ORCID Profile
0000-0003-4384-111X
Current Organisation
Western University
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Publisher: Elsevier BV
Date: 11-2016
Publisher: Elsevier BV
Date: 09-2018
Publisher: Trans Tech Publications, Ltd.
Date: 02-2014
DOI: 10.4028/WWW.SCIENTIFIC.NET/MSF.777.188
Abstract: Residual stresses in welded joints must be quantified in order to carry out structural integrity assessments on critical nuclear components. This usually requires the application of finite element models for components with wall thicknesses exceeding 50 mm. In ferritic steels, the development of residual stresses is made more complex by the strains associated with the solid-state phase transformations that occur during heating and cooling. Finite element models often do not account for factors that contribute to anisotropy in the transformation strains, such as Greenwood-Johnson plasticity and variant selection. In this work, we search for evidence that might reveal which mechanism (s) contributes to this anisotropy. Coupons of SA508 steel were subjected to simulated welding thermal cycles, with and without external loading, and in-situ X-ray diffraction was used to track changes in crystal structure. The results were checked for evidence of plastic deformation in austenite and variant selection in its daughter phases.
Publisher: American Society of Mechanical Engineers
Date: 14-07-2013
Abstract: Residual stress mitigation is a key strategy in the design and manufacture of nuclear power plant components for the prevention of component failure and the extension of power plant lifetimes. Repair welds comprise significant non-steady-state features that contribute to complex residual stress profiles that must be understood, modeled and minimized to ensure the efficiency of the repair. This is of particular importance given that in-situ measurement, and post weld heat treatment of residual stress profiles in repair welds is often impractical. Previous work indicates that the highest stresses accumulate at the ends of the repair where the weld pass stops overlap. Here we present a series of neutron diffraction measurements on two three-pass slot welds with different end slope angles to determine the effect of staggering the weld pass stop locations. It is shown that significant reductions in peak stresses can be made by decreasing the steepness of the end of the slot to stagger the weld stop locations for different beads. Additionally, these are the first reported measurements of residual stress in the new SA508 grade 4N steel which has been designed for deployment in future advanced PWR systems.
Publisher: American Society of Mechanical Engineers
Date: 20-07-2014
Abstract: The development of residual stresses in the Heat Affected Zone (HAZ) during welding of a ferritic steel can be critical to weld structural integrity. The Prior Austenite Grain Size (PAGS), the thermo-mechanical properties of the phases that develop during phase transformation, and the transformation strains are some of the key parameters that can alter residual stress development during welding. Understanding the trend in variation of these parameters is crucial for Finite Element (FE) modelling of residual stress development in weld. In this study, the effect of PAGS on the phase transformation in SA508 grade 4 was determined. For this purpose, s les were heated up to 900, 1050, 1250, and 1350°C and held for various time intervals to produce different austenite grain sizes. The measured austenite grain sizes were then used to fit parameters in an exponential equation implemented in an FE User MATerial subroutine (UMAT) for the modelling of welds. With performing various free dilatometry experiments, it is shown that the only phase that austenite transforms to upon cooling is martensite. In addition, the mechanical properties of as-received material, austenite, and martensite as a function of temperature were measured. Also, various uni-axial loads were applied during cooling cycles, and before the onset of phase transformations, to measure the evolution of transformation strain to generate an empirical formulation for numerical modelling.
Publisher: Informa UK Limited
Date: 02-02-2016
Publisher: Trans Tech Publications, Ltd.
Date: 23-05-2014
DOI: 10.4028/WWW.SCIENTIFIC.NET/MSF.783-786.2123
Abstract: Considering the significant role that residual stresses play in determining the lifetime-service of materials, it is mandatory to have a good understanding of and a means of predicting those that develop during welding processes. For this purpose, a User MATerial subroutine (UMAT) is developed to study the effects of various parameters that influence solid state phase transformations and residual stress evolution during welding of SA508 ferritic steel. The temperature dependent elastic and kinematic hardening parameters for each of the in idual phases that can potentially develop during cooling from elevated temperatures are measured and are used for calculating stress development during low (75 mm/min) and high (300 mm/min) speed gas-tungsten arc welding (GTAW) on SA508 grade 3. These two speeds are selected to cover a wide range of cooling rates in the heat affected zone so that different phase proportions would be present. The results of the numerical simulations for residual stresses are compared against those measured by neutron diffraction. It is shown here that a low speed weld results in bainite formation whereas a high speed weld results in bainitic as well as subsequent martensitic phase transformations where each welding rate results in different residual stress development.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Hamidreza Abdolvand.