Evaluation and Repair of Wrought Iron and - Purdue e-Pubs ...

47length of two inches. This value was then multiplied by 1x10 6 . The final extensometerreadings were then displayed in micro strains. The values recorded from the stroke, orthe amount the MTS machine moved, were used to verify other readings.The load cell in the MTS testing machine’s output was in pounds. This value wasconverted to stress (psi) using the average area determined before testing. This was doneby dividing the output of force in units of lbs, from the load cell, by the average netsection area of the test coupon.After all the units were converted, the stress strain diagram could then be createdby using a spreadsheet package. For the initial test, the average output from the twostrain gages were plotted against the load cell’s output to create a plot of the elasticregion of the stress strain curve for the metal. A plot of this initial elastic region for oneof the test specimens can be seen in Figure 3.15.The average output of the two strain gages was also used along with theextensometer when creating the full stress-strain curve from the second test. In the initialelastic area of the stress-strain curve, the strain found from the output from the straingages was plotted against the stress found from the output from the load cell. Once thespecimen yielded, the strain found using the output from the extensometer was plottedagainst the stress found from the output of the load cell. This plotted the inelastic nonlinearcurved section of the stress-strain curve. An example of a full stress-strain curvefound from full testing of one of the test specimens can be seen in Figure 3.16.Along with the stress verses strain curves, the amount of stretch at failure wasalso recorded. This deformation, which is a measure of the material ductility, is theamount that the eight inch gauge length (for the eyebar) had stretched at the onset offailure. This was found using a ruler and measuring the distance between the originalscribed eight inch gauge marks. The amount that the gauge length distance had changedwas then divided by the original gauge length to determine the percent elongation.