Experiment and constitutive modelling of creep deformation in the frozen silt-concrete interface

To ensure the long-term safety and stability of bridge pile foundations in permafrost regions,it is necessary to investigate the rheological effects on the pile tip and pile side bearing capacities.The creep characteristics of the pile-frozen soil interface are critical for determining the long-term stability of permafrost pile foundations.This study utilized a self-developed large stress-controlled shear apparatus to investigate the shear creep characteristics of the frozen silt-concrete interface,and examined the influence of freezing temperatures(−1,−2,and−5°C),contact surface roughness(0,0.60,0.75,and 1.15 mm),normal stress(50,100,and 150 kPa),and shear stress on the creep characteristics of the contact surface.By incorporating the contact surface’s creep behavior and development trends,we established a creep constitutive model for the frozen silt-concrete interface based on the Nishihara model,introducing nonlinear elements and a damage factor.The results revealed significant creep effects on the frozen silt-concrete interface under constant load,with creep displacement at approximately 2-15 times the instantaneous displacement and a failure creep displacement ranging from 6 to 8 mm.Under different experimental conditions,the creep characteristics of the frozen silt-concrete interface varied.A larger roughness,lower freezing temperatures,and higher normal stresses resulted in a longer sample attenuation creep time,a lower steady-state creep rate,higher long-term creep strength,and stronger creep stability.Building upon the Nishihara model,we considered the influence of shear stress and time on the viscoelastic viscosity coefficient and introduced a damage factor to the viscoplasticity.The improved model effectively described the entire creep process of the frozen silt-concrete interface.The results provide theoretical support for the interaction between pile and soil in permafrost regions.

A Simple Method of Surface Parameter Extraction for Gate Schottky Contact in 4H-SiC MESFETs

We investigate the effects of the surface states on the Schottky contacts in 4H-SiC MESFET. The Ti/Pt/Au gate metal contacts are deposited by electron beam evaporation and patterned by a lift-off process. Based on thermionic theory,a simple parameter extraction method is developed for determination of the surface states in metal/4H-SiC Schottky contacts. The interface state density and interface capacitance are calculated to be 4. 386 × 10^12 cm^-2 · eV^- 1 and 6. 394 × 10^-6 F/cm^2 ,which are consistent with the device＇s terminal characteristics.

Two Dimensional Nanoscale Reciprocating Sliding Contacts of Textured Surfaces

Detailed behaviors of nanoscale textured surfaces during the reciprocating sliding contacts are still unknown although they are widely used in mechanical components to improve tribological characteristics. The current research of sliding contacts of textured surfaces mainly focuses on the experimental studies, while the cost is too high. Molecular dynamics（MD） simulation is widely used in the studies of nanoscale single-pass sliding contacts, but the CPU cost of MD simulation is also too high to simulate the reciprocating sliding contacts. In this paper, employing multiscale method which couples molecular dynamics simulation and finite element method, two dimensional nanoscale reciprocating sliding contacts of textured surfaces are investigated. Four textured surfaces with different texture shapes are designed, and a rigid cylindrical tip is used to slide on these textured surfaces. For different textured surfaces, average potential energies and average friction forces of the corresponding sliding processes are analyzed. The analyzing results show that ＂running-in＂ stages are different for each texture, and steady friction processes are discovered for textured surfaces II, III and IV. Texture shape and sliding direction play important roles in reciprocating sliding contacts, which influence average friction forces greatly. This research can help to design textured surfaces to improve tribological behaviors in nanoscale reciprocating sliding contacts.

Study on Glow Discharge Plasma Used in Polyester Surface Modification

To achieve an atmospheric pressure glow discharge（APGD）in air and modify the surface of polyester thread using plasma,the electric field distribution and discharge characteristics under different conditions were studied.We found that the region with a strong electric field,which was formed in a tiny gap between two electrodes constituting a line-line contact electrode structure,provided the initial electron for the entire discharge process.Thus,the discharge voltage was reduced.The dielectric barrier of the line-line contact electrodes can inhibit the generation of secondary electrons.Thus,the transient current pulse discharge was reduced significantly,and an APGD in air was achieved.We designed double layer line-line contact electrodes,which can generate the APGD on the surface of a material under treatment directly.A noticeable change in the surface morphology of polyester fiber was visualized with the aid of a scanning electron microscope（SEM）.Two electrode structures-the multi-row line-line and double-helix line-line contact electrodes-were designed.A large area of the APGD plasma with flat and curved surfaces can be formed in air using these contact electrodes.This can improve the efficiency of surface treatment and is significant for the application of the APGD plasma in industries.

Application of response surface method for contact fatigue reliability analysis of spur gear with consideration of EHL

In order to consider the effects of elastohydrodynamic lubrication(EHL) on contact fatigue reliability of spur gear, an accurate and efficient method that combines with response surface method(RSM) and first order second moment method(FOSM) was developed for estimating the contact fatigue reliability of spur gear under EHL. The mechanical model of contact stress analysis of spur gear under EHL was established, in which the oil film pressure was mapped into hertz contact zone. Considering the randomness of EHL, material properties and fatigue strength correction factors, the proposed method was used to analyze the contact fatigue reliability of spur gear under EHL. Compared with the results of 1.5×105 by traditional Monte-Carlo, the difference between the two failure probability results calculated by the above mentioned methods is 2.2×10-4, the relative error of the failure probability results is 26.8%, and time-consuming only accounts for 0.14% of the traditional Monte-Carlo method(MCM). Sensitivity analysis results are in very good agreement with practical cognition. Analysis results show that the proposed method is precise and efficient, and could correctly reflect the influence of EHL on contact fatigue reliability of spur gear.

A mathematical model of rough surface contact characterization in spot welding

Based on the elastic-plastic mechanics and the contact mechanics, an asperity contact model for the resistance spot welding of the rough surface is presented. The numerical results indicate that the real contact area is only a small section of the nominal contact area. The value of the real contact area is randomly fluctuating within 20%. The real contact area’s distribution and each point’s deformation can also be obtained from this model, which is primary in the calculation of the contact resistance and the temperature field of the spot welding.

Microbial Evaluation of Meat Contact Surfaces in Red Meat Abattoirs of Bauchi State, North-Eastern Nigeria

Microbial quality (MQ) of meat contact surfaces (MCS) of six major abattoirs was evaluated with a subsequent further isolation and identification of E. coli O157. Two hundred and forty 240 swab samples (SS) from MCS that include cutting equipment, floor, tables and transport media were collected for total aerobic plate count and isolation of E. coli O157. Results of the SS indicated a mean value 7.1 ± 0.3 log10 cfu/cm2. A minimum value of 6.4 ± 0.6 log10 cfu/cm2 was recorded oncutting instrument from Ningi abattoir, while a maximum value of 7.8 ± 0.3 log10 cfu/cm2 was obtained from tables at Darazo abattoir. Only 3 (1.2%) of the 240 SS of the MCS were positive for E. coli O157 using the latex agglutination kit (Difco, Michigan, USA).

NUMERICAL APPROACH TO DETERMINING INSTANTANEOUS CONTACT REGION FOR CONJUGATE SURFACES

According to the defect of traditional method of determining instantaneous contact regions for conjugate surfaces, a numerical approach to the determination is proposed. A local coordinate system is built by using the surface unit tangent and unit normal at the contact point. Considering that the gap forming the boundary of instantaneous contact region in the direction of the common normal vectors is given, a system of nonlinear equations is built to find the instantaneous contact boundary in local coordinate system, a modified Powell＇s hybrid algorithm of finite-difference approximation to the Jacobian used to solve the system. The new method simplifies the task of determining instantaneous contact regions without calculating curvatm＇e and relative curvature. The validity of the proposed approach is verified by an example of hypoid gears.

CAD-DIRECTED INSPECTION PLANNING FOR FREEFORM SURFACE USING CONTACT PROBES

A methodology for CAD-directed measurement of freeform surface using a coordinate measuring machine equipped with a touch-trigger probe is presented, mainly including adaptive sampling of measurement points and registration of freeform surface. The proposed sampling method follows four steps： Freeform surface is fitted by bi-cubic B-spline; Curvedness measure of the surface is computed; Given a number of sampling points, an iterative algorithm is constructed for selecting a set of measurement points by employing the curvedness information; The measurement points is regularized for tradeoff between maximizing the measurement accuracy and minimizing the sampling time and cost. The aforesaid algorithm is demonstrated in term of a marine propeller blade. An offset surface registration method is presented to improve alignment accuracy of freeform objects, and Monte Carlo simulation is conducted to verify the effectiveness of the method.

Non-Thermal Atmospheric Plasma:Can it Be Taken as a Common Solution for the Surface Treatment of Dental Materials?

This study aimed to evaluate the surface roughness and wetting properties of various dental prosthetic materials after different durations of non-thermal atmospheric plasma（NTAP）treatment.One hundred and sixty discs of titanium（Ti）（n：40）,cobalt chromium（Co-Cr）（n：40）,yttrium stabilized tetragonal zirconia polycrystals（Y-TZP）（n：40）and polymethylmethacrylate（PMMA）（n：40）materials were machined and smoothed with silicon carbide papers.The surface roughness was evaluated in a control group and in groups with different plasma exposure times [1-3-5 s].The average surface roughness（Ra）and contact angle（CA）measurements were recorded via an atomic force microscope（AFM）and tensiometer,respectively.Surface changes were examined with a scanning electron microscope（SEM）.Data were analyzed with two-way analysis of variance（ANOVA）and the Tukey HSD test α=0.05）.According to the results,the NTAP surface treatment significantly affected the roughness and wettability properties（P 〈 0.05）.SEM images reveal that more grooves were present in the NTAP groups.With an increase in the NTAP application time,an apparent increment was observed for Ra,except in the PMMA group,and a remarkable reduction in CA was observed in all groups.It is concluded that the NTAP technology could enhance the roughening and wetting performance of various dental materials.

Research on fatigue evaluation method of high-speed train axle based on axle box acceleration

As a key safety component of the high-speed train, fatigue fracture of the axle would lead to major accidents such as derailment or overturning. The complexity of the axle dynamic stress test seriously enhances the difficulty of axle fatigue damage analysis. In this paper, the dynamic stress test of the high-speed train axle was carried out,the axle box acceleration was monitored on-track during the test, and the relationship between the axle stress spectrum and acceleration was analyzed on-track. The results show that the relationships between the axle equivalent stresses and the Root Mean Square(RMS) values of the axle box vertical acceleration and lateral acceleration exhibit a strong joint probability density distribution. The concept of the virtual surface density of wheel-rail contact is also proposed to realize the purpose of using axle box acceleration to deduce axle equivalent force. The results quantify the relationship between axle box acceleration and axle equivalent force, provide a new method for predicting the axle damage using the acceleration RMS values, and open up a new approach for structural health monitoring of high-speed train axles.

Probing the Affinity of Coronavirus with Contact Surfaces in Simulated Body Fluids

Transmission of viral pathogens has raised serious public health concerns,but the affinity and strength of viruses adhering to hightouch surfaces are not clear.We systematically investigated the propensities of a coronavirus,Murine hepatitis virus A59(MHV),adhering onto and releasing from four representative contact surfaces,silica,stainless steel,cellulose,and polystyrene,in simulated saliva and urine using quartz crystal microbalance with dissipation monitoring(QCM-D).We also quantified the interactions between MHV and contact surfaces using atomic force microscopy(AFM).Both initial adhesion rates and saturated adhesion mass of MHV were higher in urine buffer than in saliva buffer,which is attributed to the higher repulsions between the virus and surfaces in the presence of mucin.The maximum adhesion mass of MHV follows the order of stainless steel>silica>cellulose≈polystyrene in both urine and saliva buffers.Stainless steel and silica are surfaces with likely higher risks of virus contamination due to their highest maximum adhesion mass in both urine and saliva buffers and lower virus release percentages upon water rinse.The results of this study will provide insights into risk assessment and control of pathogens associated with contact surfaces.

Integrity of grinding face-gear with worm wheel

Aiming at the issue of the grinding integrity of face-gear with worm wheel, the envelope mathematical model of shaper, worm wheel and face-gear is established based on theories of differential geometry and gear mesh. The judgment of completely grinding the face-gear with the avoidance of singularities is established, and the mathematical expression to show the reason why singularities appear is derived, through the research on the surface contact area and singularity rules of the worm thread surface. The disadvantage of current face-gear grinding method that only part of the working surface of the face-gear can be covered is analyzed and the influence of coefficient of judgment is studied through changing the design parameters.

A study on characteristics of shock train inside a shock tube

Shock tubes are devices which are used in the investigation of high speed and high temperature flow of compressible gas. lnside a shock tube, the interaction between the reflected shock wave and boundary layer leads to a complex flow phenomenon. Initially a normal shock wave is formed in the shock tube which migrates toward the closed end of the tube and that in turn leads to the reflection of shock. Due to the boundary layer interaction with the reflected shock, the bifurcation of shock wave takes place. The bifurcated shock wave then approaches the contact surface and shock train is generated. Till date only a few studies have been conducted to investigate this shock train phenomenon inside the shock tube. For the present study a computational fluid dynamics （CFD） analysis has been performed on a two dimensional axi-symmetric model of a shock tube using unsteady, compressible Navier-Stokes equations. In order to investigate the detailed characteristics of shock train, parametric studies have been performed by varying different parameters such as the shock tube length, diameter, pressure ratio used inside the shock tube.

NUMERICAL STUDY ON FLANGING AND SPRINGBACK OF STAMPED THICK METAL PLATE

A quasi-three-dimensional shell element model, which can beeffectively used to simulate the flanging and spring-backdeformation, is introduced into the independently developed CAEsoftware, KMAS, In this model, a double surface contact algorithm,which allows the gap between punch and die to change, and a spring-back treatment scheme based on finite element meshing are described.And then the flanging and spring-back deformations of the retractor'skickstand of a railcar made of stamped thick metal plate arenumerically simulated. The simulation results of flanging deformationare compared with those of international commercial software,PAM-STAMP, and experimental ones. Finally, a predicting scheme ofspring-back quantily for this problem is given.

Contact Resistance and Arc Erosion of Tungsten-copper Contacts in Direct Currents

The arc erosion under medium direct currents in the argon flow was tested on tungsten-copper（W-Cu） contacts which were processed by hot extrusion and heat treatment. The scanning electron microscopy（SEM） and transmission electron microscopy（TEM） were used to study the microstructure of the W-Cu powders and compacts. The contact resistance, arcing energy, and arcing time were continuously measured by JF04C contact materials test system. Changes in tungsten-copper contact surface were observed by SEM. The test results showed that the arcing time and arcing energy all increase with current and voltage, but the changes of average contact resistance are more complicated. For a short arcing time, the average contact resistance decreases with increasing current due to the vaporization of Cu. However, for a longer arcing time, it slightly increases due to the formation of high resistant films, compound copper tungsten. The formation of compound copper tungsten was confirmed by the increased Rc kept in the range from 1.1 to 1.6 mΩ. The compound copper tungsten is first exposed with a tungsten and copper-rich surface, and then totally exposed due to evaporation of copper from the surface. At last a stabilized surface is created and the crystals decrease from 8 μm to 2 μm caused by the arc erosion.

Research on the influence of contact surface constraint on mechanical properties of rock-concrete composite specimens under compressive loads

The contact form of rock-concrete has a crucial influence on the failure characteristics of the stability of rock-concrete engineering.To study the influence of contact surface on the mechanical properties of rock-concrete composite specimens under compressive loads,the two different contact forms of rock-concrete composite specimens are designed,the mechanical properties of these two different specimens are analyzed under triaxial compressive condition,and analysis comparison on the stress-strain curves and failure forms of the two specimens is carried out.The influence of contact surface constraint on the mechanical properties of rock-concrete composite specimens is obtained.Results show that the stress and strain of rock-concrete composite specimens with contact surface constraint are obviously higher than those without.Averagely,compared with composite specimens without the contact surface,the existence of contact surface constraint can increase the axial peak stress of composite specimens by 24%and the axial peak strain by 16%.According to the characteristics of the fracture surface,the theory of microcrack development is used to explain the contact surface constraint of rock-concrete composite specimens,which explains the difference of mechanical properties between the two rock-concrete composite specimens in the experiment.Research results cannot only enrich the research content of the mechanics of rock contact,but also can serve as a valuable reference for the understanding of the corresponding mechanics mechanism of other similar composite specimens.

Numerical Study of Interaction of Propagated Shock with Boundary Layer Behind Contact Surface in Ducts

The interactions of the shock with the boundary layer of the cold gas behind the contact in many different conditions.i.e. three kinds of test gases and three kinds of sound speed ratios across the contact,were explored by numerical study.The trajectories of the transmitted shock in cold gas flow and the development of shock bifurcation in the process of interaction with boundary layer are illustrated by many kinds of figures(e.g.the time-distance diagrams of the acoustic impedance contours on the axis,the pressure and density contours and the static pressure distributions on the axis.).

Effects of internal factors on surface wettability of corn stalk rind

Corn stalk is one of heterogeneous materials with anisotropy and variability.As the rind of corn stalk consists of rich lignin and cellulose similar to wood properties,and possessing high mechanical strength,then can be used as raw material of stalk artificial board and paper.The corn stalk rind has significant differences in fiber morphology,chemical composition and mechanical properties at different heights.Nano-SiO2 composite material contained in the epidermis of corn stalk rind is not conducive to exert adhesive into a board.To study board-making technology by intact corn stalk rind,the wettability of corn stalk rind at different sampling heights is necessary to be analyzed by keeping or removing the epidermis.To analyze the surface wettability difference,the contact angle with water,element compositions and the chemical compositions of corn stalk rind at different sampling heights were studied before and after removal of epidermis.A Fourier transform infrared(FTIR)analysis was performed.The results showed that the removal of the epidermis could significantly improve the hydrophilicity of corn stalk rind.Before removal of the epidermis,the varying contents of elements including C and Si dominate the surface wettability differences at different sampling heights of corn stalk.With an increase in the sampling height,the mass fraction of C increases while that of Si decreases,which result in increasing hydrophilicity.After removal of the epidermis,the surface wettability of corn stalk rind is mainly determined by the mass fraction of hemicellulose,and the higher the sampling height,the larger the mass fraction of hemicellulose resulting in the increase of hydrophilicity.

Analysis of asphalt mix surface-tread rubber interaction by using finite element method

The surface texture of the pavement plays a very important role in driving the frictional properties at the tire rubber-pavement interface. Particularly, the hysteretic friction due to viscoelastic deformations of rubber depends mainly on the pavement surface texture. In the present paper, the effect of micromechanical pavement surface morphology on rubber block friction was brought in by comparing the friction results for three different asphalt mix morphological surfaces, named stone mastic asphalt （SMA）, ultra-thin surfacing （UTS） and porous asphalt （PA）. The asphalt surface morphologies of these mixes were captured by using an X-ray tornographer, from which the resulting images micromechanical finite element （FE） meshes for SMA, UTS and PA pavements were developed by means of the SimpleWare software. In the FE model, the rubber and asphalt binder were modeled as viscoelastic （V-E） materials and the formulation was given in the large deformation frame- work. FE simulations were then carried out by using contact algorithm between rubber and the road surface. It was observed that the rubber friction inversely varies with the sliding speed and positively varies with the pressure for all the pavement morphological and stiffness conditions. Furthermore, it was observed that the highly porous pavement surface results in large dissipation of energy, hence, large rubber friction which shows that the mix characteristics of pavements have a simaificant effect on rubber friction.