ABSTRACT
This section considers the way in which biological and non-biological materials behave when they are subjected to forces. The type of deformation that materials experience when they are loaded (i.e. compression, tension, bending, shear and torsion) are described, before moving on to how load and deformation are represented by stress and strain. Equations and example calculations are provided for stress and strain acting on tissues in the human body and the importance of using SI units in these calculations and presenting the outcomes with prefixes (e.g. megapascals – MPa) is explained. The behaviour of materials when exposed to loading is described using the stress–strain curve, which includes areas of elastic and then plastic deformation. Important parameters used to characterise materials, including Hooke’s Law and Young’s Modulus, are also described. This section also includes discussion of the viscoelasticity of materials, which relates to their behaviour during loading and then unloading. Other practical examples of the way in which materials are described are also considered, including point and area elastic surfaces, and hardness of running shoe midsoles.
