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1

Badanie zależności tarcia tocznego od promienia kulki łożyskowej

Koczan G., Ziomek J.

Przegląd Mechaniczny

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2018

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nr 1

21--26

PL

Istnieją dwa historyczne prawa tarcia tocznego sformułowane przez francuskich uczonych Coulomba i Dupuita. Postanowiono na nowo zweryfikować doświadczalnie, które prawo lepiej opisuje swobodnie toczące się kulki łożyskowe po twardej powierzchni. Asumptem do wykonania pomiarów była idea stałej grubości zagłębienia, która jest zgodna z prawem Dupuita. Pomiary wykonano na podstawie drgań gasnących w sferycznym wahadle tocznym. Wyniki badań wykazały lepszą zgodność z teorią Coulomba, jednakże z małymi, ale mierzalnymi odstępstwami. Odstępstwa te udało się wyjaśnić za pomocą tzw. modelu kocich łbów. Wyznaczone parametry modelu zostały pozytywnie zweryfikowane pomiarem profilu chropowatości powierzchni. Dodatkowym teoretycznym aspektem pracy jest rozpoznanie dwóch rodzajów siły tarcia tocznego: kinetycznej i dynamicznej w analogii matematycznej do dwóch rodzajów ciepła właściwego, w termodynamice gazów.

EN

There are two alternative historical laws of rolling resistance formulated by French scientist Coulomb and Dupuit. It has been decided to verify experimentally again, which of these laws describes freely rolling ball bearings on a hard surface better. An inducement to carrying out the measurements was the idea of the constant thickness of roadbed, which is consistent with Dupuit's theory. Measurements have been done using the damped oscillations in the pendulum bearings. Results have shown better consistency with the Coulomb's theory with small, but measurable deviations. These deviations were successfully explained by the so called "Cobblestones' model". Parameters designated by this model have been successfully verified by the surface roughness's profile measurement. An additional theoretical aspect of this work is distinguishing two types of rolling friction force: dynamical and kinematical in an analogy to two types of specific heat capacity in the thermodynamics of gases.

2

Unified anisotropic strength criterion rank two for fibrous materials like wood

Koczan G., Kozakiewicz P.

Drewno : prace naukowe, doniesienia, komunikaty

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2018

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vol. 61, nr 201

119--

EN

Wood is a fibrous orthotropic material additionally characterized with sign- -sensitivity. Thus, determining the universal conditions of its strength constitutes a complex task. In their work, the authors present the anisotropic generalization of the Huber criterion which is closer to Norris’s proposal, as opposed to Hill (and Hofmann) and Mises proposal. The obtained criterion incorporates conditions which are additionally imposed on a special case of Tsai-Wu criterion for composite materials.

3

The role of shear stress in the bending strength test of short and medium length specimens of clear wood

Koczan G., Kozakiewicz P.

Drewno : prace naukowe, doniesienia, komunikaty

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2017

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vol. 60, nr 199

161--175

EN

The process of wood bending displays measurable departures from the standard beam theory. The most well-known departures are caused by shear. In the mathematical part of this work we found and analysed full plane stress of wood which occur in III-point and IV-point loading. Hill-type strength criteria have been used. The role of shear is determined by the relation between shear spandepth ratio and bending-shear strength ratio. Three types of this relation have been defined, one of which specifies the concept of medium length beam. In the second part of this work we statistically described bending-shear strength ratio for European, American and exotic wood species. On this basis, we determined the shear span-depth ratio of the medium beam. The role of shear stress in the bending strength test of medium beam cannot be omitted. The work contains elements of strength theory from a historical perspective, especially concerning strength criteria. Given one result of the contact mechanics.