On April 7th we had a TRI Training Talks presentation by Dr. Trefor Evans titled “Quantifying hair breakage”. In this presentation Trefor approached three different methodologies for evaluating hair breakage, such as Tensile testing, Single Fiber Fatigue test and Repeated Grooming.
Tensile tensing is a more classical evaluation which measures the strength to break an individual hair fiber. The results of Break force (gF) are related to fibers dimension, thus measuring hair stress (Force gmf/x-sectional area µm²) results in a more consistent value. Tensile properties can also be influenced by water content on hair; thus, tests can be done in a wet or dry state, and if doing the last one it is important to control relative humidity when doing an experiment.
Fatigue tests are a different way of measuring hair strength, by submitting the fiber to a smaller deformation several times and measuring how many cycles until the fiber breaks. It can be more realistic than tensile test, since hair is not always submitted to strong forces, but usually smaller ones as from hair combing.
Figure 1: Average number of cycle-to-fail for Caucasian and Afro hair under repeated application of a 0.010g/µm² stress at 60% Relative Humidity – RH.
Last but not least, Trefor explored the repeated grooming tests which can be related to fatigue tests, evaluating how many fibers breaks while exposed to a repeated combing of the hair tress. In this excellent talk, Trefor showed how to apply these evaluations in hair claims tests to see how different treatments affects hair.
If you want to see the presentation again, you can go to https://library.triprinceton.org/1itm464/