During sliding wear in a ball on disc (BoD) configuration, given all conditions are identical i.e normal load, temperature, sliding speed and counterface material, only difference being the stiffness of the disc material. In this case what will be the effect of stiffness on the resulting friction coefficient?
According to classic tribology representation, the friction coefficient consists of two main components: adhesive (due to forces of molecular interaction of contacting surfaces) and deformational component. I think that you have in mind "stiffness of the disc material" as a elastic modulus (Young modulus) of material. The increasing of elastic modulus of the disc material reduces the depth of ball indention and thus produce the decreasing of deformational component of friction coefficient. In addition, the increasing of elastic modulus of the disc material reduces contact area and adhesive force of attraction between interacting surfaces. As a result, the friction coefficient will decrease.
From my point of view, if you enlarge the stifness, the friction coefficient will decrease.
@ Serge V. Shil’ko Thanks a lot sir. this is quite logical. but it seems that there would still be competition between the deformational component and adhesive component of friction. a decrease in contact area due to larger stiffness (lower deformation) the adhesive component will increase due to increase in contact pressure (owing to lower contact area). These opposing trends may end up not effecting the resultant friction coefficient by any considerable margin. is that right?
Dear Shaikh asad ali Dilawary, really, there is rival input in the growth of adhesion component of friction coefficient caused by increasing of pressures and, correspondingly, tangential stresses when contact area reducing due to increasing of contact stiffness. The significance of this input depends on material nature and, evidently, may be estimated in experiments.
In such case, there are two components of friction: Adhesion and Deformation.
Regards,
Emad
Dear colleagues, our discussion is hiching up very interesting idea about role of stiffness of counterbody or elastic modulus of material of counterbody.
As you know, functionally graded material may be in the form of composite (for example, multilayer material) or in the form of monocomponental material with elastic gradient caused, for example, by non-uniform distribution of residual stresses. Both kinds of graded material is widely used in tribojoints.
Let us assume the question of Shaikh asad ali Dilawary in terms of contact mechanics of gradient materials regarding fabrication of best antifrictional materials for tribojoints.
Take a look at papers by Dr. Kambiz Farhang & Dr. Ali Sepehri/ also Dr. Akay and Dr. Bengisu/ or the following reference.
https://www.sciencedirect.com/science/article/pii/S0301679X11001514
Also please refer to INTRODUCTION TO TRIBOLOGY by Bharat Bhushan (2002) .... Wiley publication... PDF is available online.
The friction in this kind of experiment is governed mainly by adhesion and abrasion. By increasing the stiffness (presuming you are referring to the Young's modulus) will decrease the contact area. A decrease in contact area would reduce the adhesive contribution, but, it would also increase the pressure and, thereby, increase the plastic deformations and the ball would appear more abrasive to the disc. Whether the decrease in adhesion would be under- or over compensated by the increase in the abrasion is, however, not easy to answer. This require much more information about the materials and operating conditions than what is stated by the question.
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