Fracture of polymers:-
All materials contain small defects of some kind impact and other formsof rapid loading (low strain rate) cause brittle fracture.
-The factors that affect on necking in polymers:-
The type of material, length and thickness of specimen, test conditions especially strain rate.
-The drawing of fibers, films and sheets in forming operations occur at very high strain rates.
-the yield stress depends on strain rate.
-Crazing and shear yielding are affected differently by Temp. and strain rate. In more ductile polymers, the most obvious effect of raising Temp. is to accelerate shear yielding.
-very short chains are unable to fom-stable crazes.
-The reasons of degradation: 1- thermal 2- Humidity especially in polymers that containing hydrolysable linkages (such as nylon and polysulphone).
- Few problems are encountered in moulding fresh material (polymer) with the addition of suitable stabilizers and processing agents to it.
-Molecular orientation is one of the most important factors that affecting on the fracture resistance of molded or formed polymeric products. Biaxial stretching in the melt state makes a polymer much more resistant to crazing and cracking under the action of stresses, and is used to improve the properties of film, sheet and other products.
-the factors that must be taken in design:- chemical resistance, fracture, fatigue, forming constraints, and V.E. limitations.
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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