As other mechanical properties, the fracture strength of polymers is much lower than that of metals. Fracture also starts with cracks at flaws, scratches, etc. Fracture involves breaking of covalent bonds in the chains. Thermoplasts can have both brittle and ductile fracture behaviors. Glassy thermosets have brittle fracture at low temperatures and ductile fracture at high temperatures.
Glassy thremoplasts often suffer grazing before brittle fracture. Crazes are associated with regions of highly localized yielding which leads to the formation of interconnected microvoids. Crazing absorbs energy thus increasing the fracture strength of the polymer.
A polymer can exhibit all intermediate range of properties between an elastic solid and a viscous liquid. Since Tg and Tm of most polymers materials are not much above ambient (and in fact may be lower as in the case of the rubber). These materials exhibit viscoelastic creep and relaxation phenomena at room temperature.
This section shows how viscoelastic behaviour of polymers can be simulated using elastic springs and viscous dashpots. The first model which discusses the viscoelastic behaviour for polymer is the Maxwell model, which consists of a spring and dashpot in series as shown
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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