Contact Surface Friction Research Articles

An Improved Torque Method for Preload Control in Precision Assembly of Miniature Bolt Joints

In this work, the improved torque method based on a mathematical model was proposed for preload control in the precision assembly of miniature bolts joint. The mathematical model was used for predicting the friction-compensated control torque. The predicted control torque is a function of preload and torque gradient which is determined by the friction of contact surfaces. Thus, the effect of friction on preload error can be reduced, and the bolts preload scatter due to frictional variables of the bolts can be decreased. Experiments were carried out to verify the proposed method using the bolts with thread of M1.6, and the results show that the scatters of preload were less than ±13.0% in the elastic range, which is more consistent than the conventional torque method. The preload control error for most bolts was less than 10%.

L-shaped piezoelectric motor-Part I: Design and experimental analysis

This paper proposes an L-shaped piezoelectric motor consisting of two piezoelectric bimorphs of different lengths arranged perpendicularly to each other. The coupling of the bending vibration mode of the bimorphs results in an elliptical motion at the tip. A detailed finite element model was developed to optimize the dimensions of bimorph to achieve an effective coupling at the resonance frequency of 246 Hz. The motor was characterized by developing rotational and linear stages. The linear stage was tested with different friction contact surfaces and the maximum velocity was measured to be 12 mm/s. The rotational stage was used to obtain additional performance characteristics from the motor: maximum velocity of 120 rad/s, mechanical torque of 4.7 × 10-(5) N·m, and efficiency of 8.55%.

Tailoring microstructure and phase segregation for low friction carbon-based nanocomposite coatings

Friction has a direct relation with the energy efficiency and environmental cleanliness in all moving mechanical systems. To develop low friction coatings is extremely beneficial for preserving not only our limited energy resources but also the earth’s environment. This study proposes a new design for low friction carbon-based nanocomposite coatings by tailoring the microstructure and phase segregation, and thereby it contributes to better controlling the mechanical and tribological properties. Experimental findings and theoretical calculations reveal that high-hardness (18.2 GPa), high-adhesion strength (28 N) as well as low-internal stress (−0.8 GPa) can be achieved by a nanocrystallite/amorphous microstructure architecture for the nc-WC/a-C(Al) carbon-based nanocomposite coating; in particular low friction (∼0.05) can be acquired by creating a strong thermodynamic driving force to promote phase segregation of graphitic carbon from the a-C structure so as to form a low shear strength graphitic tribo-layer on the friction contact surfaces. This design concept is general and has been successfully employed to fabricate a wide class of low friction carbon-based nanocomposite coatings.

Numerical study of heat duty of oil-cooled friction pair with radially positioned oil grooves in a multidisk brake

Findings from the numerical study of the heat duty of an oil-cooled friction pair in a multidisk brake of a wheel tractor are presented. The boundary problem is formulated to describe the heat processes in an oil-cooled friction pair with radially positioned oil-control grooves under frictional heating. It is solved by the finite-element method for the case of the tractor’s braking on a protracted descent. The features of the temperature field formation in an oil-cooled friction pair are identified and a functional dependence of the maximum temperature on the friction contact surface on the coefficient of overlapping of the disc friction surfaces is obtained.

Static Analysis of Friction Contact Effect on Valley Cable Force

In order to study the friction contact effect between cable and membrane in cable-membrane structures, a tensioned cable-membrane FE model which has a stable cable (valley cable) is created with FEA software ANSYS. The friction contact between the valley cable and membrane surface is simulated by contact elements in ANSYS, and the effect of friction contact surface is considered by the introduction of friction coefficients. Three different design valley cable forces (15kN, 20kN and 25kN) are considered in form-finding and static analysis, and valley cable force losses are analyzed. Results show that valley cable force loss due to friction contact should be considered obviously when design valley cable force is relatively small.

Influence of Brake Pad Thickness on Disk Brake Squeal

A squeal test using a pad with a different thickness demonstrated that a squeal with a higher frequency can be generated if a thin pad is used. The factors that changed as a result of pad thickness were termed 'difference of pad rigidity' and 'dimension difference in the thickness direction of the pad,' and the influence each factor exerted on the squeal was clarified. First, the dynamic stiffness of the pads used for the squeal tests were measured by adding a vibration that imitated the frequency and amplitude of the squeal. The measurement showed that the pad rigidity becomes hard when the pad thickness becomes thin. In addition, the pad vibrated with the same amplitude and the same phase from the frictional contact surface to the back plate in the thickness direction. The pad rigidity is in inverse proportion to the pad thickness because the pad can be viewed as springs in series in the thickness direction. Next, the influence that pad thickness exerted on squeal was analyzed by using a surface-contact-analysis model that reproduced the pad rigidity with a distributed spring and the dimension difference in the thickness direction of the pad with distance from the contact surface to the rotational center of the pad. Results showed that the squeal frequency becomes high when the pad rigidity becomes hard. If the dimension in the thickness direction of the pad becomes small, the squeal is not generated easily; however, the dimension does not influence the squeal frequency.

Effects of Near-Fault Ground Shaking on Sliding Systems

A numerical study is presented for a rigid block supported through a frictional contact surface on a horizontal or an inclined plane, and subjected to horizontal or slope-parallel excitation. The latter is described with idealized pulses and near-fault seismic records strongly influenced by forward-directivity or fling-step effects (from Northridge, Kobe, Kocaeli, Chi-Chi, Aegion). In addition to the well known dependence of the resulting block slippage on variables such as the peak base velocity, the peak base acceleration, and the critical acceleration ratio, our study has consistently and repeatedly revealed a profound sensitivity of both maximum and residual slippage: (1) on the sequence and even the details of the pulses contained in the excitation and (2) on the direction (+ or - ) in which the shaking of the inclined plane is imposed. By contrast, the slippage is not affected to any measurable degree by even the strongest vertical components of the accelerograms. Moreover, the slippage from a specific record may often be poorly correlated with its Arias intensity. These findings may contradict some of the prevailing beliefs that emanate from statistical correlation studies. The upper-bound sliding displacements from near-fault excitations may substantially exceed the values obtained from some of the currently available design charts.

Strength of shoulder during one‐handed pushing in constrained conditions

AbstractThis study hypothesizes that, by isolating the influences of contact surface friction, back foot support, and forward‐leaning body posture during pushing, the magnitude of recorded strength will be a closer estimate of physical capabilities of the shoulder. The shoulder strength of twelve participants during one‐handed pushing in constrained conditions in the coronal (frontal) plane, in a range from 5 to 30 degrees, was correlated with the anthropometric measures and two anatomical parameters of the shoulder joint. The data indicated that the acceptable loads at the handle for all the participants were lower than the recommended standards. Right arm length had the highest correlation coefficient with shoulder strength among anthropometric data, and the radius of the humerus bone among anatomical parameters. The findings from this study of one‐handed pushing will be used to help modify existing physical strength standards in an effort to reduce the high frequency of recorded shoulder injuries. © 2009 Wiley Periodicals, Inc.

Low-frequency behavior in a frictionally excited beam

A cantilevered beam excited by a periodically reciprocating friction contact surface exhibited extremely low-frequency responses (with frequencies as low as 100 times lower than the driver). Example responses near 1:1 and 1:2 resonances, between the excitation and the degree of freedom normal to the direction of sliding, show two-frequency quasiperiodicity, and in one case three-frequency quasiperiodicity. Underlying circle maps were extracted, and winding numbers were matched to response frequencies quantified in the fast Fourier transforms of the responses. A torus doubling bifurcation was documented.

Creep small-punch testing and its numerical simulations

Comparison of results of creep small-punch tests (SPTs) on miniaturized discs with results of their simulation by means of finite element method (FEM) is presented. Advanced heat-resistant chromium steel of type P91 was selected for the investigations. Two basic creep constitutive models, i.e. the Norton power-law and the exponential relationship were applied in the FEM. Parameters of both relationships were determined from stress dependences of minimum creep rate of conventional creep tests at 873 K. Two principally different FE models of the SPT were applied. The first model considers only simple boundary conditions as supports and an assumption of pressure load without the specific puncher shape; the second model includes contact elements taking in account the surface friction between all contact surfaces. Results of our numerical analyses are compared with experimental results. Results of modeling allow better understanding of the specimen behavior at higher strain rates and to estimate the influence of the contact surface friction at elevated temperatures.

The effect of friction on indentation test results

A smooth contact analysis is commonly adopted in simulated indentation. Limited studies have been performed to investigate the possibility of deviation due to this simplification. This study involves the finite element simulation of indentation by conical indenters and the Berkovich family of indenters with three different apex angles of indenter tips of 50°, 60° and 70.3°. Loading curvatures and the ratio of the remaining work done to the total work done of the load-indentation curves resulting from the simulated indentation tests considering friction and smooth contact surfaces were compared and discussed. A wide range of elasto-plastic materials obeying the power law strain hardening model were considered in this study. The results as presented herein demonstrate that the effect of friction on the two essential basic parameters from the load–indentation curves, namely, the loading curvatures and the ratio of the work done, varies depending on both mechanical properties of the target materials and the geometries of the indenter tips adopted in the investigation.

Contemporary kinematics of the Upper Rhine Graben: A 3D finite element approach

The Upper Rhine Graben (URG), a Cenozoic intra-plate rift situated in the Alpine foreland, is presently characterised by relative slow tectonic deformation and low to medium seismicity. Concurrently, it is a region with a significant amount of ongoing subsidence in two recent depocentres (0.1 to 0.2 mm/a geological, 1 mm/a geodetical rate). In this paper, the recent kinematic behaviour of the URG is simulated using a 3D finite element model, containing three lithospheric layers (upper mantle, lower crust and upper crust) with different rheological properties. First order fault structures (e.g. border faults) are implemented as frictional contact surfaces within the upper crustal layer. The stresses generated by applying lateral displacements over a time period of 10 ka are insufficient to obtain a match between predicted and observed stress magnitudes. Therefore, a technique of “combined pre-stressing” has been developed to avoid unrealistic deformation and unrealistic stress magnitudes within the model. The stress magnitudes and stress directions predicted are calibrated against in-situ stress measurements and stress indicator data. For benchmarking of the modelling results, the vertical surface displacements predicted are compared to surface uplift derived from geological and geomorphological data. Furthermore, predicted fault slip rates are compared to available geological and geodetical data. Parameters derived from the calculated stress tensor, such as fracture potential and the regime stress ratio are also analysed in order to describe the possible kinematic behaviour of the URG. The modelling results suggest that the URG is currently being reactivated as a sinistral strike–slip system with the central segment of the URG forming a restraining bend and the two recent depocentres situated in releasing bend settings. The modelling results suggest that both sinistral shearing and mantle uplift are active mechanisms driving the recent kinematics of the URG and that the recent subsidence within the two depocentres is re-enforced by ongoing mantle uplift additionally.

Kinetics of change making of a lubricant layer at friction of contact surfaces in extreme conditions

А question about prognostication development impermissible types wear - grasping and jamming is considered in article. Using method separate measuring thickness lubricating, kinetics change making thicknesses lubricating layer is shown. Intercommunication and basic conformities to law change between total thickness lubricating layer and tribotehnicheskimi parameters - moment friction and work friction is set experimentally.

浸炭材のピッチング疲労強度に及ぼすすべり条件の影響

The objective of the present paper is to clarify the effect of slip condition, ie. slip ratio, outer surface velocity, and lubrication oil temperature on the contact fatigue strength for pitting (pitting strength) of the carburized steel. Rolling contact fatigue (RCF) tests were conducted on 26mm diameter specimens made of carburized steel under oil lubrication. Then, slip ratio, outer surface velocity, and lubrication oil temperature as the slip condition were changed on the RCF tests. As a result, pitting strength decreased with the increase of slip ratio, the decrease of outer surface velocity, and the decrease of lubrication oil temperature. Furthermore, relationships between the above-mentioned three parameters, friction coefficient, and contact surface temperature were evaluated. Then slip ratio, outer surface velocity, and lubrication oil temperature influenced to friction coefficient and contact surface temperature. The friction coefficient slightly decreased when contact surface temperature increased. Lastly, it was found that the friction coefficient was main parameter which directly determines the pitting strength.

A 3D shock computational strategy for real assembly and shock attenuator

The extension of an approach, suitable for bolting structures impact computation with a large number of unilateral friction contact surfaces, and with local plasticity of the bolts, is presented. It is a modular approach based on a mixed domain decomposition method and the LATIN method. This iterative resolution process operates over the entire time–space domain. A 3D Finite-Element code is presented and dedicated to applications concerning connection refined models for which the structure components are assumed elastic. Several examples are analysed to show the method's capability of describing shocks throw real three-dimensional assembly. Comparisons between classical dynamic code LS-DYNA3D are presented.

Three-dimensional modelling and full-scale testing of stone arch bridges

Existing test results of full-scale in-service masonry arch bridges are analysed to determine appropriate material properties for the modelling of this structural type. Three-dimensional nonlinear finite element models of three masonry arch bridges are generated using a commercially available finite element package. The behaviour of the masonry is replicated by use of a solid element that can have its stiffness modified by the development of cracks and crushing. The fill is modelled as a Drucker–Prager material, and the interface between the masonry and the fill is characterised as a frictional contact surface. The bridges are modelled under service loads, and the model results are compared to the results of a program of field testing of the structures. It is found that the assumption of a reasonable set of material properties, based on visual observations of the material and construction of the structure, implemented through a program of three-dimensional nonlinear finite element analysis enable good predictions of the actual behaviour of a masonry arch bridge.

A modular approach to 3-D impact computation with frictional contact

An approach suitable for 3-D impact computation with a large number of unilateral friction contact surfaces is presented. Applications concern connection refined models for which the structure components are assumed to be elastic. It is a modular approach based on a mixed domain decomposition method and the LATIN method. The resolution process is iterative and operates over the entire time-space domain. Several examples are finally analyzed to show the method's capability of describing shocks.

Field-Scale and Wellbore Modeling of Compaction-Induced Casing Failures

Summary Presented in this paper are the results and verification of field- and wellbore-scale large deformation, elasto-plastic, geomechanical finite element models of reservoir compaction and associated casing damage. The models were developed as part of a multidisciplinary team project to reduce the number of costly well failures in the diatomite reservoir of the South Belridge Field near Bakers-field, California. Reservoir compaction of high porosity diatomite rock induces localized shearing deformations on horizontal weak-rock layers and geologic unconformities. The localized shearing deformations result in casing damage or failure. Two-dimensional, field-scale finite element models were used to develop relationships between field operations, surface subsidence, and shear-induced casing damage. Pore pressures were computed for eighteen years of simulated production and water injection, using a three-dimensional reservoir simulator. The pore pressures were input to the two-dimensional geomechanical field-scale model. Frictional contact surfaces were used to model localized shear deformations. To capture the complex casing-cement-rock interaction that governs casing damage and failure, three-dimensional models of a wellbore were constructed, including a frictional sliding surface to model localized shear deformation. Calculations were compared to field data for verification of the models.

Nonlinear analysis of a large bridge with isolation bearings

As a part of the California Toll Bridge Seismic Retrofit Program, a global nonlinear time history analysis of the Benicia-Martinez Bridge was conducted using ADINA. A key component of the retrofit strategy was the implementation of friction pendulum bearings. Proper application of the frictional contact surface and the simulation of the restoring force of the bearing were critical to the evaluation of the proposed seismic retrofit. Various local models of the bearing system were developed to study its response and sensitivity to the modeling parameters. Responses of the ADINA friction pendulum bearing representation were compared to those of other nonlinear codes. The behavior predicted by the system of elements used in ADINA for the friction pendulum bearing produced results that matched very closely with other programs. Other important issues for analyzing the Benicia-Martinez Bridge are also discussed.

The Discrete Steady Sliding Problem

This paper presents an extensive treatment of the existence of solutions to mechanical systems undergoing steady sliding on a frictional contact surface when acted on by external forces. Our treatment is based on the theory of discrete linear elasticity, Coulomb's friction law and Signorini's contact conditions; the theory of cone-linear complementarity problem (LCP) is the main tool employed in the analysis. For large friction coefficients examples of nonexistence can be given. However, for small' friction coefficients, we obtain, via several reformulations, some mechanically meaningful conditions under which the existence issue can be satisfactorily resolved.