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Stoyanov, Miroslav (2013) Investigation of small punch creep testing. PhD thesis, University of Nottingham.

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Abstract

Assessing the damage level of in-service components and obtaining material properties for welded structures exposed to creep is essential for the safe operating of power generation industry. Standard creep testing techniques require relatively large volumes of material for the machining of testing samples. For that reason they are not usually suitable for obtaining creep properties of in-service structures. It has been found that significant amount of the failures in welds exposed to elevated temperatures occur in an area formed due to the complex thermal and cooling cycles during the welding process. Because of this a different approach is needed for the derivation of creep properties from small amounts of metal. The small punch creep testing method is considered to be a, potentially, powerful technique for obtaining creep and creep rupture properties of in-service welded components. However, relating small punch creep test data to the corresponding uniaxial creep data has not proved to be simple and a straightforward approach is required.

The small punch creep testing method is highly complex and involves interactions between a number of non-linear processes. The deformed shapes that are produced from such tests are related to the punch and specimen dimensions and to the elastic, plastic, and creep behaviour of the test material, under contact and large deformation conditions, at elevated temperature. Owing to its complex nature, it is difficult to interpret small punch creep test data in relation to the corresponding uniaxial creep behaviour of the material. One of the aims of this research is to identify the important characteristics of the creep deformation results from 'localized' deformations and from the 'overall' deformation of the specimen. For this purpose, the results of approximate analytical methods, experimental tests and detailed finite element analyses, of small punch tests, have been obtained. It is shown that the regions of the uniaxial creep test curves dominated by primary, secondary and tertiary creep are not those that are immediately apparent from the displacement versus time records produced during a small punch test. On the basis of the interpretation of the finite element results presented, a method based on the reference stress approach is proposed for interpreting the result of small punch experimental test data and relating it to the corresponding uniaxial creep data. Another aim of this study is to investigate the effect of friction between the sample and the punch as well as the effects of the basic dimensions, on the small punch creep testing data.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Hyde, T.H. Sun, W.
Keywords:	Creep testing techniques, Welded components, Creep in metals
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Faculties/Schools:	UK Campuses > Faculty of Engineering
Item ID:	28105
Depositing User:	Blore, Mrs Kathryn
Date Deposited:	16 Jan 2015 09:10
Last Modified:	16 Oct 2017 08:38
URI:	https://eprints.nottingham.ac.uk/id/eprint/28105

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