Process modelling of weld repair in aeroengine components

Salerno, Gervasio (2018) Process modelling of weld repair in aeroengine components. PhD thesis, University of Nottingham.

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Abstract

Weld repair is a specific application of fusion welding processes adopted to correct defects which arise during the manufacturing process of aeroengine components and, also, to repair damage in order to extend the operative life, if safe and correctly performed. The operation is carried out by removing the anomaly and re-filling the slot with a fusion welding process.

The thermal cycles induced by fusion welding processes produce undesirable residual stresses, which significantly affect the fatigue life of the component and, in some cases, they may give a larger contribution to the total stress field than the stresses caused by the service loads themselves.

Based on the sequentially coupled thermo-mechanical analysis, two numerical methodologies have been implemented to simulate the residual stress field induced by weld repair operations. Differently from models presented in the literature, the modelling approaches allow taking into account the pre-existing stress in the component subjected to the weld repair.

The experimental work to validate the numerical models involved a full thermal characterization of the welding apparatus used to produce the welds. Residual stress predictions were validated by means of neutron diffraction measurements using the most advanced diffractometer, ENGIN-X, available at ISIS neutron source at the Rutherford Appleton Laboratory.

The model can be used a priori, in the attempt of mitigating the effects of the repair operations on the final residual stress field. It can also be used a posteriori, with the aim of determining the stress state in the component, producing the input for the analysis of the fatigue life. In order to prove the applicability of the numerical methodology in the case of aeroengine components, the model was used to study a weld repair in a demonstrative case study. The effects of number and direction of passes were investigated in the weld repair of a laser beam weld in a stainless steel pipe.

It was concluded that the interaction between the pre-existing stress in a component and the stress induced by weld repair operations cannot be generalized and established a priori. Numerical models that simulate the process by neglecting the history of the components, ignore the contribution of the pre-existing stress to the final residual stress distribution. Predictions from such models approximate the global stress distribution in the component. The entire characterization of the residual stress field in a component that undergoes a weld repair operation can only be achieved by using models which take into account the pre-existing stress.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Bennett, C.J.
Sun, W.
Becker, A.A.
Keywords: Weld Modelling - Residual stress - Finite Element- Weld Repair - Thermal - Mechanical
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 52178
Depositing User: Salerno, Gervasio
Date Deposited: 07 Aug 2018 13:34
Last Modified: 07 May 2020 18:00
URI: http://eprints.nottingham.ac.uk/id/eprint/52178

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