Cutting characteristics of beard hair

The cutting behaviour of beard hair has been investigated quantitatively and qualitatively. High speed cutting tests were conducted on beard hair samples using a purpose built cutting rig (provided by Gillette, UK) to determine the cutting forces. High speed digital video photography was used to record the cutting process. In parallel with these tests, low speed cutting tests were undertaken within a scanning electron microscope (SEM) to gain a better understanding of the cutting process. Results from the high speed cutting tests showed that the peak cutting stresses are influenced strongly by moisture (the cutting stress for ‘wet’ samples is reduced by about 30% as compared to dry samples) while the effects on the cutting stress of other variables (subject age, blade approach angle and sample ageing due to prolonged storage) appeared to be less noticeable. The angle of cut was affected by the distance of the initial contact point (between the hair and the blade) from the base of the hair with the line of cut shifting towards the hair axis with increasing distance from the base. Qualitative observations from video-recordings and still images taken during the cutting tests, conducted in-situ within the SEM as well as the high speed cutting rig, showed four main cutting mechanisms of hair, which are documented in this paper. The distance from the initial contact point to the base of the hair and the moisture level were the parameters which controlled the mechanism of failure. Qualitative observations of the sort reported here are a necessary pre-cursor to the development of finite element models to simulate a cutting operation.