Maximum Effective Stress Research Articles

Impact of Drawing Machine Parameters on Force and Energy Consumption in Borosilicate Glass Tube Production

Middle borosilicate glass tubes are critical materials for medical packaging, with the drawing machine playing a pivotal role in their production process. However, the effects of the drawing wheel’s motion parameters on the glass tube remain underexplored. Therefore, based on the finite element method simulation and validation experiment, the effects of experimental factors (angle of upper and lower drawing wheel, AUD; friction factor of glass and rubber, FFGR; and distance of upper and lower drawing wheel, DUD) on experimental indexes (maximum effective stress of glass tube, MES; rotational speed of glass tube, RSG; maximum and average forward driving force, MFDF and AFDF; maximum and average rotational driving force, MRDF and ARDF; total energy consumption and power, TEC and TPD; maximum and average forward driving power, MFDP and AFDP; and maximum and average rotational driving power, MRDP and ARDP) were analyzed. The results indicated that compared to FFGR and AUD, the influence of DUD on experimental indexes was the highest. The positive influence of AUD on RSG, ARDP, and MRDP, the positive influence of FFGR and the negative influence of DUD on MRDF, ARDF, TEC, TPD, ARDP, and MRDP were found, respectively. These findings will provide a theoretical reference for the optimization of drawing machines.

A novel approach for analyzing linear amplitude sweep (LAS) test data of asphalt binders

Fatigue cracking is one of the crucial distresses considered for the design of flexible pavements. The initiation of fatigue cracking occurs in the binder phase of an asphalt mixture. The linear amplitude sweep (LAS) test was developed to analyze the fatigue damage in the asphalt binder. AASHTO T391 provides a method to analyze the LAS test data by fitting a power equation between the fatigue parameter (G*sinδ) and damage intensity. This method has some inherent weaknesses of overfitting or underfitting of the data at different damage levels. This study proposes a new method where a total curve is divided into two parts that fit the data in two different equations and then sum them up. The first part comprises of the data up to cumulative damage corresponding to the maximum effective stress, and the second part consists of accumulated damage in the material till it reaches the maximum strain (30 %). This method is called the bifurcation method in this paper. LAS test data of 27 long-term aged bitumen samples having different physical properties is used to determine the number of fatigue life cycles (Nf) by these two methods, and results are compared in terms of mean absolute percentage error (MAPE), root mean square error (RMSE), and residual sum of squares (RSS). It is shown that there is a significant reduction in the errors when the data fitting was done using the proposed bifurcation method. Further, the ranking was allotted to the samples based on the number of fatigue life cycles (Nf) at three different strain levels (2.5 %, 5 %, and 10 %) at intermediate-temperature conditions estimated using two methods. The shift indicator parameter was used to analyze the variability in the ranking of the samples due to changes in the strain levels. The study concludes that the proposed bifurcation method fits the predicted values more accurately than the prescribed power law.

Wave–Induced Soil Dynamics and Shear Failure Potential around a Sandbar

Sandbars are commonly encountered in coastal environments, acting as natural protections during storm events. However, the sandbar response to waves and possible shear failure is poorly understood. In this research, a two–dimensional numerical model is settled to simulate the wave-induced sandbar soil dynamics and instability mechanism. The model, which is based upon the Reynolds-averaged Navier–Stokes (RANS) equations and Biot’s consolidation theory, is validated using available experiments. Parametric studies are then conducted to appraise the impact of the wave parameters and soil properties on soil dynamics. Results indicate that the vertical distribution of the maximum vertical effective stress in the sandbar is different from that in the flat seabed, which decreases rapidly along the soil depth and then increases gradually. The impact of soil permeability and saturation on the vertical effective stress distribution around the sandbar also differ from that in the flat seabed. Unlike the flat seabed, the vertical distribution of shear stress in the sandbar increases with an increasing wave period. The sandbar soil shear failure potential is discussed based upon the Mohr–Coulomb criterion. Results show that the range of shear failure around the sandbar is wider and the depth is deeper when the wave trough arrives.

Experimental and Numerical Study on the Effect of Three-Hole Simultaneous Blasting Technology on Open-Pit Mine Bench Blasting

Blasting technology is widely applied in various engineering applications due to its cost-effectiveness and high efficiency, such as in mining, transport infrastructure construction, and building demolition. However, the occurrence of cracking in the rear row has always been a major problem that disrupts mining bench blasting. To address this issue, a three-hole simultaneous blasting technology is proposed in this study. Both numerical simulations and onsite blasting experimental testing were conducted. To aid this endeavor, the three-hole simultaneous blasting and the hole-by-hole blasting methods were adopted to comparatively analyze the severity of the damage caused to the original rock and the effect of rock fragmentation in the rear row. The obtained results highlighted that the outcome of the blast produced by the three-hole simultaneous blasting method is satisfactory, with fewer flying stones and concentrated blasting piles required. Additionally, the original rock in the rear row showed no obvious sign of tensile damage and had uniform fragmentation. It was also found that a block size of less than 60 cm accounts for 100%, while a block size of less than 50 cm accounts for 98.7% of the whole blocks, with no large blocks reported. Moreover, a penetrating horizontal crack occurred in the direction of the connection of the blast hole center when the three-hole simultaneous blasting method was adopted. This resulted in a smooth and flat rear part of the rocks at the interface. Compared to the hole-by-hole blasting method, the three-hole simultaneous blasting method improved the effective stress and displacement at each measurement point. At the measurement point directly at the front of the borehole, the maximum effective stress attained 67.9 GPa, and the maximum displacement reported was 31.9 cm. Overall, it was shown that the three-hole simultaneous blasting technology is applicable in similar applications of mine bench blasting, which is conducive to addressing the rear row original rock strain for onsite bench blasting.

Study on Numerical Simulation of Surrounding Rock Structure Safety of Urban Underwater Shield Tunnel: A Case in Chongqing

Based on the engineering background of shield construction of a subway section in Chongqing, which needs to pass through a park and there is a lake inside this park, this paper adopts theoretical analysis methods and numerical simulation calculation methods to explore the distribution law of the seepage field and the characteristics of water pressure in lining segments during shield tunneling. The results show that, during the whole excavation of a double-track tunnel with EPB shield, the maximum vertical effective stress is about 4.24 MPa, which is located at the arch foot of the tunnel. The maximum effective stress in the horizontal direction is about 3.61 MPa, which is located on both side walls of the tunnel in the horizontal direction; after the left and right tunnels are excavated in sequence, a “double precipitation funnel-shaped” pore pressure distribution is formed around the tunnel; during the construction of the shield tunnel, the vertical displacement and horizontal displacement of the surrounding rock show an increasing trend and gradually tend to be stable values of 24.09 mm and 25.28 mm; the segment vault has settlement, the maximum settlement is 21.8 mm, the arch bottom has uplift, and the maximum uplift is 24.4 mm. The maximum horizontal displacement of the segment appears on both sides of the arch waist, and the maximum horizontal displacement decreases with the increase of excavation steps; the positive bending moment of the lining segment is mainly distributed on both sides of the arch crown, and the negative bending moment is mainly distributed on both sides of the arch bottom. The axial force of the lining segment is compressive stress, and the maximum axial force is mainly distributed on both sides of the arch waist. The maximum normal shear stress occurs on both sides of the segment arch bottom. The study conclusions provide theoretical foundation and a new guidance for long-term safety evaluation of underwater tunnel structures.

Blasting effects of the borehole considering decoupled eccentric charge

The investigation of the blasting effects of the borehole considering decoupled eccentric charge is scarce and lacks thorough exploration. The coupled Smoothed Particle Hydrodynamics and Finite Element Method (SPH-FEM) is adopted to study the decoupled eccentric charge blasting effects. The effective stress distribution of rock around the borehole is analyzed and the damage evolution is studied quantitatively with introducing image recognition algorithm. Further, the effect of the decoupling coefficient on blasting effects is investigated. Results show that effective stress distribution presents obvious eccentric characteristics. At the bottom coupling point, the maximum effective stress is observed, and gradually reduces towards the top uncoupling point. The lower part of rock surrounding the borehole exhibits a higher damaged area ratio compared to the upper part for decoupled eccentric charge blasting. With the decoupling coefficient increases from 1.14 to 2.00, the effective stresses at monitoring points are all decreasing and the effective stress ratio first increases and then keeps relatively stable, with the decoupling coefficient of 1.6 as inflection point. As the decoupling coefficient increases to 1.6, the damage extent ratio reaches the peak. The greatest disparity in explosion energy between the coupled and uncoupled sides occurs at a decoupling coefficient of approximately 1.6.

Determination of Optimal Cross-Section Dimensions of Rectangular Hollow Sections Under Oblique Bending: Analytical and Numerical Study.

An insignificant number of rigorous studies have been devoted to the development of analytical procedures that determine the optimal cross-section dimensions of rectangular hollow section (RHS) members subjected to oblique bending, albeit their ubiquity in numerous application fields. In response to this, an analytical procedure has been developed based on the concept of minimizing maximum effective stress in the RHS caused by an applied oblique bending moment, in order to reduce material costs without compromising strength requirements. The RHS members addressed in this study have been assumed to be produced by hollowing out rectangular solid sections at different cross-section area extraction ratios; therefore, only the wall thicknesses of the RHS members have been taken into consideration as design variables. The minimization of maximum effective stress has been achieved by establishing a functional correlation between the cross-section design variables. The proposed procedure allows specifying the optimal cross-sectional dimensions for given different cross-section area extraction ratios and bringing cost-effective use of materials. After the subtle mathematical calculations, the derived analytical expressions have been made available to practical engineering in simple math forms for use in real design applications. The analytical procedure has been validated against numerical results which have been extracted from finite element analyses carried out in Abaqus engineering software.

A general model for the small-strain stiffness of saturated residual soils: back analysis of a database and case study

A review analysis of a database of 237 small strain stiffness measurements performed on 35 different residual soils is presented. The reinterpretation of the tests was conducted with respect to the loading conditions and physicochemical parameters published in the literature. Besides, the database was completed with the results of a case study from a dam construction project in the French West Indies. On the basis of a detailed and carefully justified analysis, parameters influencing the response of saturated residual soils to small strains are identified, is proposed. The correlations between the identification characteristics of the residual soils (initial void ratio, Atterberg limits, clay fraction) and the model parameters are investigated. The article proposes a general model for the evaluation of the small-strain stiffness of saturated residual soils using, in addition to the mean effective stress (p’) and the maximum mean effective stress (p’max ) the initial void ratio (e0 ) and, for intact soils, the clay fraction (CF) or, for remoulded soils, the plasticity index (PI).

FEM simulation on forming vacuum hexagon socket screws using tube workpiece

This study proposes a new forming design concept to produce vacuum hexagon socket screws using tube workpiece, and uses the finite element simulation software DEFORM-3D to simulate the multi-pass forming process of vacuum hexagon socket screws. The simulated material is SUS-304 stainless steel, and the frictional conditions are assumed to be constant shear friction, the die is assumed to be a rigid body. In the past, the traditional vacuum hexagon socket screw manufacturing process used a multi-pass process to manufacture a standard screw using a solid workpiece (wire rod), and then drilling an air channel in the core of the screw. This process not only wastes time, but also needs to increase the processing cost. In this study, the time and cost of drilling the air channel can be reduced by forming the vacuum hexagon socket head screw through the hollow tube. The finite element simulation results confirm that this design is a feasible method. The pass schedule can be reduced from 6 stages to 3 stages, the maximum effective stress decreased by 28.13%, and the total forming force decreased by 57.66%. The research results can be provided to relevant industry as the reference.

SiO2 soot preform sintering process for the synthesis of large-size and high-purity silica glass

The indirect chemical vapor deposition (CVD) method is a promising method to synthesize high-purity silica glass. As a critical procedure of this method, the sintering process is rather complex due to the interactive physical phenomena, and an in-depth understanding is therefore required. In this paper, a comprehensive multiphase porous medium model is developed by introducing the shrinkage mechanism, which agrees well with the experimental results. With this model, the dynamic characteristics during the sintering process, including temperature distribution, volumetric deformation, hydroxyl content evolution, and internal stress development, are well predicted. A parametric sensitivity analysis is conducted then, which shows that the average porosity and hydroxyl concentration are mainly affected by the average particle radius, while the maximum effective stress is sensitive to both Young's modulus and the average particle radius. Finally, the effects of key operating parameters are explored, and it is found that a lower working pressure, an appropriate sintering temperature such as 1450 °C, or a proper initial porosity such as 80.0%, is more desirable for a sintered product with high optical performance. This study can deepen the understanding of the SiO2 soot preform sintering process, and provide a good basis for further optimization.

Study of rock damage characteristics in decoupled slit charge blasting based on computer tomography scanning

Controlling blast load damage and destruction of the remaining rock mass in rock blasting has been the focus of scientific research. By studying various decoupling ratios of the slit charges, blasting experiments and numerical calculations of the small charge were carried out on the glauconite specimen. The internal fracture and damage characteristics of the damaged specimens (post blast) were quantified by computed tomography (CT) scanning and three-dimensional (3D) model reconstruction. The results showed that the damage to the glauconite specimens was mainly radial, with the main crack surface in the slit direction and the “X-type” and “Y-type” non-slit directions. With the increase in the decoupling ratio of the slit charge, the fractal dimension of the explosion crack face tends to increase, and the degree of damage gradually increased; When the decoupling ratio was 1.67, the fractal dimension of the explosive crack surface decreased, the smallest degree of damage. LS-DYNA simulation software was used to study the dynamic fracture process and the effective stress peak of the blasthole wall in the slit and non-slit directions for different decoupling ratios of the slit charge. The numerical calculation results showed that with the increase in the decoupling ratio, the peak effective stress of the blasthole wall characteristic unit in the slit direction was larger than that in the non-slit direction; The effective stress peak showed an increasing trend, and the maximum peak effective stress was 567.7 MPa when the decoupling ratio was 1.67. Therefore, this method can be a suitable means to reconstructing the spatial distribution of internal cracks and numerical calculation to evaluate the damage mechanism of slit charge blasting; Furthermore, within the range of the optimal slit charge decoupling ratio, this method can guide the site to prevent the damage and destruction of the remaining rock mass, allowing for more, allocation and utilization of the explosion energy.

Investigation of Load-Bearing Capacity for Reinforced Concrete Foundation Retrofitted Using Steel Strut–Tie Retrofit System

To reduce the thickness of reinforced concrete foundation members used in construction and structural applications, a previous study developed and tested a strut–tie retrofit system installed in the foundations. This study proposes the optimum retrofit details of a steel-tie retrofit system for foundation members with reduced thickness via a finite element simulation-based load-bearing capacity assessment. The retrofit parameters (structural steel type, plate thickness, and number of strut frames) that significantly affected the load-bearing capacities were optimized by comparing the maximum effective stress and code-defined allowable stress limits. The optimum retrofit details were compared with those computed using a code-defined strut–tie model. Based on the load-bearing capacity assessment for the design of loading combinations, the optimum retrofit details can be reduced in transverse (by 55%) and longitudinal (by 87%) directions compared with those designed using the strut–tie model approach.

The Cold Forming Analysis of Eccentric Parts

In this study, a multi-stage cold forming process for the manufacture of eccentric parts is studied numerically with low carbon steel AISI 1022. The forming processes through five stages and four stages include two-step forward extrusion, eccentric upsetting, and backward extrusion over a moving punch. The numerical simulations of cold forming are conducted using the code of DEFORM-3D. The formability of the workpiece is studied numerically, such as the effect on forging load responses, maximum forging loads, effective stress and effective strain distributions and metal flow pattern. The maximum effective stress of 819 MPa at the third stage is the largest among the stages. The maximum effective stresses of the last stages for the four-stage forming and five-stage forming are almost the same. The effective strain distributions of the last stages for the four-stage forming and five-stage forming are very similar. The flow line distributions of the last stages both for the four-stage forming and five-stage forming are also very similar. For the maximum axial forging force and forming energy, the third stage of eccentric upsetting at the upper end is the largest among the stages. The total maximum axial forging loads from the first to the last stages are 795.8kN for the five-stage forming and 590.4kN for the four-stage forming; and the total forming energies are about 0.751kJ for the five-stage forming and 0.671kJ for the four-stage forming. Although the total maximum axial forging loads and total forming energy of the four-stage forming are smaller than those of the five-stage forming, the maximum lateral forging force in the last stage of the four-stage forming is almost five times that of the last stage of the five-stage forming. Increasing lateral forging force may lead to wear and damage of the punch. Moreover, the inner surfaces of the hexagonal cavity at the upper end are relatively uneven because of simultaneous eccentric upsetting and backward extrusion in the last stage of the four-stage forming.

Optimization of residual stress in low-pressure casting of ZL205A alloys

ZL205A alloys are prone to generate serious residual stress due to the long solidification intervals and multi-phase composition. In this study, the low-pressure casting process for ZL205A alloy hemisphere shell casting was investigated and continuously optimized. In the initial process, the knockout time, pouring temperature, preheating temperature of the sand mould, dwelling pressure, and filling rate were 3 h, 710 °C, 30 °C, 65 kPa, and 0.33 kPa·s−1, respectively. Macroscopic properties and microstructural features were simulated using a combination of ProCAST and Thermal-Calc software. Additionally, a series of experimental procedures, including EBSD, SEM, EDS, and XRD tests, were conducted to investigate the formation, morphology, and distribution of the microstructure. Current findings demonstrate that during the solidification process, the maximum temperature difference exceeds 220 °C, the maximum undercooling reaches 49.56 °C, and the maximum effective stress peaks at 301.7 MPa. The residual stress ranges from 20 to 200 MPa. Furthermore, there is no significant texture and preferred grain orientation during nucleation and solidification, and the structure field exhibits an equiaxed crystal but inhomogeneous pattern. Moreover, the finer and more homogeneous the grains and the smaller the deviation in grain orientation, the lower the residual stress. Specifically, two analytical models are developed: one between the casting parameters and the residual stress, and another between the shrinkage defects and the casting parameters. The lowest residual stress is achieved when the knockout time, pouring temperature, preheating temperature of the sand mould, dwelling pressure, and filling rate are 6 h, 725 °C, 250 °C, 95 kPa, and 1.67 kPa·s−1 respectively.

Dynamic Response Analysis of Airport Pavement under Impact Loading

The safety of the airport runway, as an infrastructure, is of considerable concern. The existing research has problems of hysteresis and unreasonable load application. In this paper, ANSYS is used to construct a coupled tire–pavement model to study the dynamic characteristics of airport asphalt pavements under impact loading. Taking the Boeing 737–800 as an example, the impact of an aircraft landing on an airport pavement is simulated by applying a dynamic load to the landing gear. The effects of tire pressure, landing pitch angle, and sinking speed on the dynamic response of the airport runway are investigated. The effects of each factor of the airport pavement are analyzed by comparing the maximum effective stress, effective strain, and displacement in the vertical direction at the same position of different structures. The results show that when the tire pressure is 2.0 MPa, the maximum values of effective stress, effective strain, and vertical displacement increase by 29.8%, 19.1%, and 22.2%, respectively, compared with 1.0 MPa. The maximum values of effective stress, effective strain, and vertical displacement at the 3.0 m/s sinking speed increase by 25.2%, 93.1%, and 77.1%, respectively, compared with that at the sinking speed of 1 m/s, which indicates that the effect of sinking speed on the dynamic response of the pavement is more significant. However, the change in the landing pitch angle has little impact on the response parameters of the pavement. Meanwhile, the flexural tensile stress at the bottom of the surface and the equivalent effect at the top of the soil foundation must be considered in the design of the airport pavement structure.

Finite element analysis of the main reactor vessel in the China Initiative Accelerator Driven System

The China Initiative Accelerator Driven System (CiADS) was proposed by China Academy of Science since 2015. The reactor in CiADS is a subcritical fast neutron reactor cooled by a liquid lead–bismuth eutectic. The reactor operates at high temperature and bears high thermal stress. In addition to the heavy weight of the whole reactor, the vessel will bear large effective stress. If the effective stress exceeds the limit of the material, defects and cracks may occur on the main reactor vessel, which will affect the safety performances of the reactor. Therefore, it is very important to analyze the effective stress field of the reactor vessel. In this paper, the finite element analysis software ADINA was applied to analyze the reactor vessel in CiADS. We can preliminarily prove that the maximum effective stress that the vessel will bear during the postulated Unprotected Loss of Flow (ULOF) and Unprotected Transient over Power (UTOP) accidents is less than the yield strength of 316L stainless steel. Therefore, we can preliminarily conclude that the current material selection and structural design of the CiADS vessel could survive the postulated transient accidents considering the effective stress effect.

FEM Simulation of Surface Micro-Groove Structure Fins Produced by Cryogenic-Temperature Extrusion Machining

In the process of metal cutting, a large amount of chips that are difficult to reuse will be produced, resulting in resource waste. As a novel metal forming process, cryogenic-temperature extrusion machining (CT-EM) can directly process chips into usable fins with a surface micro-groove structure, which has the advantage of high efficiency, energy saving and flexibility. In this study, the effects of four parameters (compression ratio λ, rake angle of the tool α, friction coefficient μ and the constraining tool corner radius R) on the effective stress, temperature and formability of micro-groove fins produced by CT-EM and room-temperature extrusion machining (RT-EM) are investigated. The results show that the maximum effective stress and formability of CT-EM are larger than that of RT-EM, which indicates that CT-EM has greater advantages in the preparation of micro-groove fins. At a λ of 0.7, the formability of CT-EM is the best. Reducing the λ and α, or increasing the μ, can improve the forming effect of the fins. CT-EM can produce micro-groove fins with the best formability when λ = 0.7, α = 5°, μ = 0.75 and R = 0.1 mm.

Determination of multiaxial stress rupture criteria for creeping materials: A critical analysis of different approaches

• Factors affecting different methods for the determination of MSRC are analyzed. • Principles in the determination of MSRC are recommended. • The factor, α , is strongly dependent on the operative creep failure mechanism. • A relation exists between multiaxial factor, α , and damage tolerance parameter, λ . Materials in engineering applications are rarely uniaxially-loaded. In reality, failures under multiaxial loading has been widely observed in engineering structures. The life prediction of a component under multiaxial stresses has long been a challenging issue, particularly for high temperature applications. To distinguish the mode of failure ranging from a maximum principal stress intergranular damage to von Mises effective stress rupture mode a multiaxial stress rupture criterion (MSRC) was originally proposed by Sdobyrev and then Hayhurst and Leckie (SHL MSRC). A multiaxial-factor, α , was developed as a result which was intended to be a material constant and differentiates the bias of the MSRC between maximum principal stress and effective stress. The success of the SHL MSRC relies on accurately calibrating the value of α to quantify the multiaxial response of the material/geometry combination. To find a more suitable approach for determining MSRC, the applicability of different methods are evaluated. Given that the resulting analysis of the various approaches can be affected by the creep failure mechanism, principles in the determination of MSRC with and without using continuum damage mechanics approaches are recommended. The viability of uniaxial material parameters in correlating with α through the analysis of available data in literature is also presented. It is found that the increase of the uniaxial creep damage tolerance parameter λ is accompanied by the decrease of the α –value, which implies that the creep ductility plays an important role in affecting the multiaxial rupture behavior of materials.

Effects of Annular-finned Tube Deformation on Thermal Stresses in a Heat Exchanger

Nowadays, along with the developments in the industry, many machines and structures are exposed to very high-temperature environments, which has caused various types of thermal load in them. These conditions have led to focused studies on thermal stresses in structures. Heat exchangers are among the structures in which the temperature difference causes thermal stress. In this paper, “finite volume” and “finite element” methods are used to solve flow equations and thermal stress equations in solids, respectively. In addition, the effect of changes in the shape of the annular finned pipe on the thermal stresses in the heat exchanger is investigated. The study results on changing the pipe shape from circular to elliptical show that by changing the pipe shape, the thermal stress in the fin can be significantly reduced; for instance, in the cases reviewed in this paper, the thermal stress has decreased by 9%. Furthermore, the results of thermal stress show that the Maximum Effective Stress point, both before and after changing the shape, is still located at the fin’s base. So, according to the results of this study, examining the effect of pipe shape changing on thermal stress is an imperative measure when designing heat exchangers.

Influence of contacting shape of partial wear on friction properties of copper-based materials for trains

In view of the fact that the contact between the pad and the disc cannot match perfectly in the actual braking process, the influence of contacting shape on the tribological performance was studied. Four copper-based brake pads in ratio (radial dimension / circumferential dimension) of 0.4, 0.6, 0.8 and 1.2 were used to perform contacting shape test on a small-scaled braking dynamometer at speeds 60 km/h, 100 km/h, 140 km/h and 180 km/h and contact pressure 0.5 MPa. The results indicated that contacting shape caused the difference of temperature of the brake system, which affected the friction performance. The peak temperature of the disc decreased from 331°C to 293.2°C with ratio increasing, and the maximum effective stress of the disc decreased 15%. In ratio of 0.4, the higher friction temperature and effective stress made the friction surface easy to plough, so the friction coefficient was low and the wear was nonuniform. In ratio of 1.2, the wear particles accumulated, resulting in high friction coefficient and uniform wear.