PSI - Issue 7

Martin Hughes / Procedia Structural Integrity 7 (2017) 33–35 Martin Hughes/ Structural Integrity Procedia 00 (2017) 000–000

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turbine, but at higher temperatures. Advances in material constitutive modelling over the past 30 to 40 years have had their impact on hot section component analysis and lifing ability. Material anisotropy, aging processes and their effect on material deformation can introduce additional complexitiesfor these alloys. Developments in material testing and monitoring methods contribute to the development and validation of these material constitutive models. Test rig control and data analysis provide the means to generate large quantities of data on the material behaviour to feed the mathematical modellers. Advanced monitoring systems enable the detection of the onset of fatigue cracking and subsequent measurement of damage development. One of the areas of growing importance in component lifing is fatigue damage development and how this is modelled. Notched fatigue tests usually include a significant proportion stable fatigue crack growth. As noted above, data from such tests provides valuable input into the modelling process. Today’s computing capability and availability of new software enables finite element modelling to routinely include cyclic damage development using explicit crack modelling. When used in combination with advanced specimen testing methods, this contributes significantly to the development of a deeper understanding of the overall cyclic failure process in individual components. This understanding of the fatigue damage development process is also highly relevant to how we deal with interacting mechanisms. One such topic is the interaction of high cycle fatigue and low cycle fatigue. A turbine blade may experience dynamic behaviour due to resonance conditions, forced response and flutter. Large numbers of start-up and shut-down cycles also contribute damage in the form of low cycle fatigue or thermo-mechanical fatigue. Some blades may experience a combination of these mechanisms at the same location. Consequently, appropriate methods may be required to ensure blade integrity isn’t compromised. The subject of damage models and lifing leads onto the question of how materials change with long time durations at temperature, i.e. aging. Longer periods of useful service operation for some components and materials may lead to changes in the material microstructure and changes in properties over time. The collection of useful information on the effects of service exposure on remaining lifetime is an important aspect of component lifetime extension. New materials introduce new challenges and opportunities. The advent of additive manufacturing and the introduction of new parts into engines requires the development of reliable manufacturing processes, the characterisation of the mechanical behaviour over a range of conditions and product forms, component inspection methods and component validation testing. The power generation industry is continuing to evolve, most notably in the development and introduction of renewable energy sources. This impacts conventional power plant significantly through the need for more flexible operation. The world is moving towards a low carbon economy. A significant element of this is through the use of renewable energy sources for electrical energy generation. This change in combination with growing electrical demand has important consequences for the operation of all electrical generation equipment. The intermittent and variable nature of wind and solar energy leads to more variations in the energy grid and, hence, less grid stability. The variability and uncertainty drives the need for flexible back-up power plants capable of fast response to rapid changes in the grid. For conventional power plant, this means faster ramp-up, increased cyclic operation and increased operation at low part load. Gas turbine engines may be affected in a number of ways, including: (a) increased deterioration of seals and bearings, (b) increased operation under low load conditions giving rise to the risk of blade flutter and fatigue damage, (c) increasing amounts of fatigue damage due to more frequent starts, load fluctuations and also due to faster loading ramp-ups. The requirements for flexible operation have been recognised by the EU under the HORIZON 2020 programme. A project now running under this heading, FLEXTURBINE, addresses a number of important topics related to these issues. In the context of component lifetime management, the project brings together several major OEMs and leading academic organisations. The outcome of the work will contribute to an improved understanding of the relevant failure processes, more advanced predictive models enabling reduced conservatism in component lifetime predictions and ultimately improved and more cost effective component lifetime utilisation in existing power generation products. Acknowledgements Thanks to the European Commission for the support given to the FLEXTURBINE Project.