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The interactions between a plate-like precipitate and two twin boundaries (TBs) ( { 10 1 ¯ 2 } , { 11 2 ¯ 1 } ) in magnesium alloys are studied using molecular dynamics (MD) simulations. The precipitate is not sheared by { 10 1 ¯ 2 } TB, but sheared by { 11 2 ¯ 1 } TB. Shearing on the (110) plane is the predominant deformation mode in the sheared precipitate. Then, the blocking effects of precipitates with different sizes are studied for { 11 2 ¯ 1 } twinning. All the precipitates show a blocking effect on { 11 2 ¯ 1 } twinning although they are sheared, while the blocking effects of precipitates with different sizes are different. The blocking effect increases significantly with the increasing precipitate length (in-plane size along TB) and thickness, whereas changes weakly as the precipitate width changes. Based on the revealed interaction mechanisms, a critical twin shear is calculated theoretically by the Eshelby solutions to determine which TB is able to shear the precipitate. In addition, an analytical hardening model of sheared precipitates is proposed by analyzing the force equilibrium during TB-precipitate interactions. This model indicates that the blocking effect depends solely on the area fraction of the precipitate cross-section, and shows good agreement with the current MD simulations. Finally, the blocking effects of plate-like precipitates on the { 10 1 ¯ 2 } twinning (non-sheared precipitate), { 11 2 ¯ 1 } twinning (sheared precipitate) and basal dislocations (non-sheared precipitate) are compared together. Results show that the blocking effect on { 11 2 ¯ 1 } twinning is stronger than that on { 10 1 ¯ 2 } twinning, while the effect on basal dislocations is weakest. The precipitate-TB interaction mechanisms and precipitation hardening models revealed in this work are of great significance for improving the mechanical property of magnesium alloys by designing microstructure.

Several types of ground improvement methods that employ fiber-reinforcement have been developed in recent years. A series of consolidated drained triaxial compression tests has been conducted here to examine the effect of short fibers on the mechanical properties of Toyoura sand. Sand with 0.0%, 0.2%, 0.4%, and 1% fiber contents, prepared to yield random distribution, was sheared under several confining pressures and controlled via their initial relative densities. The test results showed that the maximum and residual deviator stresses increased, whereas the volumetric expansion decreased with an increase in fiber content. Although the stress ratio η (=q/p’) and specific volume changed depending on the fiber content and confining pressure with shear progression, they each reached the same values for a definite fiber content at the end of shearing, independently of initial relative density. In other words, the unique critical state line can be found for a definite fiber content. Moreover, the greater the fiber content, the larger the slope of the critical state line at the end of shear. Additionally, as the length of fibers shortened with the same percentage of fiber inclusions in sand, the deviator stress and the stress ratio decreased, approaching the shear-strain-volumetric response of unreinforced sand.

A series of direct simple shear (DSS) tests were carried out on a non-plastic sandy silt lead−zinc−silver tailings to develop a relationship between undrained shearing behaviour and density for contractive states. The critical state line was also obtained through triaxial compression tests to enable the DSS tests to be viewed in a critical state framework and allow comparison with in situ testing. It was found that the gravimetric water content (GWC) used to tamp the specimens had a significant effect on the resulting undrained strengths when attempting to achieve dense states — with higher GWC giving lower strength at a given density than a lower GWC. Intact and slurry deposited (SD) samples were also tested to access denser states without inducing tamping-related stresses. These showed a more consistent trend with the loose-tamped specimens, and with other data from the literature. Plausible explanations as to the causes of the increased strength of dense-tamped samples were obtained through estimating potential preconsolidation stresses and “locked in” horizontal stresses that may occur from dense tamping. The importance of these observations on the development of density−strength profiles in engineering practice was outlined.

The effect of mechanical strength of the dispersed particle gels (DPG) on their macro plugging performances is significant, however, little study has been reported. In this paper, DPG particles with different mechanical strengths were obtained by mechanical shearing of bulk gels prepared with different formula. Young's moduli of DPG particles on the micro and nano scales were measured by atomic force microscope for the first time. The mapping relationship among the formula of bulk gel, the Young's moduli of the DPG particles and the final plugging performance was established. The results showed that when the Young's moduli of the DPG particles increased from 82 to 328 Pa, the plugging rate increased significantly from 91.46% to 97.10% due to the distinctly enhanced stacking density and strength at this range. While when the Young's moduli of the DPG particles surpassed 328 Pa, the further increase of plugging rate with the Young's moduli of the DPG particles became insignificant. These results indicated that the improvement of plugging rate was more efficient by adjusting the Young’s moduli of the DPG particles within certain ranges, providing guidance for improving the macroscopic application properties of DPG systems in reservoir heterogeneity regulation.

TC21 titanium alloy, as an important metal to fabricate the aircraft structural components, has attracted great attentions recently. A TC21 titanium alloy with widmanstatten structure was isothermally compressed. Based on the microstructure observation, the evolution of initial β grain, Grain Boundary α phase (αGB), lamellar α and interlayered β was systematically investigated. The results showed that, with the increasing of height reduction, the αGB underwent an evolution process from bending/kinking to breaking inducing the corresponding blurring of initial coarse β grain outline. Meanwhile, a significant phase transformation from α to β took place at the terminations of broken αGB. The evolution of lamellar α and interlayered β in the colony was closely related to their deformation compatibility. In the α colony, the interlayered β experienced a larger deformation amount than lamellar α. The higher distortion energy promoted the occurrence of Dynamic Recovery (DRV) and Dynamic Recrystallization (DRX) to generate many Low Angle Boundaries (LABs) and High Angle Boundaries (HABs) in interlayered β, which induced an apparent grain refinement of β phase. On the contrary, the lower distortion energy and low deformation temperature suppressed the occurrence of DRV/DRX and restrained the globularization of lamellar α. Furthermore, the microstructure observation clearly revealed that the shearing separation mechanism dominated the evolution of the α phase from lamellar to short bar-like morphology.

The ultrahigh strength 300M steel has been commonly used in the manufacture of aircraft landing gear and rotor shaft parts due to its excellent mechanical properties. Creep feed grinding is one of the essential operations during the whole component manufacturing processes. In this work, the feasibility of creep feed grinding of 300M steel by using the hard zirconium corundum wheel was theoretically and experimentally evaluated. A variety of responses including grinding forces, temperature fields, specific grinding energy, surface integrity and chip modes were carefully recorded. Besides, the mechanism of ground surface profile generation and the spatial frequency spectrum of the surface profile were tentatively analyzed. It was found that the wheel speed has a relative influence on the grinding forces and temperatures of which the work hardening effect dominates the material removal with lower wheel speed while the thermal softening becomes crucial as the wheel speed exceeds the critical value for the studied 300M steel. Furthermore, a scattered spatial frequency spectrum for the generated surface profile was noticed with lower wheel speed while the spectrum gathers towards the lower frequency values with higher amplitude as the wheel speed increases. The shearing chip and flowing chip dominates the main chip type, indicating the excellent abrasive sharpness during the grinding process. In general, the used zirconium corundum wheel presents feasibility for the creep feed grinding of 300M steel because of the high material removal rate, absence of surface burn, low wheel wear and higher compressive residual stresses.

This paper presents a mathematical modelling of a novel multiphysics (electro-mechanic coupling) problem of the shear wave propagation in laminated structures (piezoelectric - hydrogel - elastic substrate) using the wave mode method while finding the general solution for each medium. A dynamic mechanical equilibrium equation (for transverse deflection) and Maxwell equation (for electric potential) are solved in a coupled manner over each domain resulting a general closed-form solution. A specific analytical solution is then obtained enforcing the boundary conditions at the top of piezoelectric layer and the interface continuity requirements between each layer and the elastic half-space. A novel approach, to uncouple the coupled equations, is presented resulting in a final systematic solution. The effect of x coordinate (thickness) on the field variables is carefully examined for the electrically open and short cases. The jump in the stress and electric displacement components (causing delamination due to shearing mode of fracture) is present across all the interfaces due to the different bulk material constants. The key contribution of the current work is demonstrating the influence of fixed-charge concentration inside the hydrogel layer on the shear wave propagation. The present study thus provides a new concept for adjusting and controlling the elastic wave propagation in the composite structures, and provides a proper theoretical understanding of wave propagation in the damage tolerance-based design of piezotronics devices.

Fracture conformance control in reservoir can effectively improve water channel to increase crude oil displacement efficiency of subsequent waterflooding. Inspired by the remarkable underwater wet adhesion of mussel byssus, hydrogel particles which can adhere stably on the fracture rock surface in reservoir conditions could achieve long-lasting reservoir control effect. In this work, the size-controllable biomimetic functional hydrogel particles were prepared by mechanical shearing after bulk hydrogel was constructed by catechol-functionalized polyacrylamide and phenolic resin crosslinking agent. The influence of solution salinity on the aggregation and adhesion of hydrogel particles was investigated via scanning electron microscope (SEM), colloidal probe atomic force microscope (AFM) and quartz crystal microbalance with dissipation (QCM-D). The results showed that hydrogel particles maintained well-dispersed state in low-salinity water, while exhibited significant adhesion and adsorption capacity to the silica surface in simulated reservoir salinity water. This is of great importance to the practical applications that the hydrogel particles would not show enhanced adhesion to rock surfaces until the reservoir salinity water was met, which was beneficial to the in-depth migration of hydrogel particles to achieve effective deep reservoir profile control. Furthermore, the visible micro-model was designed and applied to evaluate profile control effect of hydrogel particles, and the results showed that hydrogel particles could withstand water flushing and adhere stably to the fracture surface. The waterflooding sweep efficiency was increased remarkably from 20.3%±2.0% to 38.8%±2.0%. This work would help better understand the function mechanism of hydrogel particles in reservoir control and provide novel and efficient method for the practical application in enhanced oil recovery.

Hypothesis Flow curve measurement is commonly used to characterize the flow behavior of concentrated suspensions. However, dynamic changes in the suspension inner microstructures under highly sheared conditions have not been correctly understood even though they strongly affect the measured shear stress. We hypothesize that the real particle dynamics during shearing could be effectively revealed by a systematic investigation that combines macroscopic flow curve measurements with operando microstructural observation employing an optical coherent tomography (OCT) apparatus and surface interaction measurements with the colloidal probe atomic force microscopy (AFM) method. Experiments The model system was spherical SiO2/toluene suspensions stabilized by polyethyleneimine (PEI) partially complexed with different fatty acids. Inner structures of the suspensions during flow curve measurements were observed by the OCT technique. The surface-surface interactions in toluene were analyzed using the colloidal probe AFM method. Findings Operando OCT observations revealed that during flow curve measurements, the suspensions can have completely different microscopic flow modes depending on the fatty acid species complexed to PEI and the solid concentrations. These microscopic flow modes could not be recognized using the typical flow curve measurements alone. The different flow modes can be explained by surface interactions measured by the colloidal probe AFM method.

For piezoelectric-driven compliant microgrippers, realizing flexible, stable, and accurate manipulation simultaneously is a key challenge. The bridge-type compliant displacement amplification mechanism (CDAM) with a single input force can enable stable parallel grasping and enlarge the grasping stroke by matching the output performance of typical piezoelectric actuators used in microgrippers. In this study, a nonlinear analysis of the bridge-type CDAM with a single input force was conducted to improve the prediction accuracy of the output displacement, and nonlinear optimization and testing were performed. For the expected and parasitic output displacements, a two-step nonlinear modelling method was proposed to conduct the nonlinear analysis. Using Castigliano's second theorem, small deflection-based finite element analysis (FEA), and numerical fitting, small deflection-based modelling considering the shearing effect was first performed. Then, the correction coefficients for the geometrical nonlinearity were modelled by combining geometrical nonlinear FEA and numerical fitting. By restricting the parasitic output displacement, a nonlinear constraint was derived. Thereafter, geometric parameter optimization and structural optimization of the bridge-type CDAM with a single input force was performed. Model analysis indicates that for the optimal CDAM, the expected output displacement increases with the input force, whereas a negative correlation exists between the growth rate and the input force. Finally, simulations and experimental tests were conducted to verify the effectiveness of the nonlinear models, optimization, and model analysis.

Controlling different types of forces to achieve materials with different emission responses remains a challenge. In this work, polymorphic organic crystals with blue (1-B) and green (1-G) emission based on N-(4-(1-cyano-2-phenylvinyl)phenyl)benzamide are prepared. In 1-G, the molecules form continuous π-stacking through π–π interactions, while no π–π interactions are found in 1-B. When shearing and UV irradiation are applied to 1-G, the emission blue shifts to a shorter wavelength region. Experimental investigations show that the shearing causes a crystal-to-crystal transition from 1-G to 1-B, while the UV irradiation promotes the occurrence of a photocycloaddition reaction. The external and internal factors contribute to the destruction of molecular π-stacking. In sharp contrast, under isotropic pressing, 1-G exhibits an obviously red-shifted emission owing to the formation of a tighter packing structure where the π–π interactions are reinforced. This work not only regulates molecular packing and controls emission variations in a versatile manner but also enriches the insights into mechanochromic and multifunctional materials.

An ultra-precision machining approach called green-chemical-jump-thickening polishing (GC-JTP) is explored to improve surface accuracy and to achieve high-efficiency polishing for silicon carbide (SiC) ceramics. A new concept of green-chemical-jump-thickening polishing slurry (GC-JTPS) is developed to be an environmentally-friendly fluid with including two essential capabilities: one is the chemistry-induced jump-thickening (JT) mechanism and the other is green-chemical-thickening to enhance removal efficiency. Based on Navier-Stokes's equation and flow continuity equation, the polishing pressure in the GC-JTP process is calculated. On the basis of the rheological dynamics and abrasive nano-indentation analysis, a predictive understanding model to assess material removal rate (MRR) is proposed for the machining controllability of GC-JTP. Under the GC-JTP verification experiments, the maximal proportional error between the testing results and the theoretical calculation stands at only ζ = 7.8%, which proves the accuracy and effectiveness of the new theory MRR in GC-JTP. Through the fitting error, the correction coefficient of α = 0.929 should be used in the MRR model in order to better guide the actual processing. The analysis of the maximal cutting depth and the threshold of ductile-brittle transition revealing subsurface damages might generate. Under the optimized polishing conditions of the shearing velocity vr = 2.0 m/s, the abrasive size Da = 2.0 μm, the gap depth δ0 = 1.5 mm, the sodium bicarbonate Wp = 15 wt%, the sorbitol Wo = 20 wt% and the abrasive CeO2 Wa = 30 wt%, the SiC ceramics roughness is reduced from Ra 768 nm to Ra 32 nm and the subsurface damages depth can be controlled at the range of 2.5 μm–4.5 μm to achieve good surface integrity. The work demonstrates that the GC-JTP is a green and efficient processing method for the low-damage polishing of SiC ceramics.

Landslide is a commonly occurring natural disaster and also a societal hazard in the world. Rainfall is considered as one of the major triggering factors for cause of landslide slope failures. In the present study, a constitutive model is proposed and analyzed using mathematical theory, which deals better with geomorphic changes causing landslides. The constitutive behavior of soil is characterized along the planar shear plane and comprised of different soil properties with different strength parameters. The stiffness parameter of the soil along the shearing plane is analyzed to study the effect of infiltration and seepage of rainfall. The impact of water seepage on the stability analysis of landslide were discussed with importance. The present study shows the results that rainfall infiltration on the slope and the difference in the water level can tremendously influence the stability of landslide.

To investigate the fractal dimension and its variation of intact and compacted loess, consolidated-drained (CD) triaxial tests were performed to obtain intact and compacted loess specimens at different stress-strain states, their pore-size distribution (PSD) curves were measured by using the mercury intrusion porosimetry (MIP) technique. Based on the PSDs, three models (namely, Menger sponge model, Neimark model and the model based on the law of thermodynamics) were used to determine the fractal dimensions of specimens. The results show that there have 3 or 4 fractal intervals (or fractal dimensions, i.e., Ds1, Ds2, Ds3, Ds4,) when using Menger sponge model, only Ds3 satisfies the definition of fractal dimension. Neimark model can be used to determine the fractal dimensions of inter-aggregate pores and intra-aggregate pores, respectively (i.e., DNmacro and DNmicro). Most DNmacro values are meaningless physically, DNmicro increases with the increase of axial strain during shearing, suggesting that the surfaces of pores become complex with the increase of axial strain. The model based on the law of thermodynamics is the most appropriate if only one fractal dimension (i.e., Df) is expected in the whole measurable range of pore diameter. Df increases linearly with the growth of confining stress during consolidation or axial strain during shearing for both loess soils, indicating that the roughness of the pore surfaces increases with the increase in stress or strain. Besides, the fractal dimensions of intact and compacted loess were compared. According to the variations of PSD and Df, the mechanism for the evolution of the loess soil pore structure is proposed. These findings are expected to provide new insight into establishment of the connection between microstructure and macro stress-strain state of loess.

Numerous studies in the literature are concerned with proposing new constitutive models for sands to simulate cyclic loading. Despite considerable progress in this area, there are various limitations on their simulation capabilities that are either overlooked or not communicated clearly by the developers. A number of these limitations are rather crucial for the end users, and therefore, providing discussion and analysis of them would be of great value for both applications and future developments. The present work is devoted to discussing seven characteristic limitations, which are frequently observed in cyclic loading simulations. Four advanced constitutive models are considered in this study: two bounding surface elastoplasticity and two hypoplasticity models—with the models in each category following a hierarchical order of complexity. Relevant cyclic loading experimental test data on Toyoura and Karlsruhe fine sands support the analysis. The key issues discussed include stress overshooting, one-way ratcheting in cyclic strain accumulation, liquefaction strength curves, stress attractor in strain-controlled shearing, hypoelasticity, cyclic oedometer stiffness, and effect of drained preloading. The presented results elaborate on the specific limitations and capabilities of these rather advanced models in simulating several essential aspects of cyclic loading of sands.

A series of ring shear tests were conducted to investigate the ultimate particle size distribution of a carbonate sand. The tests were carried out under different stress levels, on three types of specimens: 1) uniformly graded specimens made of dry natural sand 2) remoulded specimens of the crushed sand after first shearing to large strains 3) specimens made of natural sand grains but with the same grading as in (2). The first series of tests on type (1), carried out to very large strains, led to apparently stable gradings, distinct for each stress level. Only limited additional particle breakage could be induced by remoulding the specimens after shearing (type (2)) and subjecting them to more shearing. Tests on specimens created at the apparently stable gradings (type (3)) but from the intact sand particles however led to significantly greater breakage. For the three types a stable, fractal grading was achieved. Analyses of the soil particles’ shape showed that the aspect ratio, sphericity and circularity reach a steady value at large strains, in parallel to reaching a stable grading. The mobilized angle of shearing resistance however was not significantly different in the different types of samples, suggesting the final grading dominates the behaviour.

Forming a high-strength granular plugging zone is important to lost circulation control success in fractured oil, gas, and geothermal resources. The stability of mesoscale force chain network, which is the way to transferring contact force between particles, determines granular plugging zone strength. However, the effect of granular performance parameters on mesoscale structure stability of plugging zone remains unclear. In this work, a photoelastic method is adopted to visually observe mesoscale structure evolution accounting for fracture occurrence, plugging zone stress condition and failure mode. Results show that force chains display better symmetry along the shear direction and distribute more uniformly in a plugging zone formed with higher friction coefficient particles. Contact force transmission causes lower friction coefficient particles siding and induces plugging zone instability. Symmetry and uniformity of the strong force chain network are the two key optimal distribution parameters to improve plugging zone stability and materials selection.

Micro and nano structures of quartz schist, plagioclase granite, and granitic gneiss in the Xiaomei Shear Zone located in southeastern Hainan Island, China are observed using Scanning Electron Microscope (SEM). Ultramicroscopic analyses indicate that three types of nanoparticles were found in the samples, including spherical nanoparticles, agglomerated nanoparticles and nanofibers. These nanoparticles are mainly developed in the fracture zones. The more fractures there are, the more nanoparticles are developed. Energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) are used to ascertain the composition of the nanoparticles. The results suggest that the nanoparticles are mainly composed of silicate, dolomite and calcite, rich in O, Si, Al, Ca. Based on our results, we suggest that nanoparticle formation is a complex, plastic-brittle transition process. Thermal decomposition driven by steady shearing possibly forms well-organized nanoparticles, while fast-moving dislocations by shock-like stress release possibly forms radial nanofibers.

In this study, discrete element method (DEM) simulations of a biaxial test were used to examine the effect of particle roundness on the mechanical behavior of sands at both the macro and micro scales. First, a stack of microcomputed tomography images were binarized, segmented, and labeled using advanced image processing and analysis techniques. Second, a spherical harmonic (SH) analysis, which involves a complete set of orthogonal functions, was implemented to rebuild the natural particle shape. Then, five templates of virtual particles were built in a DEM simulation, four of which were obtained from SH degrees of 3, 8, 12, and 15, and one template was an elementary sphere. A flexible membrane was numerically generated to allow the material to deform freely under a prescribed confining stress. Finally, the effect of particle roundness on the mechanical properties of granular materials was investigated and discussed. Two shear bands were found to intersect, forming an X shape in both the rotation and displacement fields. Moreover, a lower particle roundness results in higher deviatoric stress and stronger dilation in the volumetric change. A decrease in particle roundness leads to less rotation of particles despite a higher displacement value. In addition, a larger SH degree leads to smaller normalized contact forces of the particles. This implies that decreasing the roundness results in higher anisotropy of the contact forces.

Plant roots are known to provide mechanical reinforcement to soils upon shearing and seismic loading. However, the effects of different stress paths on root reinforcement remain unclear. Moreover, whether and how roots provide resistance to soil liquefaction upon cyclic loading have rarely been studied. The objective of this study is to conduct a series of undrained triaxial tests to investigate the monotonic and cyclic behaviour of rooted sand. Roots of vetiver grass (Chrysopogon zizanioides L.), which has been advocated for use in shallow slope stabilisation purposes, were used for testing. The root diameters ranged between 0.3 and 1.5 mm, while the root volume ratios (RVRs) were 0.23%, 0.45%, and 0.67%. It was discovered that the root reinforcement effect was anisotropic and path-dependent. Along the extension path, when the major principal stress was perpendicular to the predominant root orientation, the root-induced increase in soil friction angle was approximately 10°. This increase was much greater than that along the compression path, where the change was minimal. The presence of roots prevented the limited flow failure at some RVRs and cyclic stress ratios (CSRs) (which occurred in the unreinforced sand) and the failure mode of the root-reinforced soil switched to cyclic mobility. The liquefaction resistance was improved with an increase in root volume, and this improvement was more remarkable at higher CSRs.

A pair of the inner segmentation (IS) rings is inserted in a rotating drum. The effects of the location and size of the rings on the axial and radial segregation patterns are studied. When the IS ring pair locates outside the end wall shearing zone of 10 particle diameter, the ring shearing independently affects the local mixing. The rings concentrate the larger particles at the bed periphery and smaller particles in the core, increasing the band number and degree of mixing. The drum mixing index monotonically increases with the ring width. There exists a critical IS ring width causing a 2-h long-term segregation pattern changing. The critical ring width in a 40% fill drum is ca. 30 particle diameter, covering 52% of the transverse bed area.

Paste slurry exhibits significant thixotropy, which has a significant influence on the slurry pipeline transportation resistance. This paper proposes a novel test method for the thixotropy of paste slurry, which can ensure that the slurry reaches flow equilibrium during the test. Accordingly, the influences of the solid mass concentration, cement-to-tailings ratio, and temperature on thixotropy were studied by employing a control variable method, and the influences of the above three factors on the stress overshoot and rheological parameters were evaluated. The results revealed that the solid mass concentration and temperature have significant influence on the thixotropy. Moreover, with an increase in the solid mass concentration, the time required for the slurry to reach flow equilibrium decreases. The cement content and temperature are proportional to the significance of the stress overshoot, and the change in dynamic yield stress can be considered an indicator for the effective quantification of thixotropy. In the continuous shearing cycles, the maximum apparent viscosity at the start of shearing significantly decreases on the time axis. The solid mass concentration has a significant influence on the minimum apparent viscosity in the slurry flow process, whereas the cement-to-tailings ratio and temperature have no significant influences.

This paper presents an experimental study on the bond characteristics of both sand-coated and ribbed-surface glass fiber reinforced polymer (GFRP) bars embedded in high-performance concrete (HPC). A total of 145 pullout tests were conducted in order to examine the effect of varying parameters on the bond characteristics, namely: embedment length, bar diameter, surface treatment, concrete cover and bond stress-slip relationships. The experimental results showed that the sand-coated bars exhibited better bond strength than that developed by the ribbed-surface GFRP bars, which entails lower development lengths. Besides, it was found that the increase in bar diameter was accompanied by a decrease in the bond strength. Furthermore, experimental results displayed a slight increase in the bond strength as the concrete cover increased from 40 to 60 mm. Finally, based on the material properties of the used GFRP bars and concrete patch, using HPC surrounding both sand-coated and ribbed surface GFRP bars resulted in unfavorable modes of failure. That is because in most cases GFRP bars failed by either shearing of the ribs of the ribbed-surface bars or peeling of the sand-coating layer out of the core diameter for the sand-coated bars.

Effective shearing of fine powders for surface modification and dry coating requires a compressed powder bed to prevent aeration. A device known as Mechanofusion® provides the necessary conditions using a centrifugal field, under which submicron particles are coated onto coarser host particles by shearing under great compressive forces at very high strain rates. This creates composite powders with enhanced properties, such as good flowability, surface functional effects, etc. Understanding the dynamics of particle motion, required level of shear stresses and input energy is a prerequisite for process optimisation. Here, numerical simulation by the Discrete Element Method is carried out, analysing features which are otherwise difficult to obtain by experimental work, e.g. the determination of the thickness of the zone in which particles experience shearing strains, as necessary for functional effect, compressive forces on particles, and input energy. Correlations are proposed for the energy input requirement and stresses experienced by the device as a function of rotational speed.

Recently, we corrected the Green's functions for holes/cracks in composite laminates under coupled stretching-bending deformation. Through these corrected Green's functions, the fundamental solutions required for the special boundary element of holes/cracks in composite laminates are derived. By the use of dual coordinates, the derived fundamental solutions can be further applied to the cases of inclined holes and cracks. Moreover, a formula evaluating the stress intensity factors by using boundary nodal displacements and tractions is derived. With these closed-form solutions, the special boundary element developed in this study can deal with various kinds of hole/crack problems in composite laminates. Their loads can be in-plane tension, compression, or shearing, out-of-plane force, bending or twisting, distributed or concentrated, on the surfaces or along the edges; their boundaries can be simply supported, clamped, or free edges; their defects can be a hole or a crack with horizontal or inclined orientation; their laminates can be symmetric or unsymmetric. No matter which kind of conditions, no meshes are required on the hole and crack surfaces. And the stress intensity factors of cracks can be calculated directly without requiring any meshes along the crack surfaces or near the crack tip.

The classical alpha-disc model assumes that the turbulent stress scales linearly with -- and responds instantaneously to -- the pressure. It is likely, however, that the stress possesses a non-negligible relaxation time and will lag behind the pressure on some timescale. To measure the size of this lag we carry out unstratified 3D magnetohydrodynamic shearing box simulations with zero-net-magnetic-flux using the finite-volume code PLUTO. We impose thermal oscillations of varying periods via a cooling term, which in turn drives oscillations in the turbulent stress. Our simulations reveal that the stress oscillations lag behind the pressure by $\sim 5$ orbits in cases where the oscillation period is several tens of orbits or more. We discuss the implication of our results for thermal and viscous overstability in discs around compact objects., Accepted for publication in MNRAS (8 pages, 7 figures)

Dynamic incident anti-plane shearing (SH guided wave) is considered to calculate dynamic stress and electric intensity in an infinite piezoelectric strip that contains an elliptic inclusion. By the...

There is an increasing need for tactile shear sensors, particularly for medical applications such as orthopedic rehabilitation. Examples include measuring interfacial shear stresses between a residual limb and prosthesis to monitor socket fit and improve residual limb tissue health, and tracking shearing between a foot and shoe for assessing performance in athletes. However, there are considerable challenges in implementing shear force sensors for orthopedic applications due to the requirements for noninvasiveness, low mass, low power, and robustness against motion artifacts, normal force, and/or electromagnetic fields. To address these challenges, we designed, fabricated, and characterized a simple, low-cost, optoelectronic sensor that can measure multi-axial shear stresses. This novel sensor is based on a red, green, and blue (RGB) light-emitting diode (LED) projecting a cyclic illumination of RGB light onto a color pattern surface. As shear strain causes a displacement between the LED and the color pattern, the intensities of the reflected lights change due to the shift of the color pattern position. A photodiode captures the reflected light intensity at each color illumination, allowing the determination of the color pattern surface displacement and the shear along two axes. In this paper, we also report the efficacy of the sensor under benchtop testing conditions, confirming the potential of this technology for shear monitoring in orthopedic devices such as protheses or shoes. Future efforts will focus on miniaturization and packaging of the sensors, and characterizing their performance for the aforementioned medical applications.

Finger joint is an established technique to connect small timber pieces in axial direction, creating timber with theoretical infinite length. This study was undertaken to determine the major failure modes and compression strength properties of finger joints in seven Sri Lankan timber species. Two finger lengths (13 mm and 19 mm) were used for experimental analysis on failure modes and compressive tests. Major failure modes of the finger-jointed specimens subjected to compression parallel to grain test are crushing, splitting, shearing and end rolling. Crushing, splitting, and wrinkling are shown in the specimens of compression perpendicular to grain. Significant relationships were observed between density and compression tests of clear and finger-jointed specimens.

This paper aims to study the influence of particle shape on the shear strength of superellipsoidal particles by Discrete Element Method (DEM) simulations of triaxial tests in 3D. A total of forty-nine types of equiaxed superellipsoidal particles from three evolution paths have been created. The definition of effective porosity has been proposed. Our findings show that both the particle sphericity and roundness affect the shear strength of the superellipsoidal particle system. Under the mutual impact of initial porosity and particle shape, the simulation results of shear strength and volumetric strains present a trend of initially decreasing and subsequently increasing. The microstructure evolution of superellipsoidal particles during the shearing process is observed microscopically. The anisotropy of fabric reveals the mechanism of effective porosity and sphericity influencing the macroscopic shear strength at the particle scale.

In the present work, low cycle fatigue (LCF) behavior and fracture characteristic of Ti–6Al–4V-0.55Fe alloy with bimodal microstructure, consisted of equiaxed primary α (αp), lamellar α (αl) and β matrix, are systematically investigated at room temperature. Results indicate that Ti–6Al–4V-0.55Fe alloy mainly exhibits a continuous softening behavior both at high and low strain amplitudes, due to the interaction of back stress(σb) and friction stress(σf) mainly related to the plastic deformation heterogeneity and precipitates shearing, respectively. Compared with Ti–6Al–4V alloy, LCF life of Ti–6Al–4V-0.55Fe is similar at high strain amplitudes (Δεt/2 > 1.0%), while much higher at low strain amplitudes (Δεt/2

The conventional polypropylene (PP) as a dispersed component was melt blended with ultrahigh molecular weight polyethylene (UHMWPE) in different proportions through a multi-stage melting processing strategy based on continuous rolling and forced kneading. The complex viscosity of blends was less affected by changing the content of PP under lower shearing, while it was significantly decreased in higher shearing range. Especially, by introducing a small amount of PP (5 wt%), the complex viscosity of the blend was only about 3% of original UHMWPE at 0.01 rad/s, and the crystallinity of UHMWPE component in the blend was 61.7% (about 14% higher than raw UHMWPE), which is conducive to maintaining the friction and mechanical properties of the blend. In addition, the possible different plasticization mechanisms related to the increased voids for molecular chain motion or microphase lubrication was also discussed in the present investigation.

In the present work, we focus on the large deformation of a viscoelastic droplet suspended in a Newtonian matrix. We use the constrained volume model as a basic theoretical framework for the description of droplet shape evolution, and we account for the viscoelasticity of the droplet phase using the single-mode Giesekus model. The velocity gradient term describing flow inside the droplet is modified by the viscoelastic stresses, and the resulting model—we herein call the non-Newtonian constrained volume model—is calibrated by matching its predictions to those of the model of Yu et al. [J. Rheol. 48, 417–438 (2004)] at small deformation and slow flow conditions. The non-Newtonian constrained volume model is then examined under conditions of large deformation and/or fast flow, and its predictions are compared against experimental results. The new model shows the growth of the droplet's width in the vorticity direction at conditions of large capillary number, moderate-to-large viscosity ratio, and small elastocapillary number.

The creep inconsistency between dendrite core and interdendritic region is investigated in a nickel-based single crystal superalloy under 1373 K and 137 MPa. Two specimens with higher and lower degree of elemental inhomogeneity on dendritic structures are compared. For specimen with higher inhomogeneity, stronger segregation of refractory elements reinforces the local strength in dendrite core, but damages the strength in interdendritic region. Creep strain is accumulated faster in interdendritic region giving rise to promoted dislocation shearing in γ′ phase, faster degradation of dislocation networks and facilitated topological inversion of rated structures. Although the segregation of refractory elements produces a high density of topologically close-packed (TCP) phase in dendrite core, faster accumulation of creep strain forms microcracks prior in interdendritic region that gives rise to final rupture of the specimen. In another specimen, increased solid solution time gives rise to overall reduced inhomogeneity. Creep inconsistency is relieved to show more uniform evolution of dislocation substructures and rafting between dendrite core and interdendritic region. The second specimen is ruptured by formation and extension of microcracks along TCP phase although the precipitation of TCP phase is relatively restricted under reduced inhomogeneity. Importantly, the balance of local strength between dendrite core and interdendritic region results in over 40% increase of creep rupture life of the second specimen.

Our recent continuum theory for stress-gradient-induced migration of polymers in confined solutions, including the depletion from the solid boundaries [Hajizadeh, E., and R. G. Larson, Soft Matter, 13, 5942–5949 (2017)], is applied to a two-dimensional rotational shearing flow in the gap between eccentric cylinders. Analytical results for the steady-state distribution of polymer dumbbells in the limit of dilute polymer solution c/c∗≪1 (c∗ is the chain overlap concentration) and in the absence of hydrodynamic interactions are obtained. The effects of eccentricity e and of three perturbation variables, namely, Weissenberg number Wi, gradient number Gd(which defines the level of polymer chain confinement), and Peclet number Pe on the polymer concentration pattern, are investigated. The stress-gradient-induced migration results in polymer migration toward the inner cylinder, while wall-depletion-induced migration results in near-zero polymer concentration close to flow boundaries, which couples to a stress-gradient-induced migration effect. In the presence of wall-depletion, we obtain first order concentration variation proportional to Wi. However, in the absence of wall-depletion, there is no first order contribution and, therefore, the lowest-order concentration variation is proportional to Wi2. An upper limit of Wi=1.6 exists, beyond which the numerical solution demands an excessive under-relaxation to converge. In addition, for a high degree of polymer chain confinement, i.e., for Gd greater than 0.5, the continuum theory fails to be accurate and mesoscopic simulations that track individual polymer molecules are needed.

A comprehensive experimental research was undertaken to investigate the association of undrained shear strength with B-ratio, void ratio, confinement pressure, and principal stress difference at failure of zeolite-lime-treated fine sands. For this purpose, a series of undrained triaxial shearing tests were performed on samples comprising several lime-activated zeolites. With regard to the experimental evidence, a novel trend-adjusted (TA) growth forecast was performed with exponential smoothing to extend curing ages beyond the conditions of the experimental program. Then, hybridization of the artificial neural network (ANN) was done by feeding the network with feature adjusted shear resistance values against void ratio, B-ratio, confining pressure, and binding agents over extension of projected curing period. The proposed TA-ANN model showed a boosted optimization in input selection and high accuracy and confidence rate in predicting undrained shear resistance while including extended curing periods. Finally, results of variable importance and sensitivity analysis indicate a significant impact of underlying degree of saturation to the final shear resistance followed by void ratio, confinement pressure, and zeolite content.

The uniform shear flow for the rarefied gas is governed by the time-dependent spatially homogeneous Boltzmann equation with a linear shear force. The main feature of such flow is that the temperature may increase in time due to the shearing motion that induces viscous heat and the system becomes far from equilibrium. For Maxwell molecules, we establish the unique existence, regularity, shear-rate-dependent structure and non-negativity of self-similar profiles for any small shear rate. The non-negativity is justified through the large time asymptotic stability even in spatially inhomogeneous perturbation framework, and the exponential rates of convergence are also obtained with the size proportional to the second order shear rate. The analysis supports the numerical result that the self-similar profile admits an algebraic high-velocity tail that is the key difficulty to overcome in the proof., Comment: 51 pages

Interlayer shear weakness zone (ISWZ) is a type of weak deformation zone in stratified rock masses with variable thicknesses and undulations, which is a major threat for many rock engineering construction projects on or within rock masses because of their poor mechanical properties and large-scale distributions. Existing studies mainly focused on the shear behaviours of weak interlayers of ISWZs without considering the effects of variable thickness and undulation. This study investigates the real occurrence of ISWZs located in the Baihetan Hydropower Station, and a metre-level 2D numerical geological model containing variable thickness and undulation of ISWZ was developed using the particle flow code PFC2D. A series of numerical direct shear tests were performed to investigate the shear properties of ISWZs considering the infilling ratios, joint roughness coefficient (JRC), and normal stress. The experimental results show that the infilling ratio is a vital parameter that controls the failure modes, shear strength, and shear dilatancy of ISWZs. The dilatancy and interlayer separation were found insignificant under high normal stresses compared to the cases under lower normal stresses. In case of first-order asperities, wear/striation mode failure changed to shearing off mode gradually with an increase in normal stresses. The role of structural surface asperities in shear resistance decreases with normal stress and infilling ratios. The second-order asperities tend to increase the dilatancy phenomenon if the infilling ratio is limited as well as the normal stress. The uniqueness and major finding of this study were discussed in detail. The results of this study will provide a new basis to investigate the shear properties of ISWZs at an engineering scale.

In this paper, the expressway engineering case along the west bank of Qinghai Lake is taken as the research background, and the typical “aquatic grassland” silt on the west bank of Qinghai Lake is taken as the research object. Through the geotechnical test, wet-dry cycle test, and direct shear test, the influence of moisture content and wet-dry cycle on the shear strength of silt and its indexes are studied. The results show that the shear strength index c and φ of unmodified silt first increase and then decline with the increase of water content, and the optimal moisture content of the shear strength is about 30%. The values of c, φ, and shear strength of remolded silt decrease with the increase of wetting and drying cycles. When the cycles exceed 5 times, the moisture content does not have much effect on the shearing strength.

Although ultra-precision fly grooving (UPFG) is widely applied to fabricate micro-structured surfaces, few studies have focused on the cutting force model of UPFG. The unique kinematics of UPFG leads to the trans-scale variation of undeformed chip thickness from nanoscale to microscale, in which case the influence of material microstructure and size effect is prominent. This study proposes an analytical cutting force model for UPFG with full consideration of the kinematics, chip formation mechanism, material microstructure, material elastic recovery, size effect, and tool geometry. Specifically, by correlating micro-forming theory to crystal plastic theory, a hybrid slip-line model (HSLM) is developed to determine the flow stress in primary deformation zone, which can quantify the influence of size effect and microstructure, such as grain size, grain boundary, dislocation density, and crystal anisotropy, on flow stress. Then, the normal cutting force and frictional cutting force are estimated by analyzing the stress distribution and frictional states at tool-chip interface. The rubbing force induced by material elastic recovery is determined based on indentation theory. Finally, the models are experimentally validated by fly cutting of polycrystalline copper with different machining parameters, and it is also demonstrated that the proposed HSLM can capture the periodic transformation of cutting mechanism in UPFG from ploughing (compressive stress) to shearing (tensile stress) with tool rotation.

The frictional behaviour of geological interfaces has garnered a significant amount of research attention in geophysics and geomechanics with major applications in the characterization of sediments, the analysis of hydrocarbon reservoirs and the study of deep rock mechanics problems. In the present study, we investigated the tribological behaviour of analogue sedimentary rock by performing grain-scale experiments on natural sand particles bonded with calcium carbonate (CaCO3) at their contacts. The cementation was achieved by artificially forming calcium carbonate sediments around the contact area of two particles with chemical solutions based on a newly developed laboratory method by the authors. By differentiating the stage of the chemical reaction when the solution was applied to the specimen, two types of artificial bonds were created, named as (i) the gel type and (ii) the precipitation type. The sediment crystals formed from the two bonding types were distinct based on observations from digital microscope and scanning electron microscope images. Quantitative analysis was performed based on energy-dispersive X-ray spectroscopy, and the results revealed that the percentage of calcium carbonate formed from the precipitation-type cementation was higher than its counterpart. The grain-scale experiments revealed brittle type of breakage of the bonding from both tension and monotonic shearing tests on the analogue rock specimens. A significant influence of the magnitude of normal load was noticed on the shearing strength of both types of bonded specimens, while the gel type of bonding exhibited higher mechanical strength in either tension or shearing tests.

Most of the published research on goaf-hole failures are performed using 2D numerical analyses. However, 2D analyses of the goaf-hole failure mechanism, which is truly a 3D problem, often do not provide a full picture of strata movement and stress change effect. In particular such 2D models completely fail to capture the longitudinal deformation and associated shear component yielding a false sense of goaf-hole stability. This paper uses advanced 3D numerical modelling to understand the fundamentals of goaf-hole shear failure mechanism and conceptualize the transverse, longitudinal and total shears developments during longwall extraction. A mine specific geotechnical model has been developed to compare the conceptualized goaf-hole failure mechanism with the simplified representative model. The effect of geo-mechanical properties and panel widths on shear development has also been investigated. The analysis is based on a case study; however, it is expected that the results presented in this paper will be applicable to other mines with similar geological environment or will at least highlight the need for a 3D modelling to capture the true three-dimensional strata deformation behaviour and goaf-hole shearing mechanism enabling safe and stable vertical drainage hole design. In the modelled scenario, the shear increased as the face advanced, and large shears would be experienced behind 50–100 m of the face. The longitudinal shear was dominant towards the centre of the panel and the transverse shear was dominant towards the panel edges. The layered seam appeared to generate lesser shear compared to the solid seam; this could be attributed to the dissipation of shear in the layer strata of the material.

The molecular weight of ultra-high molecular weight polyethylene (UHMWPE) fibers is severely decreased compared with raw materials due to high temperature and strong shearing in the dissolving process. In this study, we reported a novel method to assist the dissolving of UHMWPE in paraffin oil without severe degradation in order to improve the tensile strength of resultant fibers. UHMWPE fibers with relatively high molecular weight and more excellent disentanglement effect were prepared by gel-spinning with UHMWPE suspension treated with supercritical carbon dioxide (SC-CO2). The dynamic thermomechanical, mechanical and crystalline properties of UHMWPE extracted fibers and drawn fibers were researched comprehensively. UHMWPE extracted fibers obtained after SC-CO2 treatment display a higher molecular weight. More importantly, it is clear that the disentanglement of UHMWPE gel fibers gained by processing SC-CO2 has been significantly promoted compared with that without SC-CO2 treatment from dynamic thermomechanical and rheological results, which could also be demonstrated from the cross-sectional morphology of UHMWPE extracted fibers. Furthermore, the tensile strength of UHMWPE fibers prepared through SC-CO2 treating is able to attain 30.11 cN/dtex, increased by 10.3% in comparison to UHMWPE fibers gained without assistance of SC-CO2. Beyond that, the thermal behavior and crystallization performance of UHMWPE extracted fibers and drawn fibers acquired by way of SC-CO2 treatment have also been enhanced.

In addition to the shearing behavior of soil, the creep character is also considered crucial in determining the long-term shear strength. This especially holds true for the loess that possesses the metastable microstructure and is prone to landslide hazards. This study explored the potential application of straw reinforcement to enhance the shearing and creep properties of the Quaternary loess. The mechanism responsible for the straw reinforcement to elevate the peak shear strength was revealed. Furthermore, three creep characters, namely attenuating creep, non-attenuating creep, and viscous flow were identified in this study. The unreinforced and reinforced specimen behaved in a different manner under identical shear stress ratio condition. The reinforced specimen was superior in limiting the particle relative movement within the shear plane than the unreinforced specimen. The chain reaction of interparticle contact loss, accompanied with excessive viscous displacement, rapid weakening of creep resistance, and eventually accelerated creep displacement, provided an evidence for the formation mechanism of slow-moving landslide. The long-term shear strength using the isochronal stress–strain relationship may be used for optimising the design of high-fill embankment works.

The external wall insulation and fire prevention problems are hard to solve due to the lack of economical insulating and flame-retardant materials. By taking the wallboard structure as the cut-in point, a novel ceramsite concrete composite wallboard is proposed in this study, which inputs the insulation materials inbetween two wallboards to not only solve the fire prevention problem of the insulation materials thoroughly, but also prevent peeling-off of insulation wall during the construction and using processes. In order to apply this type of wallboard in shear wall structure, a T-shaped joint component of the new ceramsite concrete composite wallboard that adopts U-shaped rebar connection way is proposed in this paper as well. Three same specimens and one contrast specimen are designed in total. Meanwhile the seismic performance of the joint is also studied through the low-cyclic reversed loading experiment. And both the experimental phenomenon and the failure mechanism show that, shearing failure is the failure form of the specimen. The core area of the joint plays a dominating role during the stress process. By analyzing the seismic parameters of the specimen, such as hysteresis, skeleton, ductility and energy consumption, conclusions are made that the specimen is featured in good overall seismic performance, meeting the design requirement of “strong joint, weak component” in the specifications. The study on the T-shaped joint of the novel ceramsite concrete wallboard complements the connection methods of this new type of insulation wallboard, and provides a reliable basis for applying this type of wallboard in practical construction.

Volcanic ash soils are a common geological body in earthquake prone regions, and they are widely used as construction materials. The present study discusses the contribution of initial density, stress state and seepage time on seepage-induced internal instability, stiffness degradation, and monotonic response of volcanic ash collected from Satozuka, Japan. Reconstituted specimens are tested using an erosion triaxial apparatus. The results exhibit that the rate of erosion is influenced by initial density, stress state and hydraulic gradient. The mercury intrusion porosimeter tests are conducted to explore the distribution of constriction sizes after erosion. Post-erosion stress-strain responses are also affected by the stress state during erosion, initial density and seepage time. Particularly, internal erosion affects the dilatancy response of relatively loose specimens and has an impact on the critical state line, brittleness, and peak strength. Further, the maximum shear modulus of eroded soil is found to be greater than that of non-eroded soil, mainly due to the particle rearrangement and removal of fines. However, a sharp reduction in stiffness during monotonic shearing is maybe evidence that temporary reinforced soil packing collapses at a large strain. This indicates that the elastic yield surface has expanded for eroded soils.

The influence of different precipitate-dislocation interactions, namely dislocation shearing and bypassing mechanisms, on PLC bands and the resultant surface roughness in AlMgScZr alloy was investigated. Three-dimensional surface roughness was quantitatively measured by confocal microscopy. We find that the introduction of shearable precipitates increases the stress amplitude, decreases the PLC bands number and surface roughness. However, the stress amplitude decreases, the PLC bands number and surface roughness increase with shearable precipitates turning to nonshearable precipitates. By analyzing the precipitation strengthening mechanisms quantitatively, the influence of precipitates on PLC bands and the resultant surface roughness was explored. Furthermore, our study demonstrates that the shearable precipitates can decrease the surface roughness by decreasing the number of PLC bands, which is instructive for designing structural materials with desirable mechanical property and surface quality.

This paper aims to study the experimental behavior of web cleat, bolted between beam–to–column in terms of strength, relative rotation, and failure mechanism of web cleat leg attached to the column web. The study was carried out to understand the effect of 230 mm depth (B) of web cleat primarily subjected to a shear load. Three different parameters were considered for the study namely (i) aspect ratio (L/B = 0.15–0.42) of web cleat leg attached to the column, (ii) thicknesses of web cleat (TC = 1.5 mm, 2.0 mm and 2.5 mm), and (iii) bolt configuration (Bn = 2 and 3 numbers). The aspect ratio (L/B) was taken as the ratio of the flat distance (between the folded line and bolt line) to the depth of the clip angle. A total of thirty-eight specimens of different configurations were tested under a four-point bending test. The test results indicate an increase in the ultimate strength with the reduction in aspect ratio. Similarly, the ultimate strength increased for the specimens with a three-bolt configuration when compared to the corresponding specimens with a two-bolt configuration. A majority of the tested specimens failed due to local buckling except few specimens which exhibited shearing of bolts and bearing of the beam under the loading points. A comparison of test results with the literature indicates that the test results are un-conservative for two–bolted specimens with slenderness ratio (λ) of the web cleat lesser than 0.6. The reliability studies were performed for the design of bolted web cleat configuration with limitation.

The estimation of strength deterioration with the increase in the undrained cyclic shear-induced strain in liquefiable soils is an important topic in geotechnical earthquake engineering that is still poorly understood and needs to be properly addressed. In this paper, in an attempt to provide new insights into this topic, the post-liquefaction undrained strength and deformation of Toyoura sand were investigated through a series of laboratory tests performed by using a large-strain torsional shear apparatus. In the tests, simple shear conditions were reproduced on a medium-size hollow cylindrical specimen to apply stress conditions that soil experiences in the field during earthquakes. Specimens prepared by the air-pluviation method were first liquefied by applying a constant amplitude undrained cyclic shearing to induce a target cyclic shear-induced damage strain (γΔ). The tests were terminated at different amplitudes of γΔ and subsequently loaded monotonically in undrained conditions to obtain stress-strain and excess pore water generation responses. The test results indicate that the post-liquefaction monotonic loading (ML) stress-strain behavior of sand can be divided into three regions, namely Region 1, 2 and 3. The sand behavior changes to strain-hardening from essentially zero strength and stiffness from Region 1 to 2. While Region 3 marks the beginning of strain-softening state in the sand. It is found that the strain localization is associated with the transition of sand behavior from strain-hardening to strain-softening state. It is proposed that the sand undrained strength in monotonic shearing is the true representation of specimen response until the state of uniform deformation is maintained, based on the sudden drop of the differential stress (σd = σ v′ - σh′). The test results also revealed that there is a progressive degradation in the shear strength with the increase in the amplitude of γΔ. A correlation depicting the degradation ratio ( τ d) with the increase in the γΔ is proposed. This correlation can be used to estimate the degree of degradation with the increase in the applied γΔ, and it is valid for different density states, confining stresses and cyclic stress ratios.

Silica aerogel composite with ultralow density is a kind of highly porous solid with excellent property of thermal conductivity. It is widely used for thermal insulation in aerospace, national defense and military industries. However, silica aerogel composites are difficult to process, due to the poor mechanical properties, low strength and high brittleness. Therefore, it is necessary to investigate the processing characteristics and material removal mechanism of silica aerogel composites. In this article, a cutting model of silica aerogel composites is established firstly and the fracture mechanism of fiber was analyzed. Then the ultrasonic milling and conventional milling experiments were performed respectively to obtain the features of machined surface. Macro morphology and surface roughness of machined surfaces in different process conditions are compared to investigate the influence of different process conditions on the processing quality. Scanning electron microscope (SEM) was used to obtain the micro morphology of processed surfaces. By comparing and analyzing the micro morphology of processed surfaces, the influence of process conditions on removal mechanism was investigated. The theoretical cutting force and experiment cutting force is compared to verify the cutting model. The results show that the burrs and pits decrease with the ultrasonic vibration amplitude, and increase with the tool diameter. Processing quality of up-milling is better than down-milling. It is indicated that shearing and pulling off are the main removal mechanism of silica aerogel composites. When the silica aerogel composites are processed by rotary ultrasonic milling and up milling, the fibers will be mainly removed by shearing mechanism and the proportion of fibers removed by shearing facture mechanism will be improved with the increase of ultrasonic amplitude.