Search

The operation of roads under modern conditions associated with high speeds and traffic density results in wear of pavement and formation of a rut. When crossing the ruts, instability can occur when relatively small steering inputs lead to large changes in the trajectory. The lateral force acting on a wheel of a car is of particular importance in the study of stability and controllability. The magnitude of this force is determined by various factors: tire stiffness, speed, change in the angle of rotation of the wheel, the geometry of the transverse profile of the rut.The objective of the study refers to the problem of determining the angles of inclination of side walls of the rut that are safe for movement at different speeds. The paper considers the interaction of a car wheel with the road surface, proposes a mathematical model for interaction of a tire with ruts, considers the angle of the wheel running on the rut wall. To describe the elastic response of a tire in contact with a rut, an elastic foundation model and a plane section method are used. The lateral force was estimated based on equations of motion of the wheel when crossing the rut. The dependences of the ratio of the lateral force to the normal load for various rut depths and angles of inclination of its walls on the angle of rotation of the wheel and the speed of the vehicle were obtained. It is shown that at a rut inclination angle exceeding five degrees, the lateral force begins to increase significantly with an increase in the angle of rotation of the wheel, as well as the speed of the vehicle, and may exceed the applied normal load. According to the condition of vehicle stability against skidding on a wet surface, limiting average angles of inclination of the side walls of the rut are estimated for various values of the vehicle speed and wheel rotation angles.

We consider contact interaction of elastic bodies, one of which has a 2D texture, described by a sinusoidal function of 2n power, in partial slip conditions within two material models. The first approach based on the Cattaneo-Mindlin theory for linear elastic half-plane, the second is an elastic foundation model (EFM) which takes into account normal and tangential compliances. Analytical expressions for determining the size of the contact zone and the stick and slip zones for both models are obtained, as well as the expressions for the normal and tangential tractions. It is shown that for relatively small profile heights, both models give close results for the stick and slip zones sizes when the parameters of the EFM are selected from the developed half-plane solution. We analyze the influence of the geometric parameters (shape, profile height, and distance between the grooves) of the texture profile on the stick zone size while the tangential force increases. The EFM model allows capturing the dependence of the stick zone width on the profile height.

This paper presents the analysis of the combined effect of the surface texture and the rheological properties of material on the stress–strain state and the contact characteristics of a viscoelastic plate loaded by a rigid punch under dry friction conditions.

The contact problem concerning sliding of a solid surface with a regular relief along a fixed ring-shaped elastomer under normal load and rotational moment is studied. The concept of an effective (integral) coefficient of friction is introduced, and the aim of this study is to analyze the dependence of this value on the density of contact spots. The problem is solved by direct computer modeling in finite-element formulation. It is shown that dependences of an effective friction coefficient on time have a nonmonotonic cyclic character with transition to the steady-state regime. The amplitude values of an effective friction coefficient are higher for a lower density of contact spots at a fixed value of the normal load on the sample, whereas its averaged value is higher for a higher density of contact spots.

The axisymmetric contact problem for a spherical indenter and viscoelastic base has been considered within a cycle of increasing and decreasing of load. The loading-unloading cycle has been performed at a constant speed of indenter movment. The quasi-static approximation has been used. The study has been carried out according to linear viscoelasticity theory, while the material model allows one to take into account an arbitrary number of relaxation times. The dependence of load on the indenter on time has been defined. Expressions for determining the unknown boundary of the contact area in the loading–unloading process has been given. The hysteretic loop area at different values of the material relaxation time has been analyzed. The applicability of the offered analytical model of elastomer indentation experiments data processing has been discussed.

Background A new sensor for estimating elasticity of soft tissues such as a liver was developed for minimally invasive surgery application. Methods By measuring deformation and adjusting internal pressure of the pneumatic sensor head, the sensor can be used to do palpation (indentation) of tissues with wide range of stiffness. A video camera installed within the sensor shell is used to register the radius of the contact area. Based on finite element model simulations and the measured data, elastic modulus of the indented soft tissue can be calculated. Results and conclusions Three phantom materials, namely plastic, silicone and gelatin, with varied stiffness were tested. The experimental results demonstrated that the new sensor can obtain highly reliable data with error less than 5%. The new sensor might be served as an instrument in laparoscopic surgery for diagnosis of pathological tissues or internal organs.

A simulation of a contact interaction of the indenter and inhomogeneous soft biological tissues is carried out. The soft tissue is modeled by the incompressible elastic body which contains structural inhomogeneities (spherical or longitudinal inclusions). The elastic moduli of inclusions are higher than the bulk soft tissue modulus. These inclusions may be considered, in particular, as the models of the pathological growths. The indenter has the form of a hollow hemisphere (shell). It is the model of the mechanoreceptor developed in [1] to study the mechanical properties of soft tissues. The hydrostatic pressure can be applied inside the shell. Based on the numerical analysis, the dependences of the contact area size, and contact pressure on penetration of the indenter into the sample for several values of the inclusion size, depth, its location, the ratio of the elastic moduli of inclusion and the surrounding material, but also for various values of hydrostatic pressure inside the shell were obtained. Th...

The stress state of the carpometacarpal joint (CMJ)was studied in sound and pathologic states by methods of continuum mechanics. The CMJ geometric model was constructed according to the results of computer processing of the data of tomographic investigations in the extension position, which were obtained at Cheng Kung Medical University (Taiwan). The study of contact interactions in the CML region for a given geometry were performed numerically in the ABAQUS program code. The obtained numerical solutions of contact problems permit comparatively analyzing the stress distribution in the bone tissue for various thumb positions and study the stress state dependence on the bone tissue porosity (osteoporosis), which varies with human age.

The paper describes the theoretical model of contact between a spherical indentor and a rotating disc made of a viscoelastic material. Numerical analysis of the effect of the load and velocity conditions on the disc wear rate is carried out. It is shown that it is important to select an adequate contact model which considers the rheological behavior of the disc material when identifying the wear law from the corresponding test results.

The dependence of the contact characteristics and sliding friction coefficient on the density of the arrangement of contact spots is studied. To this end, the periodic contact problem of a system of asperities sliding on a viscoelastic base is considered. The main mechanism of the mutual effect of contact spots in the model in question manifests itself in the incomplete restoration of deformation on the free surface, with fairly dense arrangement of spots due to the imperfect elasticity of the base. The dependence is obtained of the friction coefficient on the spacing between asperities at various levels of effective loads and sliding velocities.

An indentation technique is one of effective methods to determine the elastic modulus of materials using information about contact geometry, indenter shape and applied load. This paper presents a device and a method that allow us to estimate elastic modulus of soft materials through indentation by video tactile pneumatic sensor. The device is a sealed metal cylinder ending with a soft silicone shell of a semispherical shape with 5 mm radius. During penetration by the silicone tip into investigated material the measured parameters are contact radius and displacement of the central point of the shell.

The main purpose of the study is design of the innovative tool for determination of mechanical properties of soft biological tissues during minimally invasive surgical operations. This applied problem is closely related with fundamental problems of diagnostics of pathological conditions of soft biological tissues by means of the tactile sensor. In this paper, the contact interaction between the tactile sensor and the soft biological tissue is studied. The analysis of the stress-strain state of soft tissue is carried out using the solution of boundary value problem of contact mechanics. As a first approximation, the linear elastic model of biological tissue is used in formulation of the problem of contact interaction between biological tissues and the artificial tactile sensor. A method is proposed for determination of mechanical characteristics of the studied tissue basing on measurement of the air pressure in pneumatic chamber of the sensor and on processing of images of the contact area between the sensor head and the tissue. An approach is developed for measuring the axial displacement of the central point of the sensor head and using this information in the procedure of estimation of tissue properties, which extends the potential of the proposed method. The prototype of the miniature video pneumotactile sensor is constructed and tested. Results of these experiments are in good agreement with results of numerical simulations.

The dependence of the contact characteristics and sliding friction coefficient on the density of the contact spots is stadied. The periodic contact problem for a system of indenters sliding on a viscoelastic base is considered. The imperfect reconstruction of the surface deformation in free zones due to viscous elasticity of the foundation is the main mechanism of the mutual influence in the model. This mechanism starts to work when the density of the contact spots is relatively high. One of the tasks of the investigation is to find dependence of the friction coefficient on a distance between the indenters under different loads and sliding velocities.