Shear Strain Levels Research Articles

Particle shape descriptors as a tool for classification of grain breakage

This study explores particle breakage of a calcareous sand, utilising dynamic image analysis and direct shear tests at varying normal stress levels to analyse the sand crushing mechanism. Tests were arrested at four phase transition points encountered during shear. Particle breakage was traced along a proposed scale based on the literature. Distinct behaviours in shape descriptors for particles of different diameters were observed under changing stress conditions. Agglomerated particle-level behaviour indicates that applied stress levels lead to different soil responses; at low stress, grains roll or slide, whereas at high stresses, grain movement is restricted. Particle breakage was evident even at minimal stress, with increasing grain size reduction as shear strain and stress levels heightened. This study introduces a parameter loading intensity (LI), amalgamating the effects of force chains and loading duration to model grain crushing. Relationships among the shape-angularity group indicator (SAGI), convexity (Cx) and sphericity (S) were also established, enabling calculation of these descriptors, after any loading intensity is applied, based on the initial values. Finally, a methodology for forecasting changes in S and Cx, under any given LI for materials with a known SAGI is presented.

Solid-state recycling of magnesium and its alloys via plastic deformation: An overview of processing and properties

The increasing demand for primary magnesium production poses significant environmental challenges, aggravated by the limited availability of raw materials, which can hinder supply. Consequently, the recycling of magnesium chips and waste is gaining importance. While conventional remelting techniques are prevalent as they suffer from drawbacks including high energy consumption, material loss, low purity, and inferior mechanical properties. Solid-state recycling (SSR) via plastic deformation processes has been introduced as a promising alternative for producing ultrafine-grained (UFG) magnesium materials with outstanding properties. Despite the absence of any reviews on SSR using plastic deformation methods for magnesium, this paper offers a detailed examination of SSR techniques. The mechanisms of bonding and grain refinement, crucial for determining the final properties of recycled magnesium, are explored. Furthermore, the discussion delves into corrosion, an essential aspect concerning magnesium and its alloys. Ultimately, the impact of various parameters such as process temperature, level of shear strain, chips size, and hydrostatic pressure on the quality of the final sample, to be used as guidance for the production of better-qualified specimens was examined.

Strain dependence of adiabatic shearing behaviors of CoCrFeNi high-entropy alloy fabricated via laser powder bed fusion under impact loads

Adiabatic shearing represents a prevalent mode of deformation failure in metals when subjected to impact loading. In this work, dynamic shearing interruption tests considering various shear displacements (i.e., shear strains) were conducted on of the CoCrFeNi high-entropy alloy (HEA) produced by laser powder bed fusion (LPBF) to analyze the microstructural evolution during adiabatic shearing. From the results, it was observed that the columnar grains in the shear region only distorted to different degrees at the lower levels of shear strain. Then, it was also found that the increase in shear strain caused severe distortion and refinement of the columnar grains, ultimately leading to adiabatic shearing band (ASB) at a critical shear strain threshold. During inhomogeneous deformation at high strain rate, the ASB formation was predicated on enough plastic deformation work. The interconnection between microstructural softening mechanisms and macroscopic mechanical behavior during ASB evolution and fracture was also highlighted. The nano-sized equiaxed recrystallized grains within the ASB were formed by rotational dynamic recrystallization (RDRX) rather than migratory recrystallization. Moreover, a large number of nano-twins were formed in these nano-sized recrystallized grains to motivate the mechanism of slip within nano-twins, thus accommodating the continuous plastic deformation. These results are the main reasons for the outstanding resistance to shear deformation of CoCrFeNi HEA produced by LPBF.

A low-cost bonded scrap tire rubber isolator in rural regions: Experimental, numerical and theoretical analysis on mechanical behavior

The utilization of low-cost scrap tire pads (STP) made from recycled tires presents a promising alternative to traditional rubber isolators (i.e., fiber-reinforced elastomeric isolators) in rural construction. However, the STP was limited in application to practicing structures due to stability with a shear strain level of 100 % and the significant variability of the mechanical behavior at the same parameters. For these issues, this paper presents a bonded scrap tire rubber isolators (BSTRIs), based on earthquake demand parameters for rural area buildings. In addition, a series of vertical compression and horizontal shear tests were conducted to evaluate the dependency of mechanical behavior on surface pressure (σ0), the first and the second shape factor (S1 and S2). Then, a finite element (FE) model of BSTRIs was developed and validated. The experimental and FE results show that the σ0, S1, and S2 overwhelmingly effect on mechanical behavior (i.e., critical pressure, vertical stiffness, horizontal stiffness, and damping ratio). Moreover, the new theoretical formulations on critical pressure, vertical stiffness, and horizontal stiffness were developed to evaluate the stability of BSTRIs. Finally, based on experimental result, a nonlinear dynamic response was conducted including the BSTRIs-supported and based-fixed unreinforced masonry (URM) buildings under 22 far-field and 28 near-field seismic excitations. The results indicated that the base shear of the BSTRIs-supported URM were decreased by 66.5 % and 50.1 % in far- and near-field record, respectively, compared with the response of the fixed-base URM building.

Microstructure and texture evolution in AZX311 Mg alloy during in-plane shear deformation

The current study examined the deformation mechanisms, microstructure, and texture evolution in AZX311 Mg alloy sheets subjected to in-plane shear (IPS) deformation. Different levels of shear strains, with values 0.05, 0.10, and 0.15, were applied along the rolling direction (RD) using a specialized in-plane shear testing jig. The strain measurement for the applied shear deformation was conducted utilizing the digital image correlation (DIC) technique. The strain distribution was found to be nearly homogeneous over sufficiently large areas, thereby allowing the microstructural measurements to yield relevant statistical data. A thorough microstructural examination across the thickness using electron back-scattered diffraction (EBSD) revealed that the application of IPS strain led to the formation of a significant number of tensile twins (TTWs) in the sheet. This was evidenced by the emergence of two satellite peaks at the periphery of the pole figures. As the shear strain increased, the proportion of TTWs in the material also increased, encompassing the entire parent grain and leading to the formation of what has been termed as “all-twinned microstructure”. The microstructural and texture investigation after IPS deformation revealed that TTWs were the dominant deformation mechanism that defined the microstructure and texture under IPS deformation, while dislocation slip activity was dominated by prismatic slip, as evidenced by the resolved shear stress analysis in this study. Consequently, this research highlights the effect of IPS deformation on the microstructure and texture evolution throughout the thickness of an Mg alloy sheet and elucidates the underlying mechanisms.

Effect of complex-grain-size curves on shear modulus degradation of calcareous sand

The dynamic shear modulus G and its degradation tendency G / G max are essential parameters for characterizing the dynamic properties of soil. Coastal facilities constructed on calcareous sand foundations are subjected to multiple types of cyclic loadings. To investigate the effects of the uniformity coefficient C u , effective confining pressure σ 0 ′ , relative density D r , and median grain size d 50 on the dynamic G and its degradation rule for calcareous sand, a set of resonant column tests is conducted on calcareous sand with different grain-size-distribution curves. The experimental results clearly show that the G degrades faster for calcareous sand with a lower σ 0 ′ and a larger C u . By contrast, the degradation of the G is affected less by D r and d 50 . The G / G max values decreased slightly as γ increased but remained less than 10 − 5 , whereas the G / G max curve descended rapidly as γ increased beyond 10 − 5 . Based on the test results obtained in this study and previously published data, a new mathematical model characterizing the degradation tendency of G / G max with respect to the shear strain level of calcareous sands with different gradation conditions is proposed. The relevant parameters associated with the proposed model are correlated with C u and σ 0 ′ .

Mechanistic modeling of fatigue crack growth in asphalt fine aggregate matrix under torsional shear cyclic load

Fatigue crack growth in asphalt pavements under vehicle load may primarily occur within the asphalt fine aggregate matrix (FAM) phase of the mixture. This study aims to predict fatigue crack growth in FAM by developing a mechanistic-based fatigue crack characterization model and fatigue crack growth model under torsional shear cyclic load. Initially, a fatigue crack characterization indicator, fatigue damage density, was derived using principles of torque and dissipated strain energy equivalence. Afterwards, a fatigue crack growth model was established based on the pseudo J-integral Paris’ law. Finally, the viscoelastic damage constitutive model was further constructed by coupling the fatigue crack growth model with a viscoelastic model, which was subsequently implemented in COMSOL Multiphysics. The results show that the fatigue damage density can be determined by the initial shear modulus and phase angle, as well as shear modulus and phase angle under fatigue conditions. Additionally, a logarithmic-linear correlation exists between the fatigue crack growth rate and the dissipated pseudo strain energy rate. The parameters of the fatigue crack growth model exhibit minimal variation across different shear strain levels and temperatures. Overall, the proposed numerical model can effectively simulate damaged torsional shear cyclic tests of FAM.

Evolution of the strain localization and shear-zone internal structure in the granular material: Insights from ring-shear experiments

Shear zone is widely observed in natural faults and landslides as well as laboratory experiments on granular material. Understanding the shear-zone evolution process in granular materials is crucial in studying the dynamics of the landslides and faults. However, it is still not well understood. To this end, we conducted a series of ring-shear experiments to investigate the evolution of strain localization and shear-zone internal structure in cohesive and non-cohesive granular materials. The quantitative evaluation was conducted by using high-solution X-ray computed tomography (CT). The analyses included visualization of shear-zone internal structure and quantification of particle shapes, orientations, and grain-size distributions at different shear strain levels. We found that with the increase of shear displacement, the large particles inside the shear zone became more and more rounded, but without an orientation, wear and attrition resulted in an abundance of nanoparticles within the shear zones. We also found fine-particle layers (nanoparticle layers) formed on either side of shear zones during shear localization, implying that shear development progressed from a shear zone to an interface. These findings offer some new understanding of the evolution of shear zones in granular materials.

Response of cohesive–frictional soils at small to medium shear strain levels from thermo-controlled resonant column testing

The shear modulus and damping ratio are arguably the two most crucial soil parameters to be used in seismic site-response analyses and a wide variety of other geotechnical engineering applications involving soil materials subjected to dynamic loading. The dependency of these parameters on the level of load-induced shear strains in the field has been investigated rather extensively for different types of soils. Most experimental studies, however, have relied on a limited set of controlled environmental factors and stress variables, mainly soil moisture and confinement. The present work is an attempt to gain further insights into the possible impact of an additional critical factor: soil temperature. A resonant column apparatus was upgraded to assess the dynamic response of three types of cohesive–frictional soils as they transitioned from linear to nonlinear behavior under thermo-controlled cyclic torsional loading. Emphasis was placed on shear modulus degradation, and hence variation in damping ratio, with increasing shear strain amplitude (cyclic torque magnitude). Results showed a mostly detrimental effect of increasing soil temperature on the normalized shear modulus, damping ratio, and threshold shear strain of clayey, silty, and sandy soils when subject to small to medium shear strain levels.

Design optimization of composite fan blade in aircraft engine subjected to bird strike loading

Bird strike has been a perennial problem for all airline companies in the world. It is the most important design criteria for the fan blades of an aircraft engine. As it is not possible to manufacture and test aircraft engines again and again for small design changes, through the simulation analysis, it is possible to study the ways to reduce the impact of the bird on a jet engine by using appropriate design and manufacturing methods for the blade. This research suggests using two fibers (hybrid) in place of the single fiber composite blade which is currently in use to reduce the delamination issues. In the first stage of this research, representative composite coupon models for combinations of hybrid fiber joint positions were created and linear static analysis was performed. For the validation of simulation methodology, a few coupons were manufactured and tested in the laboratory. Further, dynamic bird strike analysis on sub-element level models was carried out in the second stage with various joint location combinations. Next, the plate-level representative blade model was designed with the original dimensions of the aircraft engine fan blade, and bird strike analysis was performed. The behavior of the representative plate with hybrid interface was studied, and the levels of inter-laminar shear strain were checked, by varying the joint location of the two composites. Some of the shortlisted cases do show significant promise of being damage tolerant under bird strike loading.

Thermally activated nature of synchro-Shockley dislocations in Laves phases

Synchro-Shockley dislocations, as zonal dislocation, are the major carrier of plasticity in Laves phases at high temperatures. The motion of synchro-Shockley dislocations is composed of localized transition events, such as kink-pair nucleation and propagation, which possess small activation volumes, presumably leading to sensitive temperature and strain rate dependence on the Peierls stress. However, the thermally activated nature of synchro-Shockley dislocation motion is not fully understood so far. In this study, the transition mechanisms of the motion of synchro-Shockley dislocations at different shear and normal strain levels are studied. The transition processes of dislocation motion can be divided into shear-sensitive and -insensitive events. The external shear strain lowers the energy barriers of shear-sensitive events. Thermal assistance is indispensable in activating shear-insensitive events, implying that the motion of synchro-Shockley dislocations is prohibited at low temperatures.

Towards enhancing the ductility of AZ31 Mg alloys by controlling twin orientation at various shear strain levels

In this work, a novel texture control strategy, shear strain-induced twin orientation regulation (SITOR), was employed to fabricate the Mg–3Al–1Zn (AZ31) alloy with significantly improved ductility. The SITOR-1P sample processed at 250 °C exhibited a homogeneous microstructure and an almost ideal shear texture (c-axes of grains tilted 45° from the extrusion direction to the transverse direction), which resulted in an enhanced fracture elongation from 14.3% to 30.6% owing to the high activity of basal slip when compared with as-extruded Mg alloys. With increasing shear strain, the concentration of shear texture components in the SITOR-4P sample increased, leading to further improvement in its mechanical performance. While specimens produced by the conventional shear strain-induced orientation regulation (SIOR) method also underwent the same 4 passes of shear deformation, both their texture deflection and performance enhancement remained limited. The current investigation proposes a viable way to largely activate basal slip via the SITOR scheme, therefore offering a fresh perspective for addressing the poor plasticity of Mg.

Development and Computer Simulation of the New Combined Process for Producing a Rebar Profile

The study presents results of computer simulation by finite elements method of a new metal forming process combining the deformation of a billet with round cross-section on a radial-shear rolling mill and subsequent billet twisting in a forming die with a specific design. To analyze the efficiency of metal processing, the main parameters of the stress–strain state are considered: effective strain, effective stress, average hydrostatic pressure, and Lode–Nadai coefficient. The maximum value of effective strain up to 13.5 is achieved when a screw profile on the billet in the die is forming, which indicates an intensive refinement of the initial structure of the billet. During combined process, the nature of the deformation changes in the transverse direction from the axis of rotation to the surface. The central area of the billet is under the action of tensile stresses. In the peripheral part, compressive stresses grow. In the surface area, Lode–Nadai coefficient is 0.1 approximately, which indicates the high level of shear strain.

Amplification in Mechanical Properties of a Lead Rubber Bearing for Various Exposure Times to Low Temperature

In this paper, new formulations to predict the change in mechanical properties, namely, post-yield stiffness and characteristic strength of lead rubber bearings (LRBs) at low ambient temperatures, are proposed based on test results. Proposed formulations consider not only the effect of low temperature but also the effect of exposure time to low temperature. Accordingly, a full-scale LRB was tested dynamically after being conditioned at temperatures of −20, −10, 0, and 20 °C for 3, 6, and 24 h. During the displacement-controlled cyclic tests, various levels of shear strain were applied to the isolator with loading frequencies of 0.1 Hz and 0.5 Hz. Then, force-displacement curves of LRB were recorded, and the corresponding amplifications in its hysteretic properties were noted. The accuracy of existing equations to estimate the amount of amplification in mechanical properties was evaluated through the experimental results. It was found that the existing formulas do not represent the effect of exposure time on LRB characteristics at low temperatures. On the other hand, the proposed equations result in highly accurate estimations of post-yield stiffness and characteristic strength of LRB at low temperatures for different exposure times.

Experimental Study of the Dynamic Shear Modulus of Saturated Coral Sand under Complex Consolidation Conditions

The shear modulus is an essential parameter that reflects the mechanical properties of the soil. However, little is known about the shear modulus of coral sand, especially under complex consolidation conditions. In this paper, we present the results of a multi-stage strain-controlled undrained cyclic shear test on saturated coral sand. The influences of several consolidation state parameters: effective mean principal stress (p0′), consolidation ratio (kc), consolidation direction angle (α0), and coefficient of intermediate principal stress (b) on the maximum shear modulus (G0), the reference shear strain (γr) and the reduction of shear modulus (G) have been investigated. For a specified shear strain level, G will increase with increasing p0′ and kc, but decrease with increasing α0 and b. However, the difference between G for various α0 and b can be reduced by the increase of shear strain amplitude (γa). G0 shows an increasing trend with the increase of p0′ and kc; on the contrary, with the increase of α0 and b, G0 shows a decreasing trend. To quantify the effect of consolidation state parameters on G0, a new index (μG0) with four parameters (λ1, λ2, λ3, λ4) which is related to p0′, kc, α0, b is proposed to modify the prediction model of G0 in literature. Similarly, the values of γr under different consolidation conditions are also evaluated comprehensively by the four parameters, and the related index (μγr) is used to predict γr for various consolidation state parameters. A new finding is that there is an identical relationship between normalized shear modulus G/G0 and normalized shear strain γa/γr for various consolidation state parameters and the Davidenkov model can describe the G/G0–γa/γr curves. By using the prediction model proposed in this paper, an excellent prediction of G can be obtained and the deviation between measured and predicted G is all within ±10%.

An evaluation of the effect of matric suction on the dynamic strain-dependent parameters of an unsaturated silt

This research investigates the influence of matric suction on the variation of shear modulus and damping ratio of a silty soil in very small to medium shear strain levels. A set of laboratory experiments including three bender elements tests in addition to three resonant column-torsional shear tests have been carried out on unsaturated Firuzkuh silt specimens. In this regard, an unsaturated triaxial cell equipped with a set of bender elements and a resonant column-torsional shear device that can apply and control matric suction have been used. All specimens had an initial void ratio of 0.7 and were tested in various matric suctions under a net mean stress of 50 kPa. For this purpose, the axis translation technique has been implemented for applying matric suction, and High Air Entry Value (HAEV) ceramic discs have been used for air-water control of unsaturated silt specimens. According to the results, a significant variation of shear modulus and damping ratio has been observed with changes in matric suction and shear strain level. The output data indicate that shear modulus increases with increasing matric suction while the damping ratio decreases with an increase in matric suction. In addition, shear modulus and damping ratio decrease and increase with increasing shear strain, respectively.

Stability issues for elastomeric bearings: analytical formulations compared to experimental results

During earthquake strong motions, anti-seismic devices are subjected to large horizontal deformations combined to vertical stress due to gravity loads. For elastomeric bearings, the most widespread technology used to this aim, it is necessary to value critical load capacity under this combined effect, to ensure their stability in service. In this paper, elaborations of data from experimental campaign on full-scale rubber bearings (HDRBs) are compared to results form a brief theoretical overview, to evaluate their stability limits. To examine the effect of device geometrical characterization on bearing mechanical behavior, to check instability mode and to evaluate the interaction between vertical pressure and shear deformation, three different types of full-scale devices have been considered (ϕ500, ϕ600, ϕ700). Experimental data refers to “soft” natural rubber bearings, having a shear modulus G= 0.4MPa (at γ=100%), an equivalent damping factor ξ = 10÷15, a primary shape factor S1 varying in the range [19,44 – 22,72] and a secondary shape factor S2 varying in the range [2,8÷3,4]. Data derive from static shear tests, at increasing levels of shear strain (up to γ = 250%) combined to growing compressive stress (from 6 MPa to 20 MPa). Their elaboration has been accompanied by the use of dimensionless factors, in particular the ratio γ/S2, that results an effective design parameter to describe bearing performance. On the base of analytical formulations from literature, the experimental results have been matched with theoretical evaluations of the critical load. The experimental occurrence of buckling instability has been read also in light of design guidelines provided for rubber devices.

On evaluation of shear modulus parameter (G0) in SANISAND constitutive model

The SANISAND constitutive model has been widely employed for the simulation of sands cyclic behavior. The shear modulus constant (G0) in SANISAND should be theoretically estimated from maximum shear modulus of soil (Gmax). To estimate G0, however, majority of calibration studies have used triaxial tests data in the shear strain levels larger than those associated with Gmax. This technical note aims to demonstrate how the selection criteria forG0 parameter affects the SANISAND model predictions , particularly in terms of G-reduction (shear modulus -shear strain) curve of sands. First, experimental G-reduction curves for four sands are compared with SANISAND predictions based on the values of G0 parameter estimated from triaxial tests. Then, a new calibration set of SANISAND for a single sand is proposed based on the G0 value estimated from Gmax, obtained from resonant column tests. The results confirm that the numerical shear stiffness values fall significantly lower than the experimental values in small strain ranges when the G0 constant is estimated from triaxial tests. However, the G0 constant estimated from Gmax appropriately predicts the experimental G-reduction curve of the sand in a wide shear strain range.

New p-y model for seismic loading prediction of pile foundations in non-liquefiable and liquefiable soils considering modulus reduction and damping curves

In this study, a new p-y model is proposed for the seismic loading prediction of pile foundations using the Beam on Nonlinear Winkler Foundation (BNWF) method. It matches the desired modulus reduction curve by identifying three parameters in a hyperbolic function and a linear function using a genetic algorithm (GA), and the desired damping curve by applying the Ishihara-Yoshida rule that controls the unloading–reloading curves iteratively through the three parameters. The rate effect is integrated into the proposed PySimple5 model for clay by exerting influence on the ultimate capacity and maximum material damping through a power function, while the pore pressure effect is reflected in the proposed Pyliq5 model for sand by relating the ultimate capacity to the mean effective stress. For a single pile in non-liquefiable soil, the predicted superstructure acceleration and pile bending moment by PySimple5 agree well with those from centrifuge tests for different soil shear strain levels, while the equivalent linear and PySimple1 models underestimate them for soil shear strain levels higher than 1%. For a pile in liquefiable soil, PyLiq5 shows a reasonable agreement with the centrifuge tests in terms of the superstructure acceleration and pile bending moment by considering the pore pressure effect.

Experimental and analytical investigations of steel shear buckling-inhibited energy dissipation devices

This study presents the development and cyclic performance assessment of steel buckling-inhibited shear yielding devices (St-BISYDs). These devices consisted of thin steel plates as the main energy dissipating elements and modular built-up restrainers as the buckling inhibition mechanism. St-BISYDs are designed to achieve a shear strain of at least 20% without buckling to maximize the energy dissipation potential by minimizing the heat-affected zone (HAZ) and using the bolted connections. Ten specimens with two geometric configurations, namely, hourglass and rectangular, steel plates were experimentally tested under quasi-static displacement-controlled cyclic loading. The proposed restrainers greatly enhanced the cyclic performance of St-BISYDs and helped the St-BISYDs to reach the target shear strain level without significant strength and stiffness degradation under cyclic loading. An analytical study is conducted to predict the force-deformation characteristics of St-BISYDs. Experimental results of the tested specimens are also compared with other similar energy dissipation devices. Further, nonlinear modeling parameters are proposed for the force-deformation response of St-BISYDs which can be directly used in the design practices.