Patent GB-382758-A (GB)
Title: Improvements in systems and devices for making measurements by elasticity, particularly by photo-elasticity
IPC: G01N3/06
Filed: 1931-11-09
Abstract: 382,758. Testing physical qualities of materials. MABBOUX, G., 10, Rue Cernuschi, Paris. Nov. 9, 1931, No. 31018. Convention date, Nov. 10, 1930. [Class 106 (ii).] For the measurement of strain by a photoelasticity method, bodies or machines have permanently incorporated in their mass elements, for instance mirrors, which under the influence of the stresses to which the body is subjected become strained, thus serving, with the aid of an independent measuring instrument, to measure the strain on the bodv. A mirror 7 mounted in the body 8 is illuminated by polarized light reflected from an unsilvered mirror 5 through a compensating plate 6, the light being supplied from a source 9 through a diffusing screen 11 and lens 13. The light reflected from the mirror 7 passes through the plate 5, lens 12 and analyser 4 to an eyepiece 3. The compensator 6 is formed by a transparent screen of the same material as the mirror 7 and acted upon by a dynamometer comprising a spring 14 and micrometer screw 15 to compensate the double refraction effect of the mirror 7. The observation can be made by having recourse to a " sensitive tint " plate by placing a screen 16 of mica, set in a suitable direction, in a slide 16<1>. A transparent plate partly coated with a reflecting surface and behaving in the same manner as the mirror 7 may be substituted for the part 6, the polariscope measurement being effected by comparing the double refraction effects of the mirror 7 and in the said plate or the " decreasing tint " of the strained element with the " increasing tint " of the companion plate acted upon by the dynamometer. The principal strains may be investigated by using a rectangular element two opposite sides only of which are under stress the other two sides being free. Where the direction of the two principal strains are known two such elements arranged in this plane are used each with the free sides perpendicular to the direction of the strain to be measured. A circular element may be used to give the direction of the principal strain. The element may be fixed in a hollow passage in the body itself which passage may be filled with a transparent material which is insensible to the strains. Various mountings for the elements are described for particular purposes. Blocks of material are prepared in laboratories in which the mirror is embedded, the blocks being corrugated on the outside for connecting to the work. In the case of metallic works there may be permanently inserted in the structure elastic members carrying the element 7. The element may be mounted in an axial passage in the roller supports of structures such as bridges. Curved reflecting surfaces may be used as the elements and changes in curvature under stress measured. Fig. 22 shows a modification for observing the change of curvature of a curved reflecting surface let into an object to be strained. Light from a source 41 passes through a condenser 42 and a cruciform reticule in a screen 43 and on through a lens 44 as a parallel beam to a transparent mirror 45. The surface of the block 39 reflects the beam as a convergent beam to an eyepiece 46. A cruciform reticule 47 is arranged in the focal plane of the eyepiece. Two scales one 48 in the plane of the reticule for angles and an axial linear scale 49 enable the characteristics of the astigmatic convergent beam and hence the deformation of the curved mirror to be determined.