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.