Testing machines:

The tabulated results at the end of the test contain of the following.

a. designation of the material under test

b. original cross section dimensions of the specimen inside the gage length

c. original gage length

d. a series of often readings identifying the load and the corresponding gage length dimension

e. Last average diameter of the minimum cross section

f. last gage length

g. description of the appearance of the fracture surfaces (for instance, diagonal,  cup-cone, wolf's ear, start)

A graph of the results is made from the tabulated data. A few testing machines are equipped along with an autographic attachment that draws the graph in during the test.  (The operator required not records any load or elongation readings except the maximum for each.) A coordinate a x of the graph is strain for the x-axis or scale of abscissae, and stress for the y-axis or scale of ordinates.  An ordinate for every point plotted on the graph is found through dividing every the tabulated loads through the original cross-sectional area of the sample; a corresponding abscissa of each point is found through dividing the increase in gage length through the original gage length.  Those two calculations are made as follows.

Stress = load/area of original cross section =P/A_º = psi or lb/in.²

Strain = instantaneous gage length - original/ original gage length = elongation/ original gage length

=L -L_º  /L_º = inches per inch * 100 = percent elongation

Stress and strain, as computed here, are sometimes called as "engineering stress and strain."  They are not true stress and strain, which could be computed on the basis of the area and the gage length that exist for each increment of load and deformation.  For instance, true strain is the natural log of the elongation (ln (L/L_o)), and true stress is P/A, where A is area. The latter values are usually used for scientific investigations, but the engineering values are useful for determining the load- carrying values of a material. Given Below is the elastic limit, engineering stress and true stress are almost identical.