Research and measurement of material surface-s strain field based onphotoelastic coating

Strain gauge can measure the strain of one point, but it cannot measure the strain field of material surface. To solve this problem, photoelastic coatings were adopted to measure the material surface-s strain field. Photoelastic coatings were casted, and the strain fringe constant of the photoelastic coatings was calibrated. Experiments loading photoelastic coatings with special shapes were carried out, and the strain fringe interpretation method was studied. Photoelastic coatings were applied to measure the strain field of simply supported beam. Comparing with strain gauge, the strain value on weak spots obtained by photoelastic coatings is less than 5% on the high side. In experiments that concrete specimens were under loading of 4.4 MPa to 39.6 MPa, the variation of strain fringe in the process, of which the surface crack of the concrete specimen appeared, propagated and finally was fractured, was obtained. It is proved that photoelastic coatings can measure the variation of surface-s strain field of metal and concrete visually and credibly.