Abstract:
A jerky oscillatory motion of a body sliding over a stationary surface is termed as the stick-slip motion. Examples are earthquakes, violin string stroked by a bow, creaking of door, screeching of brakes etc. Motion of gecko, motion of malaria parasite and wear of articular joints are some examples in the realm of biology. At high velocities, inertia of the sliding body plays important role in initiating as well as sustaining stick-slip. However, under slow sliding motion, the dynamics of stick-slip cannot be explained by invoking inertia. In this work, we have studied sliding motion of a soft crosslinked polymer block on a glass surface. Shear force is imposed by pulling the top face of the block at a constant velocity. The friction force resisting the sliding motion is generated by adhesion between the pendent chains of the block with the glass surface. When pulling velocity is below a critical value stick-slip phenomenon is observed. Friction in polymeric solids is governed by stress in the chains bonded with the surface on which it is sliding, which in turn is governed by the age of the bonds. We have modified the bond population model of Scallamach (1963) by considering velocity dependant aging of the bonds. We have shown that stick-slip is a discontinuous process. In the stick-state, the solid is stationary and undergoes deformation without sliding. When shear stress crosses a limit, aged bonds of the body ( strong bonds) break and block slips . It then moves with a velocity greater than the pulling velocity, where the motion is governed make and break of unaged ( weak) bonds. Stick-slip phenomenon is associated with reversible transformation of weak bonds into strong bonds. Using this model, we have been able to explain some important characteristics of the stick-slip process of a gelatine block sliding on a glass surface.
Brief Biosketch:
Prof. Vinay Anant Juvekar did his B. Chem. Eng. (1970), M. Chem. Eng. (1971) and Ph.D (1976) from the University of Bombay. He was an Associate Lecturer, University Department of Chemical Technology, Bombay from 1971-74, a Lecturer in the same Dept. from 1974-77. He then joined M/s Industrial Processes (Maharashtra) Ltd (Tarapur, India) in 1977 and was the R&D Manager between 1979-82. He joined IIT Bombay, Dept. of Chemical Eng. In 1984 as an Assistant Professor and became a full Professor in 1990. Between 2017-18 he was an Emeritus Fellow in our Department and the last two years, Prof. Juvekar has been an Adjunct Professor at IIT Bombay. Prof. Juvekar is a Fellow of the Indian National Academy of Engineers (since 2010) , was awarded Dr. H.L. Roy Memorial Lecture Award from Indian Institution of Chemical Engineers (2019). He has been the L&T Chair Professor between 2012-2015. He has been the recipient of several awards including the Best Teacher Award from the students of Chemical Engineering Department for five consecutive years, (1986 -1990). Prof. Juvekar’s research interest lies in the field of Interfacial Science and Engineering, Electrochemical Engineering, Electrohydrodynamics, Adsorption and Ion Exchange, Polymer Dynamics/thermodynamics, Multi-Phase Reaction Engineering and has authored large number of research papers in these fields. In 2019, the Industrial and Engineering Research (I&EC, an ACS publication) published a Festschrift in his honour.