Relation between the Stress Measured by X-Ray and the Stress Indicated from Brittle Lacquer Coating
1974 Volume 23 Issue 255 Pages 1034-1038
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1974 Volume 23 Issue 255 Pages 1034-1038
The stress measurement by X-rays is based on the variation of lattice spacings of metallic crystals due to stress. It has been noted as a unique method of measuring nondestructively the local stress, especially residual stress. Recently, this X-rays stress measurement has been applied in a very wide field of engineering studies in consequence of development of X-ray equipments as well as improvement in measuring devices.
On the other hand, the stress measurement with a brittle lacquer coating is based on the crack development perpendicular to the tensile strain when the loading exceeds a certain value. In this method, the direction of principal stress and the position of stress concentration can be determined directly from the crack patterns on the specimen surface. In comparison with other stress measuring methods, however, the lacquer coating technique has not been widely employed in engineering because of its lower strain sensitivity and the susceptibility to the influence of lacquer ingredients, drying techniques, or conditions of temperature and humidity.
In this paper, the authors report the practical usefulness of infrared rays baking device for brittle lacquer of baking type. Moreover, the stress values on plain carbon steel plates determined by the lacquer coating were compared with those by the X-ray method in their elastic range during bending tests.
The results obtained are as follows:
(1) The measured temperature of a specimen coressponded well with the preset temperature of the baking device, showing the practical usefulness of the device.
(2) The stresses obtained by using the lacquer coating and the X-ray techniques at any stage of bending tests in the elastic region agreed well each other in the range from 4kg/mm2 to 20kg/mm2.
It seems easy to make a reliable stress measurement by X-ray even on the complex machine parts or structures, if the direction of principal stress and the pattern of stress distribution are preliminarily analysed by the brittle lacquer coating method.
