Torsional Apparatus Research Articles

A Novel Torsional Kolsky Bar Apparatus for Investigating Dynamic Frictional Resistance of Granular Materials Under Seismically Relevant Conditions

In the present study, a modified torsional Kolsky bar apparatus is utilized to investigate the dynamic frictional behavior of confined granular geo-materials under seismically relevant normal stresses, slip velocities and accelerations. The frictional resistance of the granular specimens is evaluated under both dry and wet conditions. Using the apparatus, slip speeds ranging between 2 and 6 m/s are achieved at normal stresses ranging between 50 and 125 MPa. The maximum slip displacement obtained during the frictional slip is about 5 mm. The usefulness of the experimental configuration is validated by presenting results for Talc under both wet and dry conditions, and 50/50 Montmorillonite/Ottawa sand under wet conditions. For the experiments on Talc, the dry specimens are found to have a coefficient of kinetic friction in the range of 0.2–0.4, with the wet specimens exhibiting lower values of 0.1–0.2. The wet 50/50 Montmorillonite/Ottawa sand specimens exhibit a low average friction coefficient value of about 0.1 for all the test conditions.

Effects of principal stress rotation on small strain stiffness of sand subjected to piping erosion

Along with the development of experimental techniques and numerical simulations, knowledge of the mechanism of the internal erosion process and the resulting failures has increased remarkably. Despite such advancements, little attention has been paid to the soil after erosion, whose dominant characteristic is the significant anisotropic fabric represented by discontinuities in the erosion planes. In this research, in order to investigate the small strain stiffness of eroded soil, a proposal for generating the local disturbance in the form of piping was achieved by dissolving pre-placed glucose in soil samples. A series of experiments on specimens with determined eroded planes was conducted in a hollow cylindrical torsional shear apparatus. For both the intact and the eroded specimens, the elastic shear modulus was evaluated at various stress states with the help of gap sensors under small-amplitude torsional cyclic loadings. The stress directional dependency of G was examined by changing the principal stress axes while keeping mean effective stress p′ and stress ratio σ′1/σ′3 constant. According to the results, a marked reduction in the shear modulus was induced after piping erosion, and the stiffness of the eroded soil was found to be sensitive to changes in the stress directions due to the resultant anisotropic fabric involving the loss of inter-particle contacts and the rearrangement of sand particles.

An Experimental Study of Torsional Properties of Polyvinylchloride

In this research, an experimental study has been performed to investigate the mechanical properties through torsion testing of polyvinylchloride (PVC) polymer specimens. For the purpose of the experimentation, specimens of PVC round bars have been prepared. Torsion testing machine apparatus of 200 Nm motor driven was used to evaluate the torsion properties of the tested bars. The apparatus provides four deformation speeds of 50°/min, 100°/min, 200°/min and 500 °/min. The tests conducted under different conditions in a room temperature and cooling of the samples and tested at different deformation speeds given by the torsion apparatus. Various tests produce the torsional moment- angle of rotation diagrams and thereafter both of torsional fracture resistance and shear modulus have been calculated. The results showed the effect of temperature change on the mechanical properties of PVC by making the material harder and can resist higher value of the applied torque where the range is from 2.9 N.m for the cooled sample to 2 N.m for the received samples tested at room temperature. Moreover the results showed an increase of shear modulus to 282 MPa for the cooled samples in compare to 140 MPa for as received samples. Finally the results provide a guideline for designers on how to use parts made of PVC in different applications where the range of both the maximum torque and failure torque with their mechanical properties of rigidity and torsional resistance were recorded.

The effect of different torque wrenches on rotational stiffness in compressive femoral nails: a biomechanical study.

Rotation instability and locking screws failure are common problems. We aimed to determine optimal torque wrench offering maximum rotational stiffness without locking screw failure. We used 10 conventional compression nails, 10 novel compression nails and 10 interlocking nails with 30 composite femurs. We examined rotation stiffness and fracture site compression value by load cell with 3, 6 and 8Nm torque wrenches using torsion apparatus with a maximum torque moment of 5Nm in both directions. Rotational stiffness of composite femur-nail constructs was calculated. Rotational stiffness of composite femur-compression nail constructs compressed by 6Nm torque wrench was 3.27±1.81Nm/angle (fracture site compression: 1588N) and 60% more than that compressed with 3Nm torque wrench (advised previously) with 2.04±0.81Nm/angle (inter fragmentary compression: 818N) (P=0.000). Rotational stiffness of composite-femur-compression nail constructs compressed by 3Nm torque wrench was 2.04±0.81Nm/angle (fracture site compression: 818N) and 277% more than that of interlocking nail with 0.54±0.08Nm/angle (fracture site compression: 0N) (P=0.000). Rotational stiffness and fracture site compression value produced by 3Nm torque wrench was not satisfactory. To obtain maximum rotational stiffness and fracture site compression value without locking screw failure, 6Nm torque wrench in compression nails and 8Nm torque wrench in novel compression nails should be used.

Effects of principal stress axis rotation on cyclic deformation characteristics of rail track subgrade materials

The cumulative plastic deformation of rail track subgrade materials under moving wheel loads is a complex problem. The plastic deformation and resilient modulus of subgrade materials subjected to moving wheel loads are a function of Principal Stress Axis Rotation (PSAR). Difficulties associated with the control of PSAR in conservative experimental methods lead to inaccurate estimations of the actual plastic deformation characteristics of rail track subgrade. Therefore, this study modifies a torsional multi-ring shear apparatus to evaluate the deformation characteristics of subgrade materials under moving wheel loads. The performance of this modified apparatus is evaluated by comparing the experimental results with those of small-scale model tests on an asphalt roadbed rail track with sandy subgrade. The evaluation suggests that the modified multi-ring shear apparatus has an excellent capability to estimate the deformation characteristics of rail track subgrade under moving wheel loads. A series of modified multi-ring shear tests is then conducted to investigate the effects of the loading conditions, the subgrade density, and the loading frequency on the deformation of subgrade materials under moving wheel loads. The results of these tests show that cyclic single-point load tests underestimate the actual deformation characteristics of subgrade materials irrespective of the subgrade density and the loading frequency. Furthermore, the ratio between the plastic cumulative deformations obtained from the moving wheel loading and from the cyclic single-point loading, referred to as the “ratio of axial strain” (Rs), is introduced to evaluate the plastic deformation characteristics of rail track subgrade materials under moving wheel loads only, using the results of cyclic single-point loading tests. Finally, an empirical formula is proposed to predict the cyclic plastic deformation of rail track subgrade materials as a function of the number of loading cycles.

Strain‐dependent partial slip on rock fractures under seismic‐frequency torsion

AbstractMeasurements of nonlinear modulus and attenuation of fractures provide the opportunity to probe their mechanical state. We have adapted a low‐frequency torsional apparatus to explore the seismic signature of fractures under low normal stress, simulating low effective stress environments such as shallow or high pore pressure reservoirs. We report strain‐dependent modulus and attenuation for fractured samples of Duperow dolomite (a carbon sequestration target reservoir in Montana), Blue Canyon Dome rhyolite (a geothermal analog reservoir in New Mexico), and Montello granite (a deep basement disposal analog from Wisconsin). We use a simple single effective asperity partial slip model to fit our measured stress‐strain curves and solve for the friction coefficient, contact radius, and full slip condition. These observations have the potential to develop into new field techniques for measuring differences in frictional properties during reservoir engineering manipulations and estimate the stress conditions where reservoir fractures and faults begin to fully slip.

High-pressure rotational deformation apparatus to 135 GPa.

A large-strain, torsional deformation apparatus has been developed based on diamond anvil cells at high pressures, up to 135 GPa with a help of hard nano-polycrystalline diamond anvils. These pressure conditions correspond to the base of the Earth's mantle. An X-ray laminography technique is introduced for high-pressure in situ 3D observations of the strain markers. The technique developed in this study introduces the possibility of the in situ rheological measurements of the deep Earth materials under ultrahigh-pressure conditions.

Ultramylonite generation via phase mixing in high‐strain experiments

AbstractDynamic recrystallization and phase mixing are considered to be important processes in ductile shear zone formation, as they collectively enable a permanent transition to the strain‐weakening, grain‐size sensitive deformation regime. While dynamic recrystallization is well understood, the underlying physical processes and timescales required for phase mixing remain enigmatic. Here, we present results from high‐strain phase mixing experiments on calcite‐anhydrite composites. A poorly mixed starting material was synthesized from fine‐grained calcite and anhydrite powders. Samples were deformed in the Large Volume Torsion apparatus at 500°C and shear strain rates of 5 × 10−5 to 5 × 10−4 s−1, to finite shear strains of up to γ = 57. Microstructural evolution is quantified through analysis of backscattered electron images and electron backscatter diffraction data. During deformation, polycrystalline domains of the individual phases are geometrically stretched and thinned, causing an increase in the spatial density of interphase boundaries. At moderate shear strains (γ ≥ 6), domains are so severely thinned that they become “monolayers” of only one or two grain's width and form a thin compositional layering. Monolayer formation is accompanied by a critical increase in the degree of grain boundary pinning and, consequently, grain‐size reduction below the theoretical limit established by the grain‐size piezometer or deformation mechanism field boundary. Ultimately, monolayers neck and disaggregate at high strains (17 <γ <57) to complete the phase mixing process. This “geometric” phase mixing mechanism is consistent with observations of mylonites, where layer (i.e., foliation) formation is associated with strain localization, and layers are ultimately destroyed at the mylonite‐ultramylonite transition.

An Experimental Study on the Strength Behavior of Compacted Loess under the Principal Stress Axis Rotation

A series of consolidated-undrained tests was carried out on compacted loess with a hollow cylinder torsional shear apparatus to investigate the stress-strain characteristics and the strength behavior of the compacted loess under different stress paths. Two kinds of stress paths were considered in these tests, including directional shear tests with fixed principal stress axes and shear tests under pure principal stress axis rotation. Test results reveal that the stress-strain curves of the compacted loess under these two kinds of stress paths followed a similar trend, in which two shear stages were observed. In the first shear stage, with the increase of the generalized shear stress, the generalized shear strain developed relatively slowly and the specimen of the compacted loess showed a rigid response. With the further increase of the shear stress, an obvious turning point appeared and the second shear stage started. In the second stage, the generalized shear strain began to develop rapidly and the specimen showed a ductile response. The results also reveal that when the directional shear was applied to the specimens of compacted loess under different principal stress directions, there was a large difference in the generalized shear stress - strain curves and the specimens showed significant anisotropic behavior. A compared with the specimens not subjected to the principal stress axis rotation, the specimens subjected to the principal stress axes rotation had remarkably higher strength. In addition, the specimens of the compacted loess had different levels of strength when they were tested at different shear rates. The decrease of the shear rate had a slight influence on the increase of the shear strength of the compacted loess.

Biaxial shear/tension failure behavior of Spectra single fibers

An experimental study is conducted to develop the biaxial failure surface of single Spectra 100d and Spectra 130d filaments in a torsion-tension environment. The cross-sectional profiles of single fibers are evaluated using scanning electron microscopy and X-ray computed tomography. In efforts to hold the polyethylene single fiber, a pin-gripping method is developed. Effects of pin diameter on failure stress for both Spectra types are characterized. Additionally, the effect of sample gauge length on fiber tensile strength is investigated. Quasi-static experiments are conducted using an MTS servo-hydraulic system to apply tensile loads on pre-twisted single fibers. A tension Kolsky bar is employed to study the biaxial shear/tensile behavior of single fibers at high strain-rates. A decreasing trend of tensile strength with increasing torsional strain is observed for both Spectra 100d and 130d. Furthermore, a torsional pendulum apparatus is used to determine the apparent torsional shear stresses in pre-twisted fibers at various levels of axial loading and a relationship between apparent shear stress and axial stress is developed. Finally, a biaxial shear/tension failure envelope of each fiber type is established.

Undrained Cyclic and Monotonic Behavior of Hormuz Calcareous Sand Using Hollow Cylinder Simple Shear Tests

Complete recognition of calcareous sediments engineering behavior considering their local expansion and wide variety of engineering properties is very important. In south parts of Iran, there are some carbonate hydrocarbon reservoirs which are covered by calcareous deposits. Hormuz Island in is one of the most strategic areas in Hormuz Strait between the Persian Gulf and Oman Sea. In this study, a series of undrained monotonic and cyclic simple shear tests was performed on saturated Hormuz calcareous sand specimens using hollow cylinder torsional apparatus. The tests were carried out on specimens with various relative densities under different effective consolidation stresses. Based on the results, pore pressure generation, shear strain development, stress–strain characteristics of the specimens are presented and compared with the technical literature. In addition, dissipation of strain-based energy during the cyclic loading and its relation to excess pore water pressure is described. The cyclic resistance curves of specimens with different initial conditions are plotted. Also the results of monotonic and cyclic tests are compared together for better interpretation of Hormuz calcareous sand under undrained torsional loading.

Fully Softened Shear Strength for Soil Slope Stability Analyses

AbstractThe fully softened shear strengths of soils, mudstones, and shales of different plasticities and gradations were measured at low (10 and 25 kPa), intermediate (50 and 100 kPa), and high (200, 300, and 400 kPa) effective normal stresses. A torsional ring shear apparatus was used for the strength measurement. The effects of the change in nonlinearity of the fully softened shear strength envelope over the utilized normal stress ranges on slope stability analyses were investigated. An empirical correlation was developed to predict the fully softened shear strength as a function of plasticity index and a wide range of effective normal stresses. The correlation is presented as a revised version of those previously developed for a limited number of normal stresses that do not cover the range mobilized in the vast majority of reported long-term first-time landslides. A numerical expression was also introduced to allow for direct incorporation of the fully softened shear strength correlation in slope stabi...

The effect of fluid composition, salinity, and acidity on subcritical crack growth in calcite crystals

AbstractChemically activated processes of subcritical cracking in calcite control the time‐dependent strength of this mineral, which is a major constituent of the Earth's brittle upper crust. Here experimental data on subcritical crack growth are acquired with a double torsion apparatus to characterize the influence of fluid pH (range 5–7.5) and ionic strength and species (Na2SO4, NaCl, MgSO4, and MgCl2) on the propagation of microcracks in calcite single crystals. The effect of different ions on crack healing has also been investigated by decreasing the load on the crack for durations up to 30 min and allowing it to relax and close. All solutions were saturated with CaCO3. The crack velocities reached during the experiments are in the range 10−9–10−2 m/s and cover the range of subcritical to close to dynamic rupture propagation velocities. Results show that for calcite saturated solutions, the energy necessary to fracture calcite is independent of pH. As a consequence, the effects of fluid salinity, measured through its ionic strength, or the variation of water activity have stronger effects on subcritical crack propagation in calcite than pH. Consequently, when considering the geological sequestration of CO2 into carbonate reservoirs, the decrease of pH within the range of 5–7.5 due to CO2 dissolution into water should not significantly alter the rate of fracturing of calcite. Increase in salinity caused by drying may lead to further reduction in cracking and consequently a decrease in brittle creep. The healing of cracks is found to vary with the specific ions present.

Cyclic plastic deformation characteristics of subgrade under moving train wheel load

Cyclic plastic deformation of subgrade and other engineered layers is generally not taken into account in the design of railway bridge transition zones, although the plastic deformation is the governing factor of frequent track deterioration. Actual stress behavior of fine grained subgrade/embankment layers under train traffic is, however, difficult to replicate using the conventional laboratory test apparatus and techniques. A new type of torsional simple shear apparatus, known as multi-ring shear apparatus, was therefore developed to evaluate the actual stress state and the corresponding cyclic plastic deformation characteristics of subgrade materials under moving wheel load conditions. Multi-ring shear test results has been validated using a theoretical model test results; the capability of the multi-ring shear apparatus for replicating the cyclic plastic deformation characteristics of subgrade under moving train wheel load conditions is thus established. This paper describes the effects of principal stress rotation (PSR) of the subgrade materials to the cyclic plastic deformation in a railroad and impacts of testing methods in evaluating the influence of principal stress rotation to the track deterioration of rail track.

Microstructure and internal friction of Ni–Ti alloys absorbing hydrogen

The microstructure and internal friction of Ni–Ti alloys after hydrogen absorption have been investigated by means of optical microscopy, X-ray diffraction, differential scanning calorimetry and low frequency torsional internal friction apparatus. The results show that, after hydrogen absorption, the grains tend to be elongated, and the nucleation and growth of hydrides are mainly concentrated at the grain boundaries. In addition, a new phase ultimately identified as Ti2NiH0·5 phase forms after absorption of hydrogen. The hydrogen induced martensite promotes the emergence of a two-stage transformation. However, the growth of hydrides causes a reduction of the hydrogen induced martensite. The hydrides act as strong pinning points, resulting in a dramatic increase in the internal friction. In addition, the marked change of the internal stress, caused by the microscopic strain and the mismatching of the volumes, also improves the internal friction.

Residual shear strength of fine-grained soils and soil–solid interfaces at low effective normal stresses

A laboratory research program was undertaken to study the large-strain shear strength characteristics of fine-grained soils under low effective normal stresses (∼3–7 kPa). Soils that cover a wide range of plasticity and composition were utilized in the program. The interface shear strength of these soils against a number of solid surfaces having different roughness was also investigated at similar low effective normal stress levels. The findings contribute to advancing the knowledge of the parameters needed for the design of pipelines placed on sea beds and the stability analysis of shallow soil slopes. A Bromhead-type torsional ring-shear apparatus was modified to suit measuring soil–soil and soil–solid interface residual shear strengths at the low effective normal stresses. In consideration of increasing the accuracy of assessment and depicting the full-scale field behavior, the interface residual shear strengths were also measured using a macroscale interface direct shear device with a plan interface shear area of ∼3.0 m2. Correlations are developed to estimate the soil–soil and soil–solid interface residual shear strengths at low effective normal stresses. The correlations are compared with soil–soil and soil–solid interface drained residual shear strengths and correlations presented in the literature.

Anisotropic behavior of the Bushehr carbonate sand in the Persian Gulf

The anisotropy effect is exhibited more prominently in sedimentary depositions, and it relates the soil’s mechanical specifications to the directions of imposed loads. Even though this phenomenon has been comprehensively explored in silica sands, few research has been conducted for studying the anisotropic behavior of marine carbonate sands. To bridge this gap, the present study investigates the anisotropy effect on the mechanical behavior of Bushehr carbonate sand acquired from the north shelf of the Persian Gulf in Iran. Toward this end, some undrained principal stress rotation tests are conducted using a hollow cylinder shear torsional apparatus in such a manner that the direction of the applied principal stresses are fixed along a desired orientation and the total mean stress and intermediate principal stress ratio are kept constant. Furthermore, prior to shearing, the samples are consolidated under three confining pressures and two isotropic and anisotropic states. The results show that dilative behavior is observed in all loading directions after initial contraction; this contradicts the response observed in silica sands. The anisotropy response of soil follows two different trends in the contractive and dilative phases. The relation of soil’s mechanical properties shows a descending trend with the angle of maximum principal stress in the contractive phase; on the other hand, the anisotropy behavior shows a dominant parabola trend in the dilative phase, where the maximum ultimate pore pressure and minimum soil strength occur in the stress direction with an angle of α = 30°. By increasing the confining pressure in the soil element, the intensity of the anisotropy in some mechanical properties except the soil deformation is reduced. Furthermore, the deviatoric-to-effective mean stress ratio in the phase transformation state from contraction to dilation is independent of the loading direction and consolidation stress state, and it is considered one of the intrinsic properties of sand.

A novel torsion testing technique for micro-scale specimens based on electromagnetism.

A novel torsion apparatus for micro-scale specimens is developed based on electromagnetism, in which a coil-magnet component is used for actuating and torque measuring. When the current gets through the coil, the torque, produced by Ampere force, can be easily measured by recording the current. A laser displacement sensor is applied to measure the rotation angle. The torque is calibrated using Sartorius BP211D balance. The calibration results demonstrate there is a perfect linear relationship between the torque and the current. The torque capacity is 4.0 × 10(-4) N m with noise-floor of less than 10(-8) N m. The rotation angle capacity is 60° with noise-floor of less than 0.02°. Two sets of copper wire specimens, with diameter of 100 μm and 140 μm, are tested using this apparatus. Experimental results, with good resolution and repeatability, successfully demonstrate the effectiveness of the torsion testing technique for micro-scale specimens.

Torsional response of closed FRP composite sections

Predicting torsional response of pultruded fiber reinforced polymer (FRP) composite member with closed cross-sections is complex due to the inhomogeneous nature of section properties, which are dependent on fiber architecture and constituent material properties. Presented herein are the methods and results of an experimental study on the response of such sections to torsional loading, including prediction of shear modulus (G) and angle of twist (θ). A literature review was performed, leading to many hypothesized methods for prediction. Results presented herein will exhibit the effectiveness of a Simplified Classical Laminate Theory analysis for shear modulus (G) determination (less than 5% error), and will demonstrate good correlation between full-scale and coupon test results. For this experiment, a torsional testing apparatus was designed and developed to accommodate samples up to 144in. in length and up to 6in. by 6in. cross-sectional dimensions. Failure behavior of the cross-sections was also examined, noting that all test samples failed after reaching maximum strength of the material and exhibiting no signs of local or global buckling.

Residual-state creep behavior of typical clayey soils

Few researchers have studied the creeping displacement behavior of clayey soils using a triaxial compression cell and oedometer; however, in most cases, they have concentrated on the pre-peak state of shear. Clayey soil from a landslide is assumed to have already reached the residual-state, necessitating a study on residual strength to understand the creeping displacement behavior of clayey soils from landslides. In this work, an existing torsional ring shear apparatus was modified to understand the creeping displacement behaviors of typical clayey soil. The newly developed creep test apparatus is capable of measuring the displacement with respect to time under the application of a constant creep stress. This paper focuses mainly on residual-state creep behaviors of typical clayey soils. Residual-state creep failure prediction curves are also proposed, which may be used to predict failure time and displacement of creeping landslides in the future.