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Title: Identification of plastic strain using thermoelastic stress analysis
Author: Howell, Geoffrey Peter
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2017
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Identification of regions containing plastic strain arising from the welding process is performed through the application of thermoelastic stress analysis (TSA) and finite element (FE) modelling. An approach is developed that removes the requirement to have a physical reference specimen for the component studied by developing a 'synthetic reference bitmap' using finite element analysis. The regions containing plastic strain can be identified with TSA by collecting data from a 'reference' plastic strain free specimen from the TSA data and creating a resultant bitmap. Here, a synthetic bitmap is developed that mimics the thermoelastic response of a physical reference specimen. The approach is validated against physical reference specimens of different geometries and materials (AL2024 and 316L stainless steel) and is shown to accurately model the thermoelastic response. The newly developed synthetic bit map approach is applied to specimens containing welds and it is shown that the regions that contain plastic strain in the heat affected zone (HAZ) of a double bead welded 316L stainless steel specimen can be revealed. The predicted changes in thermoelastic response are compared to plastic strain predictions generated by thermomechanical modelling of the welded specimen and the distribution of plastic strain found by the TSA matches that given by the model. The relationship between the change in thermoelastic response and plastic strain has been investigated and the results suggest there is a change in the thermoelastic response as a result of plastic straining. However, uncertainties in the data resulting from detector noise and other errors mean that further development of the experiments and the equipment is required to provide a conclusive and quantitative relationship. It has also been demonstrated that TSA can be used outside of the laboratory in onsite trials in two coal fired power stations. Thermoelastic data was successfully recorded from pipe welds in-situ. To achieve this a new means of loading the pipes was devised based on vibration excitation, and the difficulties of performing surface measurements on heavily corroded pipes were overcome. The results from the onsite tests show that TSA can be used as an in-situ assessment technique and that is no longer restricted to being a laboratory based technique.
Supervisor: Barton, Janice Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available