Shear Stress-strain Relationship Research Articles

Assessment of shear strength and compressibility characteristics of a newly developed lunar highland soil simulant (LSS-ISAC-1) for Chandrayaan lander and rover missions

The engineering properties (shear strength and compressibility) of lunar soils influence the design of landers, rovers, and their mobility behavior on the lunar surface. Assessing such properties is important for any lunar-based studies, and it is usually being determined by using suitable lunar soil simulants. This paper explains the shear strength parameters, stress-strain relationships, and volume change behavior of the newly developed lunar highland soil simulant (LSS-ISAC-1), apart from particle size distribution, which have a profound influence on the engineering behavior. In addition, to the above, other engineering properties such as critical state of the angle of internal friction, dilatancy angle, Young's modulus, Poisson's ratio, internal erodibility, small-strain shear wave velocity, and shear modulus have also been evaluated and presented. Mohr-Coulomb and friction-dilatancy theories are considered as a base for the analysis with the use of statistical predictive equations. The relative density and confining pressures are used as functions in the predictive equation to assess the behavior of the LSS-ISAC-1. The comparison of properties with the actual lunar highland soil samples of the Apollo 16 mission reveals a reasonable similarity of LSS-ISAC-1 with the lunar highland soils.

Measurement of Pure Shear Constitutive Relationship From Torsion Tests Under Quasi-Static, Medium, and High Strain Rate Conditions

Abstract Torsion tests provide important shear stress and shear strain relationships to reveal the fundamental plastic flow response of a material. Bespoke torsion techniques complemented by digital image correlation are developed to accurately measure the shear stress–strain relationship at quasi-static, medium rate 9/s, and high strain rate above 1000/s. The equipment used includes a screw-driven mechanical system, a hydraulic Instron machine and a Campbell thin-walled tube split Hopkinson torsion bar equipped with an ultrahigh-speed camera. A near alpha Ti3Al2.5V alloy was used as a model material in this study. A four-camera digital image system has been constructed to monitor the material deformation and failure during a low rate torsion test, to gain further insight into plastic deformation of the tubular specimen. Shear stress–strain relationship of the Ti3Al2.5V alloy exhibits noticeable strain rate sensitivity. Observations of the strain hardening rate evolution indicate that the hardening capacity of Ti3Al2.5V is both strain and strain rate dependent. High strain rate torsional stress–strain relationship shows lower strain hardening, compared to the response obtained from a shear compression specimen. The present techniques are demonstrated to be suitable for the measurement of pure shear constitutive relationship, including rate sensitivity and failure of the material.

True Triaxial Study on Aeolian Sand Subgrade

The drained shear tests of aeolian sand in Tengger Desert were carried out by using the British GDS true triaxial apparatus, and the shear strength and stress-strain relationships of aeolian sand were studied under the conditions of constant average principal stress and different intermediate principal stress coefficients. The test results showed that the variation trends of principal strains in the three principal stress directions were correlated with the variation of the intermediate principal stress coefficient, and the stress-strain relationships in the three principal strain directions were hardening type. With the increase of intermediate principal stress coefficients, the shear strength of the specimen decreased, and the peak value of shear strength was the lowest when b = 0.8.

Strength and Deformation Characteristics of Fiber Reinforced Longdong Loess and Experimental Study of Modified Duncan -Chang Model

Fiber yarn reinforced loess is prepared through mixing plain loess with a certain proportion of polyester fiber yarn, which is formed by loosening, carding and cutting waste synthetic textile polyester fabric and has rough surface properties and good acid-alkali corrosion resistance. The strength and deformation characteristics of Longdong Loess reinforced by fiber yarn were studied. The test results show that the uniaxial compressive strength of fiber yarn reinforced loess increases with the increase of fiber yarn proportion and fiber yarn length, and decreases with the increase of fiber yarn fineness. Combined with the uniaxial compressive strength data of fiber yarn reinforced loess under the optimal water content and liquid limit water content, an index which can comprehensively reflect the reinforcement performance of fiber yarn reinforced loess is proposed-- Fiber reinforced index. The shear stress-strain relationship of triaxial consolidation drainage of fiber-reinforced loess with different proportion of fiber yarn is strain hardening type. The hypothesis of hyperbolic form is in accordance with Duncan Chang model. By discussing the relationship between the parameters of fiber yarn reinforced loess and plain loess model, the empirical expression of model parameters considering the influence of fiber yarn reinforced loess is obtained. A modified Duncan-Chang E-B model reflecting the influence of different fiber yarn blending ratio was constructed. The rationality of the model is verified by comparing the test curve with the model prediction curve.

Post-Yield characteristics of electrorheological fluids in nonlinear vibration analysis of smart sandwich panels

The present study deals with the nonlinear free vibration analysis of sandwich plates containing electrorheological (ER) fluid as the core layer. Since yield stress of the ER fluid is relatively low, the fluid widely operates in the post-yield region in which the shear stress and shear strain relation is no longer linear. This study employs an equivalent linearized complex shear modulus to quantify the storage and loss moduli of the fluid in different levels of shear strain amplitude and electric field intensity. Also, Classical Plate Theory (CPT) along with von Kármán kinematic formulations are incorporated to extract governing equations of motion of the ER based sandwich plates, in a finite element formulation. The nonlinear governing equations of motion of the structure are solved using a displacement control strategy to evaluate the resonant frequencies and corresponding loss factors of the sandwich plate. Then, the primary attention is focused on the effect of post-yield characteristics of ER fluid on the nonlinear dynamic behavior of the ER based sandwich structure. Furthermore, the effect of applied electric field, boundary conditions and plate parameters such as core layer thickness on the natural frequencies and damping of the structure are comprehensively investigated.

Mechanical properties of recycled aggregate concrete under compression-shear stress state

Mechanical properties including failure mode, strength, and stress–strain relation of recycled concrete specimens are tested under compression-shear stress state. Replacement ratio of recycled coarse aggregate (RCA), stress ratio of applied compression (σ/ƒcu) and reinforcement ratio (ρv) are designed as the main factors which affect mechanical properties of concrete. The results show that the failure mode is mainly affected by σ/ƒcu, both ρv and σ/ƒcu take an effect on shear strength, the strength value increases with the ρv and σ/ƒcu goes up. RCA replacement ratio gives a negative effect on shear strength due to the initial damage initiated in crushing process, the strength value decreases with RCA replacement ratio increases. Appropriate formula has been selected to describe the change of shear strength combined with σ/ƒcu and ρv under different RCA replacement ratios, and the predicted strength curves match well with the experimental data based on regression analysis. The shear stress–strain curve of the plain concrete is influenced by both σ/ƒcu and RCA replacement ratio, the initial slope and the whole shape of the curve are effected by the two factors, a fitting equation is proposed to describe the shear stress–strain relationship of plain concrete under compression-shear composite stress state.

A simplified model for inelastic seismic analysis of RC frame have shear hinge in beam-column joints

This paper presents a simplified beam-column joint modeling technique for the inelastic analysis of reinforced concrete moment-resisting frames. The joint model consists of a zero-length link element that is provided with moment-rotation lumped plasticity hinge, provided at the intersection of beam/column elements, to simulate the nonlinear shear behavior of the joint panel. The backbone of the moment-rotation constitutive law was defined using the empirical shear stress-shear strain relationship proposed by Kim and LaFave. The hysteretic response of the joint was simulated using the multi-linear hysteretic rule proposed by Sivaselvan and Reinhorn. The modeling technique was applied to two portal frames tested under quasi-static cyclic loads for predicting the cyclic force-displacement hysteretic response. The prediction was found in good agreement with the experimental response; the numerical models were efficient in simulating the shear behavior of the joints, loading/unloading stiffness and pinching behavior of the frames’ lateral force-displacement hysteretic response. The modeling technique was extended to two-story frames for nonlinear response history analysis for both design base and maximum considered earthquakes. Inter-story drift demands were obtained and critically compared to highlight the efficacy of the accurate modelling of beam-column joint using lumped plasticity shear simulation hinges. The study also confirms the beneficial role of beam-column joint detailing in resisting both design base and maximum considered earthquakes without exceeding the life safety and collapse prevention limit states respectively.

A method for characterization of multiple dynamic constitutive parameters of FRCs

We propose a method to measure multiple dynamic material constitutive parameters of unidirectional fiber reinforced composites (FRCs) in a single experiment. Dynamic short-beam shear (DSBS) experiments were performed on a modified Kolsky compression bar, with integration of high-speed imaging and digital image correlation (DIC). The unidirectional FRCs investigated were S-2 glass fiber reinforced matrix of TGDDM-Jeffamine® D230 with monoamine functionalized partially reacted substructures (mPRS) and commercially available SC-15. Analytical solutions of normal and shear strains of a composite beam were derived based on Timoshenko beam theory, assuming material to be transversely isotropic and have different moduli in tension and compression in each principle material orientation. Tensile and compressive moduli were inversely computed through monitoring normal strain slope when specimen was constantly loaded at a speed of ~7.3 m/s within a small deflection. Non-linear shear stress-strain behavior of the composite was described via Ramberg–Osgood equation. Finite element (FE) analysis was conducted in ABAQUS, simultaneously defining via user subroutine UMAT the transverse isotropy of material, bi-modulus constitutive model, and non-linear shear stress-strain relation. The method proposed in this work was validated by comparing strain distributions computed by FE model and DIC measurements. Comparing with traditional dynamic tensile, compressive, and shear experiments on FRCs, this method significantly simplifies the specimen preparation and design of complicated gripping fixtures for multiple experiments. Furthermore, systematic errors resulting from variations of specimen geometry and dimension, loading direction, and instrumentation are reduced, thereby providing compatible data for numerical studies on impact behavior of composites.

Three-dimensional elasto-plastic damage model for gravelly soil-structure interface considering the shear coupling effect

The gravelly soil-structure interface was observed to exhibit a significant coupling effect among the orthogonal shear directions due to the three-dimensional shear application in different experimental investigations, which governs major three-dimensional features of the interface. In this paper, initially, a three-dimensional modeling framework is established based on the analyses of interface behavior under different shear coupling conditions. A series of concepts and assumptions are derived in this framework, banking on which a three-dimensional model scheme is proposed by reasonably modeling the shear coupling effect. Afterward, a three-dimensional elasto-plastic damage interface model is developed based on the proposed model scheme and modified formulations of a previous two-dimensional EPDI model. Only a single new parameter is introduced in the three-dimensional shear stress-strain relationship modeling scheme to quantify the three-dimensional shear response of the interface besides already known parameters of the EPDI model. The model can simulate the monotonic and cyclic response of interface along two and three-dimensional shear paths in a unified manner. The performance of the model is validated based on test data from the literature. The model can capture different essential features of the gravelly soil-structure interface behavior under three-dimensional conditions, e.g., coupling effect, volumetric change behavior and aeolotropy.

Granular flow of an advanced ceramic under ultra-high strain rates and high pressures

The dynamic rheology of a complex granular material system strongly depends on the imposed stress state. However, drawing a clear physics based picture of dynamic granular flow is challenging due to the heterogeneous nature of granular materials, as well as the overwhelming difficulties in carrying out dynamic experiments. Here, pressure-shear plate impact (PSPI) is utilized to load a granular boron carbide ceramic in a multi-axial fashion with strain rates on the order of 105s−1 and pressure levels ranging from 1 to 3 GPa. Comparisons between the shear flow stresses and the superimposed normal stress indicate a strong pressure dependence in the constitutive response, along with an effective friction coefficient measured to be around 0.16. Both the normal and shear stress-strain relations are obtained. Granular boron carbide shows a highly compressible behavior with a significant amount of volume compaction achieved as the result of the large uniaxial normal strain. Due to the compaction, the estimated granular wave speed increases with density. Microstructure characterization of the deformed particles shows that fracture and amorphization are active deformation mechanisms besides the grain-grain frictional interactions and particle rearrangement. This study will contribute to the development of integrative modeling for behavior of granular boron carbide at ultra-high strain rates and confinement pressures.

An Innovative Procedure for the In-situ Characterization of Elastomeric Bearings by Using Nanoindentation Test

ABSTRACT Control and inspection of the conditions of elastomeric bearings used for seismic isolation purpose is a fundamental activity in ensuring and preserving the performance of a structure. The methods currently used, such as visual inspections, Operational Modal Analysis (OMA), release tests, very often present strong limitations due to their qualitative nature or else to the costs associated with their implementation and functioning. An innovative procedure based on the use of nanoindentation tests is proposed and validated through an experimental campaign. Its main benefits consist in the possibility of quantitatively estimating the current characteristics of elastomeric bearings, in conjunction with low implementation costs and influence on the isolating devices. The innovative procedure consists of coring a very small sample of rubber from a bearing and testing it with a nano-indenter in order to estimate the actual characteristics in terms of shear stress-strain relationships. The experimental tests showed good agreement between the properties calculated with the proposed method and the ones obtained directly through a traditional shear test, making such procedure a promising tool.

Free vibration analysis of thick sandwich cylindrical panels with saturated FG-porous core

In this paper a numerical solution is presented for free vibration analysis of sandwich cylindrical panels made of a saturated functionally graded porous (FG-porous) core and two similar homogenous face sheets. The panel is modeled based on the third order shear deformation theory (TSDT) and stress-strain relations are considered based on the linear poroelasticity theory of Biot. Natural frequencies are calculated for various boundary conditions and a parametric study is presented to study the effects of various parameters on the natural frequencies including geometrical parameters, porosity parameter, porosity distribution pattern, thickness of the porous core and compressibility of porefluid.

The influence of material shear nonlinearity on predictive failure envelopes of multidirectional laminates

In present study, laminates with the type of [±θ°]S and [0°2/±θ°]S are investigated in order to clearly show the effect of material shear nonlinearity, and then theoretical predictions are compared with experimental data. In the whole process of generating failure envelopes, secant shear modulus instead of initial shear modulus is used for accurate shear stress-strain relation. The modulus values are recalculated every time when the combining load is changed. Final failure envelopes are then compared between numerical models. It is found that the variation in the size of safe regions from nonlinear analysis is closely related to the way of combing load and fiber directions. So in the process of improving failure theories or in the applications of failure theories, the effect of material nonlinearity can be considered appropriately.

Damage and viscoplastic behavior of sintered nano-silver joints under shear loading

Compared with most of the traditional solder materials, sintered nano-silver shows better high-temperature service performance and is expected to replace the traditional packaging materials in the next-generation of electronic devices. However, there exist substantial voids inside the sintered nano-silver layer after sintering, and the conventional continuum damage mechanics has certain limitation to describe the shear stress-strain relationship of sintered nano-silver materials. To analyze the void evolution and microstructure of sintered nano-silver, gold-plated sintered nano-silver specimens were tested under shear loading at different temperatures. A unified viscoplastic constitutive model is proposed to describe the properties of sintered nano-silver specimen under shear loading, in which the viscous overstress is replaced by the potential function of Gurson-Tvergaard-Needleman model and the effects of void on the yield surface of viscoplastic material is considered. To describe the influence of void evolution to the deterioration of mechanics properties at high temperatures, a damage variable is incorporated into the drag strength to indicate the damage mechanism with respect to the softening of sintered nano-silver material. The numerical predictions are compared with the experimental data, which shows that the developed model can describe the shear constitutive behavior of sintered nano-silver specimen with reasonable accuracy.

A new Dynamic Plasticity and Failure Model for Metals

A new plasticity and failure model is developed herein for metallic materials subjected to dynamic loadings on the basis of the analysis of some available material test data and previous work. The new model consists of two parts: a strength model and a failure criterion. The strength model takes into consideration both tension and shear stress-strain relationships, as well as the effect of Lode angle, while the failure criterion takes into account both the effects of stress triaxiality and Lode angle. Furthermore, the effects of strain rate and temperature are also catered for in the model. In particular, new non-linear functions are suggested for the effects of strain rate and temperature in the strength model in order to describe accurately the mechanical behavior of metallic materials at very high loading rates and temperature. The new model is compared with available material test data for 2024-T351 aluminum alloy, 6061-T6 aluminum alloy, oxygen free high conductivity (OFHC) copper, 4340 steel, Ti-6Al-4V alloys, and Q235 mild steel in terms of stress–strain curves in both tension and shear, strain rate effect, temperature effect and fracture under different loading conditions. The new model is also compared with the JC constitutive model with the respective JC and BW fracture criteria by conducting numerical simulations of quasi-static smooth and notched bar tensile tests and ballistic perforation tests on 2024-T351 aluminum alloy in terms of cup and cone failure pattern, ballistic limit, residual velocity and failure mode. It transpires that the new plasticity and failure model can be used to predict the response and failure of metallic materials and structures under different loading conditions. It also transpires that the new model is advantageous over the existing models.

Shear Behavior of Multi Leafs Masonry Panels with Transversal Connections

The historical masonry buildings are generally characterized by a load-bearing structure constituted by walls that should resist to both gravitational and horizontal actions. In several existing constructions, masonry panels are made by two external leafs with higher mechanical properties and an inner core with very low, or even negligible, mechanical characteristics. In some cases the connection between the external leafs was provided by inserting a certain number of bricks in the transversal direction (namely diatones); while sometimes, the leafs were totally independent. Often in the case of horizontal forces, as those due to earthquakes, the multi-leafs walls collapse has been observed, because of the leafs separation. Nowadays, there are different connecting systems available in the market and utilized to guarantee the collaboration of the external leafs, in order to finally improve the wall bearing capacity.In this scenario, the present paper is aimed to investigate the shear strength of small-scale multi-leafs panels, coupled with different types of connector, such as: diatones, L-shaped glass; glass and steel rope and helical steel bars. In plane shear tests have been performed in order to evaluate the shear stress-strain relationship. The results are herein reported and discussed, aiming to determine the effectiveness of the different connections systems.

Exact results for sheared polar active suspensions with variable liquid crystalline order.

We consider a confined sheared active polar liquid crystal with a uniform orientation and study the effect of variations in the magnitude of polarization. Restricting our analysis to one-dimensional geometries, we demonstrate that with asymmetric boundary conditions, this system is characterized, macroscopically, by a linear shear stress vs. shear strain relationship that does not pass through the origin: At a zero strain rate, the fluid sustains a non-zero stress. Analytic solutions for the polarization, density, and velocity fields are derived for asymptotically large or small systems and are shown by comparison with precise numerical solutions to be good approximations for finite-size systems.

Molecular dynamics simulation of shear deformation of multi-layer graphene sheets with Tersoff potential

The failure process of multi-layer graphene sheets with AB stacking order under shear deformation is simulated using molecular dynamics method with Tersoff potential. Shear stress-strain relationships and shear failure modes of zigzag and armchair graphene sheets are obtained, while the effect of the number of graphene layers on the shear properties of zigzag and armchair graphene sheets is investigated. The results indicate that the shear modulus of graphene sheets is inclined to diverge with the increase of the number of graphene layers. Moreover, the ultimate stress and shear failure strain of zigzag and armchair graphene sheets are reduced gradually with the increase of the number of graphene layers.

Molecular dynamics simulation of shear deformation of multi-layer graphene sheets with Tersoff potential

The failure process of multi-layer graphene sheets with AB stacking order under shear deformation is simulated using molecular dynamics method with Tersoff potential. Shear stress-strain relationships and shear failure modes of zigzag and armchair graphene sheets are obtained, while the effect of the number of graphene layers on the shear properties of zigzag and armchair graphene sheets is investigated. The results indicate that the shear modulus of graphene sheets is inclined to diverge with the increase of the number of graphene layers. Moreover, the ultimate stress and shear failure strain of zigzag and armchair graphene sheets are reduced gradually with the increase of the number of graphene layers.

Experimental and numerical evaluations of Kirkuk field soil treated with waste shredded tire

In this study, an experimental and numerical investigation of Kirkuk real field soil treated with waste tire has been examined. Field soil samples from Kirkuk city have been collected and tested experimentally to evaluate the basic soil properties. The field soil has been treated with waste shredded tires and up to 10%. A series of direct shear tests under different normal stresses and unconfined compression tests with two different rates have been performed on both untreated and waste tire treated soils. For the untreated soil, the maximum shear stress measured by the direct shear test increased by 150% when the normal shear stress increased from 50 kPa to 150 kPa. For the 5% and 10% waste tire treated soils, the maximum shear stresses measured by the direct shear test increased by 110% and 105% when the normal stress increased from 50 kPa to 150 kPa respectively. The peak uniaxial stress measured by the unconfined compression test increased by 83% and 98% as the waste tire treatment increased from 0% to 10% for both testing rates of 0.125 mm/min and 0.25 mm/min respectively. Finally, finite element method using three different models represented by elastic, hyperbolic and Mohr-Coulomb elastic-plastic models have been used to model unconfined compression tests for both untreated and 10% waste tire treated soils. For both untreated and waste tire treated soils, the elastic model over predicted the shear stress versus shear strain relationship whereas the elastic-plastic model had a very good agreement with the experimental data. However, the hyperbolic model had a good prediction for the initial part of the shear stress versus shear strain relationship for both untreated and waste tire treated soils with an overestimation for the second part of the experimental data.