Chap 9: Mechanical Properties of Biological Tissues

Elastic Materials

= E

Reversible in the elastic range and generallynot dependent on time. Most engineering materialswe stay in this elastic region.

Nonlinear Elasticity

“Rubber Band”

Hookean Elasticity

Pseudoelasticity

Hysteresis

Definitions involving Viscoelasticity

Stress relaxation – when a body is suddenly strained (deformed) and then thestrain is maintained constant, the corresponding stresses induced inthe body decrease with time

Creep – if the body is suddenly stressed (loaded) and the stress (load) is maintainedconstant afterward, the body continues to deform with time

Hysteresis – cyclic loading gives a situation wherein the loading and unloading processesare somewhat different, pseudoelastic

Creep Under Constant Loading

Relaxation under Constant Deformation

Models of Viscoelasticity

These models comprise a spring (elastic) with a dashpot (viscous) wheremis the Hookean spring constant and is the viscosity.

Spring gives an instantaneous deformation proportional to the load (F), whereasthe dashpot provides a velocity proportional to the current velocity.