Shear Direction Research Articles

Experimental study on sand anisotropy using hollow cylinder apparatus

This study investigated sand anisotropy experimentally using a hollow cylinder apparatus. The effect of the initial anisotropy on the shear behavior of sand was illustrated by conducting experiments on specimens with bedding planes and systematically varying the density, principal stress direction, and intermediate principal stress. The change in induced anisotropy during shearing was experimentally captured by re-shearing the specimens subjected to prior shear history. The experimental results revealed the following: (a) Anisotropy in sand, whether initial anisotropy developing during specimen preparation or induced anisotropy developing due to shear history, causes pseudo-density changes in the mechanical behavior, in which sand of the same density behaves as if it has a different density depending on the direction of shear. (b) The changes in induced anisotropy, due to shearing in the same direction as that of the prior shear, make the soil behave similarly to dense sand, whereas shearing in a direction perpendicular to the prior shear makes the soil behave similarly to loose sand. (c) The larger the prior shear, the more pronounced the pseudo-density changes that appear in the subsequent behavior. Moreover, the significance of induced anisotropy in liquefaction and compaction phenomena was experimentally demonstrated through single and double swing cyclic shear tests. The results obtained from the study will be useful for validating models that incorporate induced anisotropy.

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A reflectional quantitative differential phase microscopy (RQDPM) based on polarized wavefront phase modulation and partially coherent full‐aperture illumination is introduced for imaging thick and opaque samples. RQDPM utilizes the polarization‐dependent characteristic of a phase‐type spatial light odulator to divide the object wave into two identical copies with a certain shear distance. When loading different modulation images to the spatial light modulator, phase derivative images with different shearing directions and phase shifts can be obtained. Finally, the phase distribution of the sample is obtained.For further details please visit the article by Ying Ma, Taiqiang Dai, Lan Yu, Lin Ma, Sha An, Yang Wang, Min Liu, Juanjuan Zheng, Liang Kong, Chao Zuo, and Peng Gao (e202200325).image

Examination of interface roughness and particle morphology on granular soil–structure shearing behavior using DEM and 3D printing

Understanding the mechanical behavior of soil-structure interaction (SSI) is crucial for the safety and stability of infrastructures. From mesoscale to macroscale, the coupled effects of particle morphology and structural surface roughness on SSI has received little attention. Herein, a series of interface shear tests and simulations were carried out by combining 3D printing and discrete element method (DEM). To quantitatively characterize particle shape and structural surface roughness, modified particle shape parameter Sh and interface morphology factor λ are introduced. The results indicate that increasing the inclination of asperities 1/λ promotes lateral slip displacement of particles and results in significant delamination at the interface. In the vertical shear direction, particle displacement exhibits two patterns: backward falling and maximum displacement at the top of the shear zone, and continuous forward displacement decrease along the height of the specimen. Thus, a new index (i.e., maximum backward falling displacement of particles) is proposed to define the shear zone thickness. Particle shapes and interface roughness have different effects on the particle displacement in the vertical shear direction. An increase in Sh reduces relative displacement, while an increase in 1/λ can increase the magnitude of the relative displacement of particle lateral sliding. The overall strength of particles depends on the coupling effect of particle shapes and interface roughness, both of which have corresponding thresholds. As the interface roughness or Sh increases, three parameters used to describe the contact state of clusters first increase until reaching a turning point and then remain stable or slightly decrease. This paper aims to broaden the understanding of the coupling effects of interfaces with various roughness and particles with different shapes on SSI, with the ultimate goal of contributing to the design of structural interfaces more effective and safety in sandy soil area.

Molecular Mechanisms of Self-mated Hydrogel Friction

Hydrogel-like structures are responsible for the low friction experienced by our joints when we walk or by our eyelids when we blink. At low loads, hydrogel contacts show extremely low friction that rises with velocity beyond a threshold speed. Here we combine mesoscopic simulations and experiments to test the polymer-relaxation hypothesis for this velocity dependence, where a velocity-dependent regime emerges when the perturbation of interfacial polymer chains occurs faster than their relaxation at high velocity. Our simulations quantitatively match the experimental findings, with a friction coefficient that rises with velocity to some power of order unity in the velocity-dependent regime. We show that the velocity-dependent regime is characterized by reorientation and stretching of polymer chains in the direction of shear, leading to an entropic stress that can be quantitatively related to the shear response. The detailed exponent of the power law in the velocity-dependent regime depends on how chains interact: We observe a power close to 1/2 for chains that can stretch, while pure reorientation leads to a power of unity. These results show that the friction of hydrogel interfaces can be engineered by tuning the morphology of near-surface chains.

Effect of Mg/Si Ratio on the Bendability and Anisotropic Bend Behavior of Extruded 6000-Series Al Alloy.

Extruded Al-Mg-Si profiles applied in the automotive industry are required to achieve an appropriate combination of strength and bendability. In order to investigate the effect of Mg/Si ratio on the bendability and anisotropic bending behavior, AA6005 and AA6061C were extruded to 2 mm thick plates. More Goss texture and anisotropic particle clusters exist in AA6005 alloys with a low Mg/Si ratio, which leads to a high tendency of surface roughing and cracking and to strong anisotropy in their bendability. However, more low-angle grain boundaries, cubic texture and comparatively random distribution of particles exists in AA6061C alloys with a high Mg/Si ratio, which blunts the surface roughing and crack process. The surface undulation is the outcome of the strain-intense localization of several layers of grains in the vicinity of the outer elongated surface. The strain localization and surface undulation lead to shear band initiation near the valleys. Several cooperating micro-mechanisms in AA6005, including grain clusters with Goss and Cubic orientation, heterogeneously nucleated particles and grain boundary spatial arrangements, lead to the grain boundary decohesion along a shear direction. AA6005 shows for predominately intergranular fractures in nature, with some areas exhibiting grain boundary decohesion during bending in the TD. However, AA6061C shows a predominately transgranular in nature, with some areas exhibiting intergranular fracture, which is affected by shear band development.

Induced kink boundary in Mg-Y-Zn alloy by tube-shape forming

The secondary formability and the effect of shape application on induced kink boundaries are examined using Mg-9at.%Y-6at.%Zn alloy through experimental and numerical studies. A tube-shape is successfully formed without any cracks. This tube-shaped alloy includes kink boundaries associated with the applied shear strain. In the numerical study, a substantial shear strain is created at the contact region, but the shear direction becomes opposite after tube formation. This suggests that de-kinking behavior, such as shrinkage of kink boundaries, has a possibility to occur. In contrast, this formed alloy exhibits higher hardness by a magnitude of 30 Hv than the un-processed alloy. The correlation between kink density and hardness in this tube-shaped alloy is consistent with literature results obtained from several wrought-processed Mg-Y-Zn alloys.

Engineering twin boundaries for enhancing strength and ductility of thermoelectric semiconductor PbTe

Twin boundary engineering is a potential strategy for achieving robust mechanical properties of materials. Our previous molecular dynamics simulations indicated that the nanotwin could significantly enhance the ductility of thermoelectric (TE) semiconductors PbTe due to coherent twin boundary (CTB) migration accompanied by the ‘catching bond’ at room temperature. To further improve the mechanical strength or ductility of PbTe, we investigated the role of the shear direction, the CTB orientation and the temperature on mechanical properties of nanotwinned PbTe. Under the shear stress along [11̅0] loading direction, the partial dislocations with a/6 [12̅1] and a/6 [21̅1̅] Burgers vectors are preferentially activated on (111) twin plane with higher yield strength and ultimate shear strength than that of the (111)[112̅] slip system. The nanotwinned PbTe with CTB orientation ranging from 125° to 161° has both higher fracture strain and larger ultimate shear strength than 0° CTB orientation. This is attributed to the motion of the twinning partial dislocation significantly enhancing the ductility while the blocking of dislocations by CTBs further improving the shear strength and deformability of PbTe. Moreover, the low temperature (below 100 K) energetically enables the partial dislocation to nucleate and glide on the strong Te-CTB plane, which induces successive CTB migration along Pb- and Te-CTB planes, resulting in enhanced ductility of nanotwinned PbTe.

Enhanced rheological and tribological properties of nanoenhanced greases by tuning interparticle contacts

HypothesisDespite the wide spectrum of available nanoparticles, their utilization in lubricant and grease formulations remains challenging. To enhance their performance, an improved link between the interparticle contacts, brittleness of the resulting particle network, time-dependent rheology and tribology is required. ExperimentsWe systematically changed interparticle contacts and examined their effect on the colloidal stability, microstructure, rheological and tribological behavior of model greases by investigating four types of nanoclays: montmorillonite (Cloisite Na+), oleic-acid functionalized Cloisite Na+ (OA-Cloisite Na+), organomodified montmorillonite (C20A) and oleic-acid functionalized C20A (C20A-OA). FindingsWe observed a range of behaviors, starting from the lack of colloidal stability in greases derived with Cloisite Na+ and OA-Cloisite Na+ to semi-solid type systems with C20A and C20A-OA. Consistent with previous studies, the rheological and tribological properties of C20A systems scale with nanoclay loadings. Surprisingly, the functionalized C20A-OA system exhibited a delayed transition towards hydrodynamic lubrication, and enhanced lubrication properties, both of which were largely independent of nanoclay loadings. Coupled microstructural investigation and time-dependent rheology reveal that this behavior is governed by increasing repulsive forces, decreasing inter-particle friction between C20A-OA nanoparticles, and faster reorganization of the C20A-OA nanoparticle network under shear. Increased interparticle repulsion enables C20A-OA nanoclays to pass each other under shear and align in direction of shear, which reduces the overall viscosity, while the presence of OA on nanoclays decreases inter-particle friction and particle-steel surface friction.

Determining elastic properties of CSEB masonry using FEA-based homogenization technique

The world today is embracing a sustainable approach in all sectors. The construction industry is grappling with the problem of minimizing energy consumption and lowering carbon emissions involved in the manufacture of construction materials. Soil blocks are an alternative to fired clay bricks. Soil bricks are inexpensive, recyclable, environmentally friendly, and provide better thermal comfort. However, masonry walls built with soil blocks have several drawbacks. They are bulky, have poor durability properties and their strength capacity reduces significantly when saturated due to rain. The remedy for this problem is a Cement Stabilized Earth Block (CSEB). An engineered mixture of soil-sand-cement-moisture compacted at predefined levels offers superior strength and durability properties. The percentage of cement added is minimal in comparison to the soil-sand mixture content. In this study, a numerical model to predict the elastic properties of masonry comprised of CSEB and soil–cement mortar is developed. Both the constituents, CSEBs, and soil–cement mortar have different elastic properties. The presence of bed joints and perpends lends orthotropic behavior to masonry. The present study considers the Finite element analysis (FEA)-based homogenization technique to predict the elastic properties of CSEB masonry. A small periodic part of masonry called a repetitive unit cell (RUC) is considered, which is representative of the block-mortar arrangement in masonry. The three-dimensional masonry RUC is modelled using FE-based ABAQUS-CAE software. A user-defined Python script is developed to apply PBCs (Periodic boundary conditions) to RUC. The six far-field unit strains are applied to the RUC model in three normal and three shear directions. Finally, volume-averaged stress components are computed to determine the elastic properties. The modulus of elasticity and Poisson’s ratio of CSEB masonry along three directions are determined. The proposed approach is governed by mechanics and not by empirical relationships and provides satisfactory results.

Local flow and loads estimation on wake-affected wind turbines using graph neural networks and PyWake

The estimation of the flow conditions throughout a modern wind farm is a relevant albeit complex problem involving several different modelling scales. In this context, recent years have seen the rise of the demand - normally industry-driven - of quick, computationally inexpensive, wind farm flow field simulators upon which further calculations might be undertaken (e.g. power output, fatigue loads, etc.). Naturally, the trustworthiness of such models hinges upon their ability to accurately estimate wakes, under the evident trade-off between computational time and accuracy. One such simulator that has been recently gaining traction within the wind community is PyWake, a Python-based flow solver, with several possible add-ons and modularity options. Based on runs from PyWake, this contribution studies the applicability of graph neural networks (GNN) as a simultaneous wind turbine fleet, wind inflow and loads surrogate. As graphs are discrete mathematical sets of dependent objects, one can see how the layout-dependent interaction between wind turbines’ aerodynamics, from which wake arises, lends itself to be modelled as a graph. Thus, we introduce the use of GNNs for layout-agnostic joint modelling of rotor-averaged wind speed, turbulence intensity, power production and damage equivalent loads (DEL) on individual turbines of wind farms. To this end, probabilistic samples of inflow conditions from a Weibull distribution for wind speed, uniform wind direction and conditional normal distributions of wind shear and nacelle yaw angles are generated as main inflow properties in the numerical simulations. Additionally, arbitrary wind farm layouts are created based on varied geometric shapes with random parametrization (varying orientations, length/width ratio). Both the arbitrary layouts and the random inflow conditions are then used as inputs for PyWake. PyWake’s output, namely, rotor averaged wind speed, turbulence intensity, power production and DELs of each individual wind turbine in the wind farms, are used to train a general GNN model. We elect to implement an Encode-Process-Decode GNN as a graph learning model. We compare the performance of various approaches of the relational dependency representation (edge-forming techniques) amongst the nodes (wind turbines) on the graph, such as Delaunay triangulation, KNN, radius-based methods and fully connected scheme. In our analysis, we evaluate the accuracy of GNNs and its ability to generalize their joint predictions for unseen layouts and varying inflow conditions.

Static investigation of martensitic nucleation criticality in an atomistic model material

ABSTRACT This contribution investigates the nucleation of martensitic transformations in the bulk of austenitic single crystals. The transformation is associated with a decrease in the potential energy that is the driving force for the transformation. The coordinated atom displacements, which generate the martensite, produce large elastic strains in the material, which are associated with an elastic energy that opposes the transformation. A thermodynamic nucleation criterion for this type of transformations is derived. The criterion is evaluated by the method of static lattice relaxation for homogeneous nucleation in an atomistic 2D model material. The potential energy of martensitic clusters of different sizes and shapes, embedded in a stabilised austenitic matrix are calculated. The results exhibit non-monotonous progressions of the potential energy with the cluster size. This indicates that the elastic strain energy scales non-linearly with the size to allow the formation of local energy maxima at critical cluster sizes, interpreted as nucleation barriers. These barriers separate domains of stability from domains of instability in the configurations space, similar to Kelvin's classical theory of spherical fluid phase nucleation. The critical nuclei sizes are in the order of 100–150 unit cells, and their shapes are plate-like with long dimension parallel to the shear direction. The critical size of twinned clusters decreases with the twinning multiplicity.

An Estimation Model of the Ultimate Shear Strength of Root-Permeated Soil, Fully Considering Interface Bonding

Roots can be seen as natural soil reinforcement material. The prediction and quantitative evaluation of the shear strength of root-permeated soil is the focus of vegetation slope protection, in which the bonding effect of the root–soil interface is the key factor. Taking the roots of Chinese fir trees as an example, the shear resistance test of root–soil interface bonding strength and the direct shear test of root-permeated soil with different root area ratios and inclination angles were carried out. The results indicated that the bonding strength of the root–soil interface could be quantified by interfacial cohesion and friction angle. The shear strength of root-permeated soil increased with the root area ratio, and its relationship with the inclination angle of root relative shear direction was: 45° > 90°. In addition, an estimation model of the ultimate shear strength of root-permeated soil was developed, in which the bonding effect of the root–soil interface was quantified by the interface bonding strength parameters. The soil stress, root diameter, root length, and the initial angle between the root and shear direction can be considered in the estimation model. The rationality and accuracy of the estimated model were verified through the comparison of experimental results and Wu’s model. The proposed model can be used to calculate the stability of the biotechnical reinforcement landslides and evaluate the shear strength of the root-permeated soil.

Experimental Investigation of Material Removal in Elliptical Vibration Cutting of Cortical Bone

To benefit tissue removal and postoperative rehabilitation, increased efficiency and accuracy and reduced operating force are strongly required in the osteotomy. A novel elliptical vibration cutting (EVC) has been introduced for bone cutting compared with conventional cutting (CC) in this paper. With the assistance of high-speed microscope imaging and the dynamometer, the material removals of cortical bone and their cutting forces from two cutting regimes were recorded and analysed comprehensively, which clearly demonstrated the chip morphology improvement and the average cutting force reduction in the EVC process. It also revealed that the elliptical vibration of the cutting tool could promote fracture propagation along the shear direction. These new findings will be of important theoretical and practical values to apply the innovative EVC process to the surgical procedures of the osteotomy.

Morphological Features of Fractures Developed by Direct Shearing of Intact Granites after Water Cooling Cycles.

Rock fractures are considered as favorable objects for enhanced geothermal development. The fracture morphologies play an important role in enhanced geothermal development. Therefore, the study of fracture morphologies has a certain guiding significance for the geothermal reservoir. Water cooling and water cooling cycles can change the morphology of fracture surfaces formed by the shear failure of intact granites. To date, however, there is little work on the effect of water cooling and water cooling cycles on the morphology of fracture surfaces formed by direct shearing of intact granites. In this study, the direct shear tests of intact granites treated by water cooling cycles at different temperatures were conducted, and the variations in the laws of shear strength of intact granites and morphologies of fracture surfaces with temperature or cycle times were analyzed. Test results showed that the shear strength and shear stiffness of intact granites decreased nonlinearly with the increase of temperature or cycle times, but the height and apparent dip angle of asperities on the fracture surface increased with the increase of temperature or cycle times, and the overall uniformity of the fracture surface was improved. The height distribution frequency of asperities on fracture surfaces can be divided into four types: right-biased peak type, left-biased peak type, left-biased middle peak, and left-biased flat peak. The asperities on the fracture surface formed by the shearing of intact granites have asymmetric characteristics. The maximum apparent dip angle and average apparent dip angle in the reverse shear direction are larger than those in the shear direction, and the initial contact area ratio between the shear direction and reverse shear direction is in the range of fluctuation between 1.4 and 2.

Numerical Analysis of Disclinations in Connecting Kink Bands Formed by Multiple Basal Shear

We analyzed the kinematic (geometric) aspects of kink bands with multiple basal shear using rank-1 connection to investigate the type of disclination and annihilation of disclinations in kink microstructures. We found that wedge disclinations occur in connecting kink bands for realistic magnitude of shear that can occur, regardless of the shear direction. The normal vector of the junction plane between kink bands and Frank vector of the resulting wedge-disclination varied continuously with respect to the changes in the magnitude and direction of the basal shear. Annihilation of disclinations is possible even between the kinks which are formed by multiple basal shears. Kinematical model of the three-dimensional wavy kinks are proposed using the obtained results.

Surrogate model assisted design optimization of composite bone plates to achieve selective stress shielding

ABSTRACT Optimal composite bone plate is designed for Periprosthetic Femoral Fracture (PFF) fixation using genetic algorithm (GA) by hybrid and varying fiber orientation. The bone plate should allow higher displacement in axial direction and minimum movement in shear direction. Composite material is considered for the bone plate, the most important constraint in this design problem is that the axial movement and shear movement are limited to 2 and 0.5 mm, respectively. The simulated data from the finite element analysis (FEA) are used for creating the artificial neural network (ANN) surrogate models for the bone displacements in both the directions, which act as the objective functions for the GA-driven optimization in the multi-objective fashion. FEA is used to validate the solutions derived through the design optimization process. The FE simulations have shown only 10% deviation in the simulation output when compared to the achieved optimum solutions.

High Pressure Torsion of Copper; Effect of Processing Temperature on Structural Features, Microhardness and Electric Conductivity.

By optimizing the fabrication method, copper components featuring (typically contradicting) advantageous electric conductivity and favorable mechanical properties can be acquired. In this study, we subjected conventional electroconductive copper to a single revolution of high pressure torsion (HPT) at room temperature (RT), searched for the conditions which would yield comparable structure characteristics (grain size) when deformed at a cryogenic temperature, and finally compared the mechanical and electric behaviors to assess specific differences and correlate them with the (sub)structural development. 180° revolution of cryo-HPT imparted structure refinement comparable to 360° revolution of room temperature HPT, i.e., the average grain size at the periphery of both the specimens was ~7 µm. The 360° RT HPT specimen exhibited preferential (111)||SD (shear direction) texture fiber in all the examined regions, whereas the 180° cryo-HPT specimen exhibited more or less randomly oriented grains of equiaxed shapes featuring substantial substructure development of a relatively homogeneous character and massive occurrence of (nano)twins. These structural features resulted in the increase in microhardness to the average value of 118.2 HV0.2 and the increase in the electric conductivity to 59.66 MS·m-1 (compared to 105 HV0.2 and 59.14 MS·m-1 acquired for the 360° RT HPT specimen). The deformation under the cryogenic conditions also imparted higher homogeneity of microhardness distribution when compared to RT processing.

Experimental study on strength and failure characteristics of sandstone rock mass with complex cataclastic structure using 3D printing models

A cataclastic rock mass is a poor type of engineering geological rock mass. The determination of the shear failure characteristics and shear strengths of cataclastic rock masses can provide key basis for the design and construction of infrastructure. Physical model samples of a sandstone cataclastic rock mass were first produced by a combination of three-dimensional (3D) printing technology and manual pouring. Shear tests were conducted with respect to the shear stresses parallel to the trace line plane and perpendicular to the trace line plane of the cataclastic rock mass model. Based on an extensive analysis of the shear failure characteristic, shear stress evolution characteristic curve and shear strength. When the shear stress was parallel to the trace line plane, and when the rock block that was cut and confined by the trace line exhibited a significant tip, the end stress concentration effect of the cataclastic rock mass was more significant during the shear process with the anisotropy of the rock block increased. In addition, the shapes of the rock blocks that were confined and cut by the joints were the main influencing factors of the strength of the cataclastic rock mass. When the shear stress was perpendicular to the trace line plane, the structure of the rock wall was the main influencing factor of the deformation and failure process of the shear failure plane and the shear strength. The physical and mechanical properties of the shear failure plane of the cataclastic rock mass were found to be closely related to the joint–rock wall system characteristics of the cataclastic rock mass. Therefore, when determining the shear strength of cataclastic rock mass, the shape and combination form of the rock block, shear direction, and structural failure characteristics of the rock wall should be comprehensively considered during the shear process.

Mechanical investigation of inverse FML under mode II loading using acoustic emission and finite element method

Fibre metal laminates (FML) are a specific type of material made of both metal and fibre-reinforced composite layers. In this paper, the authors analyse the behaviour of fibre metal laminates with unusual thermoplastic matrices in composite layers under mode II loading. A three-point bending setup was used along with end notched flexural specimen (ENF) to determine behaviour and of the interface between metal and composite layers under shear stress. Due to nonstandard layup configuration, mixed experimental–numerical method is proposed by authors to determine fracture energy. The finite element method is used to analyse conducted tests. A model with cohesive elements is applied to determine damage in the interface layer. For the purpose of understanding the damage process in particular layers, Acoustic Emission analysis was conducted for each specimen and parameters like amplitude, frequency, duration, root-mean-squared level of noise were obtained. As a result of conducted research critical energy in mode II was obtained GIIC=0.05Nmm as well as critical stress value in local shear direction (initiation criterion) tso=10MPa. The result obtained can be used as part of the material model in assessing the mixed-mode state of the researched material.

Simultaneously enhancing mechanical properties and electrical conductivity of Cu-0.5%Cr alloy as 5G connector material

With the rapid development of the 5 G communication, materials such as the high-speed backplane connector and the integrated circuit lead frame require higher strength and electrical conductivity. Copper alloys have been widely concerned due to their excellent electrical conductivity, thermal conductivity and good strength. A new method of preparing the Cu-0.5%Cr alloy by equal channel angular pressing (ECAP), deep cryogenic treatment (DCT) and aging treatment (AT) was proposed. The electrical conductivity, mechanical properties and microstructure of the Cu-0.5%Cr alloy were investigated, and the precipitation kinetics was analyzed. The results show that ECAP deformation and DCT treatment make the grains elongate and refine along the deformation shear direction. After four ECAP passes and DCT (12 h), the lamellar grains with the thickness of 200–300 nm were obtained, and the dislocation density was evidently increased. After the subsequent AT treatment, the fine Cr phase disperses uniformly at the grain boundaries and within the grains, and distributes on the matrix and along the dislocation lines. Compared with the solid solution, the results showed that after four passes of ECAP + DCT (12 h) + AT (425 ℃ × 1 h), the microhardness increased from 60.5 HV to 210 HV, the electrical conductivity changed from 27.9 % IACS to 69 % IACS, the strength improved from 262 MPa to 587 MPa, the elongation to failure decreased from 44.2 % to 21.9 %. The electrical conductivity was enhanced due to the second phase charge analysis showed that the scattering effect on electrons is weakened. The improvement of strength could be attributed to grain refinement and increase of dislocation density. Based on the Avrami empirical equation of precipitation kinetics analysis, the electrical conductivity equation and the phase change kinetics equation were established, and the relationship between aging time and electrical conductivity was established.