Hey there! While reading my mechanical design book, I had hard time to understand a particular paragraph if anyone could help. Attached to this post are two figures. 2-6 a and b. The first one is pretty simple to understand; the engineering normal stress strain curve accompanied with cold working. It is then given as follows in the book for the second picture " It is possible to construct a similar diagram as in Fig 2-6b where the abcissa is the area deformation and the ordinate is the applied load. The reduction in area corresponding to the load pf at fracture is defines as R= 1- (Af/A0) " ... My precise question is WHAT IS THE AREA DEFORMATION?? What is the units of it? What does the are under the graph present and how do we calculate the area deformation in the first place?