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research-article

Modelling and measuring residual stress in autofrettaged hollow cylinders through the Initial Strain Distribution Method

[+] Author and Article Information
Matteo Loffredo

Mechanical Engineer Baker Huges, a GE company Via F. Matteucci 2, Florence, Italy, 50127
matteo.loffredo@bhge.com

Andrea Bagattini

Senior Mechanical Engineer Baker Huges, a GE company Via F. Matteucci 2, Florence, Italy, 50127
andrea.bagattini@bhge.com

Bernardo D. Monelli

DICI, Università di Pisa Largo Lucio Lazzarino 2, Pisa, Italy, 56126
bernardo.disma.monelli@unipi.it

Marco Beghini

DICI, Università di Pisa Largo Lucio Lazzarino 2, Pisa, Italy, 56126
marco.beghini@unipi.it

1Corresponding author.

ASME doi:10.1115/1.4038227 History: Received August 11, 2017; Revised October 09, 2017

Abstract

The paper presents a method for modelling and measuring the residual stress field in axi-symmetric autofrettaged elements. The method is based on the assumption that an Initial Strain Distribution, originated by the plastic strain previously induced during the autofrettage process, is the source of residual stresses. The Initial Strain Distribution is the quantity to be evaluated and, after being determined, it can be used, by means of a dedicated Finite Element model, to evaluate the Residual Stress field in the component or in any part extracted from it. The Initial Strain Distribution is obtained by elaborating the relaxed strains produced by cutting the autofrettaged component in incremental steps. Properly formulated Influence Functions were developed in order to become the kernel of a set of Fredholm's integral equations whose unknown is the Initial Strain Distribution. After a general discussion of the Residual Stress induced by the autofrettage and the effect of the plastic properties of the material under process, the methods for obtaining the relaxed strains by a rational experimental set-up and the procedures for obtaining the Influence Functions are presented and discussed. The whole methodology is applied to evaluate the Residual Stress field in a hollow cylinder for which the autofrettage was modelled by a Finite Element simulation. The consistency of the method is verified and useful indications for the experimental activities were obtained.

Copyright (c) 2017 by ASME
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