Lattice strain measurements on sandstones under load using neutron diffraction

Neutron diffraction methods (both time-of-flight- and angle-dispersive diff raction) are applied to intracrystalline strain measurements on geological samples undergoing uniaxial increasing compressional load. The experiments were carried out on Cretaceous sandstones from the Elbezone (East Germany), consisting of >95% quartz which are bedded but without crystallographic pr eferred orientation of quartz. From the stress-strain relation the Young's modulus for our quartz sample was determined to be (72.2 +/- 2.9) GPa using results of the neutron time-of-flight method. The influence of different k inds of bedding in sandstones (laminated and convolute bedding) could be de termined. We observed differences of factor 2 (convolute bedding) and 3 (la minated bedding) for the elastic stiffness, determined with angle dispersiv e neutron diffraction (crystallographic strain) and with strain gauges (mec hanical strain). The data indicate which geological conditions may influenc e the stress-strain behaviour of geological materials. The influence of bed ding on the stress-strain behaviour of a laminated bedded sandstone was ind icated by direct residual stress measurements using neutron time-of-flight diffraction. The measurements were carried out six days after unloading the sample. Residual strain was measured for three positions from the centre t o the periphery and within two radial directions of the cylinder. We observ ed that residual strain changes from extension to compression in a differen t manner for two perpendicular directions of the bedding plane. (C) 2000 El sevier Science Ltd. All rights reserved.