Tensile Testing of Hair
The mechanical properties of hair are a direct reflection of the internal structure, and considerable changes result from treatments or conditions that alter this structure. For example, chemical treatments of hair, or even changes in relative humidity, are well-known to induce significant differences. Such experiments are performed by generating stress-strain curves, followed by analysis of parameters that provide information about different portions of the hair structure.
Individual fibers are crimped between brass ferrules and mounted on the testing tray. The dimensions of each fiber are measured using a laser micrometer. Each fiber is then mechanically extended in turn until breakage occurs. The data analysis portion of the instrument software allows for quantification of various tensile parameters, which provide information about different portions of the hair structure.