NE Seminars

Thursday, January 31, 2008 at 4:00 p.m.

• Joint Nuclear Engineering / Mechanics and Materials Seminar
• Thak Sang Byun
  Materials Science & Technology Division
  Oak Ridge National Laboratory
  
  
• "Advances in Understanding Deformation in Irradiated Metallic Materials: True Stress Parameters and Deformation Mode Maps"
  
  
• Abstract
  Irradiation with energetic particles at low temperatures hardens metallic materials by producing numerous defect clusters and prompts microscopic and macroscopic strain localizations and embrittlement. In the past decade a large database of engineering tensile property has been produced at ORNL to characterize the effects of low temperature irradiation. This talk will suggest a new way to interpret the mechanical property data with a special emphasis on the use of true stress parameters. Results for the majority of the metallic materials show that the true stress parameters such as the plastic instability stress (PIS) and true fracture stress (FS) are nearly independent of dose and therefore that the ratio between these parameters is consistent for each crystal type. It is found, however, that the values of these parameters can vary with phase change, temperature, or embrittlement. Macroscopic deformation mode maps were formed by using the true stress parameter versus dose curves to display mechanical property data in an integrated way. Low temperature irradiation changes microscopic deformation mechanisms from the glide of individual dislocations to that involves multiple dislocations. A theoretical explanation is attempted to explain the discrepancy between the dose dependent deformation mechanism and the dose independent macroscopic stress parameters and strain hardening behavior.
  
  
  

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