Applied Viscoelasticity

  • S. I. Krishnamachari


The term viscoelasticity stands for all the aspects of time dependent response of stress to strain and vice versa. It is the characteristic that contrasts the behavior of plastics most from that of metals. It manifests itself in the form of many different time dependent phenomena. In the description of such phenomena we may consider applied stress, loading types, loading rate, strain, strain rate, time elapsed, and lastly the temperature, as independent variables. Temperature is perhaps the strongest variable of all. Because of the large number of variables involved, the description of viscoelasticity has to be made necessarily through its aspects, namely creep, relaxation and recovery. Creep is the strain response to a stress that is constant with time. Relaxation is the stress response to an applied constant strain. Recovery is the strain response to a stress that has been removed. Besides these aspects, a whole range of special behaviors and properties are revealed when periodic loading is applied. In a manner very similar to voltage and currents in alternating current electric circuits, there is time difference between applied stress and resulting strain. Strain lags behind applied stress. A description of viscoelasticity in three dimensions is very complex. Nonlinearities in viscoelastic behavior only add to the complexity. Furthermore, there are no simple failure criteria in the context of viscoelastic behavior. Depending upon the level of stress, the time elapsed, and the type of material, the material can “fail” due to crazing, ductile creep rupture, or brittle creep rupture. The different modes of failures correspond to different and independent mechanisms.


Creep Strain Strain Cycling Relaxation Modulus Creep Compliance Correspondence Principle 
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Copyright information

© Springer Science+Business Media New York 1993

Authors and Affiliations

  • S. I. Krishnamachari
    • 1
  1. 1.L.J. Broutman & Associates, Ltd.ChicagoUSA

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