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A numerical study of the effects of shot peening on the short crack growth behaviour in notched geometries under bending fatigue tests

A numerical study of the effects of shot peening on the short crack growth behaviour in notched geometries under bending fatigue tests
A numerical study of the effects of shot peening on the short crack growth behaviour in notched geometries under bending fatigue tests
The current paper presents a numerical analysis of the effects of shot peening on short crack growth in a low pressure (LP) steam turbine material, FV448. The fatigue behaviour of this material has been experimentally evaluated using a U-notched specimen (representing the fir tree root geometry of the turbine blade) under 3-point bend tests. Two different shot peening intensities were considered in this study: an industrially applied shot peening process and a less intense shot peening process.

In the modelling work, a 2-D finite element (FE) model with static short cracks has been developed, incorporating both compressive residual stress and strain hardening distribution effects caused by shot peening. Both linear-elastic (LEFM) and elasto-plastic (EPFM) fracture mechanics were used to characterise the crack driving force in the un-peened and shot-peened conditions, taking into account the effects of stress redistribution caused by residual stress relaxation and crack opening. The stress intensity factor used in the LEFM approach was calculated using the weight function method, and the equivalent stress intensity factor used in the EPFM approach was calculated from the J-integral, which was evaluated using the cracked FE model. These results could explain the mechanism of (experimentally observed) retardation of crack growth through the shot-peening-affected layer and also quantified this influence on fatigue life. The relative contributions of compressive residual stresses and strain hardening were assessed by investigating them separately. The sub-surface compressive residual stress distribution produced by shot peening could effectively reduce crack propagation but the strain hardening distribution, in contrast, can accelerate it. However, strain hardening is expected to hinder the crack initiation process by restricting the plastic deformation during cyclic loading. Predictions of the fatigue life of the shot-peened notched specimens were made based on this numerical analysis. Acceptable results were obtained using both the LEFM and EPFM approaches and the difference between them is discussed.
99-111
You, Chao
1970d34b-ab33-4098-9363-2df30f36dda1
Achintha, Mithila
8163c322-de6d-4791-bc31-ba054cc0e07d
He, Binyan
0c154394-797d-42ad-b812-3fbbaea0238a
Reed, Philippa
8b79d87f-3288-4167-bcfc-c1de4b93ce17
You, Chao
1970d34b-ab33-4098-9363-2df30f36dda1
Achintha, Mithila
8163c322-de6d-4791-bc31-ba054cc0e07d
He, Binyan
0c154394-797d-42ad-b812-3fbbaea0238a
Reed, Philippa
8b79d87f-3288-4167-bcfc-c1de4b93ce17

You, Chao, Achintha, Mithila, He, Binyan and Reed, Philippa (2017) A numerical study of the effects of shot peening on the short crack growth behaviour in notched geometries under bending fatigue tests. International Journal of Fatigue, 103, 99-111. (doi:10.1016/j.ijfatigue.2017.05.023).

Record type: Article

Abstract

The current paper presents a numerical analysis of the effects of shot peening on short crack growth in a low pressure (LP) steam turbine material, FV448. The fatigue behaviour of this material has been experimentally evaluated using a U-notched specimen (representing the fir tree root geometry of the turbine blade) under 3-point bend tests. Two different shot peening intensities were considered in this study: an industrially applied shot peening process and a less intense shot peening process.

In the modelling work, a 2-D finite element (FE) model with static short cracks has been developed, incorporating both compressive residual stress and strain hardening distribution effects caused by shot peening. Both linear-elastic (LEFM) and elasto-plastic (EPFM) fracture mechanics were used to characterise the crack driving force in the un-peened and shot-peened conditions, taking into account the effects of stress redistribution caused by residual stress relaxation and crack opening. The stress intensity factor used in the LEFM approach was calculated using the weight function method, and the equivalent stress intensity factor used in the EPFM approach was calculated from the J-integral, which was evaluated using the cracked FE model. These results could explain the mechanism of (experimentally observed) retardation of crack growth through the shot-peening-affected layer and also quantified this influence on fatigue life. The relative contributions of compressive residual stresses and strain hardening were assessed by investigating them separately. The sub-surface compressive residual stress distribution produced by shot peening could effectively reduce crack propagation but the strain hardening distribution, in contrast, can accelerate it. However, strain hardening is expected to hinder the crack initiation process by restricting the plastic deformation during cyclic loading. Predictions of the fatigue life of the shot-peened notched specimens were made based on this numerical analysis. Acceptable results were obtained using both the LEFM and EPFM approaches and the difference between them is discussed.

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Accepted/In Press date: 24 May 2017
e-pub ahead of print date: 26 May 2017
Published date: October 2017
Organisations: Engineering Mats & Surface Engineerg Gp, Infrastructure Group, Engineering Science Unit, Faculty of Engineering and the Environment, Southampton Marine & Maritime Institute, Education Hub

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Local EPrints ID: 410076
URI: http://eprints.soton.ac.uk/id/eprint/410076
PURE UUID: f0935b42-7933-41aa-8c3b-08914b49c4df
ORCID for Chao You: ORCID iD orcid.org/0000-0003-0118-0771
ORCID for Mithila Achintha: ORCID iD orcid.org/0000-0002-1732-3514
ORCID for Philippa Reed: ORCID iD orcid.org/0000-0002-2258-0347

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Date deposited: 03 Jun 2017 04:02
Last modified: 07 Oct 2020 05:49

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Author: Chao You ORCID iD
Author: Binyan He
Author: Philippa Reed ORCID iD

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