The stress and strain relation is commonly shown by means of a stress-strain diagram. These diagrams are obtained by drawing a graph or curve from the data obtained in a tensile test .
There are resulting changes in length which can be observed and recorded by strain measuring devices. Stress-strain for different engineering materials are shown in Fig. 8.3.
In the case of ductile materials, at the beginning of the test, the material extends elastically. The strain (both longitudinal and lateral) at first increases proportionally to the stress and the sample or specimen returns to its original length on removal of the stress. The limit of proportionality (stress ? strain) is the stage up to which the specimen, i.e., material obeys Hooke’s law perfectly (Fig. 8.3(a)).
On further increasing the applied stress, i.e., beyond the elastic limit, it produces plastic deformation so that a permanent extension remains even after the removal of the applied load, i.e. stress. The resultant strain, in this stage begins to increase more quickly than the corresponding stress and continues to increase till the yield point is reached. We must note that at the yield point the material suddenly stretches.
The ratio of applied load to original cross-sectional area is called the normal stress and this continues to increase with elongation, due to work hardening or strain hardening, until the tensile stress is maximum. This is the value of stress at maximum
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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