The mechanics of fracture of human hair.

Premature fracture and splitting of human head hair is cosmetically undesirable and at worse, unsightly. It is often regarded both by the hair's owner and by others as indicative of hair in poor condition and attracts considerable expenditure on hair toiletry products in sometimes vague attempts to prevent or repair the damage. This paper defines the mechanical events which underlie the fracture of hairs as they occur on the head and insofar as they satisfy the different fracture morphologies seen under the scanning electron microscope. Factors affecting propensity for fracture are considered. A significant conclusion is that hair 'strength', as might be assessed by the consumer, has little to do with the tensile mechanical properties of the fibres but that bending and associated longitudinal shear processes are of much greater relevance.