In situ neutron diffraction measurements of the shear moduli G _HKLfor 12LI4 steel

Shear is often the predominant loading case and failure mechanism in real engineering systems. To guide development and validation of material deformation models for torsional and combined loads, a compact torsion-tension load frame was designed. The load frame was integrated with the sample positioner, and control of the frame was merged with the data collection software at ORNL's High Flux Isotope Reactor instrument NRSF2. Precision alignment was achieved with a laser tracker and SScanSS software. The high neutron flux allows for 1 mm ³ gauge volumes with moderate counting times for the (110), (200) and (211) hkl' s. The position of measurement was determined to <100 microns. The automated system enabled extended runs with changes in load and hkl. A series of in situ measurements were completed on a fine grain, 6 mm diameter 12L14 steel rod. Data from within the elastic loading region provides insight on the anisotropy of the Shear modulus (G_hkl)- Subsequent experiments have explored samples subjected to plastic deformation by tension and torsion. The strain tensor was obtained after unloading for plastically deformed samples subjected to pure tension and pure torsion.