Residual Stress Measurement in EP 823 Using Non-Destructive Evaluation Techniques
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Recent approaches to residual stress measurements in transmutation target materials using Non-Destructive methods have been given due importance. One such target material is Alloy EP 823. Non-Destructive techniques such as Positron Annihilation Spectroscopy (PAS) and Neutron-Diffraction are primarily used to evaluate residual stresses in engineering materials. The data generated will be compared to that obtained by a destructive technique such as Ring-core method. Prior to any measurement, alloy EP-823 will be heat treated to produce fully tempered martensitic microstructure. The stress analyses are being carried out on three types of specimens namely welded, bent (three point bend) and cold deformation.
The purpose of using the PAS technique is to develop a highly penetrating sensitive probe for stress analysis in thick materials based on the γ-ray induced positron annihilation spectroscopy. In this method Positrons created through pair production technique thermalize and annihilate with the material electrons emitting annihilation radiations. These radiations are then analyzed to find the various parameters that corresponds to the residual stresses induced.
Neutron diffraction is based on measuring the spacing between two atomic planes of a crystal lattice. When a neutron beam of known wavelength is impinged upon a material , neutrons are diffracted at an angle the depends on the spacing. With accurate measurement of the diffraction angle, the spacing between the lattice planes can be calculated to determine the residual stresses.
The ring core method is a destructive technique used to evaluate the residual stress as a function of depth in materials. A special three-element strain gage rosette is installed on the test specimen at the point where residual stresses are to be determined. A precision milling guide is attached to the test part and accurately centered over a drilling target on the rosette. After zero-balancing the gage circuits, a small, shallow hole is drilled through the center of the rosette. Readings are made of the relaxed strains, corresponding to the initial residual stress. Using special data-reduction relationships, the principal residual stresses and their angular orientation are calculated from the measured strains.
Data analyses are currently being done at three research laboratories namely, Idaho Accelerator Center, Los Alamos National Laboratory and Lambda Research. These data will be presented at the TRP conference.
Alloys; Deformations (Mechanics); Linear accelerators; Residual stresses; Strains and stresses
Alloys; Deformations (Mechanics); Linear accelerators
Engineering Science and Materials | Materials Science and Engineering | Metallurgy | Nuclear Engineering | Oil, Gas, and Energy
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Residual Stress Measurement in EP 823 Using Non-Destructive Evaluation Techniques.