E-Thesis 633 views
Life Assessment based on the Small Punch Test and the Wilshire Equations / THOMAS WILLIAMS
Swansea University Author: THOMAS WILLIAMS
DOI (Published version): 10.23889/SUthesis.63768
Abstract
Uniaxial creep data plays a key role in predicting the life cycle of different alloys and parts present in power generation and aero engines, such as RR1000 which is used in turbine disc components. Modern studies have found success in using the Wilshire equations as a creep lifing method, making it...
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Swansea, Wales, UK
2023
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| Institution: | Swansea University |
| Degree level: | Doctoral |
| Degree name: | Ph.D |
| Supervisor: | Evans, Mark. and Williams, S. J. |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa63768 |
| Abstract: |
Uniaxial creep data plays a key role in predicting the life cycle of different alloys and parts present in power generation and aero engines, such as RR1000 which is used in turbine disc components. Modern studies have found success in using the Wilshire equations as a creep lifing method, making it possible to obtain long term life predictions, up to 100,000 hours, from short accelerated uniaxial tests typically lasting up to 5000 hours. Improvements in extrapolative ability can be achieved by uniaxial testing, at accelerated temperatures but operational stresses (or visa versa), utilising specimens cut from components that have not yet failed but have been in service for long periods of time. The shorter residual lives then require less extrapolation with respect to stress or temperature - but creating such test specimens leads to component destruction which is very costly. To further build on the idea behind abridged testing, the small punch test has been developed to produce data from service parts in power plants without compromising the ongoing structural strength of the component. This is achieved by obtaining thin slices of material from component and then applying a constant load - via a punch – to a machined disc. However, there has been little application of the Wilshire technique to either abridged uniaxial data or to virgin or abridged punch test data. A complication with the small punch test, however, is that the recorded failure time is dependant not just on temperature and load (as in a uniaxial test) but also on the geometries of the specimen and the test rig (punch radian, disc diameter, disc thickness, clamp material etc). Clearly there is a need to minimise the impact of these variables on the test result (and so maximise the sensitivity to any pre-existing damage). To date there has been minimal research on what these geometries should be and how different clamp materials can effect residual stress present in the discs as a result of differing coefficients of expansions – being confined mainly to numerical modelling. Furthermore, the results of the Small Punch creep test are shown by time/displacement curves which while appearing comparable to that of conventional uniaxial creep data, in reality the creep mechanism present in each test technique are quite unique. Therefore data obtained from Small Punch Creep (SPC) tests cannot be used to find or to compare to the values of conventional creep parameters, hence the need for a form of correlation to bridge the gap between the two test types. |
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| Item Description: |
A selection of third party content is redacted or is partially redacted from this thesis due to copyright restrictions. |
| Keywords: |
Creep, Small Punch Creep, Creep Lifing, Nickel Superalloy, Wilshire Equation |
| College: |
Faculty of Science and Engineering |