Materials can behave in unexpected ways when they are under internal
stress. It has been known since the industrial revolution that internal
stress in metals can lead materials to prematurely fracture or buckle.
However, it is also used intentionally in manufacturing to strengthen
materials, such as bullet proof glass.
Internal stress also plays a vital role in biological tissues, where it is
used to preserve ideal mechanical conditions. For instance, arterial walls
can thicken in response to an increase in blood pressure.
The process that forms this internal stress is varied, complex, and mostly
unknown. So it is important to be able to measure the internal stress,
irrespective of its origins. To use elastic deformations and waves to
measure this stress, first we need to couple internal stress with
elasticity, which will be the main focus of this talk. We will also see how
conservation of energy can lead to some interesting insights into modelling
internally stressed materials.