Understanding Elastic Band Stretch: Causes and Predictions

[Red_CCF]

I'm wondering why, when I pull on an elastic band for instance, that only one section of the band seem to stretch while the other parts do not. The stretch is isolated to one location and not evenly distributed as I expected it to.

I assume that by the normal stress-strain relationship (the linear portion) that the material would stretch evenly and not like this, is this right?

How is it possible to predict where and at what applied force a material will break in this instance if most of the stretching is done on one portion? In this instance would does the material still follow the standard stress-strain relationship?

 

[Studiot]

The phenomenon is called necking.

You could look here

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VJS-475B8TB-1&_user=10&_coverDate=12%2F31%2F2002&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1369668499&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=8c09bd9e30ab30a1044cb4896b6cabeb