The High Flux Isotope Reactor at ORNL produces a beam of thermal neutrons from which a single-wavelength beam is selected by a crystal monochromator. The particular monochromator crystal and diffraction angle are selected to locate a particular diffraction peak around 90 degrees 2-theta. Strain parallel to the diffraction vector is determined by measuring the Bragg diffraction peak position and comparing it with the position from a strain-free sample. To see this diagramatically see Principles of Stress Mapping by Neutron Diffraction. 

High resolution linear position sensitive detectors are used to simultaneously record the full diffraction peak profile. Incident and diffracted beam slits are used to define the sampling or gage volume within a specimen. Measurements have been successfully completed using gage volumes smaller than one cubic millimeter in materials such as iron and nickel. Enhanced instrumentation under development should improve this by a factor of 10. 

Features:

• Highest-flux thermal neutron source in the United States 
• Selectable wavelength and diffraction angles 
• Specimen-positioning equipment: 
• Y and Z translations of +/- 100 mm, with precision of +/- 0.02 mm 
• Specimen and detector rotations 
• Specimens to 100 kg and 40 cm x 40 cm x 20 cm 
• ORDELA position sensitive detectors: 
• Active area of 2.5 by 10 cm 
• Seven-detector array in operation 
• Automated data collection and on-line analysis 
• Multilocation automated data collection 
• Position-sensitive detector and scattering-angle calibration 
• Peak profile fitting 
• Gage volume of 0.3 to 20 cubic mm, depending on scattering power of material and required resolution 
• Typical peak position fitting precision to +/- 0.003 degrees 2-theta 
• Triaxial strain measurement and stress analysis 
• Load frame for tensile loading: 
• Diffraction elastic constants 
• Multiphase response to load in composites 
• Remote Collaboration: 
• Remote Viewing of Experimental Area
• E-Notebook
• Remote Instrument Control 
• Security
• MMC Overview

Acknowledgment