Nonuniform Contact Pressure Distribution Research Articles

Leakage Model of Tubing and Casing Premium Connection Based on Sinusoidal Contact Simulation between Rough Surfaces

This paper proposed a semi-theoretical model to quantitatively predict leakage rate of tubing and casing premium connections. The geometric parameters of the sealing surface profile approximated by a sinusoidal micro-convex surface were first obtained based on the random normal distribution sampling method. With the actual area prediction formula for elastic–plastic contact of an axisymmetric sinusoidal micro-convex body based on the equivalent simulation principle, the circumferential leakage width and radial average leakage height of the micro-leakage channel between sealing surfaces were then acquired with the surface roughness and geometric mean contact pressure. At last, the actual micro-leakage rate of the premium connection was derived by considering the non-uniform contact pressure distribution between sealing surfaces. An example was investigated to validate the model and reveal the sealing and leakage characteristics, and anti-leakage measures were proposed. The results show that average contact pressure, circumferential leakage width, and radial average leakage height between sealing surfaces were non-uniformly distributed. The leakage rate of a premium connection decreases exponentially with an increase in radial interference between sealing surfaces. In order to reduce leakage rate, it is beneficial to increase radial interference and lower sealing surface roughness.

Experimental and theoretical studies on friction contact of bolted joint interfaces

This paper presents experimental and theoretical modeling studies on the tangential contact stiffness and friction hysteresis of bolted joint interfaces under transversal vibration. A new test rig was developed to measure the interface fretting response of bolted joints. This rig is based on a servo-hydraulic fatigue testing system in which the contact surfaces are arranged symmetrically to avoid bending of the specimen that could affect the friction measurement. Force-displacement curves were measured under different tangential loads and compared with those found in the literature. A multi-scale contact modeling method was proposed to calculate the tangential contact stiffness and reproduce the friction hysteresis of bolted joint interfaces. This method overcomes the complexity of identifying contact stiffness, which usually requires a model of the dynamic behavior of the joint and frequency responses measured with dedicated fretting test stands. Specifically, this method comprehensively considers the multi-scale features of randomly rough surfaces, the non-uniform contact pressure distribution, and the convenience of phenomenological contact models in simulating frictional hysteresis, relying on fractal contact theory and discretized Iwan model. The effectiveness of the proposed method was verified by comparing the simulation results with the experimental counterparts in different cases of tangential loading. The successful validation demonstrates the potential of the proposed modeling method for application to structures with bolted joint.

Misalignment-Induced Micro-Elastohydrodynamic Lubrication in Rotary Lip Seals

In literature the lubrication of rotary lip seals is explained by hydrodynamic action on a microscopic scale. This theory assumes perfect concentricity between the seal and the shaft which in reality seldomly occurs. Focusing on the stern tube seals application, an analysis is performed on the phenomena distorting the axisymmetric operation of rotary lip seals. Radial and angular shaft misalignments together with pressure and temperature gradients have been modelled. The model predictions are validated using a dedicated setup. Additionally, applying the soft-EHL film thickness expressions at the asperity level, an equivalent film thickness along the circumferential direction is estimated. The Reynolds PDE is solved to predict the misalignment-induced hydrodynamic pressure build-up. The film thickness variation derived and accompanying non-uniform contact pressure distribution was shown to be sufficient for hydrodynamic action and, depending on the minimum film thickness, the hydrodynamic pressure build-up can exceed the static contact pressure. Additionally, significant differences were observed between the radial and angular misalignment configurations.

Coupled thermo-mechanical analysis and shape optimization for reducing uneven wear of brake pads

In vehicle braking systems, the non-uniform contact pressure distribution on the brake pad is a major cause of uneven wear. The experimental approach of the wear phenomenon is the time consuming and costly. For this reason, a threedimensional finite element (FE) model of a brake system is presented for numerical simulation in this paper. A coupled thermo-mechanical analysis is carried out to confirm the non-uniform contact pressure distribution. A correlation between the non-uniform contact pressure and uneven wear is confirmed by measuring the amount of wear in the brake pad. The shape optimization of the brake pad is performed to reduce the uneven wear. In addition, the simulation results, such as natural frequency and temperature, are compared to experimental results.

Investigations of the Armature–Rail Contact Pressure Distribution in a Railgun

In the process of electromagnetic launch, the nonuniform contact pressure distribution on the armature-rail interface kept changing with the armature moving forward. At first, the contact pressure was mainly provided by the deformation of the trailing arm, from which it could keep a good metal-metal contact at the armature-rail interface. After the pulse current was constructed, the magnetic pressure would dominate the contact pressure because it was much larger than the mechanical interference pressure. In this paper, the 3-D modeling of contact pressure distribution was carried out with the finite-element method. In the simulation of 3-D contact calculations, the current entered the armature from the trailing edge. The electromagnetic force perpendicular to the armature trailing arm was equivalent to the uniform load on the inner surface of the trailing arm. A typical contour pattern of nonuniform contact pressure distribution was acquired. Some nonuniform coefficients of contact pressure distribution were proposed and analyzed to evaluate the contact performances between the armature and rails. A series of simulations was conducted at different magnitudes of magnetic pressure, and with different armature structure parameters. The characteristics of the nonuniform coefficients were investigated and discussed. The dependences of the nonuniform coefficients on the equivalent uniform load and armature structure parameters were obtained.

Optimization of a Mechanical Bridge Joint Structure in a Stacked HTS Conductor

The mechanical bridge joint (bridge-type lap joint) of a stacked high-temperature superconducting conductor has been investigated for a “remountable” or a segment-fabricated high-temperature superconducting magnet. In a previous study, joint resistivities were evaluated experimentally for the bridge joints of single-layer and double-layer stacked GdBCO coated conductors. However, the joint resistivity increased with an increase in the number of layers due to nonuniform contact pressure distribution caused by a gap or misalignment in the joint region. In this study, therefore, we were aiming at the reduction of joint resistance by achieving more uniform contact pressure distribution. In addition, we investigated the effects of temperature while applying pressure to the joint and positioning the joint structure to investigate its application in an actual large-sized magnet. First, we inserted an indium film between the joint surfaces to make contact pressure uniform. Experimental results showed that joint resistivity with the indium film did not depend on the number of layers. In addition, applying force at room temperature was more effective in decreasing joint resistivity than that at 77 K. Finally, we examined the effect of the joint structure with screw bolt tightening. The result showed that the structure of the convex plate has better joint performance than others.

플랫 블레이드 윈드실드 와이퍼의 역전 진동 저감에 관한 연구

This research introduces a new method to attenuate flip-over vibration generation in the flat blade windshield wiper by adjusting the contact pressure between the windshield glass and the blade. The knocking force in the flip-over action of the blade is decreased by inducing gradual tilting-over along the rubber strip of the blade. This gradual tilting-over is induced by introducing a non-uniform contact pressure distribution between the blade and windshield glass. The contact pressure distribution is adjusted by controlling the unloaded profile of the body spring in the blade using a procedure proposed in a previous study. Two blades, one blade designed to generate a uniform pressure distribution and the other designed to generate non-uniform pressure distribution, are developed using the procedure. Contact pressure distributions of the developed blades are measured using a special device and compared with the intended distributions confirming the similarities between the two groups. Vertical and lateral vibrations of the two blades are measured under realistic operating condition simulated by a wiper test rig. The vertical vibrations of the blade with non-uniform contact pressure are substantially smaller than corresponding vibrations of the blade with uniform contact pressure over the entire rubber strip.

Backup roll contour of a SmartCrown tandem cold rolling mill

SmartCrown was a new system developed by VAI for improving the strip profile and flatness control first applied in 1700 mm tandem cold rolling mills at Wuhan Iron & Steel (Group) Corporation (WISCO). After tracing and testing, the application of the conventional crown backup roll matching the SmartCrown work roll of the production mill led to heavy and nonuniform wear, and the edge spalling of the backup roll often occurred. A 3-dimension finite element model of roll stacks was established, which was used to analyze the above-mentioned problems, and it was found that the main reason was the highly nonuniform contact pressure distribution between the work roll and the backup roll. A new FSR (flexible shape backup roll) was developed and applied in 1700 mm tandem cold rolling mills. A lot of good actual effects of FSR, such as evident improvement in profile and flatness of strips, non-occurring edge spalling, wear uniform, and remarkable decrease in roll consumption were validated by long-term industrial applications.

A finite-element simulation of asperity flattening in metal forming

A three-wavelength finite-element model for asperity flattening has been developed based on an analysis of measurement data for steel sheet surface. The simulation of asperity-flattening procedure indicates a non-uniform contact pressure distribution and a large stress concentration appearing on the contact surface. Evolution of contact ratio and surface roughness are investigated by a simulation under various friction conditions and comparison with other models is made. The effect of relative sliding between the workpiece and tool and friction factor is discussed. An equation of the contact area ratio as a function of load, friction and sliding velocity is also presented based on the simulation results. The results are in reasonable agreement with experimental measurements.

Effect of Shear Stiffness of Fixed Joints on Thermal Deformation of Machine Tools

The role of fixed joints in the nonlinear thermoelastic behaviour of machine tool structures has been established in previous studies. This behaviour results from the effect of the nonuniform contact pressure distribution on the distribution of the compliance and the thermal contact conductance along the joint. Initial mathematical modelling of contacting surfaces considered only the normal stiffness of the interface. In the present study the additional effect of the shear stiffness of the interface on the thermal deformation of machine tool structure is presented. Experimental values for normal and shear stiffness derived for the interface alone, has been found to be higher than for the whole specimen. Both normal and shear deformation of the interface rise with normal pressure until they reach their maximum values, above which the deformation remain constant while the stiffness tend to infinity. An integrated computer program models the response of the structure through the cycle of consecutive iterations until the state of equilibrium is reached. The finite element idealization incorporates contact elements with spring linkage, normal and shear stiffness of which represent the elastic characteristics of the interface. The effect of combined normal and shear stiffness is shown in an example, which indicates, that not accounting for the shear stiffness of the interface may lead to errors in predicting the profile of thermal deformation, both in linear displacement and angular deviation.