Anisotropic Shear Strength Behavior of Soil–Geogrid Interfaces

This paper presents an experimental study on the anisotropic shear strength behavior of soil–geogrid interfaces. A new type of interface shear test device was developed, and a series of soil–geogrid interface shear tests were conducted for three different biaxial geogrids and three different triaxial geogrids under the shear directions of 0°, 45° and 90°. Clean fine sand, coarse sand, and gravel were selected as the testing materials to investigate the influence of particle size. The experimental results for the interface shear strength behavior, and the influences of shear direction and particle size are presented and discussed. The results indicate that the interface shear strength under the same normal stress varies with shear direction for all the biaxial and triaxial geogrids investigated, which shows anisotropic shear strength behavior of soil–geogrid interfaces. The soil–biaxial geogrid interfaces show stronger anisotropy than that of the soil–triaxial geogrid interfaces under different shear directions. Particle size has a great influence on the anisotropy shear strength behavior of soil–geogrid interfaces.

Anisotropic strength behavior of single-crystal TATB

High-rate strength behavior plays an important role in the shock initiation of high explosives, with plastic deformation serving to localize heat into hot spots and as a mechanochemical means to enhance reactivity. Recent simulations predict that detonation-like shocks produce highly reactive nanoscale shear bands in the layered crystalline explosive TATB (1,3,5-triamino-2,4,6-trinitrobenzene), but the thresholds leading to this response are poorly understood. We utilize molecular dynamics (MD) to simulate the high-rate compressive stress-strain response of TATB, with a focus on understanding flow behavior. The dependence of strength on pressure and loading axis (crystal orientation) is explored. The deformation mechanisms fall broadly into two categories, with compression along crystal layers activating a buckling/twinning mode and compression normal to the layers producing nanoscale shear bands. Despite the complexity of the underlying mechanisms, the crystal exhibits relatively straightforward stress-strain curves. Most of the crystal orientations studied show rapid strain softening following the onset of yielding, which settles to a steady flow state. Trajectories are analyzed using five metrics for local states and structural order, but most of these metrics yield similar distributions for these deformation mechanisms. On the other hand, a recently proposed measure of intramolecular strain energy is found to most cleanly distinguish between these mechanisms, while also providing a plausible connection with mechanochemically accelerated decomposition kinetics. Localization of intramolecular strain energy is found to depend strongly on crystal orientation and pressure.

Flexural behavior of flat and folded geopolymer ferrocement panels

This paper presents the impact of fiber and wire mesh layers on the strength behavior of flat as well as folded fly ash-based geopolymer ferrocement panels. The behavior, including flexural strength, ductility, stiffness, and cracking patterns are observed. With an objective of decreasing CO2 emissions, the concrete utilizes wastes such as fly ash disposed by industrial sectors. Six panels (three flat and three folded) were cast utilizing fly ash dependent geopolymer mortar of size 1000mm x 400mm x 30mm. Heat curing in a temperature-controlled chamber maintaining 75○C to 80○C for 24 hours was done after 24 hours of resting period. The experimental results indicated that the flexural strength got enhanced by 33 percent by increasing the quantity of wire mesh layers, but the ductility got decreased by 30 percent for the flat panels; however, there was no noticeable impact in case of folded panels. The flexural strength of folded panels was found to be three times greater than that of flat panels. In addition, it is noticed that the behavior of fiber reinforced flat as well as folded panels of single layer mesh is stronger than double layer wire mesh panels with regard to cracking and ultimate load. The energy absorbed at failure was directly proportional to the volume of the reinforcement provided in the panels.