This program was concerned with an exploratory study of four different experimental techniques to ascertain which technique is best suited for a comprehensive test program for the analysis of stresses in ligaments. In particular, this study was expected to establish the feasibility, accuracy and, to the extent possible, the economy of the Photostress technique.
The four experimental techniques used to conduct this study were:
(a) Photostress;
(b) Bonded electric strain gages;
(c) Photoelasticity (three-dimensional); and
(d) Stresscoat.
For techniques (a), (b) and (d), stresses were measured on the surface of a 2-in. thick 7075-T6 aluminum specimen loaded in tension, the holes being in a triangular array, with the exception of a single reference hole located in an area remote from the triangular array of holes. This permitted a check on the accuracy of each technique with the classical theoretical solution for a single hole in a finite width plate.
The stresses or strains were measured at several points across the minimum width of selected ligaments. This was followed by a comparison of the results of each of the four techniques, and on the basis of this comparison, and cost considerations, it was recommended that the Photostress Method (or Stresscoat-Strain Gage Method) be used in those applications where measurements of the stresses at the surface of the model are sufficient. For those applications in which the variation in stress through the thickness is such that the value of stress on the surface of the specimen differs materially from the maximum stress, which occurs below the surface, it is recommended that the Photoelastic Method (three-dimensional) be used. These recommendations, strictly speaking, are applicable only for in-plane loadings; however, cursory Photostress birefringence measurements, under lateral loading, made as an adjunct to this study, indicate that the same recommendations may be made for lateral loadings.
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| Number of Pages : | 33 |
| Published : | 1960 |
