Search results for "kitka"

Friction of Shear-Fracture Zones

2017

A shear fracture of brittle solids under compression undergoes a substantial evolution from the initial microcracking to a fully formed powder-filled shear zone. Experiments covering the entire process are relatively easy to conduct, but they are very difficult to investigate in detail. Numerically, the large strain limit has remained a challenge. An efficient simulation model and a custom-made experimental device are employed to test to what extent a shear fracture alone is sufficient to drive material to spontaneous selflubrication. A “weak shear zone” is an important concept in geology, and a large number of explanations, specific for tectonic conditions, have been proposed. We demonstra…

Shape optimization in contact problems with friction

1985

Shape optimization for Stokes problem with threshold slip boundary conditions

2017

This paper deals with shape optimization of systems governed by the Stokes flow with threshold slip boundary conditions. The stability of solutions to the state problem with respect to a class of domains is studied. For computational purposes the slip term and impermeability condition are handled by a regularization. To get a finite dimensional optimization problem, the optimized part of the boundary is described by B´ezier polynomials. Numerical examples illustrate the computational efficiency. peerReviewed

Analytical approach for the problems of dynamics and stability of a moving web

2015

Problems of dynamics and stability of a moving web, modelled as an elastic rod or string, and axially travelling between rollers (supports) at a constant velocity, are studied using analytical approaches. Transverse, longitudinal and torsional vibrations of the moving web are described by a hyperbolic second-order partial differential equation, corresponding to the string and rod models. It is shown that in the framework of a quasi-static eigenvalue analysis, for these models, the critical point cannot be unstable. The critical velocities of one-dimensional webs, and the arising non-trivial solution of free vibrations, are studied analytically. The dynamical analysis is then extended into t…

Rock friction measurements with stonegrinder apparatus

2016

Liikkuvien tektonisten laattojen välillä kitkan oletetaan olevan suuri. Olettamuksen vastaisia havaintoja on kuitenkin tehty useissa tutkimuksissa. Kuuluisin esimerkki on San Andreasin siirros. Siirrosvyöhykkeellä on matala lämmöntuotto, minkä perusteella on arveltu myös kitkan olevan matala. Syynä matalaan kitkaan voivat olla pyöreät kulumapartikkelit, jotka toimivat kuulalaakereiden tavoin. Kitkan tutkimista varten suunniteltiin ja rakennettiin ainutlaatuinen laite, kivenjauhin (engl. Stonegrinder). Kivenjauhimen tarkoitus on jauhaa kahta kairasydäntä toisiaan vasten ja samalla mitata kitkan muutoksia. Laite mittaa jauhamisen aikana vääntömomenttia, josta laskennallisesti saadaan kitkaker…

Tribological properties of thin films made by atomic layer deposition sliding against silicon

2018

Interfacial phenomena, such as adhesion, friction, and wear, can dominate the performance and reliability of microelectromechanical (MEMS) devices. Here, thin films made by atomic layer deposition (ALD) were tested for their tribological properties. Tribological tests were carried out with silicon counterpart sliding against ALD thin films in order to simulate the contacts occurring in the MEMS devices. The counterpart was sliding in a linear reciprocating motion against the ALD films with the total sliding distances of 5 and 20 m. Al2O3 and TiO2 coatings with different deposition temperatures were investigated in addition to Al2O3-TiO2-nanolaminate, TiN, NbN, TiAlCN, a-C:H [diamondlike car…

The Development and Precision of a Custom-Made Skitester

2021

In the sport of cross-country skiing, equipment has a direct influence on results. Ski teams do extensive testing of different ski base grinds and products on a yearly basis. To achieve reliable results, the quality of methods used for testing skis needs to be taken in to account in addition to factors including the physical characteristics of testing personnel and changes in weather conditions. The aim of this study was to introduce a custom-made skitester, that was developed for testing skis on real snow, in laboratory conditions, and to evaluate its precision. The current skitester is capable of glide testing both classic and skate skis as well as kick simulation for the testing of grip …