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[en] This paper enlarges an undergraduate student project in non-holonomic mechanics (Janova et al 2009 Eur. J. Phys. 30 1257-69) by considering rolling friction. In the original problem of coupled rolling motion, the agreement of theory and experiment was demonstrated for the initial part of motion with rolling friction being neglected. As expected, the reality is that rolling friction plays a decisive role during the whole experiment. Extending the correspondence of the model to reality by considering rolling friction, in this paper it is demonstrated that the model satisfactorily explains not only the initial part but also the whole period of the motion observed. Together with the original problem, this paper is an interesting demonstration of the influence of rolling friction and its physical modelling for undergraduate physics education. It also demonstrates that a relatively simple theoretical background can be used for describing realistic situations in mechanics and for explaining experimental results. Moreover, this paper itself can be used by physics teachers as an interesting project in theoretical mechanics that may be solved both separately from and as a follow-up project to Janova et al (2009).
[en] The mechatronic system of the DUO-300 rolling mill is analyzed. The influence of the roller’s linear velocity on the distribution of frictional forces in the rolling region is studied. A nonlinear relation is found between the load and the roller speed. The conditions of self-oscillation in rolling are determined. Methods of damping the self-oscillation are considered.
[en] A coefficient of contact friction with rolls has been theoretically determined from a forward flow on dependence on reduction during stainless steel rolling. The problem was solved with provision for true nonuniform pressure along a tangential arc. A degree of divergence for the coefficients of friction has been revealed
[en] Given are the results of the study on substructure changes in Mo monocrystals during plastic deformation. The method of diffraction of wide divergent X-ray beam is applied. It is shown that for the degrees of total deformation above 50% the improvement of the structure takes place, which is characterized by the decrease in subboundary angles and the decrease in local stresses and lattice distortions over a subgrain body
[en] Profile and shape control are required to assure the dimensional quality of rolled strip. Occurrence of waves either at the edges or centre of strips is attributed to inconsistency between the entry and exit cross-section profiles of the stock within a given rolling pass. The exit profile of the strip can be computed by considering that the such profile is the complement of that of the roll-gap, which is affected by wear, thermal expansion and distortion of the work rolls. A computer model was developed to predict the profile of the roll-gap taking into account the thermal gradient within the work roll and the distortion caused by the acting forces. It was possible to establish a good correlation between the profiles of strips obtained from trials carried out on site, and the predictions of the model. The model allows for the prediction of the onset of shape defects from changes in the profile of rolled strips. (Author) 17 refs
[en] Highlights: • Five key states of droplet on hydrophobic surfaces have been proposed for quantitative interpretation of contact angle hysteresis. • The solid fraction plays a decisive role in transition from being hydrophilic to hydrophobic for rough surfaces. • The dynamic methodology can predict contact angle hysteresis and provide a criterion for designing superhydrophobic surfaces. Contact Angle Hysteresis (CAH) is critical to the hydrophobicity of a surface, which describes the dynamic characteristic of droplets. In this paper, two different micro-structured surfaces respectively with micro-channel and micro-pillar structures (20 samples for each structure, with a range of channel and pillar widths between 25 and 250 μm) were fabricated by mechanical micro-milling process to investigate the effect of structural parameters on hydrophobicity of surfaces. It was found that the solid fraction plays a decisive role for a surface in the transition from being hydrophilic to hydrophobic. Quantitative interpretation was conducted and a dynamic methodology was established based on the physical nature of the controllable motion of a droplet. The five key states of a droplet including the initial, pre-forward, forward, pre-backward and backward were the main focus of this research. The prediction results based on the established model showed good consistency with experiments. The proposed model can estimate the advancing and receding angles very well. The outcome of this research will lead to new methodologies for preparing hydrophobic surfaces with micro-machining technology and play an important theoretical guiding role in fabrication of superhydrophobic surfaces.