Abstract
Der Einfachscherversuch ist ein anspruchsvoller Laborversuch, der bereits in vielen Studien für die Untersuchung von statischem und zyklischem Bodenverhalten eingesetzt wurde. Trotz der ...vielfältigen Einsatzmöglichkeiten wird der Einfachscherversuch nicht verbreitet angewendet und es existieren weder eine Euronorm noch eine deutsche Norm für diese Art von Versuch. In diesem Beitrag werden die Anforderungen an ein Einfachschergerät definiert und die theoretischen Grundlagen zur Ermittlung des Spannungszustands dargestellt. Dazu werden die verschiedenen Gerätetypen für Einfachscherversuche vorgestellt und diskutiert. Um den Einfluss der Testrandbedingungen besser einschätzen zu können, werden monotone Versuche mit Sand an einem eigenen Gerät mit verschiedenen Zellenkonstruktionen durchgeführt. Für die Untersuchung der Probenverformung wird die PIV‐Methode eingesetzt. Anhand der Versuchsergebnisse werden die verschiedenen Randbedingungen und deren Einflüsse aufgezeigt und diskutiert sowie Hinweise für die Anwendung und Interpretation von Einfachscherversuchen gegeben.
Abstract
Investigations of cell construction and evaluation of monotonic simple shear test with sand
The simple shear test is a sophisticated laboratory test which has been used in several studies to investigate static and cyclic soil behaviour. Despite the wide range of possible utilization, the simple shear test is not commonly used and there is no European or German standardization for these types of test. In this article, the requirements for the boundary conditions of a simple shear test are defined and the theoretical principles for determining the stress state are presented. For this purpose, the different types of devices for simple shear tests are shown and discussed. In order to evaluate the influence of the boundary conditions, monotonic tests with sand are carried out on a device with different cell constructions. The PIV method is used to study specimen deformation. Based on the test results, various boundary conditions and their influences are shown and discussed. Furthermore, these results can be used as references for the interpretation of the simple shear tests.
Most soft interlayers tend to be key factors affecting rock slope stability due to their low strengths. A series of ring shear tests is conducted on reconstituted overconsolidated soft interlayers to ...investigate the influences of remolded water content and normal stress on shear behavior under drained conditions. The soft interlayer raw samples taken from a potential landslide site in China are first remolded into overconsolidated samples with different water contents but the same dry density and further drained under different normal stresses. The peak strength, residual strength, corresponding shear displacement of the soft interlayers and the loss rate of water content are positively correlated with water content and normal stress. Transformation of strain softening to strain hardening occurs for samples under higher normal stresses. Variations in water contents have notable effects on the shear strengths. Meanwhile, displacements, fragmentations and orientations of samples differ, showing strain softening and hardening behaviors of soft interlayers.
•Stress-strain characteristics of soft interlayers are systematically investigated.•Ring shear test is utilized successfully for shear behavior studying.•Variation in compaction moisture content has an obvious effect on shear strength.•Shear behaviors are closely related to the microstructure of soft interlayers.
Reduced graphene oxide (rGO) was synthesized from graphite flakes utilizing improved Hummers method via graphene oxide (GO) precursor. The oxidation of graphite and subsequent reduction of GO were ...confirmed by using FTIR, XRD, Raman spectroscopy and TEM techniques. The nanocomposite adhesives were developed using GO and rGO with different loading of 0–1.0 wt%. The adhesive strength was studied by conducting lap shear test and it was noticed that, Ep-0.5 GO adhesive exhibited the highest strength among all adhesive formulations and showed ∼50% increment than pristine epoxy. Impact strength evidenced noticeable enhancement with decrease in notch depth from 2.54 to 0.5 mm for all adhesive systems clearly indicating brittle to ductile transition due to the declining stress concentration area. The fracture analysis of impact samples and extent of fillers dispersion were visualized by SEM. SEM micrographs evidenced clear surface contrast of samples based on variable notch depth. The electrical resistivity in Ep-rGO systems showed 93% decrease with 1 wt% rGO loading, while thermal conductivity of Ep-0.5 GO revealed 211% increment as compared to pristine epoxy.
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•Synthesis of reduced graphene oxide (rGO) using improved Hummers method.•Superior mechanical properties for Ep-GO adhesives than their rGO counterparts.•Adhesive's impact strength increased with decreasing notch depth from 2.54 to 0.5 mm.•ρ of Ep-rGO systems was superior than Ep-GO systems, while contrary result for Tc.•Tg of all nanocomposite adhesives diminished with inclusion of nanomaterials.
Poor flowability of compressible biomass particles poses severe handling challenges in all processes of biorefineries, which results in poor energy-yielding in conversion. This paper presents the ...characterization of the flow behavior of a widely used compressible biomass material (ground loblolly pine) using a combination of physical characterization and numerical simulation. An advanced hypoplastic model with implementation and validation in Abaqus VUMAT is adopted. A workflow is established to calibrate material parameters directly from index tests, an oedometer test, and a Schulze ring shear test, and indirectly from numerical simulations of those tests. The finite element simulation of axial shear tests and hopper flow tests using the calibrated hypoplastic model is shown to capture key flow attributes, such as the maximum shear stress in shear tests, as well as the mass flow rate and flow pattern in hopper. The results demonstrate that a subset of the laboratory tests needs to allow large strains for adequate characterization of compressible granular flow, and numerical models developed for non-compressible materials can accurately predict the flow behavior of compressible biomass material, even though strain magnitudes are not scaled correctly. This study provides a potent tool to decipher and resolve material handling upsets in biorefineries and other energy industries that utilize forest products.
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•A method is developed to determine a full set of flow properties for pine chips.•Numerical simulations with different shear test characterize the full stress state.•A hypoplastic model accurately predicts the flow behavior of pine chips.•Multiple types of shear tests and pilot-scale hopper tests validate the model.
The computation time of Discrete Element Method (DEM) simulations increases exponentially when particle size is reduced or the number of particles increased. This critical challenge limits the use of ...DEM simulation for industrial applications, such as powder flow in silos. Scaling techniques can offer a solution to reduce computation time. In this paper, we have developed a hybrid particle-geometric scaling approach with a focus on Elasto-Plastic Adhesive contact models. It established relationships between particle scaling factors and DEM contact input parameters. The isolated effects of varying particle size and geometric dimensions on bulk properties were also evaluated using uniaxial consolidation, static angle of repose, and ring shear tests. This paper shows how the particle scaling can be applied together with geometric scaling to incorporate two important aspects of bulk materials, their Elasto-Plastic behaviour and their cohesive forces.
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•Scaling laws for an Elasto-Plastic Adhesive DEM contact model are established.•A hybrid particle-geometric scaling approach is applied.•Scaling is demonstrated for quasi-static regime by three different test setups.•Particle scaling factors from 0.2 to 12 are achieved.•DEM particles and geometry should be scaled separately for cohesive materials.
•Existing shear test apparatuses for assessing bolt shear performance are briefly reviewed.•Key influencing factors to consider when designing a shear test apparatus are discussed.•A comparative ...analysis has been conducted highlighting the differences between the single and double shear tests.
The shear performance of cable bolt is important in assessing its load transfer capacity for effective rock strata reinforcement, which has not yet been thoroughly investigated and understood. Tests carried out in laboratory to study the cable shear performance can be simply classified into two types, the Single Shear Test (SST) and the Double Shear Test (DST). A variety of single and double shear test apparatuses developed in the past were reviewed and the main controlling factors when designing a new shear test apparatus were concluded based on the existing shear test apparatuses and their application. Four cable bolts were tested in laboratory conditions using the DST apparatus developed in the University of Wollongong, the British Standard Single Shear Test apparatus (BSST) and the Megabolt Single Shear Test apparatus (MSST) to compare and assess these different shear test apparatuses. Test results showed that the MSST results were completely different from the BSST results but similar to the DST results. Cable bolts tested in BSST tended to fail at small shear force and shear displacement in the form of inclined shear failure surfaces, whilst cable bolts installed in MSST and DST both tended to fail at greater shear force and shear displacement in the form of tensile cone and cup with bending deformation. It is concluded that both single and double shear test methods can effectively assess cable bolt shear performance as long as suitable apparatus dimensions and boundary conditions are used.
•Compressive-shear tests were conducted on transversely isotropic rock with different inclinations.•The micro-scale fracturing process of transversely isotropic rock with different inclination are ...analyzed.•The effects of bedding plane strength and spacing are analyzed.
The failure and mechanical behavior of transversely isotropic rock are significantly affected by the original bedding planes. Until now, few studies have been performed to investigate the influence of the geometrical and mechanical parameters of the bedding planes on the fracture characteristics of transversely isotropic rocks under planar shear fracture loading conditions. For this purpose, experimental and numerical compression-shear tests on double-notched specimens are conducted to investigate the fracturing characteristics of transversely isotropic rock under planar shear fracture loading. The experimental study that focuses on the influence of bedding plane inclination on fracture load, fracture pattern and AE evolution, and six inclination angles is conducted in this study. Based on the flat joint contact model (for the rock matrix) and smooth joint contact model (for the original bedding plane) in PFC2D (particle flow code), the microscale fracturing process of transversely isotropic rock with different inclinations is simulated and analyzed. The results show that the inclination has an important influence on the fracture load and fracture pattern, and the maximum and minimum fracture loads are obtained for specimens with inclination angles of 30° and 60°, respectively. Moreover, the strength and spacing of the original bedding planes also play an important role in fracture loads. Higher bedding plane strength and wider bedding plane spacing result in higher fracture loads. In addition, with a moderate inclination angle, transversely isotropic rock with higher bedding plane strength tends to form cracks that cut through the rock matrix. However, with the decrease in the bedding plane strength, more fractures form along the bedding planes.
Shear cell tests are now commonly applied in particulate calibration procedures for the discrete element method. Usually, only the shear stresses at the shear plane in the particle bed are examined ...in short-time instances. This work aimed to find the regularities between the internal friction angle, the vertical position of the shear lid, and the rearrangements of particles in the layers during the shear test with the time instance duration of tens to hundreds of seconds. The Schulze RST Ring Shear Tester was used to compare real experiments to numerical DEM models of non-cohesive materials. The shear tests were investigated for different contact models and DEM input parameters. We also simultaneously monitored the overall specimen stiffness, material dilatancy during calibration, and shear stress. Particle bed stiffness increases with increasing shear modulus and coefficient of static friction for two contact models. The internal friction angle, which is a bulk property of the material determined by a set of particle properties, determines the ability (or resistance) to make displacements of rigid non-deformable particles in the shear testing process. The angle of the resultant of the vector of particle motion in space from the horizontal plane correlates with the angle of internal friction (at each location of the shear cell).
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•Shear tests were performed on the RST to establish a range of values for the DEM simulations.•A correlation between the pre-shear stress and vertical lid position was found.•Hertz-Mindlin and linear-spring contact models were used for DEM with various input data.•A link was found between the particle rearrangement with the angle of internal friction in the layers.•Particle bed contraction/dilatancy via the shear lid should be part of DEM calibration process.
A study on the liquefaction resistance of calcareous sands reinforced with polypropylene fibers was reported. Stress-controlled cyclic simple shear tests were conducted on specimens prepared at a ...relative density of 50%, with and without fiber reinforcements. The liquefaction behavior was investigated by considering the effects of fiber contents ranging from 0% to 1%, fiber lengths varying from 3 mm to 12 mm and loading patterns. The results indicated that increasing fiber content and fiber length resulted in a decrease in the deformation, a reduction in pore pressure accumulation rate, and improved the liquefaction resistance of calcareous sands. Additionally, the risk of soil liquefaction could be significantly reduced when the fiber content was greater than 0.8%. The multidirectional loading had a considerable effect in reducing the liquefaction resistance compared to unidirectional loading. Further, the stiffness degradation of calcareous sands decreased with increasing fiber content and fiber length. The pore pressure generated in the cyclic tests was analyzed and was found to be affected by fiber content. A pore pressure prediction model was proposed to obtain the pore pressure characteristics of fiber-reinforced calcareous sands under various fiber content conditions.
•The effect of fibers on the liquefaction behavior of calcareous sands is investigated.•The liquefaction resistance of calcareous sands significantly increases by increasing the fiber content and fiber length.•The multidirectional loading increases the liquefaction susceptibility of fiber-reinforced calcareous sands.•A modified pore pressure prediction model considering the effect of fiber contents is proposed.
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