Abstract: This paper presents a method for measuring small displacement under water by laser speckle photography.Its accuracy in measuring small displacement in a plane under water at constant temperature is calibrated,and reaches 3 percent, satisfactory in industrial measurement. When water drops falling from 1 meter high with a dropping velocity of 0.2 drop per second are used as disturbance, and when the exposure time varies from 1 second to 10 seconds, the double photographic speckle diagrams of the small displacement are taken.The interference fringes of the speckle diagram may be distinguished and measured by using the analysis method of point by point. The spread displacements on the surface crack center of 16MnR plate sample and on the internal surface crack center of 16MnR spherical sample filled with oil can be measured.The corresponding surface crack stress intensity factor K₁ is calculated with the combined use of the SCOD method.The test value of the plate sample under this condition is compared with that under normal conditions and with the calculated value of Newman-Raju solution and the results coincide with each other.The test value of K₁, wkich is the stress intensity factor of the spherical sample filled with oil on surface crack or on internal surface crack is compared with the calculated result based on Schmitt-Kiem formula and the results also coincide with each other. If the influence of water corrosion and other factors is not considered,the measurement of the surface crack stress intensity factor K₁ of a structure might not be made in water.The calculation of the surface crack stress intensity factor K₁ of a spherical tank with its ratio of diameters approaching l,can be considered as a suitable plate solution disregarding the effect of the curvature.

摘要： 一种水下微小位移的激光散斑照相测试方法.标定恒温时水下微小位移的精度可以达到3%.在水面上1m高处以每秒0.2滴水的滴定速率的扰动下,从每次曝光1～10秒,能得到微小位移的双曝光散斑图.测量了16MnR板试件表面裂纹中心张开位移,结合SCOD法计算了相应的表面裂纹应力强度因子K₁.把板试件的测值与通常情况下的测值和Newman-Raju解的计算值作了比较,三者符合得很好.把内充油球形容器内表面裂纹应力强度因子K₁的测值和球形容器外表面裂纹应力强度因子K₁的测值,分别与Schmitt-Keim式的结果作了对比,结果符合得很好.径比接近1的工业球罐表面裂纹应力强度因子K₁的计算,可以不考虑曲率的影响而选择合理的平板解.

关键词: 激光散斑照相, 容器表面裂纹, 水下照相测试