三轴试样全息变形实时测量系统的搭建、验证与应用

Set up,validation,and application of a full-field real-time deformation measurement system for triaxial specimen

针对三轴试样体积与变形精确测量的难题,文章基于传统三轴仪搭建了一个全息变形(包括:试样顶面、底面和360o侧面)测量系统,通过6台固定相机实时拍摄试样不同角度的照片,融合摄影测量、前方交汇以及光线追踪技术实现试样在持续加载过程中全息变形的实时测量。为验证该系统软、硬件的可行性与精度,文章基于所搭建系统开展了一个标准钢柱和多个土样在不同围压下的三轴试验。钢柱试验结果表明该系统用于三轴试样表面点阵和体积测量时的点阵与总体体积测量误差分别为0.086mm,0.151%;土样三轴试验表明该系统能够实现试样不同分辨率全息变形的精细测量;基于全息变形测量结果可进一步分析获取试样在连续加载条件下的总体体积、三维模型以及位移场与应变场。文章所搭建的系统通过固定位置相机简化了摄影测量分析过程,减小了系统测量误差;配套开发的GeoTri3D软件通过融合前方交汇技术显著提高了测量与测量结果后处理的效率。全息变形的精细测量能力为土体以及其他工程材料的强度与变形特性深入研究提供了有力支撑。

In view of the difficulties in volume and deformation measurement of triaxial specimen,this work proposes a full-field deformation measurement system based on a conventional triaxial test apparatus.The cameras with fixed positions in the system for real-time picture capturing,with the aids of photogrammetry,forward intersection,and optical ray tracing,are used to measure the volume and deformation of soil specimen during testing.To validate the feasibility and accuracy of the proposed method,a multi-camera system was established and triaxial test on a steel cylinder and several silt specimens under different confining stresses were conducted.The accuracy of the proposed system for point measurement is 0.086 mm and for volume measurement is 0.151%.Triaxial tests on soil specimens revealed that the proposed system is capable of full-field deformation measurement,including the lateral surface and two end surfaces of soil specimen.The full-field measurement results can be further utilized to extract soil volume,3D reconstruction,axial displacement,axial strain,radial strain,and circumferential strain.By taking advantage of a fixed camera system,the proposed method may significantly simplify photogrammetric analysis,reduce systematic error and improve measurement accuracy with the aids of software package GeoTri3D.The full-field,fine and accurate deformation measurement provides a new tool for advanced characterization of the behavior of soil and other engineering materials.