Study of applied, residual strain, and texture on a granite rock using neutron time-of-flight diffraction at EPSILON and SKAT / JINR Dubna

The investigation of residual and applied intra-crystalline strain in polycrystalline materials can be carried out using X-ray or neutron diffraction diffraction. The advantage of neutron diffraction is the depth penetration depth of neutrons in matter. In addition, most of the rock-forming elements have low absorption properties for neutrons. The application of neutron time-of-flight is advantageous for the investigation of polycrystalline materials, containing lower-symmetrical crystals, because of the achieved high resolution.

The neutron time-of-flight diffractometer EPSILON has been designed for the investigation of strain/stress on polycrystalline materials. Using the neutron flight path of about 107 m a resolution of 5 x 10^-3 is achieved. Using the available wavelength up to 7.1 Å the investigation of lattice spacing up to d = 5.1 Å can be carried out. The detectors system, consisting of 9 detector units allows the simultaneous detection of the strain in axial and radial direction at in situ applied strain experiments. The neutron time-of-flight texture diffractometer SKAT, which is equipped with 19 detectors at 2Θ=90° at a flight path of about 103 m allows the investigation of the crystallographic preferred orientation of polycrystalline materials using one sample revolution. The neutron guide cross section is H x W = 95 x 50 mm², so that samples with a diameter up to 50 mm can be investigated. The resolution is 5x10^-3 at d = 2 Å.

A cylindrical granite sample (d = 30 mm, l = 60 mm) consisting of quartz, plagioclase and biotite was investigated with respect to residual strain and its crystallographic preferred orientation of the constituent minerals. In situ applied strain experiments at four uniaxial stress levels up to 100 kN were carried out on the neutron time-of-flight diffractometer EPSILON with simultaneous recording of acoustic emissions. For each loading step, the applied and residual strains were determined. In addition, a residual strain scan was performed around the sample axis. The texture of the sample has been determined using the SKAT texture diffractometer.