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.

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.

Effect of deep cryogenic treatment on the microstructural,mechanical and ballistic properties of AA7075-T6 aluminum alloy

The study focused on investigating the effect of Deep Cryogenic Treatment(DCT)on the mechanical and ballistic properties of AA7075-T6 aluminum alloy.The microstructure,microhardness,tensile strength,and impact strength of the Base Material(BM)and DCT-treated 7075 samples were analyzed through metallographic analysis and mechanical tests.The microstructure of the DCT-treated 7075 samples revealed fine grains and a distribution of secondary phase particles.The tensile strength,impact strength,and microhardness of DCT-treated samples increased by 7.41%,4%,and 9.68%,respectively,compared to the BM samples.The fractography analysis of the tensile samples showed cleavage facets,microvoids,and dimples in both the samples.The ballistic behavior of the BM and DCT target plates were studied by impacting hard steel core projectiles at a velocity of 750±10 m/s.The target plates failed due to petaling and ductile hole enlargement,and the depth of penetration(DOP)of the DCT target was less than that of the BM target,indicating a higher ballistic resistance.The post-ballistic microstructure examination of the target plates showed the formation of an Adiabatic Shear Band(ASB)without any cracks.It was concluded that the DCT treatment improved the mechanical and ballistic properties of the aluminum alloy due to grain refinement and high dislocation density.

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.

Digital mapping of soil physical and mechanical properties using machine learning at the watershed scale

Knowledge about the spatial distribution of the soil physical and mechanical properties is crucial for soil management,water yield,and sustainability at the watershed scale;however,the lack of soil data hinders the application of this tool,thus urging the need to estimate soil properties and consequently,to perform the spatial distribution.This research attempted to examine the proficiency of three machine learning methods(RF:Random Forest;Cubist:Regression Tree;and SVM:Support Vector Machine)to predict soil physical and mechanical properties,saturated hydraulic conductivity(Ks),Cohesion measured by fall-cone at the saturated(Psat)and dry(Pdry)states,hardness index(HI)and dry shear strength(SS)by integrating environmental variables and soil features in the Zayandeh-Rood dam watershed,central Iran.To determine the best combination of input variables,three scenarios were examined as follows:scenarioⅠ,terrain attributes derivative from a digital elevation model(DEM)+remotely sensed data;scenarioⅡ,covariates of scenarioⅠ+selected climatic data and some thematic maps;scenarioⅢ,covariates in scenarioⅡ+intrinsic soil properties(Clay,Silt,Sand,bulk density(BD),soil organic matter(SOM),calcium carbonate equivalent(CCE),mean weight diameter(MWD)and geometric weight diameter(GWD)).The results showed that for Ks,Psat Pdry and SS,the best performance was found by the RF model in the third scenario,with R2=0.53,0.32,0.31 and 0.41,respectively,while for soil hardness index(HI),Cubist model in the third scenario with R2=0.25 showed the highest performance.For predicting Ks and Psat,soil characteristics(i.e.clay and soil SOM and BD),and land use were the most important variables.For predicting Pdry,HI,and SS,some topographical characteristics(Valley depth,catchment area,mltiresolution of ridge top flatness index),and some soil characteristics(i.e.clay,SOM and MWD)were the most important input variables.The results of this research present moderate accuracy,however,the methodology employed provides quick and costeffective information serving as the scientific basis for decision-making goals.

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.

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.

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.

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.

Shear resistance characteristics and influencing factors of root-soil composite on an alpine metal mine dump slope with different recovery periods

Artificial vegetation restoration is the main measure for vegetation restoration and soil and water conservation in alpine mine dumps on the Qinghai-Tibet Plateau,China.However,there are few reports on the dynamic changes and the influencing factors of the soil reinforcement effect of plant species after artificial vegetation restoration under different recovery periods.We selected dump areas of the Delni Copper Mine in Qinghai Province,China to study the relationship between the shear strength and the peak displacement of the root-soil composite on the slope during the recovery period,and the influence of the root traits and soil physical properties on the shear resistance characteristics of the root-soil composite via in situ direct shear tests.The results indicate that the shear strength and peak displacement of the rooted soil initially decreased and then increased with the increase of the recovery period.The shear strength of the rooted soil and the recovery period exhibited a quadratic function relationship.There is no significant function relationship between the peak displacement and the recovery period.Significant positive correlations(P<0.05)exists between the shear strength of the root-soil composite and the root biomass density,root volume density,and root area ratio,and they show significant linear correlations(P<0.05).There are no significant correlations(P>0.05)between the shear strength of the root-soil composite and the root length density,and the root volume ratio of the coarse roots to the fine roots.A significant negative linear correlation(P<0.05)exists between the peak displacement of the rooted soil and the coarse-grain content,but no significant correlations(P>0.05)with the root traits,other soil physical property indices(the moisture content and dry density of the soil),and slope gradient.The coarse-grain content is the main factor controlling the peak displacement of the rooted soil.

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 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.

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.

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.

Effect of minor Nb addition on mechanical properties of in-situ Cu-based bulk metallic glass composite

In-situ formed （Cu0.6Zr0.3Ti0.1）95Nb5 bulk metallic glass （BMG） composite with Nb-rich dendrite randomly dispersed in hard glassy matrix was prepared by casting into a water-cooled copper mold. The dendrite has much smaller hardness and elastic modulus than glassy matrix, and the stress concentration at interface provides a channel for the initiating and branching of shear bands upon loading, thus leading to a high compressive fracture strain of 6.08% and fracture strength about 2200 MPa. Comparing with other Cu-based BMG composite, the fracture strength of present （Cu0.6Zr0.3Ti0.1）95Nb5 composite is not significantly reduced, indicating that the addition of Nb in the current work is an effective and effortless way to fabricate new practical BMG composites with enhanced strength and good plasticity.

Mechanical Properties of Methane Hydrate-Bearing Interlayered Sediments

The complex distribution of gas hydrate in sediments makes understanding the mechanical properties of hydrate-bearing sediments a challenging task.The mechanical behaviors of hydrate-bearing interlayered sediments are still poorly known.A series of triaxial shearing tests were conducted to investigate the strength parameters and deformation properties of methane hydrate-bearing interlayered sediments at the effective pressure of 1 MPa.The results indicate that the stress-strain curves of hydrate-bearing interlayered sediments are significantly different from that of hydrate-bearing sediments.The peak strength,Young's modulus,initial yielding modulus,and failure mode are deeply affected by the methane hydrate distribution.The failure behaviors and mechanism of strain softening and hardening patterns of the interlayered specimens are more complicated than those of the integrated specimens.This study compares the different mechanical behaviors between integrated and interlayered specimens containing gas hydrate,which can serve as a reference for the prediction and analysis of the deformation behaviors of natural gas hydrate reservoirs.