Browsing by Author "Rajkumar, Roy"

Now showing 1 - 4 of 4
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    Data mining and knowledge reuse for the initial systems design and manufacturing: Aero-engine service risk drivers
    (Elsevier, 2013-09-27) Morar, Nicolau; Rajkumar, Roy; Mehnen, Jorn; Redding, Louis E.; Harrison, Andrew
    Service providers of civil aero engines are typically confronted with a high cost of maintenance, replacement and refurbishment of the service damaged components. In such context, service experience becomes a key issue for determining the service risk drivers for operational disruptions and maintenance burden. This paper presents an industrial case study to produce new knowledge on the relationships between degradation and component design to manufacture. The study applied semantic data mining as a methodology for an efficient and the consistent data capture, representation, and analysis. The paper aims at identifying the service risk drivers based on service experience and event data. The analysis shows that the 3 top mechanisms accounting for 32% of the mechanism references have a strong Pareto effect. The paper concludes with missing information links and future research directions.
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    Expert Judgement in Cost Estimating: Modelling the Reasoning Process.
    (Sage Publications, 2001-01-01T00:00:00Z) Rush, Christopher; Rajkumar, Roy
    Expert Judgement (EJ) is used extensively during the generation of cost estimates. Cost estimators have to make numerous assumptions and judgements about what they think a new product will cost. However, the use of EJ is often frowned upon, not well accepted or understood by non-cost estimators within a concurrent engineering environment. Computerised cost models, in many ways, have reduced the need for EJ but by no means have they, or can they, replace it. The cost estimates produced from both algorithmic and non-algorithmic cost models can be widely inaccurate; and, as the work of this paper highlights, require extensive use of judgement in order to produce a meaningful result. Very little research tackles the issues of capturing and integrating EJ and rationale into the cost estimating process. Therefore, this paper presents a case with respect to the wide use of EJ within cost estimating. EJ is examined in terms of what thought processes are used when a judgement is made. This paper highlights that most judgements are based on the results of referring to historical costs data, and then adjusting up or down accordingly in order to predict the cost of a new project. This is often referred to as analogy. The reasoning processes of EJ are identified and an inference structure has been developed, which represents an abstraction of the reasoning steps used by an expert as they generate an estimate. This model has been validated through both literature and interviews with cost estimating experts across various industry sectors. Furthermore, the key inferences of the experts are identified. These inferences are considered as those where many of the assumptions and expert judgements are made. The thesis of this paper is that through modelling the reasoning processes of EJ, it becomes possible to capture, structure, and integrate EJ and rationale into the cost estimating process as estimates are being generated. Consequently, the rationale capture will both improve the understanding of estimates throughout a product life cycle, and improve management decisions based upon these cost estimates.
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    Investigating dependencies between laser drilling process parameters, recast layer thickness and corrosion-fatigue life for turbine vane cooling film holes.
    (Cranfield University, 2017-07) Morar, Nicolau Iralal; Rajkumar, Roy; Mehnen, Jorn
    Manufacturers of aeroengines are currently being confronted with service related degradation process such as fatigue, thermal fatigue, creep, hot corrosion, wear, corrosion-fatigue and fretting. These degradation modes are causing engine operational disruption, unscheduled maintenance burden, and costly components replacement. Degradation of components and systems is a continuous process that results in loss of function and performance when exposed to fluctuating loads and an adverse operating environment. Understanding of factors and drivers influencing premature degradation and early damage on critical aeroengine mechanical components is needed. As such, the purpose of the present research was to develop an understanding of the impact of manufacturing process and parameters used on the corrosion-fatigue life of an aeroengine turbine vane based on the past degradation information. Based on the service experience data, turbine vane cooling film holes shown to be life limiting feature, which are exposed to high cyclic stresses and temperatures in harsh environment. Therefore, understanding of fatigue life degradation of turbine vane cooling holes and impact of drilling method and environment provides an insight and knowledge for the changes in effusion cooling holes design and/or optimisation of drilling parameters. The research has been able to establish the effects of key laser drilling process parameters, such as the influence of peak power, pulse frequency and trepan speed on the recast layer thickness and surface cracks formation in a Ni-base CMSX-4 superalloy angled cooling holes. The results indicate that trepan speed and peak power had significant influence on the thickness of the recast layer and cracks formation around the sidewalls of cooling holes, both statistically and physically. The metallography examinations show that the recast layer has an altered morphology. Furthermore, elemental analysis and nano indentations measurements on the recast layer show that there is change in alloy chemistry and mechanical properties, respectively. Therefore, less resistant to fatigue crack initiation and corrosion than base alloy. The high temperature corrosion-fatigue of critical components and features such as laser drilled cooling holes has received very little attention. The occurrence of high temperature corrosion is associated with an accelerated oxidation and sulphidation assisted cracking, driven by salt and sulphur concentration. In high temperature corrosion, formation of thick oxide scale and micro pits in the recast and alloy surface leads to potential early onset of fatigue crack initiation and accelerated crack advance on the pre-existing cracks. Therefore, impacting the life performance of laser drilled components. As such, research into interaction between laser drilling, recast layer thicknesses and high temperature corrosion-fatigue life has been undertaken. The representative laser drilled cooling holes specimens were tested in laboratory with different range of recast layer thickness and representative of service conditions. The corrosion-fatigue in CMSX-4 bare specimens found to give life debit between 20 to 25% from the air fatigue data. Corrosion-fatigue tests result show that laser drilled fatigue specimens provide a fatigue life debit between 30 to 40% from un-drilled specimens tested under similar conditions. The recast layer thickness had significant influence of the corrosion-fatigue strength degradation of cooling holes, particularly in crack nucleation. The role of environment was also significantly in both crack nucleation and short crack growth. The research work developed in this thesis contributes to the understanding of the role of laser drilling process parameters and recast layer thickness interaction and their effects on the corrosion-fatigue life and surface crack initiation in cooling holes, and how empirical methods can be used to extend the lives of turbine vane cooling film holes.
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    Pulse thermography-based ageing assessment of thin thermal barrier coatings.
    (Cranfield University, 2019-06) Tinsley, Lawrence; Zhao, Yifan; Rajkumar, Roy; Mehnen, Jorn
    With the motivation to drive gas turbines at increasing power and efficiency, the increase of combustion temperatures is highly desirable, while turbine temperatures are met by material limitations where the temperatures readily exceed the melting point of the metals used to make the components. In response to this, engine manufacturers implement thermal control systems, from air cooling of the component, to Thermal Barrier Coatings (TBCs) applied on the component surfaces, reflecting radiant heat energy and providing an insulating layer. These materials reduce the temperature experienced by the component materials, enabling higher operational temperatures; while the metallic bond coat in between also protects against oxidation and corrosion attack. With TBCs playing such a crucial role in the standard operation of gas turbines at the edge of its performance capability, standing between materials performing one of the most stringent engineering roles ever designed, and the hot gases capable of melting them; the durability of the TBC to resist its own degradation and their ensuing material life are vital. The assessment of TBC health and its Remaining Useful Life (RUL) are of key interest in the maintenance of aero engine components. This thesis presents a review of Non-Destructive Testing (NDT) methods utilised in the inspection of TBCs, proceeding to evaluate the use of pulsed-active flash thermography NDT for ageing assessment of thin TBCs undergoing cyclic oxidation ageing, selected for study to adapt the method to the more challenging context at the cutting edge of gas turbine performance. The coatings were inspected with and without emissivity-improving soot coating to evaluate a realistic inspection scenario – where contamination may not be justifiable – with ideal inspections performed in parallel. In order to address the challenge of capturing a fast thermal event through a thin TBC, an inspection framework was developed to optimise the data capture and analysis parameters. Through-depth diffusivity has been measured during oxidation ageing of six 150µm thick TBCs deposited via Electron Beam Physical Vapour Deposition (EB-PVD), showing a repeatable trend with distinct features, which can be exploited for ageing characterisation, with automation of thermographic NDT of TBC parts demonstrating the potential for rapid implementation of the technique. The research provides through-life captures of each of the TBC samples uniquely coupled with parallel captures in the non-ideal inspection condition without application of an emissivity improving soot coating, simulating a real-world inspection scenario in which a wide area un-treated surface inspection is desired. Additionally, a novel inspection framework has been developed for establishing the multiple coupled parameters required to tackle the complexities introduced when applying optical flash for thermography of thin EB-PVD TBCs.