Editing Constantan (section)

==P alloy==
For the [[measurement]] of very large strains, 5% (50,000 [[microstrain]]) or above, annealed constantan (P alloy) is the grid material normally selected. Constantan in this form is very [[ductility|ductile]]; and, in gauge lengths of {{convert|0.125|in|mm}} and longer, can be strained to >20%. It should be borne in mind, however, that under high cyclic strains the P alloy will exhibit some permanent resistivity change with each cycle, and cause a corresponding [[0 (number)|zero]] shift in the strain gauge. Because of this characteristic and the tendency for premature grid failure with repeated straining, P alloy is not ordinarily recommended for cyclic strain applications. P alloy is available with S-T-C numbers of 08 and 40 for use on [[metal]]s and [[plastic]]s, respectively.