Significance of Creep-Fatigue Interactions in Strctural Integrity Assessment

Creep-fatigue interaction is a special phenomena that have a detrimental effect on the performance of metal parts of components operating at elevated temperatures. This paper deals with the simultaneous interactions between creep and fatigue. The effect of hold time, hold position, temperature and creep ductility on creep-fatigue interaction life and damage modes of several high temperature alloys are presented in detail. The inherent deficiencies and potentially serious consequences of over-or under- design by using the classical Linear Time and Cycle-Fraction rule for predicting structural durability under high temperature creep-fatigue conditions are presented. The potential of a strain based approach in accurately predicting creep-fatigue life for ensuring structural integrity is outlined

Baldev Raj (1947-2018)

Baldev Raj (BR), a distinguished scientist and technologist of India passed away on 6 January 2018 at Pune while he was on official duty. BR was born on 9 April 1947 in Jammu. He lost his father at a very early age. In 1969, he graduated with a gold medal in the engineering discipline (metallurgy) from Ravishankar University, Raipur. In 1970, he joined the 14th batch of Bhabha Atomic Research Centre (BARC) Training School in Trombay. After successful completion of training, he joined BARC as a Scientific Officer. BR obtained his Ph D from the Indian Institute of Science (IISc), Bangalore in 1990 in the Faculty of Engineering, in a multidisciplinary area encompassing collaboration between the Department of Metallurgy and Aerospace Engineering

Principles of Contract Design

Economic contract theory postulates two obstacles to complete contracts: high transaction costs and high enforcement (or verification) costs. The literature has proposed how parties might solve these problems under a stylized litigation system, but it does not address the question of how parties design contracts under the existing adversarial system, that relies on the parties to establish relevant facts indirectly by the use of evidentiary proxies. We advance a theory of contract design in a world of costly litigation. We examine the efficiency of investment at the front-end and back-end of the contracting process, where we focus on litigation as the back-end stage. In deciding whether to express their obligations in specific or vague terms, contracting parties implicitly choose their allocation of costs between the front- and back-end. When the parties agree to vague terms (or standards), such as best efforts or commercial reasonableness, they delegate to the back-end the task of selecting proxies: e.g., the court selects market indicators that serve as benchmarks for performance. When the parties agree to specific terms(or rules), they invest more at the front-end to specify proxies in their contract and thereby leaving a smaller task for the enforcing court. In this Article, we explore the choice between rules and standards in terms of this tradeoff, and offer an explanation for why contracts in practice have a mix of vague and specific provisions. We then suggest that parties can achieve further contracting gains by varying procedural rules governing the prospective enforcement of their disputes. We illustrate by examining provisions in commercial contracts that allocate burdens and standards of proof. If the parties can improve the cost-effectiveness of litigation in this manner, they can reduce back-end costs. They thereby create opportunities to further lower contracting costs (or to improve the incentive gains from contracting) by shifting more investment to the back-end by increasing their use of vague terms. Vague terms have fallen into disfavor with contract theorists and this Article offers a justification for why they are nevertheless commonplace in commercial practice. Our analysis highlights the general and valuable lesson that the anticipated path of litigation is relevant to contract design

Effect of Processing Route on Strain Controlled Low Cycle Fatigue Behavior of Polycrystalline NiAl

The present investigation examines the effects of manufacturing process on the total axial strain controlled low cycle fatigue behavior of polycrystalline NiAl at 1000 K, a temperature above the monotonic Brittle-to-Ductile Transition Temperature (BDTT). The nickel aluminide samples were produced by three different processing routes: hot isostatic pressing of pre- alloyed powders, extrusion of prealloyed powders, and extrusion of vacuum induction melted ingots. The LCF behavior of the cast plus extruded material was also determined at room temperature (below the BD77) for comparison to the high temperature data. The cyclic stress response, cyclic stress-strain behavior, and strain-life relationships were influenced by the alloy preparation technique and the testing temperature. Detailed characterization of the LCF tested samples was conducted by optical and electron microscopy to determine the variations in fracture and deformation modes and to determine any microstructural changes that occurred during LCF testing. The dependence of LCF properties on processing route was rationalized on the basis of starting microstructure, brittle-to-ductile transition temperature, deformation induced changes in the basic microstructure, deformation substructure, and synergistic interaction between the damage modes

Temperature and Strain-Rate Effects on Low-Cycle Fatigue Behavior of Alloy 800H

The effects of strain rate (4 x 10(exp -6) to 4 x 10(exp -3)/s) and temperature on the Low-Cycle Fatigue (LCF) behavior of alloy 800H have been evaluated in the range 750 C to 950 C. Total axial strain controlled LCF tests were conducted in air at a strain amplitude of +/- 0.30 pct. LCF life decreased with decreasing strain rate and increasing temperature. The cyclic stress response behavior showed a marked variation with temperature and strain rate. The time- and temperature- dependent processes which influence the cyclic stress response and life have been identified and their relative importance assessed. Dynamic strain aging, time-dependent deformation, precipitation of parallel platelets of M(23)C6 on grain boundaries and incoherent ledges of twins, and oxidation were found to operate depending on the test conditions. The largest effect on life was shown by oxidation processes

Технологические решения для строительства разведочной вертикальной скважины глубиной 2620 метров на нефтяном месторождении (Красноярский край)

Технологический проект на сооружение разведочной вертикальной скважины глубиной 2620 метров на нефтяном месторождении (Красноярский край). В проекте закладываются меры по предотвращению осложнений, а также мероприятия по отбору керна для подсчета запасов, оценки пригодности месторождения к освоению, а также определения геологического строения и составления проектов разработки в целях определения технологии бурения эксплуатационных скважин.Technological project for the construction of an exploratory vertical well with a depth of 2620 meters at an oil field (Krasnoyarsk Territory). The project includes measures to prevent complications, as well as measures to select the core for calculating reserves, assessing the suitability of the field for development, as well as determining the geological structure and drawing up development projects in order to determine the technology for drilling production wells

Temperature Dependent Cyclic Deformation Mechanisms in Haynes 188 Superalloy

The cyclic deformation behavior of a wrought cobalt-base superalloy, Haynes 188, has been investigated over a range of temperatures between 25 and 1000 C under isothermal and in-phase thermomechanical fatigue (TMF) conditions. Constant mechanical strain rates (epsilon-dot) of 10(exp -3)/s and 10(exp -4)/s were examined with a fully reversed strain range of 0.8%. Particular attention was given to the effects of dynamic strain aging (DSA) on the stress-strain response and low cycle fatigue life. A correlation between cyclic deformation behavior and microstructural substructure was made through detailed transmission electron microscopy. Although DSA was found to occur over a wide temperature range between approximately 300 and 750 C the microstructural characteristics and the deformation mechanisms responsible for DSA varied considerably and were dependent upon temperature. In general, the operation of DSA processes led to a maximum of the cyclic stress amplitude at 650 C and was accompanied by pronounced planar slip, relatively high dislocation density, and the generation of stacking faults. DSA was evidenced through a combination of phenomena, including serrated yielding, an inverse dependence of the maximum cyclic hardening with epsilon-dot, and an instantaneous inverse epsilon-dot sensitivity verified by specialized epsilon-dot -change tests. The TMF cyclic hardening behavior of the alloy appeared to be dictated by the substructural changes occuring at the maximum temperature in the TMF cycle

High speed nanoindentation aided correlative study between local mechanical properties and chemical segregation in equiatomic MoNb and MoNbTi alloys

Chemical segregation at various length scales directly impacts the material behaviour during service, wherein homogeneous response is mostly desired. Our recent efforts on development of equiatomic MoNb and MoNbTi alloys have indicated propensity for chemical segregation that in turn influences the mechanical properties. In this regard, recent advances in high speed nanoindentation mapping have demonstrated the ability to accurately measure mechanical properties at the micrometer length scale. In this work, we extend this capability to establish a quantitative link between the local chemistry measured via energy dispersive spectroscopy (EDS) and nanoindentation mapping for as-cast and heat treated equiatomic MoNb and MoNbTi alloys. Excellent correlation between chemical composition and hardness is observed. This work provides a simple framework to study the effect of chemical segregation on the local mechanical properties of multi-principal element alloys, which can be gainfully used to tailor the microstructure and properties of these alloys

Building on knowledge base of sodium cooled fast spectrum reactors to develop materials technology for fusion reactors

The alloys 316L(N) and Mod. 9Cr-1Mo steel are the major structural materials for fabrication of structural components in sodium cooled fast reactors (SFRs). Various factors influencing the mechanical behaviour of these alloys and different modes of deformation and failure in SFR systems, their analysis and the simulated tests performed on components for assessment of structural integrity and the applicability of RCC-MR code for the design and validation of components are highlighted. The procedures followed for optimal design of die and punch for the near net shape forming of petals of main vessel of 500 MWe prototype fast breeder reactor (PFBR); the safe temperature and strain rate domains established using dynamic materials model for forming of 316L(N) and 9Cr-1Mo steels components by various industrial processes are illustrated. Weldability problems associated with 316L(N) and Mo. 9Cr-1Mo are briefly discussed. The utilization of artificial neural network models for prediction of creep rupture life and delta-ferrite in austenitic stainless steel welds is described. The usage of non-destructive examination techniques in characterization of deformation, fracture and various microstructural features in SFR materials is briefly discussed. Most of the experience gained on SFR systems could be utilized in developing science and technology for fusion reactors. Summary of the current status of knowledge on various aspects of fission and fusion systems with emphasis on cross fertilization of research is presented

Design, development and characterization of fast breeder reactor materials and components

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