三轴试样径向变形激光量测系统的改进

IMPROVEMENT OF LASER MEASUREMENT SYSTEM FOR RADIAL DEFORMATION OF TRIAXIAL SPECIMENS

利用激光光电检测技术和高精度位置敏感探测器(PSD)的优点,对三轴试样径向变形的激光量测系统进行相关改进。共做了3个方面的改进工作:(1)将圆形压力室改为方形压力室,可解决光垂直入射时发生的光线偏折现象。(2)由于原系统使用1个PSD,无法解决三轴剪切试验中试样容易发生偏心的问题,使用2个PSD分别对试样径向左右两侧进行量测,可提高量测的精度。(3)将控制传感器升降的微动机械控制单元的普通电机转换成由计算机指令控制的步进电机,每一行程都能回到同一初始位置。运用该套系统对标准件、压力室中的标准件和压力室加水的标准件进行标定,得出电信号变化与直径变化的函数关系,并对饱和含黏砂土试样进行固结试验,将测试结果同计算结果相比较,证明该套系统测试三轴试验试样的体变结果较为可靠。该系统可用于研究三轴试样的局部变形和端部约束等问题,并对当前土体本构关系中的应变局部化、剪切带形成以及非饱和土体变量测等方面也有比较广泛的应用前景。

Taking advantages of laser photoelectricity measurement technique and position sensing detector（PSD） with high precision,the laser measurement system for measuring radial deformation of triaxial specimens is improved. Three aspects of improvement have been done as follows：（1） In order to avoid the deflection of vertical incident light,the square pressure chamber is adopted instead of the circular one. （2） Two PSDs are used to measure radial deformation in left and right sides of specimen instead of one PSD in original system,which couldn′t take into account the specimen eccentricity in triaxial shear tests. So the measuring precision would be enhanced. （3） A stepper motor of controlling transducer lift and down is used instead of common motor. It can ensure the transducer goes back to the same initial position. This system is used to measure standard specimen,standard specimen in the pressure chamber and standard specimen in the pressure chamber full of water. The function relationship between change in electrical signal and change in diameter is obtained. The consolidation tests on saturated sand containing clay are carried out. The comparison of measured and calculated results indicates that the volumetric changing results obtained by the improved triaxial measurement system are reliable. This system can be applied to study the problem of triaxial specimens,such as local deformation and end restraint;it also has great prospect to study deformation localization,formation of shear zone and volumetric changing measurement of unsaturated soils.