Speaker
Description
The NCNR has upgraded and added new capabilities to the Diffractometer for Texture and Residual Stress (DARTS) The purpose of the instrument is to non-destructively measure tri-axial residual stresses in industrial parts and structural materials at spatial resolutions 1 mm3. Stresses are determined from the measurement of elastic changes in the interatomic lattice spacing at depths up to several centimeters. Another important application is the measurement of sheet metal yield functions using specialized straining devices. Here, the neutron measurement of applied multi-axial stresses is combined with simultaneous strain measurements based on digital image correlation (DIC).
The upgraded instrument now features a large, high-pressure 10 bar 3He area detector (25 cm 38 cm) for high-efficiency neutron detection. Optimized neutron flux on the sample is provided by single and multi-wavelength Si-Crystal mono¬chromators with variable curvature. Sample environment equipment consists of two multi-axial high-capacity straining devices (shear device and Octo-strain), a uni-axial load frame, separate sample stages for small and large samples, and a digital image correlation system for the measurement of plastic strain during multiaxial loading.
Octo-Strain has eight individually controlled actuators (40 kN each) that can produce strain paths and straining modes common in sheet metal forming. Compressive stresses are possible but may need anti-buckling measures. The shear device has two actuators for producing a variety of shear deformation modes. Both devices can be rotated (Octo-strain: 190; shear device: 135) to allow different measurement directions necessary for determining the stress tensor and the principal directions of deformation.
Key Words
Diffractometer, Residual Stress, Strain, Shear, Octo-Strain, Multi-Axial