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Fatigue and Long Term Strength of Thermoplastics

  • K. V. Gotham

Abstract

Thermoplastics are complex materials in their response to applied loads. They do not obey Hooke’s law, being non-linear in their relationship between stress and strain. They are also viscoelastic in nature. This property is seen either as a time dependent response in stress (stress relaxation), when held under conditions of constant strain, or as a time dependent response in strain (creep), when subject to a constant continuously applied load. As a general rule their mechanical properties are more dependent upon temperature than metals which they seek to displace in engineering components. As a class of materials they have, in their unmodified form, comparatively low modulus and low strength. In addition to this complicated response to continuously applied loads, which results in a progressive decrease in strength with elapsed time under load, thermoplastics still suffer from ‘fatigue’ under cyclic loads. Hence the qualification implied within the title. At one time1 these responses were known as static and dynamic fatigue, but this terminology led to some confusion with engineers. Consequently, as a matter of convention nowadays, the term ‘fatigue’ is restricted to the effects of cyclic or intermittent loads only, as is the case for metals, and ‘long-term strength or creep rupture’ to the effect of continuously applied loads.

Keywords

Crack Initiation Fatigue Resistance Brittle Failure Stress Concentration Factor Creep Rupture 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Elsevier Applied Science Publishers LTD 1986

Authors and Affiliations

  • K. V. Gotham
    • 1
  1. 1.Rubber and Plastics Research AssociationShawbury, ShrewsburyUK

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