Completed 
          (May 2002-Dec 2006)

 

Title  Use of Positron Annihilation Spectroscopy  for Stress-Strain Measurements	Researchers A. Roy  Collaborators Stuart A. Maloy, Ph.D., AFCI Materials Team Leader, Los Alamos National Laboratory J. Frank Harmon, Ph.D., Director, Idaho Accelerator Center, Idaho State University Doug Wells, Ph.D., Associate Professor, Department of Physics, Idaho State University Farida Selim, Ph.D., Post Doctoral Researcher, Idaho Accelerator Center, Idaho State University
Background  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 types of operations can cause premature failures in structural materials unless these stresses are relieved by thermal treatments, which are commonly known as stress-relief operations.  During the past academic year, this project was focused on the characterization of residual stress in welded specimens consisting of austenitic and martensitic stainless steels using an activation technique based on the Positron Annihilation Spectroscopic (PAS) method.  The extent of residual stress was expressed in terms of three line-shape parameters (S-, W- and  T-).  Further, efforts were made to characterize linear lattice defects such as dislocations in the vicinity of Fusion-Line (FL), Heat-Affected-Zone (HAZ), and the base material of the welded specimens using Transmission Electron Microscopy (TEM). The metallurgical microstructures at these three regions have also been evaluated by optical microscopy. T-Parameter versus Distance from FL for Welded Specimens of Similar Materials	Research Objectives and Methods The primary objective of this task was to evaluate the feasibility of the characterization of residual stresses in plastically-deformed and welded structural materials using a new nondestructive technique based on PAS. The residual stresses measured by a modified PAS method have been compared to those measured by three other techniques, namely the Ring-Core (destructive), X-Ray Diffraction (non-destructive), and Neutron Diffraction (non-destructive).  All four techniques have been used to evaluate residual stresses in cold-worked, plastically deformed and welded specimens of austenitic Type 304L Stainless Steel (SS), and martensitic Alloys EP-823 and HT-9. Alloy EP-823 is a leading target structural material to contain the molten lead-bismuth eutectic nuclear coolant needed for fast spectrum operations of an Accelerator-Driven Transmutation System. Type 304L SS is a universally-known corrosion resistant low-carbon iron-nickel-chrome alloy having optimum formability and weldability. Alloy HT-9 is known for its superior high temperature tensile properties. The metallurgical microstructures and the nature of defects have been analyzed by optical microscopy, scanning electron microscopy, and TEM.
Students  Srinivas Chanda G Subhra Bandyopadhyay G Satish Babu Dronavalli G Silpa Suresh G Vikram Marthandam G Bhagath Yarlagadda G Anand Venkatesh G Raghunandan Karamcheti G Bhagath Yarlagadda G	Department Mechanical Engineering
Final Report	Annual Report  Task 14 Year 1 Academic Year 2001
Proposal 04/02/02 Task 14 Year 2 Task 14 Year 3	Quarterly Reports  06/01/02-08/31/02 06/01/03-10/31/03  06/01/04-08/31/04 09/01/04-11/31/04 12/01/04-02/28/05 04/01/05-06/30/05
Papers Residual Stress Measurements in Type 304 Stainless Steel Using Non-Destructive Techniques - ANS 4/2-5/03 Residual Stress Measurements EP 823  Using Non-Destructive Evaluation Techniques - ANS 4/2-5/03	Researchers V. Marthandam   A. Venkatesh

 Thesis
M.S. Mechanical Engineering, Satish Dronavalli, “Residual Stress Measurements and Analysis by Destructive and Non Destructive Techniques” Aug. 2004 (TRP Task 14)
M.S. Mechanical Engineering, Anand Venkatesh, “Comparative Analyses of Residual Stresses in Target Sub-System Materials” Aug. 2004 (TRP Task 14)
M.S. Mechanical Engineering, Vikram Marthandam, “Metallurgical Characterization and Residual Stress Measurements of Target Structural Materials” Aug. 2004 (TRP Task 14)