Tensile testing human hair is a common practice among manufacturers of various hair products, such as shampoos, dyes, and gels. It is important to be able to characterize the strength of hair to determine whether these products weaken or strengthen it. Similar to single strand textiles, there are many challenges associated with tensile testing of hair. Hair is normally very fine and often not long enough to be used in a cord and yarn style grip. In addition, hair is typically inconsistent, so it is important to test large sample sizes.
We were asked to provide a system that could test various hair samples. In this particular case, the manufacturer wanted to conduct tests on untreated human hair. The equipment would later be used to test hair before, as well as after being subjected to the company's various hair products to determine if there were any changes in strength.
Hair may be tested in single strands or multi-strands. When testing multi-strands, we recommend to prepare the specimens in such a way that the individual hairs are bonded together. Adhesives, waxes, and other materials can be used to prepare specimens.
We evaluated single strands of hair and were successful in determining a suitable test configuration. 250 N capacity pneumatic side acting grips were used along with 25x25 mm rubber coated jaw faces, which were necessary to avoid specimen failures at the jaw faces. Pieces of masking tape, approximately 50 mm long, were folded and adhered to each end of the specimens to serve as tabs (these tabs make it easier to manipulate the specimens and insert them into the grips). The tape also helped to reduce specimen failures at the jaw faces by providing additional cushion. Specimens were tested at 25 mm/min and the data capture rate was 100 Hz.
A suitable system for testing hair would be our 3300 or 5900 electromechanical testing machine with Bluehill® software.