A round bar having a length of 2 m and a diameter of 10 mm is made of an aluminum alloy for which the stressstrain diagram can be described mathematically by the following equation:
![1170_8d907932-f910-4a40-9422-6bface34290b.png](https://secure.tutorsglobe.com/CMSImages/1170_8d907932-f910-4a40-9422-6bface34290b.png)
in which σ has units of megapascals (MPa). The shape of this stress-strain diagram is shown in the figure. The bar is axially loaded by tensile forces P = 20 kN, after which the loads are removed. What is the permanent set of the bar?