Influence of Alignment Errors on Contact Pressure during Straight Bevel Gear Meshing Process

Straight bevel gears are widely applied in automotive, aerospace, chemical and many other fields as one of the most common type of gears. Currently, the researches on straight bevel gears have focused on the fields of fatigue, wear, noise and vibration, while little attention is paid to the effect of multiple alignment errors on the gear tooth wear. To study the influence of alignment errors on the gear tooth wear, a simulated model of a straight bevel gear pair is established. Then, the contact pressure on the tooth surface is analyzed under the various alignment errors according to the Archard wear relationship. The main combinations of alignment errors played vital roles on the tooth wear are investigated. The result shows that under the single alignment error, the contact pressure moves to the tooth heel and increases greatly at here when ？P=0.1 or ？G=0.1; when ？E=–0.03, the contact pressure greatly increases at the tooth heel, but it obviously increases at the tooth toe when ？E=0.03; the alignment error ？γ=1 has little effect on the contact pressure on the tooth surface. Moreover, the combination of ？P, ？G, ？E〈0 and ？γ is the most dangerous type among the multiple alignment errors. This research provides valuable guidelines for predicting the tooth wear under various alignment errors.

ESTIMATION OF RESIDUAL CONTACT PRESSURE IN HYDRAULICALLY EXPANDED CRA-LINED PIPE

The mechanically bonded CRA-lined pipe is developed to meet the need forcorrosion-resistant alloy steel pipe. Residual contact pressure at the interface of lined pipe isimportant factor that governs the quality of lined pipe. A simplified theoretical method ispresented to predict the residual contact pressure created by hydraulic pressure. The calculatingequation related hydro-forming pressure to the residual contact pressure between two metal faces isderived. And the validation of the proposed equation is accomplished by comparing its result tothose obtained by experimental investigation.

Evaluation of Contact Pressure in Bending under Tension Test by a Pressure Sensitive Film

The contact pressure acting on the sheet/tools interface has been studied because of growing the concern about the wear of tools. Recent studies make use of numerical simulation software to evaluate and correlate this pressure with the friction and wear generated. Since there are many studies that determine the coefficient of friction in sheet metal forming by bending under tension (BUT) test, the contact pressure between the pin and the sheet was measured using a film that has the ability to record the applied pressure. The vertical force applied to pin was also measured. The results indicate that the vertical force is more accurate to set the contact pressure that using equations predetermined. It was also observed that the contact area between the sheet and the pin is always smaller than the area calculated geometrically. The friction coefficient was determined for the BUT test through several equations proposed by various authors in order to check if there is much variation between the results. It was observed that the friction coefficient showed little variation for each equation, and each one can be used. The material used was the commercially pure aluminum, alloy Al1100.

Strain hardening rate dependency of deformation shape,strain distribution,and contact pressure during wire flat rolling

The effect of the strain hardening exponent(n)of a material on the changes in shape,strain inhomogeneity,and contact pressure was investigated during wire flat rolling to understand its effect on the deformation behavior of a flat-rolled wire and to determine the optimal working conditions with materials.The deformation behaviors of wires with various n values were systematically compared using finite element method.The shape of the deformed wire was found to depend on the n value of the material.Both the contact width and lateral spreading of the wire decrease with increasing n,resulting in a large reduction in area with the n value.The strain homogeneity of the wire increases with the n value of the wire.The improvement in the strain homogeneity with the n value is attributable to two factors:a lower strain concentration in the central region and a higher overall elongation as n increases.In addition,the average effective strain of the wire cross section decreases with the n value of a material during wire flat rolling.The contact pressure distribution on the surface of the wire differs significantly depending on the n value.In materials with a low n value,the contact pressure exhibits a higher value at the entry and edge zones of the contact surface.By contrast,materials with high n values exhibit a higher contact pressure at the exit zone.This behavior can be explained by the strain hardening behavior of the material during wire flat rolling.

Investigation of contact behavior on a model of the dual-mobility artificial hip joint for Asians in different inner liner thicknesses

BACKGROUND The four components that make up the current dual-mobility artificial hip joint design are the femoral head,the inner liner,the outer liner as a metal cover to prevent wear,and the acetabular cup.The acetabular cup and the outer liner were constructed of 316L stainless steel.At the same time,the inner liner was made of ultra-high-molecular-weight polyethylene(UHMWPE).As this new dual-mobility artificial hip joint has not been researched extensively,more tribological research is needed to predict wear.The thickness of the inner liner is a significant component to consider when calculating the contact pressure.AIM To make use of finite element analysis to gain a better understanding of the contact behavior in various inner liner thicknesses on a new model of a dual-mobility artificial hip joint,with the ultimate objective of determining the inner liner thickness that was most suitable for this particular type of dual-mobility artificial hip joint.METHODS In this study,the size of the femoral head was compared between two diameters(28 mm and 36 mm)and eight inner liner thicknesses ranging from 5 mm to 12 mm.Using the finite element method,the contact parameters,including the maximum contact pressure and contact area,have been evaluated in light of the Hertzian contact theory.The simulation was performed statically with dissipated energy and asymmetric behavior.The types of interaction were surface-to-surface contact and normal contact behavior.RESULTS The maximum contact pressures in the inner liner(UHMWPE)at a head diameter of 28 mm and 36 mm are between 3.7-13.5 MPa and 2.7-10.4 MPa,respectively.The maximum von Mises of the inner liner,outer liner,and acetabular cup are 2.4–11.4 MPa,15.7–44.3 MPa,and 3.7–12.6 MPa,respectively,for 28 mm head.Then the maximum von Mises stresses of the 36 mm head are 1.9-8.9 MPa for the inner liner,9.9-32.8 MPa for the outer liner,and 2.6-9.9 MPa for the acetabular cup.A head with a diameter of 28 mm should have an inner liner with a thickness of 12 mm.Whereas the head diameter was 36 mm,an inner liner thickness of 8 mm was suitable.CONCLUSION The contact pressures and von Mises stresses generated during this research can potentially be exploited in estimating the wear of dual-mobility artificial hip joints in general.Contact pressure and von Mises stress reduce with an increasing head diameter and inner liner’s thickness.Present findings would become one of the references for orthopedic surgery for choosing suitable bearing geometric parameter of hip implant.

Wavelet neural network applied for prognostication of contact pressure between soil and driving wheel

This paper describes the measurement of contact pressure in the context of wheel–terrain interaction as affected by wheel load and tire inflation pressure when fusion of the wavelet transform with the back-propagation(BP)neural network is applied to construct the wavelet neural network contact pressure prediction model.To this aim,a controlled soil bin testing facility equipped with single-wheel tester was utilized while three levels of velocity,three levels of slippage and three levels of wheel load were applied.Using image processing technique,contact area values were determined which were subsequently used for quantification of contact pressure.Performances of the different predictor models incorporated of various mother wavelets were evaluated using standard statistical evaluation criteria.Root mean square error and coefficient of determination values of 0.1382 and 0.9864 achieved by the optimal wavelet neural network are better than that of BP neural network.The proposed tool typifies a high learning speed,enhanced predicting accuracy,and strong robustness.

Effect of Contact Pressure during Quenching on Microstructures and Mechanical Properties of Hot-stamping Parts

An experimental apparatus with cooling system and pressure-adjustment assembly for simulating quench- ing was constructed to investigate the effect of contact pressure on the microstructures and mechanical properties of hot stamping parts. Qualitative and quantitative analyses of the microstructures of the as quenched parts were con- ducted; moreover, hardness and tensile tests were performed to measure their mechanical properties. The results in- dicated that contact pressure during quenching strongly affected the structures and performances of hot-stamping components. An excessive low contact pressure led to insufficient martensitic transformation. The critical contact pressure for complete martensitic transformation for 4.0 mm 22MnB5 steel was 0.4 MPa when the temperature of the coolant was 20 ℃. However, in consideration of the efficiency of practical production, a contact pressure higher than 1.25 MPa is recommended.

Surface contact behavior of functionally graded thermoelectric materials indented by a conducting punch

The contact problem for thermoelectric materials with functionally graded properties is considered.The material properties,such as the electric conductivity,the thermal conductivity,the shear modulus,and the thermal expansion coefficient,vary in an exponential function.Using the Fourier transform technique,the electro-thermoelastic problems are transformed into three sets of singular integral equations which are solved numerically in terms of the unknown normal electric current density,the normal energy flux,and the contact pressure.Meanwhile,the complex homogeneous solutions of the displacement fields caused by the gradient parameters are simplified with the help of Euler’s formula.After addressing the non-linearity excited by thermoelectric effects,the particular solutions of the displacement fields can be assessed.The effects of various combinations of material gradient parameters and thermoelectric loads on the contact behaviors of thermoelectric materials are presented.The results give a deep insight into the contact damage mechanism of functionally graded thermoelectric materials(FGTEMs).

Low friction under ultrahigh contact pressure enabled by self-assembled fluorinated azobenzene layers

Extensive efforts have been made to pursue a low-friction state with promising applications in many fields,such as mechanical and biomedical engineering.Among which,the load capacity of the low-friction state has been considered to be crucial for industrial applications.Here,we report a low friction under ultrahigh contact pressure by building a novel self-assembled fluorinated azobenzene layer on an atomically smooth highly-oriented pyrolytic graphite(HOPG)surface.Sliding friction coefficients could be as low as 0.0005 or even lower under a contact pressure of up to 4 GPa.It demonstrates that the low friction under ultrahigh contact pressure is attributed to molecular fluorination.The fluorination leads to effective and robust lubrication between the tip and the self-assembled layer and enhances tighter rigidity which can reduce the stress concentration in the substrate,which was verified by density functional theory(DFT)and molecular dynamics(MD)simulation.This work provides a new approach to avoid the failure of ultralow friction coefficient under relatively high contact pressure,which has promising potential application value in the future.

A research on the contact stress of roller bearing based on crowning analysis

According to elastic contact theory, contact model between roller and race is established. Compared with the Hertz results, the results are proved, based on which contact stress distribution of different crowning and initial contact length is given, then the appropriate value is derived. On the basis, inertia force and different radial force is given into consideration. Via analysis, it con- cludes that under balanced pure radial load condition the largest contact stress between roller and race increases along with crowning value increasing. With the same crowning value, the largest contact stress between roller and race decreases in the first and increases at the end along with initial contact length increasing. Contact stress between roller and outer race increases along with revolution speed increasing.

Nondestructive measurement of thermal contact resistance for the power vertical double-diffused metal-oxide-semiconductor

To obtain thermal contact resistance（TCR） between the vertical double-diffused metal-oxide-semiconductor（VDMOS） and the heat sink, we derived the relationship between the total thermal resistance and the contact force imposed on the VDMOS. The total thermal resistance from the chip to the heat sink is measured under different contact forces, and the TCR can be extracted nondestructively from the derived relationship. Finally, the experimental results are compared with the simulation results.

Theoretical and experimental study of the thermal strength of anticorrosive lined steel pipes

Bimetallic lined steel pipe （LSP） is a new anti-corrosion technology. It is widely used to transport oil, gas, water and corrosive liquid chemicals. At present, the hydroforming pressure for LSP has been investigated theoretically and experimentally by most researchers. However, there are a few reports on the thermal strength of bimetallic LSP. Actually, the bimetallic LSP will be subjected to remarkable thermal load in the process of three layer polyethylene （3PE） external coating. Reverse yielding failure may occur on the inner pipe of the bimetallic LSP when it suffers from remarkable thermal load and residual contact pressure simultaneously. The aim of this paper is to study the thermal load and strength of the bimetallic LSP. A mechanical model, which can estimate the thermal strength of the bimetallic LSP, was established based on the elastic theory and the manufacture of the bimetallic LSP. Based on the model, the correlation between the thermal strength of the bimetallic LSP and residual contact pressure and wall thickness of the inner pipe was obtained. Reverse yielding experiments were performed on the LSP （NT80SS-316L） under different thermal loads. Experiment results are consistent with calculated results from the theoretical model. The experimental and simulation results may provide powerful guidance for the bimetallic LSP production and use.

THREE-DIMENSIONAL FINITE ELEMENT SIMULATION OF TOTAL KNEE JOINT IN GAIT CYCLE

Based on CT scanning pictures from a volunteer＇s knee joint, a three-dimensional finite element model of the healthy human knee joint is constructed including complete femur, tibia, fibular, patellar and the main cartilage and ligaments. This model was validated using experimental and numerical results obtained from other authors. The pressure distribution of contact surfaces of knee joint are calculated and analyzed under the load action of ‘heel strike＇, ‘single limb stance＇ and ‘toe-off＇. The results of the gait cycle are that the contact areas of medial cartilage are larger than that of lateral cartilage; the contact force and contact areas would grow larger with the load increasing; the pressure of lateral meniscus is steady, relative to the significant variation of peak pressure in medial meniscus; and the peak value of contact pressure on all components are usually found at about 4570 of the gait cycle.

Sealing Performance and Optimization of a Subsea Pipeline Mechanical Connector

Researchers seldom study the optimum design of a mechanical connector for subsea oil-gas pipeline based upon the sealing performance. An optimal design method of a novel subsea pipeline mechanical connector is presented. By analyzing the static metal sealing mechanism, the critical condition of the sealing performance is established for this connector and the formulation method of the contact pressure on the sealing surface is created. By the method the minimum mean contact pressure of the 8.625 inch connector is calculated as 361 MPa, which is the constraint condition in the optimum design of connector.The finite element model is created in ANSYS Parametric Design Language(APDL) and the structure is optimized by the zero-order method, with variance of contact pressure as the objective function, and mean contact pressures and plastic strains as constraint variables. The optimization shows that variances of contact pressure on two sealing surfaces decrease by 72.41% and 89.33%, respectively, and mean contact pressures increase by 31.18% and 52.84%, respectively. The comparison of the optimal connectors and non-optimal connectors in the water pressure experiments and bending experiments shows that the sealing ability of optimized connectors is much higher than the rated pressure of 4.5 MPa, and the optimal connectors don’t leak under the bending moment of 52.2 kN·m.This research provides the formulation to solve contact pressure on the sealing surface and a structure optimization method to design the connectors with various dimensions.

THE VARIATIONS OF WATER IN HUMAN TISSUE UNDER CERTAIN COMPRESSION:STUDIED WITH DIFFUSE REFLECTANCE SPECTROSCOPY

The reflectance spectrun has been widely adopted to extract diagnosis information of human tissue because it possesses the advantages of noninvasive and rapidity.The external pressure brought by fiber optic probe may influence the accuracy of measurement.In this paper,a sys-tematic study is focused on the effects of probe pressure on intrinsic changes of water and scattering particles in tissue.According to the biphasic nonlinear mixture model,the pressure modulated reflectance spectrum of both in vitro and in vivo tissue is measured and processed with second-derivation.The results indicate that the variations of bulk and bonded water in tissue have a nonlinear relationship with the pressure.Diferences in tissue structure and morphology contribute to site specific probe pressure effects.Then the finite element(FEM)and Monte Carlo(MC)method is employed to simulate the deformation and reflectance spectrum variations of tissue before and after compression.The simulation results show that as the pressure of fiber optic probe applied to the detected skin increased to 80kPa,the effective photon proportion form dermis decreases significantly from 86%to 76%.Future designs might benefit from the research of change of water volume inside the tissue to mitigate the pressure applied to skin.

Determination of the Friction Coefficient in the Flat Strip Drawing Test

Current work is focused on the influence of friction in deep drawing process. Friction measurements were also conducted using a modified tribotester based on strip sliding between tools. Four different tool surfaces were tested under similar contact conditions regarding contact area, normal pressure, sliding speed, lubricant and surface characteristics to calculate the friction coefficient between the tool surface and a high strength low alloy steel sheet HSLA 380. The results showed that friction coefficient varies over a wide range with different lubricating conditions and different sliding velocities. For some sliding velocities, the coefficient of friction is stable and low, while for others it is unstable and higher. Results of the experiments reveal that this novel tribotester is a very useful tool to evaluate and compare the friction between steel sheet and tool surfaces in alloyed steel for cold working applications. The outcomes have only small dispersion within the different test series, which indicates a stable process with good repeatability. The test method enables comparison of different surface finishes and treatments, lubricants and coatings in terms of friction and galling under conditions similar to those found in sheet metal forming processes. The four different types of surfaces considered for this study were grinded, polished, nitrided and quenched/tempered. The main difference among the tested tools in this work was the surface roughness, which was found to have a strong influence on friction.

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.

Finite element analysis of tibio-femoral contact mechanics of a customised knee spacer

With one-third of patients having osteoarthritis predominantly in one compartment of the knee,unicompartmental knee spacers have been introduced as a less invasive alternative to total knee replacement.However,patients with the knee spacer implanted were seen to have persistent pain,resulting in high revision rates.A static finite element model of the knee and its interaction with a knee spacer implant at full extension and 90°flexion was used to investigate the tibio-femoral contact mechanics of the knee joint after a knee spacer surgery.Three different knee spacer designs(contoured,flat and C-shaped)were modelled and prescribed with cobalt-chrome,ultra-high molecular polyethylene and polyurethane material properties.The results suggested that a softer spacer is generally preferred as this helps in the conformity of knee spacer to the condyle,effectively distributing the load subjected to the implant.Flat spacers that result in high stresses resulting from lower contact areas should be avoided.

A new mechanism for friction-induced vibration and noise

For years,friction-induced vibration and noise(FIVN)has puzzled many researchers in academia and industry.Several mechanisms have been proposed for explaining its occurrence and quantifying its frequencies,notably for automotive brake squeal,clutch squeal,and even rail corrugation.However,due to the complex and complicated nature of FIVN,there is not yet one fundamental mechanism that can explain all phenomena of FIVN.Based on experimental results obtained on a simple test structure and corresponding numerical validation using both complex eigenvalue analysis(CEA)and transient dynamic analysis(TDA),this study attempts to propose a new fundamental mechanism for FIVN,which is the repeated cycles of partial detachment and then reattachment of the contact surfaces.Since friction is ubiquitous and FIVN is very common,the insight into FIVN reported in this paper is highly significant and will help establish effective means to control FIVN in engineering and daily life.

Galling Failure Analysis in Sheet Metal Forming Process

Galling is a known failure mechanism in sheet metal forming operations,and it can lead to fracture of the products and jamming of the tool. The temperature field and normal contact pressure distributions of the tool and the blank were studied with a finite element analysis model under the action of different blank holder force and frictional coefficient. A series of forming tests of the high strength steel were conducted to validate the finite element model. The characteristics of galling failure,the damaged surface of the product and the adhesive wear of the tool,were analyzed during the forming process. The results demonstrate that die corner is the region where temperature and normal contact pressure are high and galling failure initiates. The blank surface passing through the die corner usually has the galling problem. The blank holder force and the tool surface topography have strong effects on the galling behavior in sheet metal forming processes. The methodology using finite element analysis to predict galling failure behavior can be used to perform parametric and material studies on the galling failure.