Longitudinal-transverse bending of physically nonlinear reinforced concrete beams

В работе рассматриваются экспериментальные диаграммы деформирования бетонов марок B10, B30, B50. Методом наименьших квадратов приведены аппроксимации диаграмм деформирования полиномами второго и третьего порядка. Указанные расчеты выполнены как для случая одинаковых коэффициентов для зон растяжения и сжатия, так и различных. Приведен алгоритм решения задачи продольно-поперечного изгиба балки в случае использованных данных аппроксимаций диаграмм. The paper considers experimental deformation diagrams of concrete grades B10, B30, B50. The approximation of the deformation diagrams by polynomials of the second and third order is given by the least squares method. The calculations were performed both for the case of the same coefficients for the zones of tension and compression, and different ones. An algorithm for solving the problem of longitudinal-transverse bending of a beam in the case of the used data of approximations of diagrams is given.

Strain Localization at Constant Strain Rate and Changing Stress Conditions: Implications for Plate Boundary Processes in the Upper Mantle

We present results from a natural deformed shear zone in the Turon de Técouère massif of the French Pyrenees that directly addresses the processes involved in strain localization, a topic that has been investigated for the last 40 years by structural geologists. Paleopiezometry indicates that differential stresses are variable both spatially across the zone, and temporally during exhumation. We have, however, also calculated strain rate, which remains constant despite changes in stress. This result appears to be at odds with recent experimental deformation on monophase (olivine) rocks, which indicate that strain localization occurs dominantly as a result of constant stress. We hypothesize that in the Turon de Técouère massif—and many natural shear zones—strain localization occurs as a result of reactions, which decrease the grain size and promote the activation of grain size sensitive deformation mechanisms. From a tectonics perspective, this study indicates that the deformation rate in a particular plate boundary is relatively uniform. Stress, however, varies to accommodate this deformation. This viewpoint is consistent with deformation at a plate boundary, but it is not the typical way in which we interpret strain localization.

Discussion on “Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions: Mechanical Properties and the Influence of Rock Fabric” of Schuster, V., Rybacki, E., Bonnelye, A., Herrmann, J., Schleicher, A.M., Dresen, G.

The testing procedure and results on saturated samples of Opalinus Clay in the work of Schuster et al. (Rock Mech Rock Eng https://doi.org/10.1007/s00603-021-02474-3, 2021) were conducted and presented using strain rates two to four orders of magnitudes higher than the rates needed to allow pore pressure equilibrium in the material, both in drained and undrained conditions. This leads to an erroneous estimation of the mechanical properties in saturated conditions. We discuss this aspect in the context of shale testing. We also discuss the effect of drying-induced fissuring on the mechanical properties of geomaterials tested in dry conditions.

Microstructural Analysis of a Mylonitic Mantle Xenolith Sheared at Laboratory-like Strain Rates from the Edge of the Wyoming Craton

Combined observations from natural and experimental deformation microstructures are often used to constrain the rheological properties of the upper mantle. However, relating natural and experimental deformation processes typically requires orders of magnitude extrapolation in strain rate due to vastly different time scales between nature and the lab. We examined a sheared peridotite xenolith that was deformed under strain rates comparable to laboratory shearing time scales. Microstructure analysis using an optical microscope and electron backscatter diffraction (EBSD) was done to characterize the bulk crystallographic preferred orientation (CPO), intragrain misorientations, subgrain boundaries, and spatial distribution of grains. We found that the microstructure varied between monophase (olivine) and multiphase (i.e., olivine, pyroxene, and garnet) bands. Olivine grains in the monophase bands had stronger CPO, larger grain size, and higher internal misorientations compared with olivine grains in the multiphase bands. The bulk olivine CPO suggests a dominant (010)[100] and secondary activated (001)[100] that are consistent with the experimentally observed transition of the A to E-types. The bulk CPO and intragrain misorientations of olivine and orthopyroxene suggest that a coarser-grained initial fabric was deformed by dislocation creep coeval with the reduction of grain size due to dynamic recrystallization. Comparing the deformation mechanisms inferred from the microstructure with experimental flow laws indicates that the reduction of grain size in orthopyroxene promotes activation of diffusion creep and suggests a high activation volume for wet orthopyroxene dislocation creep.