Experimental study on shear properties and resistivity change of soil-rock mixture

The deterioration of shear resistance in rock and soil masses has resulted in numerous severe natural disasters,highlighting the significance of long-term monitoring for disaster prevention and mitigation.This study explores the use of a non-destructive method to quickly and accurately evaluate the shear properties of soil-rock mixture.The shear stress,shear strain,and resistivity of the soil-rock mixture were tested simultaneously using a combination of direct shear and resistivity tests.The test results show that the resistivity of the soil-rock mixture gradually decreases with increasing shear strain.The resistivity of all specimens ranged approximately from 60 to 130Ω.m throughout the shear process.At the end of the shear test,the vertical failure resistivity showed an irregular“W”shape with increasing rock content.It exhibited a significant negative linear functional relationship with the shear strength.With reference to the determination of cohesion and internal friction angle on the shear strength envelope,the horizontal angle of the vertical failure resistivity-normal stress curve is defined as the resistivity angle,and the intercept of the curve is the resistivity at the initial moment of shear.It has been observed that the resistivity angle is negatively and linearly correlated with the internal friction angle.At the same time,there is a linear growth relationship between resistivity at the initial moment of shear and cohesion.It has been demonstrated that an increase in rock content contributes to a general escalation in both the average structure factor and average shape factor.Meanwhile,a decrease in the anisotropy coefficient has also been noted.These alterations are indicative of the extent of microstructural transformations occurring during the deformation process of the soil-rock mixture.The research results verify the feasibility of real-time deformation monitoring and characterization of shear strength parameters using resistivity.

A PREDICTIVE APPROACH TO THE IN-PLANE MECHANICAL PROPERTIES OF STITCHED COMPOSITE LAMINATES

This contribution attempts to model the alteration of the in-plane elastic properties in laminates caused by stitching, and to predict the in-plane effective tensile strength of the stitched composite laminates. The distortion of in-plane fibers is considered to be the main cause that affects the in-plane mechanical properties. A fiber distortion model is proposed to characterize the fiber misalignment and the fiber content concentration due to stitching. The undistorted region, the fiber distortion region, the resin-rich pocket and the through-thickness reinforcement section are taken into account. The fiber misalignment and inhomogeneous fiber content due to stitching have been formulated by introducing two parameters, the distortion width and maximum misalignment. It has been found that the ply stress concentration in stitched laminates is influenced by the two concurrent factors, the stitch hole and inhomogeneous fiber content. The stitch hole brings about the stress concentration whereas the higher fiber content at the local region induced by stitching restrains the local deformation of the composite. The model is used to predict the tensile strength of the [0/45/0/-45/90/45/0/-45]58 T300/QY9512 composite laminate stitched by Kevlar 29 yarn with different stitching configurations, showing an acceptable agreement with experimental data.

Physical and mechanical properties and microstructures of submarine soils in the Yellow Sea

In recent years,the exploration of seabed has been intensified,but the submarine soils of silt and sand in the Yellow Sea area have not been well investigated so far.In this study,the physical and mechanical properties of silt and sand from the Yellow Sea were measured using a direct shear apparatus and their microstructures were observed using a scanning electron microscope.The test results suggest that the shear strength of silt and sand increases linearly with the increase of normal stress.Based on the direct shear test,the scanning electron microscope was used to observe the section surface of sand.It is observed that the section surface becomes rough,with many“V”‐shaped cracks.Many particles appear on the surface of the silt structure and tend to be disintegrated.The X‐ray diffraction experiment reveals that the sand and silt have different compositions.The shear strength of sand is slightly greater than that of silt under high stress,which is related to the shape of soil particles and the mineral composition.These results can be a reference for further study of other soils in the Yellow Sea;meanwhile,they can serve as soil parameters for the stability and durability analyses of offshore infrastructure construction.

Mechanical properties and fracture behaviors on 6061 aluminum alloy under shear stress state

The mechanical properties and fracture behaviors of 6061 aluminum alloy were investigated by the tensile shear tests and in-situ tensile shear tests with tensile shear specimen devised. The results indicate that many slip bands parallel to tensile direction are produced on the surfaces of the specimens. With shear strain rates increasing, the shear yield stress and shear ultimate stress of 6061 aluminum alloy remain constant basically, but the shear fracture strain decreases obviously. The shear strain rates have no influence on the fracture surfaces. The grain boundaries of 6061 aluminum alloy are the weakest area and microcracks initiate at the grain boundaries parallel to tensile direction under shear stress. With the shear stress increasing, the microcracks extend and coalesce. The fracture of specimens is due to coalescence or shearing between the microcracks.

Recent advances in the in-plane shear testing of Mg alloy sheets

Sheet-metal products are integral parts of engineering industries and academia research. Various testing techniques have revealed the deformation behaviors of sheet metals under complex stress states. Information obtained from tensile and compression tests, however, are insufficient for the identification of material parameters relevant to modern constitutive laws, which require experimental setups capable of generating various loading conditions and applying great amounts of strain to sheet metals. In-plane shear testing has emerged as an important method to overcome the challenges associated with tension and compression tests and can provide additional information about deformation behaviors under large plastic strains. Materials such as Mg alloys with poor levels of both ductility and formability cannot accommodate large plastic strains. Therefore, tension and compression tests have limitations in explaining the material behaviors that occur during sheet metal forming where large plastic strains are introduced. Many studies have been conducted to explain the deformation behaviors of Mg alloys under shear deformation techniques. These include severe plastic deformation(SPD), especially the equal channel angular pressing(ECAP)and equal channel angular extrusion, rolling combined with shear deformation i.e. differential speed rolling(DSR), and also in-plane shear for sheet metals, particularly under large levels of plastic strain. These in-plane shear technique involves the Miyauchi shear test, ASTM shear test, and twin bridge shear tests. Moreover, many experimental results have revealed that the evolution of microstructure and texture during in-plane shear is closely related to the failure behavior of materials. Therefore, this review is focused on techniques for in-plane shear testing that have been reported thus far, on the effect of in-plane shear on the microstructure development of Mg alloy sheets, and on the usefulness of in-plane shear testing to evaluate the formability of Mg alloy sheets.

A roughness parameter considering joint material properties and peak shear strength model for rock joints

This study aims at proposing a reasonable roughness parameter that can reflect the peak shear strength(PSS)of rock joints.Firstly,the contribution of the asperities with different apparent dip angles to shear strength is studied.Then the shear strength of the entire joint asperities is derived.The results showed that the PSS of the entire joint asperities is proportional to a key parameter hs,which is related to the geometric character of the joint surface and the joint material properties.The parameter hsis taken as the new roughness parameter,and it is reasonable to associate the PSS with the geometric characteristics of the joint surface.Based on the new roughness parameter and shear test results of 20 sets of joint specimens,a new PSS model for rock joints is proposed.The new model is validated with the artificial joints in this paper and real rock joints in published studies.Results showed that it is suitable for different types of rock joints except for gneiss joints.The new model has the form of the Mohr-Coulomb model,which can directly reflect the relationship between the 3 D roughness parameters and the peak dilation angle.

Shear resistance properties of TPS modified bitumen binders and asphalt mixtures

Shear resistance properties of the virgin bitumen and modified bitumen binders with Tafpack Super(TPS) modifier and SBS modified bitumen were discussed.Dynamic shear rheometer(DSR) was used to measure the laboratory creep data for these binders over a wide range of constant shear stresses at 20 ℃ to characterize the shear creep behaviors of all kinds of asphalt binders,and the rutting test system was used to investigate the permanent deformation of porous asphalt mixtures using the above bitumen binders for a fixed compressive stress.The shear strain rate and shear creep modulus were used to characterize the shear creep behavior of the TPS modified bitumen,and the rutting test results were used to show the consistency of porous asphalt mixtures with the bitumen binders.Results indicate that a distinction of shear creep strain can be made among different contents of TPS modified bitumen at the same stress level,where the shear creep strain-time response curve of the SBS modified bitumen binder is between the curves of the 8% TPS and 12% TPS modified bitumen binders.The shear strain rate and the shear creep modulus of the TPS modified bitumen binders are obtained to compare with those of the SBS modified bitumen binder which results in the same trend as the shear creep strain-time response curve.Permanent deformation results of all the porous asphalt mixtures from the rutting test show reasonable agreement with the findings of the shear strain rates and shear creep modulus over the range of shear stress levels.

Mechanical properties and deformation behavior of Zr-based bulk metallic glass composites reinforced with tungsten fibers or tungsten powders

The tungsten fibers or powders reinforced Zr_(52)Cu_(32)Ni_(6)Al_(10),(Zr_(52)Cu_(32)Ni_(6)Al_(10))_(98)Nb_(2),and(Zr_(52)Cu_(32)Ni_(6)Al_(10))_(98)Be_(2)bulk metallic glass composites(BMGCs)were fabricated using the infiltration casting method.In this study,the wettability between the amorphous alloy melts and tungsten substrates was investigated using the sessile drop method,revealing excellent wettability at 1,010℃.Consequently,an infiltration temperature of 1,010°C was chosen for composite material fabrication.Structural characterization and mechanical property test of both composites were conducted through scanning electron microscopy(SEM),and X-ray diffraction(XRD),and universal mechanical testing.Both tungsten fiber or tungsten powder reinforced Zr_(52)Cu_(32)Ni_(6)Al_(10)and(Zr_(52)Cu_(32)Ni_(6)Al_(10))_(98)Be_(2)composites exhibit the formation of W-Zr phase.In contrast,the tungsten fiber or tungsten powder reinforced(Zr_(52)Cu_(32)Ni_(6)Al_(10))_(98)Nb_(2)composites does not show the formation of W-Zr phase.X-ray diffraction patterns confirm the presence of W reinforcement phases in both composites.The successful fabrication of both composites is evidenced by their remarkable mechanical properties under room temperature compression.The yield strength of all the three tungsten fiber-reinforced composite sample exceeds 2,400 MPa,with the plastic strain exceeding 3.9%,while the yield strength of all the three tungsten powder-reinforced composite sample surpasses 2,700 MPa,with the plastic strain exceeding 30%.Fracture analysis reveals longitudinal splitting in the tungsten fiber-reinforced composites,contrasting with brittle fracture in the tungsten powder-reinforced composites.The denser the shear bands on the amorphous matrix of the two types of composite materials,the better their mechanical properties.

Numerical simulation of direct shear tests on mechanical properties of talus deposits based on self-adaptive PCNN digital image processing

The macro mechanical properties of materials with characteristics of large scale and complicated structural composition can be analyzed through its reconstructed meso-structures.In this work,the meso-structures of talus deposits that widely exist in the hydro-power engineering in the southwest of China were first reconstructed by small particles according to the in-situ photographs based on the self-adaptive PCNN digital image processing,and then numerical direct shear tests were carried out for studying the mechanical properties of talus deposits.Results indicate that the reconstructed meso-structures of talus deposits are more consistent with the actual situation because the self-adaptive PCNN digital image processing has a higher discrimination in the details of soil-rock segmentation.The existence and random distribution of rock blocks make the initial shear stiffness,the peak strength and the residual strength higher than those of the "pure soil" with particle size less than 1.25 cm apparently,but reduce the displacements required for the talus deposits reaching its peak shear strength.The increase of rock proportion causes a significant improvement in the internal friction angle of talus deposit,which to a certain degree leads to the characteristics of shear stress-displacement curves having a changing trend from the plastic strain softening deformation to the nonlinear strain hardening deformation,while an unconspicuous increase in cohesion.The uncertainty and heterogeneity of rock distributions cause the differences of rock proportion within shear zone,leading to a relatively strong fluctuation in peak strengths during the shear process,while movement features of rock blocks,such as translation,rotation and crossing,expand the scope of shear zone,increase the required shear force,and also directly lead to the misjudgment that the lower shear strength is obtained from the samples with high rock proportion.That,however,just explains the reason why the shear strength gained from a small amount of indoor test data is not consistent with engineering practice.

Flocculation properties of cohesive fine-grained sediment in the Three Gorges Reservoir under variable turbulent shear

Sediment flocculation is a key process for the deposition of fine-grained sediments in the Three Gorges Reservoir(TGR)of China.Sediment flocculation influences the evolution of the river regime,but also hampers the smooth navigation in the long term.However,the flocculation process and its controlling factors are poorly understood.We experimentally determined the flocculation properties of cohesive sediment of samples from the TGR(predominantly a mixture of clay and silt)over a range of turbulent shear rates and sediment concentrations.The experiments were conducted in an almost isotropic turbulence field,which was simulated by an array of horizontal oscillating grids in a water tank.Sediment flocculation was recorded by a camera and investigated by image analysis.Our new data indicate that flocculation is generally a response in equilibrium median floc size(d_(f,50))to the increase of the shear rate G.The peak value is attained at G=16.5 s^(-1),where d_(f,50) is 81.3μm(for the suspended sediment concentration(ssc)=0.4 g/L)and 107μm(for ssc=0.7 g/L),respectively.At low shear rates(G<16.5 s^(-1)),the equilibrium floc sizes d_(f,50) increase with rising shear rate G and isinversely related to the Kolmogorov micro length scale η.We attribute this variability to an insufficient deposition time of the sediment flocs in the water tank.Settling velocities,calculated from our experimental data of the floc sizes,are almost consistent with in-situ measured settling velocities,and are ten times larger than the terminal settling velocity of primary particles as calculated from Stokes'law.

Bending and Rolling Shear Properties of Cross-Laminated Timber Fabricated with Canadian Hemlock

In this paper,bending performance and rolling shear properties of crosslaminated timber(CLT)panels made from Canadian hemlock were investigated by varied approaches.Firstly,three groups of bending tests of three-layer CLT panels with different spans were carried out.Different failure modes were obtained:bending failure,rolling shear failure,bonding line failure,local failure of the outer layer and mixed failure mode.Deflection and strain measurements were employed to calculate the global and local modulus of elastic(MOE),compared with the theoretical value.In addition,a modified compression shear testing method was introduced to evaluate the rolling shear strength and modulus,compared with the results from strain measurements in bending shear tests.According to testing results,bonding line failure and rolling shear failure were dominant failure modes in bending tests,and the theoretical value of bending property was beyond the average level of the calculating results obtained from both deflection and strain measurements.In addition,the rolling shear strength and modulus obtained from compression shear tests were relatively smaller than those from bending tests.

Simple shear extrusion versus equal channel angular pressing:A comparative study on the microstructure and mechanical properties of an Mg alloy

Two severe plastic deformation(SPD)techniques of simple shear extrusion(SSE)and equal channel angular pressing(ECAP)were employed to process an extruded Mg-6Gd-3Y-1.5Ag(wt%)alloy at 553 K for 1,2,4 and 6 passes.The microstructural evolutions were studied by electron back scattered diffraction(EBSD)analysis and transmission electron microscopy(TEM).The initial grain size of 7.5μm in the extruded alloy was reduced to about 1.3μm after 6 SPD passes.Discontinuous dynamic recrystallization was suggested to be operative in both SSE and ECAP,with also a potential contribution of continuous dynamic recrystallization at the early stages of deformation.The difference in the shear strain paths of the two SPD techniques caused different progression rate of dynamic recrystallization(DRX),so that the alloys processed by ECAP exhibited higher fractions of recrystallization and high angle grain boundaries(HAGBs).It was revealed that crystallographic texture was also significantly influenced by the difference in the strain paths of the two SPD methods,where dissimilar basal plane texture components were obtained.The compression tests,performed along extrusion direction(ED),indicated that the compressive yield stress(CYS)and ultimate compressive strength(UCS)of the alloys after both SEE and ECAP augmented continuously by increasing the number of passes.ECAP-processed alloys had lower values of CYS and UCS compared to their counterparts processed by SSE.This difference in the mechanical responses was attributed to the different configurations of basal planes with respect to the loading direction(ED)of each SPD technique.

Experimental study on the shear behavior of grout-infilled specimens and micromechanical properties of grout-rock interface

The grout-rock interfacial property is one of the key factors associated with the strength of grouted rock masses.In this study,direct shear tests and nanoindentation tests were adopted to investigate the mechanical properties of the grout-rock interface at both the macroscale and microscale.The cohesion of the cement specimens was higher than that of the grout-infilled joint specimens,while their internal friction angle was lower than that of the grout-infilled joint specimens.A“separation method”for identifying the different phases according to the qualitative and quantitative estimations was introduced,and the irregular interfacial transition zone(ITZ)thickness and elastic modulus were estimated.The ITZ thickness of the grout-infilled sandstone specimen ranged from 0 to 30μm,whereas it was within the range of 10-40μm for the grout-infilled mudstone specimen.The average elastic modulus of the ITZ in grout-infilled sandstone and mudstone specimens was approximately 58.2%and 54.1%lower than that of the bulk grout,respectively.Regarding the incidence of the rock type,the interlacing between the grout and sandstone was better developed.The ITZ with a higher porosity and lower modulus had a significant effect on the mechanical properties of the grout-infilled specimens.

Short beam shear properties and failure modes of the wood-based X-type lattice sandwich structure

A wood-based X-type lattice sandwich structure was manufactured by insertion-glue method.The birch was used as core,and Oriented Strand Board was used as panel of the sandwich structure.The short beam shear properties and the failure modes of the wood-based X-type lattice sandwich structure with different core direction(vertical and parallel),unit specification(120 mm×60 mm and 60 mm×60 mm),core size(50 mm and 60 mm),and drilling depth(9 mm and 12 mm)were investigated by a short beam shear test and the establishment of a theoretical model to study the equivalent shear modulus and deflection response of the X-type lattice sandwich structure.Results from the short beam shear test and the theoretical model showed that the failure modes of the wood-based X-type lattice sandwich structure were mainly the wrinkling and crushing of the panels under three-point bending load.The experimental values of deflection response of various type specimens were higher than the theoretical values of them.For the core direction of parallel,the smaller the unit specification is,the shorter the core size is,and the deeper the drilling depth is,the greater the short beam shear properties of the wood-based X-type lattice sandwich structure is.

Research on Mechanical Model and Properties of New-type Negative Offset Structure in Spatial Seven-bar Heavy Shear

According to revised Cailikefu’s rolling shear force formula,motion path equation of spatial seven-bar path is built,and mechanical model,with such new structural features as negative offset,is thus successfully established for 2 800 mm heavy shear of some Iron&Steel Company. Shear force and bar force of steel plate,before and after adoption of negative offset structure,are analyzed,as well as horizontal force component of mechanism that influences pure rolling shear and back-wall push force that keeps blade clearance. The discovery is that back-wall push force could be kept large enough at rolling start-up (i.e. the time that the maximum rolling shear produces),meanwhile,back-wall push force is the most approximate to side forces with adoption of 60 mm-100 mm offset. Theoretical results and on-site shear quality both indicate that new structural features such as negative offset plays an important role in ensuring pure rolling shear and keeping blade clearance constant,which provide an effective means to improve quality of steel plate.

Mechanical Properties of New Type Negative Offset Structure During Shearing Process of Heavy Steel Plate

According to the revised Cailikefu＇s rolling shear force formula, motion path equation of spatial seven-bar path was built, and a mechanical model, with the new structural feature of negative offset, was thus successfully established for 2 800 mm heavy shear of some iron and steel company. Shear and bar forces of steel plate, before and after the adoption of negative offset structure, were analyzed, as well as horizontal force component of mechanism that influences pure rolling shear and back-wall push force that keeps blade clearance. It was found that the back-wall push force keeps large even at the time that the maximum rolling shear was obtained; meanwhile, back-wall push force is the most approximate to side forces when 60--100 mm of offset was adopted. Both theoretical results and onsite shear quality show that the negative offset plays an important role in ensuring the stability of pure rolling shear and keeping blade clearance constant.

Comparison of mechanical properties in welded joint for CO_2 arc welding by using the micro－shear test and impact test

A micro shear testing method which can suit to measure the mechanical properties of heterogeneous materials is introduced, and the properties in each zone of welded joint for CO2 arc welding can be evaluated by using this method in this paper. Moreover, these results are compared with those results of Charpy V-notch impact test and their correlation is discussed.

Evaluation of in-plane shear test methods for composite material laminates

In-plane shear properties of composite material laminates are very important in structural design of composite material. Four commonly used in-plane shear test methods were introduced in this paper. In order to study the differences of various shear test methods, two ASTM standard in-plane shear test methods for composite material laminates were experimentally investigated. They are ±45° tensile shear test (ASTM D3518) and V-notched rail shear test (ASTM D7078). Five types of composite material laminates composed of E-glass fiber fabric and vinyl ester resin were utilized, whose stacking sequences are 03s, 0/903s, CSM/0/902s, ±453s and (0/90)2/(±45)2/(0/90)2s, respectively. The test results indicate that the ±45° tensile shear test can predict shear moduli of composite material laminates accurately. However, the predictions of shear strength using ±45° tensile shear test are significantly lower than those of V-notched rail shear test.

Evaluation of the Out-of-Plane Shear Properties of Cross-Laminated Timber

The out-of-plane shear properties of cross-laminated timber(CLT)substantially influence the overall mechanical properties of CLT.Various testing methods and theories related to these properties have recently been developed.The effects of the number of layers(three and five layers)and testing method(short-span three-and four-point bending tests)on the out-of-plane shear properties of CLT were evaluated.The out-of-plane shear strength values were calculated based on different theories for comparison.The failure mode in the short-span four-point bending(FPB)method was mainly the rolling shear(RS)failure in the cross layers,indicating that the FPB method was appropriate to evaluate the RS strength of CLT.The out-of-plane shear capacity obtained using the three-point bending(TPB)method was higher than that tested by the FPB method.The testing methods significantly influenced the out-of-plane shear capacity of the three-layer specimens but not that of the five-layer specimens.With an increase in the number of layers,the out-of-plane shear strength of the specimens decreased by 24%.A linear correlation was found among the shear strength values obtained from different theories.

Rheological properties of warm mix asphalt binder by DSR test at medium temperature

The rheological properties including the complex modulus G＊ and the phase angle δof matrix and warm mix asphalt （WMA）binders were measured by using the dynamic shear rheometer （DSR ） test at the medium temperature ranging from 16 to 40 ℃,and the relationships between the fatigue factor G＊ sinδand the matrix binder property,WMA additive and test temperature were established.It is found that G＊ decreases with the increasing temperature while δincreases inversely,and G＊ of the asphalt binder with high WMA additive dosage is large,and δis small.G＊sinδexponentially decreases with the increasing temperature and linearly increases with the increase in additive dosage,and the amplitudes of variation are large at low temperatures and high additive dosages.The effect of WMA additive on the rheological property is more remarkable for the matrix asphalt binder with low G＊.Besides,aging has a great effect on the property of matrix asphalt binder,and a slight effect on the interaction between asphalt and additive.The high additive dosage can increase the fatigue cracking potential of the asphalt binder.