The mechanical resistance of a fiber is usually related to its resistance to traction, that is, to the force necessary to break the fiber when being moved by tractions, or, as it is commonly known, when being pulled.
the viscoelastic behavior of a fiber in a chart of tension-deformation for two different regimens of humidity and separates the curves in three distinct regions.
Hookean Regions or Elastic region of the fiber, in which the force applied is proportional to the dislocation. In this region, the fiber behaves like a spring undergoing small dislocations, i.e., it maintains the point of balance. In other words, whatever is the force applied, the fiber tends to come back to its original size. In this region, it is possible to quantify the module of fiber elasticity, parameter related to the stiffness of a certain material. In other words, how easy the fiber deforms. This parameter is very altered when, for example, a chemical treatment such as straighteners or dyes are applied to the hair;
After point A, the fiber loses its elastic property and gets in the plastic phase or region, in which the deformation is more evident. Notice the size of the deformation for a small force variation. In this region, the hair does not return to its original position anymore and a small force can easily alter the size of the hair fiber;
From point B, or point of no return, the fiber gets in the region of rupture in which many bonding chains were broken and the hair becomes extremely fragile, making the breakage easier. In this region, the point of bigger attention is point C. It is in this point where the hair breaks and, through the chart, it is possible to observe the force necessary for breakage. Usually, the maximum force or rupture force is the most analyzed parameter, when it is desire to verify the maximum mechanical resistance of a fiber.
The hair, in a situation of small humidity presents a more rigid behavior (less deformation) compared to a wet hair. Wet hair is usually indicated as more malleable and, therefore, a measure of the total extension of this hair can indicate how malleable the hair is at the moment.
Control of humidity during the tests, since the hair strands themselves will already present differences between each other, it is essential, during the study, to ensure a smaller possible variation in humidity so as to avoid a high variability in the results.
Some other parameters, in addition to force, elasticity module and extension can be explored in the same test. It is possible, for example, knowing the diameter of the fiber, to calculate the maximum rupture tension. It is possible to calculate, also, the work necessary to break the hair fiber or, in other words, the amount of energy necessary to break the fiber. Each parameter will be more appropriate to a certain perspective of analysis required. Therefore, for more information, request a proposal or contact our team.