Abstract
Shaving is an everyday act for many people and Gillette is at the forefront of this market. The complex process of designing a razor involves understanding the interaction between the cartridge and the face which are complicated systems in their own right. Wet shaving is a complex tribological process for which the mechanisms and parameters are not well understood. The time and high cost associated with designing razors are a major driving force for developing a technical model of shaving. Friction has been identified as an important parameter influencing consumer relevant attributes such glide and comfort. This thesis focused on breaking the problem down into two key areas, skin friction and hair cutting friction. By combining in-vivo and in-vitro testing capabilities, the key parameters affecting skin friction were determined and quantified. Due to the limited knowledge of the relative contribution of adhesion and deformation friction to total friction in the biotribology field, this thesis has confirmed past results and expanded on previous knowledge regarding the relative proportion of adhesion and deformation in three lubrication cases, namely, dry, water and oil contacts. Empirical models of skin friction for these three cases were developed to estimate the relative proportion of adhesion and deformation friction. The primary parameters affecting relative proportion of adhesion and deformation included the contact lubrication, probe material, sliding speed, and probe geometry. Further, the results indicated for the oil contact case, for high normal loads and sliding speeds, deformation friction contributed as much as 50% of the total friction. Hair cutting friction was also investigated focusing on two parameters, hair density and hair cutting profile. These two parameters significantly affected hair cutting friction, where increasing hair density and the area under the curve (hair cutting profile) increased hair cutting friction significantly. Two case studies were considered that combined data from skin friction and hair cutting to estimate the relative proportion of adhesion, deformation and hair cutting friction to shaving friction. The results showed, for contacts with water as a lubricant, hair cutting and adhesion friction contribute on average the same proportion (40-40%) and depends on the type of hair cutting profile considered. For contacts with oil as a lubricant, relative contribution of hair cutting friction significantly increases and can be as high as 80% of the shaving friction depending on the hair cutting profile considered.