o-rings and seals

Problem Solving Products, Inc. Logo
Problem Solving Products, Inc.

7108 S. Alton Way, Unit I
Centennial, Colorado 80112
(303) 758-2728

(303) 758-2728

Home > O-ring, Seal Design > Three Considerations

O-ring and Seal Design Theory

Three Considerations

Incompressibility

A material is incompressible if it exhibits zero volumetric change (isochoric) under hydrostatic pressure. Theoretically, Poisson's ratio is exactly one-half (0.5) and the bulk modulus is infinite (and det f = 1).

Near incompressibility means that Poisson's ratio is slightly less than 0.5.

Viscoelasticity

Rubber exhibits a rate-dependent behavior that can be modeled as a viscoelastic material whose properties change with temperature and time. Features of viscoelastic materials are:

  • Under constant stress leads to creep
  • Under constant strain leads to stress relaxation
  • During loading/unloading leads to hysteresis
    1. Internal friction-rearrangement of molecular structure under load.
    2. Strain-induced crystallization-formation and melting of crystallized regions.
    3. Stress softening (Mullin's effect).
    4. Structural breakdown-the breakdown of reinforcing filler/ polymer bonds.
    5. Domain deformation-dispersed inclusions contribute to hysteresis.

Thermomechanical

  • Temperature change causes thermal strains.
  • Material properties change. Heat flow may occur.

Next Topic Nonlinear Finite Element Analysis (FEA)

 

 

We are located in the Denver Technological
Center in a suburb of Denver, Colorado
©1997-2017, Problem Solving Products, Inc.
Website Map | Privacy Statement | Terms of Use