Yield and Crazing in Polymers

摘要: The present article discusses yield and crazing in polymeric materials. After introducing the definitions of stress strain states, we a brief summary general stress–strain responses for polymers under uniaxial tensile compressive loading. We introduce various regimes behavior, from almost linear elastic through nonlinear response to rubber-like behavior. also include concepts necking cold drawing Considere construction determining whether material will undergo either these processes. history development criteria models is then examined some details. Yield criteria, which may be considered as macroscopic relating applied state critical value yielding, are first discussed modifications pressure dependence introduced. These while useful an engineering point view that they offer method estimate likelihood failure given loading situation, provide no insight into microscopic or molecular mechanisms give rise yield. Early theories (eg adiabatic heating induced dilatation), though now incorrect, mentioned their historical context. A number presented consider activated process. In models, resistance yielding being due inter- and/or intramolecular forces. Application (or associated strain) affects energy landscape such barrier this reduced can occur. More complex address not only but subsequent strain-softening strain-hardening events observed. conclude section on by brief, observations dislocation plasticity, ultimate shear strength, dilatometry calorimetry, computer modeling, finally discussion semi-crystalline materials. The second current chapter phenomenon crazing. Crazing microscopically localized phenomenon, involves large degree plastic deformation. Yet, generally precursor macroscopically brittle at low craze densities. An overview morphology familiarize reader with main structural features crazes. conveniently subdivided three stages—initiation, growth, failure—and each stage separately. As section, initiation context considering, variously, cavitation stress, strain, presence inherent microvoids grow local discussed. There consensus growth. Craze tip advance thought occur Taylor meniscus instability mechanism, thickening bulk–fibril interface. Both on, example, weight cross-link density terms fibril completed considering other factors formation (effect cross-tie fibrils, environmental-stress cracking, fatigue failure). Keywords: Craze; crazing; failure; mechanical properties; plastic deformation; polymer; amorphous polymer; semicrystalline polymer; yield; yield criteria; yield