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Use Of Positron Annihilation Spectroscopy For Stress-Strain Measurements: Quarterly Progress Report (March – May 2005), Ajit K. Roy
Transmutation Sciences Materials (TRP)
Accomplishments:
● Analyses of defects (dislocations) in martensitic Alloy EP-823, cold-reduced to different levels, have been performed by using transmission electron microscopy. The dislocation density has been related to the degree of cold-reduction and residual stress in terms of a line-shape parameter determined by the positron annihilation spectroscopy (PAS).
● Additional PAS measurements are ongoing on tensile, welded and cold-worked specimens of Alloys EP-823 and HT-9 at the Idaho Accelerator Center of ISU. Both Subhra and Silpa are involved in these measurements.
● Silpa is performing neutron diffraction (ND) measurements at the Atomic Energy of Canada Limited (AECL), Chalk River …
Use Of Positron Annihilation Spectroscopy For Stress-Strain Measurements: Quarterly Progress Report (December 01, 2004 – February 28, 2005), Ajit K. Roy
Transmutation Sciences Materials (TRP)
The purpose of this collaborative research project involving the University of Nevada Las Vegas (UNLV), the Idaho State University (ISU), and the Los Alamos National Laboratory (LANL) is to evaluate the feasibility of determining residual stresses in cold-worked, plastically-deformed (bent), and welded materials using a nondestructive method based on positron annihilation spectroscopy (PAS). This technique uses γ-rays from a small MeV electron Linac to generate positrons inside the sample via pair production. This method is known to have capabilities of characterizing defects in thick specimens that could not be accomplished by conventional positron technique or other nondestructive methods. The data …
Use Of Positron Annihilation Spectroscopy For Stress-Strain Measurements: Quarterly Progress Report (September 01 – November 30, 2004), Ajit K. Roy
Transmutation Sciences Materials (TRP)
Accomplishments:
● A technical paper titled “Residual Stress Characterization in Structural Materials by Destructive and Nondestructive Techniques” has been accepted for publication in the Journal of Materials Engineering and Performance, ASM International, Ohio.
● The PAS method has been applied to develop calibration curves for line shape parameters (S and T) using unstressed and stressed (different magnitude) tensile specimens of martensitic stainless steels. These curves will enable the determination of residual stresses in plastically-deformed materials once the magnitude of S or T parameter is determined by the PAS technique.
● The tensile and welded specimens have been irradiated by low …
Use Of Positron Annihilation Spectroscopy For Stress-Strain Measurements, Ajit K. Roy
Use Of Positron Annihilation Spectroscopy For Stress-Strain Measurements, Ajit K. Roy
Transmutation Sciences Materials (TRP)
Engineering metals and alloys, when subjected to tensile loading beyond a limiting value, undergo plastic deformation resulting in lattice defects such as voids and dislocations. These imperfections interact with the crystal lattice, producing a higher state of internal stress, also known as residual stress, which can be associated with reduced ductility. Residual stresses are also generated in welded structures due to rapid solidification and resultant dissimilar metallurgical microstructures between the weld and the base metals. Development of these internal stresses is often influenced by incompatible permanent strain resulting from thermal and mechanical operations associated with welding and plastic deformation. These …