Abstract
Spatially resolved measurement of creep deformation across weldments at high temperature cannot be achieved using standard extensometry approaches. In this investigation, a Digital Image Correlation (DIC) based system has been developed for long-term high-temperature creep strain measurement in order to characterise the material deformation behaviour of separate regions of a multi-pass weld. The optical system was sufficiently stable to allow a sequence of photographs to be taken suitable for DIC analysis of creep specimens tested at a temperature of 545 °C for over 2000 h. The images were analysed to produce local creep deformation curves from two cross-weld samples cut from contrasting regions of a multi-pass V-groove weld joining thick-section AISI Type 316H austenitic stainless steel. It is shown that for this weld, the root pass is the weakest region of the structure in creep, most likely due to the large number of thermal cycles it has experienced during the fabrication process. The DIC based measurement method offers improved spatial resolution over conventional methods and greatly reduces the amount of material required for creep characterisation of weldments.
Highlights
Pressure vessel and piping systems operating at high temperature, where material may deform in a time dependent manner, are vulnerable to creep damage accumulation leading to cavity nucleation and growth around welded regions
This paper presents an experimental technique for measuring the creep deformation response at millimetre length-scale spanning a Bcross-weld^ specimen during creep rupture testing
It has been demonstrated that a Digital Image Correlation (DIC) monitoring technique can provide measurements of local variations of elastic, plastic and creep strain in inhomogeneous materials at elevated temperatures
Summary
Pressure vessel and piping systems operating at high temperature, where material may deform in a time dependent manner, are vulnerable to creep damage accumulation leading to cavity nucleation and growth around welded regions. Resolved measurement of room temperature tensile properties in cross-weld samples has been applied in several laboratories using DIC [3,4,5,6,7,8] This method involves testing a tensile specimen containing the main part of the weldment within its gauge length, and mapping the full deformation field along the gauge section through computational tracking of contrasting surface features (speckle patterns) on a sequence of digital images of the specimen’s gauge section taken during the test. The external creep specimen failed in the parent material, and the internal specimen in the 45o inclined HAZ region This diagram marks the failure location of cross-weld tensile tests conducted at room temperature and 545 °C, details of which can be found elsewhere [10, 18]. The rupture occurred entirely in the HAZ material with the fracture face lying parallel to the fusion boundary
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