ABSTRACT
When an engineering material or a biological tissue is subjected to
forces, it is deformed depending on its mechanical characteristics
and the amount and direction of the forces. It is crucial to
understand such mechanical response of the material from the
standpoint of mechanical design when it is supposed to be used as
a part of mechanical device. It is also fundamental to characterise
the mechanical behaviour of the tissue from the biomechanical
point of view because the remodelling of the tissue is known
to be controlled by the mechanical environment surrounding the
tissue and its mechanical properties. The macroscopic deformation
behaviour of materials is usually characterised by expressing the
relationship between the stress and the strain. Fundamental stress-
strain relation can be obtained frommechanical tests such as tensile,
compression and shear tests. Multi-axial mechanical tests are also
sometimes performed to understand more complex mechanical
response of the materials. The basic mechanical properties such as
elastic moduli, Poisson’s ratio, yield strength and failure strength
are then determined from the testing results obtained. It is however
very difficult to characterise the three-dimensional mechanical
response of the materials, although in the most of real situations,
they are subjected to three-dimensional loadings. As examples, the
stress-strain relations of various types of polymers under tensile
condition are shown in Fig. 1.1. These macroscopic mechanical
characteristics strongly depend on the microstructures and the
rheological conditions of macromolecules of the polymers.
