Use of photostress techniques to characterize the mechanical behavior of weldments

Photoelastic coatings are useful to view strains in a large field and to examine strain gradients in the field. Contrary to strain gages which average strains along their length, photoelastic coatings provide measurements of strain over a gage length of essentially zero (at a point). When testing is done using specimens having welds between parent material, there are, in general, four zones in which strains may be significantly different. These zones are: (1) the weld material; (2) the fusion boundary; (3) the heat affected zone; and (4) the parent material. To date, most all strain measurement on welded specimens has been done using strain gages to measure in the various zones, thereby averaging across the strain gradient and across zone boundaries in some cases. In an effort to eliminate strain averaging, photoelastic coatings were used to characterize the mechanical behavior of weldments when tested in uniaxial tension. Data were taken at various points along the specimen and were used to construct stress-strain curves