Inst. Mechanik

159 Items

Recent Submissions
Stress Tensor and Gradient of Hydrostatic Pressure in the Half-Space Beneath Axisymmetric Bodies in Normal and Tangential Contact

Forsbach, Fabian (2020-06-26)

The stress state in the volume of contacting bodies may essentially influence the material behavior. For evaluating various modes of inelastic behavior and/or failure, such as plastic deformation, crack initiation, and propagation or fatigue, the complete stress tensor beneath the contact interface may be of importance. For many geotechnical and biomechanical applications, the hydrostatic press...

Untersuchungen zu ungeschmiertem Schwingungsverschleiß an 100Cr6-Kugeln gegen 100Cr6-Ebenen

Reichelt, Manuel (2020)

Die vorliegende Doktorarbeit handelt von der Bestimmung vom Verschleißvolumen und vom Verschleißkoeffizienten bei Modellversuchen an 100Cr6-Ebenen und -Kugeln unter Schwingungsbeanspruchung. Es wird in der Tribologie häufig beobachtet, dass der Verschleißkoeffizient, definiert vom Archard-Gesetz als der Proportionalitätsfaktor zwischen dem Verschleißvolumen und dem Produkt aus Normalkraft und ...

Calculation of the BEM Integrals on a Variable Grid With the FFT

Benad, Justus (2020-05-27)

In this study, an exemplary application of the pFFT is shown for the 2D Navier equation for a linear elastic continuum. Using this example, it is illustrated how the pFFT might be extended in order to decrease the computational complexity of the method. In the standard pFFT approach, all panel influences which are not calculated directly are obtained using a single regular grid. In the present ...

On the influence of external stochastic excitation on linear oscillators with subcritical self-excitation and gyroscopic influence with application to brake squeal

Nguyen-Thai, Minh-Tuan ; Wulff, Paul ; Gräbner, Nils ; Wagner, Utz von (2020-06-17)

In a linear analysis for brake squeal, an unwanted type of sound in the kHz-range produced during the braking process of vehicles, usually only the stability of the system is examined. However, with the appearance of additional stochastic excitation, the vibration of a linear system with subcritical self-excitation, i.e. having self-excitation but due to damping still an asymptotically stable t...

Relaxation damping in oscillating contacts

Popov, Mikhail ; Popov, Valentin L. ; Pohrt, Roman (2015-11-09)

If a contact of two purely elastic bodies with no sliding (infinite coefficient of friction) is subjected to superimposed oscillations in the normal and tangential directions, then a specific damping appears, that is not dependent on friction or dissipation in the material. We call this effect “relaxation damping”. The rate of energy dissipation due to relaxation damping is calculated in a clos...

On the role of scales in contact mechanics and friction between elastomers and randomly rough self-affine surfaces

Popov, Valentin L. ; Dimaki, Andrey V. ; Psakhie, Sergey ; Popov, Mikhail (2015-06-09)

The paper is devoted to a qualitative analysis of friction of elastomers from the point of view of scales contributing to the force of friction. We argue that – contrary to widespread opinion – friction between a randomly rough self-affine fractal surface and an elastomer is not a multiscale phenomenon, but is governed mostly by the interplay of only two scales – as a rule the largest and the s...

Impact of an elastic sphere with an elastic half space revisited: Numerical analysis based on the method of dimensionality reduction

Lyashenko, Iakov A. ; Popov, Valentin L. (2015-02-16)

An impact of an elastic sphere with an elastic half space under no-slip conditions (infinitely large coefficient of friction) is studied numerically using the method of dimensionality reduction. It is shown that the rebound velocity and angular velocity, written as proper dimensionless variables, are determined by a function of only the ratio of tangential and normal stiffness ("Mindlin-ratio")...

A Review of the Method of Dimensionality Reduction in Contact Mechanics: Applications for Structural Damping, Wear and Adhesion

Popov, Valentin L. ; Heß, Markus ; Popov, Mikhail (2015-11-26)

In the method of dimensionality reduction (MDR), contacts of three-dimensional bodies are mapped to the contact problem with a one-dimensional elastic or viscoelastic foundation. This is valid for the normal contact, the tangential contact and the normal contact of viscoelastic bodies. For the above classes of contact problems, several examples are considered and discussed in detail. This inclu...

Numerical analysis of the geometrical and material criteria of acceleration of shear crack to supershear velocity in brittle nanoporous solids

Shilko, Evgeny V. ; Psakhie, Sergey G. ; Popov, Valentin L. (2016-07-21)

The paper is devoted to the study of dynamic propagation of mode II cracks in porous brittle materials with nanoscale pore size. We compared static (shear strength) and dynamic parameters of crack growth in dry and fluid saturated nanoporous brittle materials at different degrees of confinement. We have shown that pore fluid in nanoporous brittle materials influences mainly the dynamics of crac...

Active control of friction by transverse oscillations

Benad, Justus ; Nakano, Ken ; Popov, Valentin L. ; Popov, Mikhail (2018-03-16)

The present paper is devoted to a theoretical analysis of sliding friction under the influence of in-plane oscillations perpendicular to the sliding direction. Contrary to previous studies of this mode of active control of friction, we consider the influence of the stiffness of the tribological contact in detail and show that the contact stiffness plays a central role for small oscillation ampl...

Particle-based modeling of the mechanical behavior of porous fluid-saturated viscoelastic solids

Shilko, Evgeny V. ; Dimaki, Andrey V. ; Popov, Valentin L. (2019-11-01)

In the paper, we developed a macroscopic discrete element model of permeable fluid-saturated materials with solid skeleton characterized by viscoelastic rheological properties. The Biot's linear model of poroelasticity was used as a mathematical basis for describing the mechanical interrelation between the solid skeleton and interstitial fluid. Using this model, we numerically studied the depen...

Role of Adhesion Stress in Controlling Transition between Plastic, Grinding and Breakaway Regimes of Adhesive Wear

Dimaki, Andrey V. ; Shilko, Evgeny V. ; Dudkin, Ivan V. ; Psakhie, Sergey G. ; Popov, Valentin L. (2020-01-31)

A discrete-element based model of elastic-plastic materials with non-ideal plasticity and with an account of both cohesive and adhesive interactions inside the material is developed and verified. Based on this model, a detailed study of factors controlling the modes of adhesive wear is performed. Depending on the material and loading parameters, we observed three main modes of wear: slipping, p...

Universal limiting shape of worn profile under multiple-mode fretting conditions: theory and experimental evidence

Dmitriev, Andrey I. ; Voll, Lars B. ; Psakhie, Sergey G. ; Popov, Valentin L. (2016-03-16)

We consider multiple-mode fretting wear in a frictional contact of elastic bodies subjected to a small-amplitude oscillation, which may include in-plane and out-of-plane translation, torsion and tilting (“periodic rolling”). While the detailed kinetics of wear depends on the particular loading history and wear mechanism, the final worn shape, under some additional conditions, occurs to be unive...

Influence of tangential displacement on the adhesion strength of a contact between a parabolic profile and an elastic half-space

Popov, Valentin L. ; Lyashenko, Iakov A. ; Filippov, Alexander E. (2017-08-30)

The adhesion strength of a contact between a rotationally symmetric indenter and an elastic half-space is analysed analytically and numerically using an extension of the method of dimensionality reduction for superimposed normal/tangential adhesive contacts. In particular, the dependence of the critical adhesion force on the simultaneously applied tangential force is obtained and the relevant d...

Strength of adhesive contacts: Influence of contact geometry and material gradients

Popov, Valentin L. ; Pohrt, Roman ; Li, Qiang (2017-09-06)

The strength of an adhesive contact between two bodies can strongly depend on the macroscopic and microscopic shape of the surfaces. In the past, the influence of roughness has been investigated thoroughly. However, even in the presence of perfectly smooth surfaces, geometry can come into play in form of the macroscopic shape of the contacting region. Here we present numerical and experimental ...

Stick–slip boundary friction mode as a second-order phase transition with an inhomogeneous distribution of elastic stress in the contact area

Lyashenko, Iakov A. ; Borysiuk, Vadym N. ; Popov, Valentin L. (2017-09-08)

This article presents an investigation of the dynamical contact between two atomically flat surfaces separated by an ultrathin lubricant film. Using a thermodynamic approach we describe the second-order phase transition between two structural states of the lubricant which leads to the stick–slip mode of boundary friction. An analytical description and numerical simulation with radial distributi...

60 years of Rabinowicz' criterion for adhesive wear

Popova, Elena ; Popov, Valentin L. ; Kim, Dae-Eun (2018-08-20)

60 years ago, in 1958, Ernest Rabinowicz published a 5 page paper titled “The effect of size on the looseness of wear fragments” where he suggested a criterion determining the minimum size of wear particles. The criterion of Rabinowicz is based on the consideration of the interplay of elastic energy stored in “asperities” and the work of separation needed for detaching a wear particle. He was p...

Adhesive wear and particle emission: Numerical approach based on asperity-free formulation of Rabinowicz criterion

Popov, Valentin L. ; Pohrt, Roman (2018-08-20)

In 1953 Archard formulated his general law of wear stating that the amount of worn material is proportional to the normal force and the sliding distance, and is inversely proportional to the hardness of the material. Five years later in 1958, Rabinowicz suggested a criterion determining the minimum size of wear particles. Both concepts became very popular due to their simplicity and robustness,...

Adhesive contact of rough brushes

Li, Qiang ; Popov, Valentin L. (2018-09-07)

The adhesive contact between a rough brush-like structure and an elastic half-space is numerically simulated using the fast Fourier transform (FFT)-based boundary element method and the mesh-dependent detachment criterion of Pohrt and Popov. The problem is of interest in light of the discussion of the role of contact splitting in the adhesion strength of gecko feet and structured biomimetic mat...

The JKR-adhesive normal contact problem of axisymmetric rigid punches with a flat annular shape or concave profiles

Willert, Emanuel ; Li, Qiang ; Popov, Valentin L. (2016)

The JKR-adhesive frictionless normal contact problem is solved for the flat annular and the conical or spherical concave rigid punch indenting an elastic half space. The adhesive solution can be derived analytically from the non-adhesive one, the latter one being calculated by the boundary element method. It is found that the annular flat punch will always start to detach at the outer boundary....