm thickness) at 793 K employing stress levels ranging from100 to 275 MPa. In both the forging and the plate, the stress dependence of secondary creep rate obeyed powerlaw creep and exhibited two stress regimes with stress exponent values of ~4 in the low stress regime and~10 in the high stress regime. Comparison of creep rupture properties of the plate material with that of tubeplate forging suggested better creep strength of the plate material in terms of lower secondary creep rate andhigher rupture life. The secondary creep rate of the plate material was lower than that of the forging by factorsof ~3.25 and ~3 in the high and low stress regimes, respectively. Similarly, rupture life values of the platematerial was higher by a factor of ~2 in high stress regime. No significant difference in creep ductility valueswas observed between the plate and tube plate forging. The ductility values remained high in both the materialconditions. The fracture mode remained transgranular characterised by dimples resulting from coalescence ofmicro-voids. The inferior creep-rupture properties of tube plate forging were ascribed to the coarseness ofmicrostructure.



EFFECT OF TEMPERATURE ON LOW CYCLEFATIGUE BEHAVIOUR OF 316L(N) AND 304L(N)

STAINLESS STEELS

R. Kannan, M.Valsan, V.S. Srinivasan, K. Bhanu Sankara Rao and S.L.MannanMaterials Development Group

Indira Gandhi Centre for Atomic ResearchKalpakkam 603 102, India



ABSTRACT

The low cycle fatigue (LCF) behaviour of 304L(N) and 316L(N) austenitic stainless steels in the temperaturerange 298-923 K is presented. Total axial strain controlled fatigue tests were performed in air employing astrain rate of 3!10-3s-1 and at a fixed strain amplitude of ±0.6%. Dynamic strain ageing (DSA) was foundto influence the cyclic deformation behaviour of the alloys under appropriate testing conditions. The manifestationsof DSA observed include negative temperature dependence of half-life cyclic stress, decrease in half-life plasticstrain amplitude and serrations in the plastic portions of stress – strain hysteresis loops. The fatigue life ofboth the alloys exhibited a peak at an intermediate temperature. The lower fatigue life noticed at 298 K hasbeen attributed to the occurrence of deformation induced martensite and its adverse influence on crack initiationlife.



A COMPARATIVE EVALUATION OF LOW CYCLEFATIGUE AND CREEP-FATIGUE INTERACTION

BEHAVIOUR OF 316 AND 316(N) WELD METALS ANDWELD JOINTS

M. Valsan, A. Nagesha, K. Bhanu Sankara Rao,R. Sandhya, S.L. Mannan and Baldev Raj

Materials Development GroupIndira Gandhi Centre for Atomic Research, Kalpakkam 603 109, India



ABSTRACT

In this paper, a comparative study of the low cycle fatigue (LCF) and creep-fatigue interaction behaviour of316L(N) base metal, 316, 316(N) weld metals and weld joints is presented. Cyclic stress response of the weldmetal and weld joints exhibited a softening regime. In general, the LCF and creep-fatigue lives exhibited bythe base metal were higher than that of the weld metal. Weld joints exhibited the lowest life. It was observedthat fatigue endurance of 316(N) weld metal-grade 2 was higher than that of the 316(N) weld metal grade 1.Further, 316 SS weld metal and weld joints showed superior fatigue lives compared to 316(N) weld metalsand joints. The differences in fatigue and creep-fatigue lives of the weld metals and base metal under varioustesting conditions have been found to be associated with the basic differences in chemical composition anddifferences in the fatigue cracking mode. The LCF and creep-fatigue data compared well with that availablefrom the literature and RCC-MR best fit curves.



LOW CYCLE FATIGUE PROPERTIES OF A SA-508GRADE CARBON STEEL WELDS AND WELD JOINTS

Sunil Goyal, M. Valsan, K. Bhanu Sankara Rao and S.L. MannanMaterials Development Group

Indira Gandhi Center for Atomic ResearchKalpakkam 603 102, INDIA.E-mail : [email protected]


ABSTRACT

In this paper the low cycle fatigue properties of SA-508 carbon steel bimetallic weld joint and weld metal ispresented. The bimetallic weld joints are prepared initially by buttering on both sides of the base metal withInconel 600 by Shielded Metal Arc Welding (SMAW) process using ENiCrFe3 electrodes. The weld root passis carried out by Gas Tungsten Arc Welding (GTAW) by using ERNiCr3 electrodes and subsequently bySMAW process using ENiCrFe3 electrodes. Ultrasonic testing of the butted layer, radiography of the weldmetal and liquid penetrant tests of the root pass are performed to ensure soundness of the weld pad.

Fully reversed total axial strain controlled low cycle fatigue tests were carried out on all-weld and weld jointsamples taken from the top, middle and bottom portions of bi-metallic joint. The fatigue tests were conductedat room temperature employing strain amplitudes in the range ±0.3 to ±0.5% at a constant strain rate of3 ! 10 –3 s–1. Both the weld metal and the weld joint samples exhibited an initial hardening followed by acontinuous softening regime that ends with stress saturation prior to failure. Comparison of the fatigue life ofthe specimens from root pass region (bottom) indicates that all-weld samples have a better fatigue life thanthe weld joints. However, weld joint specimens from the top and the middle portions of the weld pad showeda better fatigue life than the corresponding all-weld samples. Fatigue life is found to increase with decreasein strain amplitude. In this paper the observed differences in fatigue life are discussed with the evidences fromfractography and metallography conducted on the longitudinally sectioned samples.



ON THE APPLICABILITY OF A DAMAGEMECHANICS BASED MODEL FOR STRESS

CONTROLLED VERY LOW CYCLE FATIGUE

A. Satya Devi1, S.M. Sivakumar2 and S.S. Bhattacharya3

1 Department of Mechanical EngineeringG.V.P. College of Engineering, Visakhapatnam – 530041, INDIA

2 Department of Applied Mechanics3 Department of Metallurgical Engineering

Indian Institute of Technology Madras, Chennai - 600036, INDIAE-mail : [email protected]


ABSTRACT

Study of the Very Low Cycle Fatigue (VLCF) behavior of materials assumes importance in the context ofdesign of structures that are subjected to extreme loading conditions such as rocket components, earthquakesand accidents. During VLCF, large plastic strains are encountered and the number of cycles to failure is inthe range of less than 100. In general, models based on damage mechanics approaches mimic closely thephysical phenomena that occur during VLCF and, therefore, are very good candidates suitable for lifeprediction under such circumstances. In the present study, a simple damage mechanics model based on anearlier proposed model, is considered for the description of stress controlled VLCF. In this model, the lifeof a material undergoing VLCF is expressed in terms of the maximum stress and the plastic strain. At present,the capability is limited to uniaxial loading but can be extended to multiaxial loading with due modifications.For the numerical validation of the model, uniaxial stress controlled very low cycle fatigue tests have beencarried out on commercial steel and mild steel at different stress levels. It is shown that the life predicted bythe present model is in close agreement with the experimental results.



TP 1943

THERMAL CREEP PROPERTIES OF ALLOY D9 FUELCLAD TUBES OF FAST BREEDER REACTOR

S. Latha, M.D. Mathew, K. Bhanu Sankara Rao and S.L. MannanMaterials Development Group, Indira Gandhi Centre for Atomic Research

Kalpakkam-603 102, IndiaE-mail : [email protected]


ABSTRACT

Uniaxial thermal creep rupture properties of 20% cold worked alloy D9 fast reactor fuel clad tubes have beenevaluated at 973 K in the stress range of 125 to 250 MPa. The results are compared with existing data on20% cold worked type 316 stainless steel cladding tubes. Alloy D9 exhibited lower minimum creep rates,higher rupture lives and lower rupture ductilities at all the stress levels.



THERMAL CREEP EXPERIMENTS ON ZIRCONIUMALLOYS USING PRESSURISED CAPSULES

P.K. Chaurasia, K.A. Gopal and S. MuruganIDEAS Section, Metallurgy and Materials Group

Indira Gandhi Centre for Atomic Research, Kalpakkam – 603 102, INDIAE-mail : [email protected]


ABSTRACT

Alloys of Zirconium (Zircaloy-2 and Zr-2.5% Nb alloy) are used as pressure tube materials in PressurisedHeavy Water Reactors (PHWRs). The data on the creep rate of these materials during the actual servicecondition is required to predict the performance of the pressure tubes during their service lifetime. In theirradiation experiments carried out in Fast Breeder Test Reactor (FBTR), miniature pressure tubes with 15.3mm O.D. and wall thickness of 0.65 mm were used in the form of pressurised capsules to determine the in-reactor creep rate of these materials. The pressurised capsules were subjected to biaxial stress conditions withstress levels that are allowable in pressure tubes. The creep strain obtained in irradiation experiments includesstrain due to thermal and irradiation creep, and irradiation growth. An out-of-pile experimental work wascarried out to determine the steady state thermal creep rate in the pressurised capsules to know the contributiondue to thermal creep. In this work, pressurised capsules of Zircaloy-2 and Zr-2.5% Nb alloy were subjectedto temperatures of 579 K and 613 K in an electrical furnace. The creep strain accumulated due to thermal creepwas measured after predetermined intervals of time and the steady state creep rate was determined. Theexperimental procedure of thermal creep experiments and the comparison of the creep strain between thermaland irradiation experiments are given in this paper.



CHARACTERIZATION OF FATIGUE CRACKINITIATION AND PROPAGATION IN MICRO

ALLOYED STEEL WELDMENTS

R.K. Pandey, G.K. Purohit and R.S. ParmarDepartment of Applied Mechanics

Indian Institute of TechnologyHauz Khas, New Delhi-110016, INDIA.



ABSTRACT

Fatigue initiation and propagation behavior have been studied in a micro-alloyed steel in the parent metal aswell as in the weld joint of the steel. The fatigue initiation is studied and compared in terms of a thresholdparameter (%K /&')th where ' is the notch tip radius and %K is the stress intensity range at threshold. Thefatigue propagation is studied by determining da/dN vs %K diagrams and using Paris law. The effect of notch/crack orientation with respect to stressing axis has been studied on the fatigue initiation and propagationcharacteristics for the parent metal, weld metal and the HAZ. The role of inclusions, strength properties andmicrostructure has been discussed.

TP-1945Trans. Indian Inst. Met.


TP 1946

CREEP RESISTANCE BEHAVIOR AT 923 K OF AMODIFIED 12CrMoVNb STEEL FOR POWER

STATIONS

C. Gupta1, R. Agamennone2, J.K. Chakravartty1 and W. Blum2

1 Materials Science Division, Bhabha Atomic Research Centre, Trombay, 400085, Mumbai, India2 Institut für Werkstoffwissenschaften, LS1, Technische Fakultät, Universität Erlangen-Nürnberg

Martenstraße 5, 91058 Erlangen, GermanyE-mail : [email protected]


ABSTRACT

The creep properties of a new 12CrMoVNb steel (modified by additions of 5%Co and 2%W and micro-alloyedwith B, Al, and N) have been investigated at 923 K. The fine initial sub-grain structure of the steel (averagesub-grain size 480 nm) results from the martensitic transformation, and the recovery of the dislocation structureaccompanied with precipitation of carbo-nitrides during final heat treatment. Creep tests at 923 K lead tofurther precipitation of Laves phase and coarsening of subgrains in dependence of strain and stress. Coarseningof the subgrain during creep leads to onset of tertiary creep with final fracture. The creep resistance of thepresent alloy at 923 K is distinctly higher than that of the well known alloy P92 in the investigated range duringshort term creep tests. Extrapolation of creep rate minima to low stresses was found to overestimate the creepresistance determined from long term tests due to the precipitation of Z phase.



EFFECT OF QUATERNARY ADDITIONS ONMECHANICAL PROPERTIES OF AN (O+B2) ALLOY

Archana Paradkar, T.K. Nandy, A.K.Gogia and D.BanerjeeDefence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad-500058, India



ABSTRACT

The current understanding of the metallurgy of ternary (O+B2) alloys is adequate to attempt a systematicevaluation of quaternary alloying effects, especially in relation to improving creep resistance while retainingthe current levels of tensile and fracture properties. This is particularly important since the search for newcompositions with superior mechanical properties continues. An effort is therefore made for an enhancementof creep properties by quaternary additions in (O+B2) ( system. Based on the previous studies, Ti-24Al-20Nbis chosen as a reference alloy for generating base-line information and studying the alloying effects. Preliminarywork in DMRL and information available in the literature suggest that Mo and Zr additions result in hightemperature strengthening and enhanced creep properties of conventional titanium alloys. Therefore, the effectof small additions of quaternary elements such as Mo and Zr in an (O+B2) alloy Ti-24Al-20Nb was evaluatedfor improvement in strength and creep resistance. It is observed that the quaternary additions improve thehigh temperature strength , decrease the steady state creep rate, 100 hrs strain and primary strain. The resultswill be discussed and compared with those of recently published literature on similar investigations.



THERMOMECHANICAL FATIGUE BEHAVIOUR OFTYPE 316L(N) AUSTENITIC STAINLESS STEEL

A. Nagesha, M. Valsan, K. Bhanu Sankara Rao, R. Kannan and S.L. MannanMaterials Development Group

Indira Gandhi Centre for Atomic Research Kalpakkam 603 102, IndiaE-mail : [email protected]

(Received 23 September 2003 ; in revised form 8 April 2004)

ABSTRACT

In-phase (IP) and out-of-phase (OP) thermomechanical fatigue (TMF) tests were carried out on a 316L(N)austenitic stainless steel on cylindrical hollow tubular samples using different mechanical strain amplitudes inthe range, ± 0.25% to ± 0.6% at a constant strain rate of 6.4 ! 10–5 s-1. The temperature cycles employedconsisted of two different categories namely (a) an identical temperature range with increasing peak temperature(573-823, 623-873 and 673-923 k) and (b) a constant peak temperature with increasing temperature range(673-873, 623-873, 673-923 and 623-923 K). In- phase and out-of-phase tests yielded a compressive and atensile mean stress, respectively. The TMF life was seen to decrease with increasing peak and mean temperaturesof thermal cycling. Further, lives under OP cycling were found to be lower than those under IP conditionsin the low temperature regimes, while the converse holds good when the upper temperature encompassed thecreep-dominant regime. Influence of creep on the TMF damage was evident in the form of extensive intergranularcracking in the 673-923 K IP test. The isothermal tests conducted at the peak temperatures of the thermal cyclesdisplayed lower lives compared to both the IP and the OP cycling. Detailed metallographic and fractographicstudies were conducted to understand the behaviour of the material under TMF conditions.



TP 1949

CREEP BEHAVIOR OF MODIFIED 9Cr-1Mo FORGEDSTEEL AND ITS WELD JOINT

K. Laha, K. S. Chandravathi, K. Bhanu Sankara Rao and S.L. MannanMaterials Development Group, Indira Gandhi Centre for Atomic Research

Kalpakkam - 603 102, IndiaE-mail : [email protected]


ABSTRACT

Creep deformation and fracture behavior of modified 9Cr-1Mo (grade 91) forged steel and its fusion-weldedjoints have been studied at 823, 873 and 923 K over a stress range of 80 – 300 MPa. The weld joint at allthe test temperatures possessed lower creep rupture strength than the base metal, except at higher appliedstresses at 823 K and 873 K. The magnitude of the reduction in creep strength of the weld joint comparedto the base metal increased with the increase in testing temperature and decrease in applied stress. Microstructureand micro hardness of the weld joints were evaluated in the as welded, post weld heat-treated and creep testedconditions. A hardness trough was observed in the intercritical region (ICR) of the heat-affected zone. Therecovery of the substructure and coarsening of intragranular carbides and carbonitrides led to lower hardnessin the intercritical heat affected zone (HAZ) of the joints contributing to lower creep strength. The creep failurein the ICR has been found to be associated with intergranular cavitation.



EFFECT OF WELD PROFILE ON CREEP-FATIGUEDAMAGE OF PFBR STEAM GENERATOR TUBES

R.Srinivasan, P.Chellapandi, S.C.Chetal and S.B.BhojeIndira Gandhi Center for Atomic Research, Kalpakkam 603 102, INDIA.

Email : [email protected]


ABSTRACT

In Fast Breeder Reactors, Steam Generator is a critical component as its availability decides the capacity factorof the plant. Operating experiences have shown that many sodium leak and consequent sodium water reactionshave occurred at the tube to tubesheet welds. To have reliable joint, the internal bore welding of tube to spigot(machined from tubesheet) is chosen, so as to have weld away from the stress concentration zone. In the viewof the unavoidable manufacturing deviations, creep-fatigue damage is evaluated as per RCC-MR for variousweld profiles by detailed FEM analysis. In the analysis, loss of thickness due to corrosion is considered. Forvarious failure modes, appropriate reduction factors from literature are applied to take into account the effectsof weldments. Inspite of the assumption of a sharp corner at the junction of weld to base metal, fatigue damageis negligible and creep damage is governing for all the cases. From creep damage consideration, convexity oninside diameter (ID) with matching concavity on outside diameter (OD) is the most damaging configuration.A convexity of 0.5 mm on ID associated with weld thinning of 0.2 mm results in a creep damage of 0.88.Conservatively, maximum convexity of 0.35 mm and weld thinning of 0.2 mm are recommended which willresult in a creep damage in the range of 0.5-0.6 and fatigue damage less than 0.1.



FATIGUE LIFE EVALUATION OF THE PIPINGSYSTEMS FOR THE LIFE EXTENSION OF HEAVY

WATER PLANT, KOTA

Rajesh Mishra, K.K.Vaze and H.S.KushwahaReactor Safety Division, Hall No.7

Bhabha Atomic Research Centre, Mumbai-400085, INDIA.E-mail : [email protected]

(Received 30 September 2003 ; in revised form 3 May 2004)

ABSTRACT

Heavy Water Plant, Kota commissioned in 1985, is nearing completion of its originally postulated design life.Exercises have been performed to carry out fatigue life evaluation to assess the remaining fatigue life of thepiping components with the aim to extend the life of the plant. Considering process parameters and past historyof the plant performance, process critical piping systems connected with 25 equipment nozzle locations wereidentified for this task. Static analyses were carried out to find out the induced stress levels as per the designcode. A few locations where results showed high stress due to the sustained loadings were suggested to keepunder constant monitoring. Fatigue life evaluation has been carried out for the locations where high thermalstresses were observed. This paper details the strategy adopted for fatigue life evaluation and life extensionof the piping systems of the plant alongwith a few typical case studies



THERMOMECHANICAL FATIGUE BEHAVIOUROF A )))))-TiAl SHEET MATERIAL

P. Schallow and H.-J. ChristInstitut für Werkstofftechnik, Universität Siegen, D-57068 Siegen, Germany


(Received 1 October 2003 ; in revised form 17 May 2004)

ABSTRACT

The monotonic stress-strain behaviour, LCF and TMF behaviour of a Ti-46.5at.%-4at.%(Cr,Nb,Ta,B) alloyingot metallurgically processed was investigated in the temperature range between 773 K and 1023 K. Theductile-to-brittle transition temperature (DBTT) was found to be 923 K. The cyclic stress-strain (CSS) responseof LCF-tested specimens is characterized by an immediate state of cyclic saturation which continued up tofailure. An increased fatigue life which is observed at elevated temperature is associated with a change of thefracture morphology from a transgranular cleavage type of fracture to a more dimple intergranular type. IPloaded specimens show the onset of dynamic recrystallisation which leads to an increased fatigue life ascompared to LCF tests carried out at maximum temperature. OP loading is most detrimental with a well-reduced fatigue life, when compared to LCF tests carried out at the minimum temperature.



FRACTURE MECHANICS BASED REMAINING LIFEPREDICTION SOFTWARE

A. Rama Chandra Murthy, G.S. Palani and Nagesh R. IyerScientist, Structural Engineering Research Centre, Taramani, Chennai–600 113, India.



ABSTRACT

This paper presents the details of the software, which can be used for remaining life prediction of crackedstructural components. The computation of Stress Intensity Factor (SIF) and remaining life prediction is basedon Linear Elastic Fracture Mechanics (LEFM) principles. The remaining life is estimated either by incrementalcrack growth approach or cycle-by-cycle approach. This software is Graphical User Interface (GUI) based anduser-friendly, which is developed under windows environment using VC++ for front end and MS-Access forthe back end. This software maintains database of SIF for standard cracked structural components includingtubular joints with the facility for linear interpolation of SIF values. Various crack growth models such asParis, Ratwani, Erdogan- Ratwani, Forman, etc., are available in the software for remaining life prediction.There is facility for graphical plot of crack growth history (crack length vs. SIF and crack length vs. No. ofcycles) and report generation. Studies have been conducted to validate the software using the values reportedin the literature. The remaining life obtained using the software is found to be in good agreement with theexperimental values.



TP-1954

EXPERIMENTAL AND NUMERICALINVESTIGATIONS ON WELD AND REPAIR WELD

BEHAVIOUR

Karl Maile and Andreas KlenkMPA Stuttgart, Pfaffenwaldring 32, D-70569 Stuttgart, Germany



ABSTRACT

To increase efficiency of fossil fired power plants, the process parameters, in particular the temperature, havebeen increased more and more. The newly developed 9 Cr and 10 Cr steels opened the way for thisdevelopment. Subsequently there is a strong need to know the long time behaviour of weldments in components.Due to the different material properties in the different zones (heat affected zones, weld metal and base metal)stress redistribution, strain and damage behaviour and location is complicated. A change in fracture locationfrom weld metal to fine grained heat affected zone is usually observed. Numerical simulation of weldmentswas used to investigate local stress state and deformation which can be correlated to damage behaviour andlocation. To develop engineering assessment methods for welds and repair welds reliable design and calculationtools are necessary. To enable numerical simulation of welded and repair welded components geometrical andmaterial models were developed. Methods for geometrical modelling of partly and fully repaired welds andmaterial have been investigated. Crossweld tests were simulated to validate the models. To determine thematerial behaviour of the welds a number of creep tests on laboratory specimens have been carried out. Featuretests with pipes and T-pieces with different weld and repair weld configurations will be simulated in order tosupport the development of lifetime assessment methods for welded and repair welded components.



FATIGUE FAILURE OF A CONNECTING ROD OFA PISTON ENGINE

S.K. Bhaumik, M.A.Venkataswamy, T.A.Bhaskaran, R.Rangaraju,M. Sujata and R.V. Krishnan

Materials Science DivisionNational Aerospace Laboratories, Bangalore-560 017, INDIA


(Received 20 September 2003 ; in revised form 22 June 2004)

ABSTRACT

Fatigue failures are frequently observed in various components of piston engines. The reasons for such failurescan be improper material selection, improper design, misalignment, improper lubrication etc. In this paper,failure of a connecting rod of a piston driven aeroengine is described. The connecting rod is manufactured froman alloy steel of nominal composition Fe(base)-0.4C-0.8Mn-0.3Si-0.5Ni-0.5Cr-0.3Mo. The engine servedabout 350 h of life, since the last overhaul against the Time Before Overhaul (TBO) life of 1200 h. Analysisshowed that intermittent breakdown of the lubricant film led to fatigue failure at the big end of the connectingrod.



LOW CYCLE FATIGUE BEHAVIOUR OF NEAR*****-TITANIUM ALLOY IMI 834 AT ROOM

TEMPERATURE AND AT 673 K

K.V. Sai Srinadh and Vakil SinghCentre of Advanced Study

Department of Metallurgical EngineeringInstitute of Technology

Banaras Hindu UniversityVaranasi – 221 005, INDIA.



ABSTRACT

Low cycle fatigue (LCF) behaviour of the near *- titanium alloy IMI 834 was studied, for the (*+() solutiontreated, air cooled and stabilized condition, at room temperature (RT) and at 673K. It had bimodal microstructurewith nearly 12 vol. % of primary * in the matrix of lamellar transformed (. LCF tests were conducted atdifferent total strain amplitudes (%$t/2) from ± 0.75% to ± 1.3%, with triangular waveform of loading, ata constant strain rate of 0.008 s-1

-. While there was cyclic softening at room temperature, there was cyclichardening followed by softening at 673K. Further, while there was bi-linear behaviour in Coffin-Manson(C-M) relationship at room temperature, there was only linear behaviour at 673K, over the entire range of thetotal strain amplitude studied.



FRACTURE ANALYSIS OF CRACKED PLATE PANELSUSING NI-MVCCI TECHNIQUE

G.S. Palani1, Nagesh R. Iyer1 and B. Dattaguru2

1 Structural Engineering Research Centre, Chennai-600 112, India.2 Indian Institute of Science, Bangalore-560 012, India.



ABSTRACT

The objective of this paper is to propose a numerically integrated modified virtual crack closure integral (NI-MVCCI) technique for fracture analysis of cracked plate panels. NI-MVCCI technique is generalized one andthe expressions for computing the strain energy release rate (SERR) are independent of the finite elementemployed. NI-MVCCI technique has been demonstrated for 4-noded, 8-noded (regular and quarter-point) and9-noded isoparametric finite elements. Numerical studies on fracture analysis of 2-D crack (mode-I and mode-II) problems have been conducted employing these elements. SERR and stress intensity factors (SIF) have beencomputed for these problems and found to be in good agreement with the respective analytical solutionsavailable in the literature. The appropriate Gauss numerical integration order to be employed for each of theseelements for accurate computation of SERR and SIF has been recommended based on the studies.



FATIGUE BEHAVIOUR OF COLD-FORMED STEELLIPPED ANGLES

S. Vishnuvardhan*, S. Kandasamy** and G. M. Samuel Knight**** Ph. D. Research Scholar in Civil Engineering, Anna University, Chennai-600 025, India.

** Assistant Professor of Civil Engineering, Government College of Engineering, Salem, India.***Professor of Civil Engineering, College of Engineering, Anna University, Chennai-600 025, India.



ABSTRACT

Cold-formed steel sections are increasingly used nowadays in structural applications, due to their inherentproperties like lightweight and high strength to weight ratio. Angles and channels, both with or without lipsare the most common shapes used in practice. Cold-formed steel sections are thin and hence their behaviouris governed by local buckling. Even though static behaviour of cold-formed elements is well established, theirfatigue behaviour under fluctuating loads needs to be investigated. The present investigation examines theperformance of cold-formed lipped single angle members subjected to fatigue loading. Fatigue tests wereconducted on seventy six specimens under constant amplitude sinusoidal and stepped tensile loading conditionsby varying the load ratio and the load level ratio for both low yield and high yield strength steel membersunder 5 Hz and 2 Hz respectively. The influence of fatigue parameters like maximum stress, stress range andtype of loading on fatigue life is studied. An empirical relation is arrived at and the number of cycles to failureis proposed. Fatigue failure surface is also evolved for the two different grades of steel.



PROBABILISTIC STUDY OF FRACTURE STRENGTHOF THROUGH-WALL CRACKED PIPES

D. Prem Navin and D.S. Ramachandra MurthyStructural Engineering Research Centre, Chennai 600113, INDIA.



ABSTRACT

Fracture strength of piping components used in primary heat transport system of nuclear power plant is of greatimportance to ensure safety against improbable accidental loads. The theoretical plastic collapse load for thenet cross section is used to calculate the strength of pipes having flaws/cracks. The results of the 55experiments conducted by several investigators on through-wall circumferentially cracked pipes were statisticallyanalyzed for their maximum load capacity. Frequency distribution of experimental moments normalized bytheir theoretical plastic collapse moments was studied and a best fit was found using goodness of fit test. Basedon the study, reduction factor has been suggested for net-section plastic collapse load of through-wallcircumferential crack pipes for different percentages of confidence.



ELASTIC-PLASTIC FRACTURE MECHANICS BASEDPREDICTION OF FRACTURE INSTABILITY IN A

CIRCUMFERENTIALLY THROUGH-WALL CRACKEDPIPE IN BENDING

Sanjeev Saxena* and D.S. Ramachandra Murthy**

* Presently in Regional Research Laboratory, Bhopal-462003, INDIA.** Structural Engineering Research Centre, Chennai-600 113, INDIA.


(Received 25 September 2003 ; in revised form 21 July 2004)

ABSTRACT

Elastic-plastic fracture mechanics methods are now increasingly being used in the evaluation of structuralintegrity of flawed piping components. Among the several methods currently being used, the J-integral tearingmodulus approach (J-T) has received much attention. Using J-T approach, the present study has been carriedout on 406 mm outer diameter circumferentially through-wall cracked (TWC) pipes to predict the limiting load,which will cause fracture instability. The solutions are found to have good comparison with the maximumexperimental load, indicating the dominance of ductile tearing phenomenon. Hence, the tearing modulusapproach can be used to predict fracture instability in piping components having a crack.



FATIGUE CRACK GROWTH ANALYSIS OF A PLATEWITH SEMI-ELLIPTICAL SURFACE CRACK

SUBJECTED TO TENSION

S.Anne Ligoriaa, G.M.Samuel Knighta and D.S. Ramachandra Murthyb

aStructural Engineering Division, Anna University, Chennai - 600 025, IndiabStructural Engineering Research Centre, Chennai - 600 113, India


(Received 30 September 2003 ; in revised form 21 July 2004)

ABSTRACT

A thick plate with a semi-elliptical surface crack of different initial crack sizes subjected to tension fatigueloading was considered for the analysis. The material was assumed to have isotropic fracture toughness inthe surface and thickness directions and the property values reported by Burande and Sethuraman were used.Mode I Stress Intensity Factor (SIF) under plane strain condition was calculated using Finite Element technique(ANSYS Software) and compared with the predictions using the expression from SIF Handbook. The crackgrowth rates were further calculated by Foreman’s equation. MathCAD software was used to perform theiterations of the crack growth study until failure. The finite element model underestimates the cycles to failureby 4% as compared to that predicted using SIF equation.



APPLICATION OF A FRACTURE MECHANICSCONCEPT TO LIFE PREDICTION OF AUSTENITIC

STAINLESS STEELS UNDER TMF LOADINGCONDITIONS

V. Bauer and H.-J. ChristInstitut für Werkstofftechnik, Universität Siegen, D-57068 Siegen, Germany


(Received 2 October 2003 ; in revised form 5 August 2004)

ABSTRACT

In the present study, a life prediction method based on fatigue crack propagation is suggested in order toaccount for damage caused by thermomechanical loading conditions. The cyclic J-integral or the J-integralextended by the C* parameter has been correlated with crack propagation rates representing the evolution offatigue and creep/fatigue damage. This approach was proposed by Riedel (DCF-parameter) for isothermalfatigue conditions and has been successfully applied in several works.

The excellent accordance of the DCF-parameter with isothermal fatigue test data promises reasonable predictionresults for the application of this parameter to thermomechanical loading conditions. For this purpose, datafrom crack propagation experiments were collected from publications of the last two decades and analysed withregard to the effects of several test parameters. The influence of temperature, cycle frequency, loadingwaveform and cyclic stress ratio on crack growth rates were considered as relevant for the present study. Toaccount for different environments, crack length data from tests executed in sodium and vacuum environmentswere evaluated separately for the calculations.

In order to verify both the applicability of the fracture mechanics approach to TMF and the resulting predictivecapabilities of the method, the isothermal and thermomechanical fatigue test data generated on a type 304Laustenitic stainless steel were used.



TP 1963

MODELLING DEFORMATION AND DAMAGE OFHIGH TEMPERATURE STEELS UNDER

CREEP-FATIGUE LOADINGA. Klenk, J. Schemmel and K. Maile

MPA Stuttgart, Pfaffenwaldring 32, D-70569 Stuttgart, GermanyE-mail : [email protected]

(Received 29 September 2003 ; in revised form 30 August 2004)

ABSTRACTThe deformation and damage under uniaxial and multiaxial testing conditions has been characterised byconducting tests at 823 K and 873 K on a 10CrMoWVNbN steel. The material behaviour was modelled usingvisco-plastic material models and validated with the experimental data.



CREEP BEHAVIOUR OF SHORT FIBRE REINFORCEDQE22 MAGNESIUM ALLOY USING IMPRESSION

CREEP TEST

M.A. Azeem, A.K. Mondal and S. KumarDepartment of Metallurgy, Indian Institute of Science, Bangalore – 560 012, INDIA.



ABSTRACT

Creep properties of QE22 magnesium based alloy and composites reinforced with 20 volume percent of short-fibers - Maftech®, Saffil® or Supertech®, were evaluated using the impression creep test. In the impression creeptest, a load is applied with the help of a cylindrical tungsten carbide indenter of 1 mm diameter. This hasadvantages over conventional creep testing in terms of small specimen size requirement and simple machining.Depth of impression is recorded with time and steady state strain rate is obtained from the slope of thesecondary strain (depth of impression divided by indenter diameter) vs. time plot. The results are comparedwith the creep obtained from conventional creep performed in tension on the same materials earlier. Microstructuralexamination of the plastically deformed regions is carried out to explain creep behaviour of these composites.

T NOTETrans. Indian Inst. Met.


STRESS RUTPURE BEHAVIOR OF TRANSITIONJOINTS BETWEEN MODIFIED 9Cr-1Mo

STEEL AND 316 L(N) SS

S. Sundaresan, Shaju K. Albert*, M. Sireesha, J. Swaminathan** and M. KamarajDepartment of Metallurgical and Materials Engineering

Indian Institute of Technology Madras, Chennai 600 036, INDIA.* Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, INDIA.

** National Metallurgical Laboratory, Jamshedpur 831 007, INDIAE-mail : [email protected]

(Received 26 September 2003 ; in revised form 17 June 2004)

ABSTRACT

Stress rupture tests were performed on welded joints between modified 9Cr-1Mo steel and Alloy 800 as partof a trimetallic (Grade 91 - Alloy 800 - 316 L(N) SS transition joint. For comparison, tests were also conductedon direct bimetallic (Grade 91 - 316LN) joints. The results show that the performance of the Grade 91 - Alloy800 weldments is only a marginal improvement over the Grade 91 - 316LN joints. However, both these areconsiderably superior to joints involving the conventional 2.25Cr-1Mo steel as the ferritic component. Mostfailures occurred in the Grade 91 HAZ 1-2 mm from the weld interface. Metallographic characterization revealedfeatures that correlated well with the softening that occurred in this region during creep testing.

T NOTETrans. Indian Inst. Met.


FOREWORD

Creep, low cycle fatigue and creep-fatigue interaction are importantconsiderations that govern the design and performance assessment of components ina wide range of applications such as aerospace, thermal and nuclear power generation,and petrochemical and process industries. The need to raise operating efficiency ofnew plants requires development of new materials and processes based on soundunderstanding of the mechanisms of deformation and damage evolution in thematerial. The vast economic and environmental advantages that accrue from extendingthe life of existing plants demand that structural integrity analysis takes into accountadvances in non-destructive techniques for damage assessment, improvement indesign codes, and availability of long-term materials properties.

This special issue of Transactions of The Indian Institute of Metals consists ofthe papers presented in the 4th Conference on Creep, Fatigue and Creep-FatigueInteraction which was held at Indira Gandhi Centre for Atomic Research (IGCAR),Kalpakkam, India during October 8-10, 2003. The conference was inaugurated by Dr.Baldev Raj, Director, IGCAR. In his inaugural address, he pointed out that thisconference was being held at an appropriate time when the construction activityrelated to India’s first Prototype Fast Breeder Reactor (PFBR) has commenced atKalpakkam. In the design of PFBR structural components, creep, low cycle fatigueand creep-fatigue interaction play a very critical role. He highlighted the importanceof understanding the high temperature behaviour of welds since the integrity ofwelded components is largely determined by the behaviour of the weld joints.

16 invited papers and 45 contributed papers were presented over 10 technicalsessions. More than 150 delegates from India and abroad, drawn from academicinstitutes, national laboratories and private industries and public sector undertakingsattended the conference. The papers presented in the Conference covered a widespectrum, encompassing both basic research as well as engineering applications.There was emphasis on behaviour of welds, multiaxial loading, modelling, componentstesting, thermomechanical fatigue, superplasticity, condition monitoring and failureanalysis. All the papers have been subjected to rigorous peer review by leadingexperts.

The Editors wish to acknowledge Dr. E. Isaac Samuel and Mr. V. Ganesan fortheir assistance in bringing out this issue.

S.L. MannanDirector

Metallurgy and Materials Group, IGCAR

M.D. MathewApril 2005 HeadKalpakkam Creep Studies Section, IGCAR

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