Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 150314

150314 - Friction of Soft Solid Surfaces Created by Controlled Fracture 

Advancements in needle-based bio-mechanical procedures such as robotic surgeries can achieve precise placement using in-situ imaging or fast kinematic feedback. However, the ability to predict forces during needle insertion is limited because there are no models that explicitly include material properties. Additionally, the lack of knowledge of the interrelation between friction, surface topography and fracture hinder the development of needle insertion research, as the needle simultaneously cuts and slides against the soft material. The goal of this study is to contribute to this knowledge gap, to understand the interdependency of friction and fracture of the soft solid materials and to predict the forces inferred during needle-insertion procedures which are otherwise difficult to determine solely by material properties. To achieve controlled surfaces for friction measures, oil-infused silicone materials are fractured by the Y-shaped cutting method. By varying the experimental conditions, the cutting energy required for the crack to propagate can be controlled. We observed that the resulting characteristics of the fractured surface have a relationship to the cutting energy. The observation led to the hypothesis that friction is related to the cutting energy that creates the surfaces. To determine the relationship, an experimental frictional study was conducted on three characteristic silicone surfaces (i.e. smooth, randomly rough, and periodic) created by controlled fracture. In order to precisely measure the friction, a custom micro-tribometer apparatus integrated with Python which can record simultaneous changes in data such as position, time, speed, applied normal load, and sliding friction was developed. The motion of the micro-tribometer stage is controlled through ground-up programming, allowing for simultaneous actuation and precise data collection which is essential for micro or nanoscale experimentation.

The friction study is comprised of an experimental matrix of sliding speeds and normal loads, to assess frictional dependence on applied speed or pressure. Speeds at the probe-sample interface were prescribed at 5 levels spanning 0.1 to 5 mm/s, which covers typical speeds of needle-insertion procedures. Normal loads were prescribed at 5 levels between 10mN-300mN to access pressures in the range of 10s to 100s of kPa. The data for several cycles were combined to determine the accurate output under different sliding conditions providing valuable insights into the friction behavior. The results show that the friction is controlled by surface morphology, and it is surface geometry dependent which signifies the importance of this correlation. The study concludes that there is a relationship between the cutting energy needed to create a soft solid surface and the resulting friction on that surface. If the friction instabilities due to uneven surface roughness (rather than perfectly flat surfaces) can be eliminated by controlling the cutting energy over the surfaces, it can have the potential to be further applied to develop new soft materials with tailored frictional properties, which can improve the performance and longevity of soft materials paving the way for future innovations in surface engineering and tribology.

Keywords: Friction, surface topography, cutting energy, soft solid materials, tribology, micro-tribometer.

Presenting Author: Abrar Ahmed Mohammed University of Florida

Presenting Author Biography: Abrar Mohammed is a graduate research student pursuing his master's in mechanical and aerospace engineering from University of Florida. His expertise are in design, analysis and experimental domains. He showcased a few research articles previously at the platforms- 'International conference on Aeronautics and beyond (2021)', 'Graduate Research in Engineering and Technology (GRET)' and 'ResearchGate'. Currently, he is working at the Bio/Materials tribology laboratory, UF focusing on soft-materials, tribology and material science.

Authors:

Abrar Ahmed Mohammed University of Florida
Srividhya Sridhar University of Illinois
Shaobo Zhan University of illinois
Hutchens Shelby University of illinois
Alison C. Dunn University of Florida