基于图像检索技术的受载煤样裂隙演化规律

Fracture Evolution Law of Loaded Coal Samples Based on Image Retrieval Technology

在煤岩试样破坏过程中进行计算机断层(computed tomography,CT)扫描测试,可实现煤岩试样内部裂隙结构可视化表征,但是在加载过程中,因试样位移变形会引起CT扫描层定位误差,进而影响试验结果准确性。为了解决这一问题,利用图像相似性检索技术,检索出受载试样在不同应力水平下的最相似的CT图像,从而更加准确地描述受载煤样裂隙演化规律。研究结果表明:在三轴压缩破坏过程中,试样应力应变曲线分为5个明显的阶段,即初始压密阶段、线弹性变形阶段、塑性屈服阶段、峰值破坏阶段以及残余变形阶段。基于感知哈希算法的图像检索技术能够准确识别并定位不同应力阶段相似度最高的CT图像,且CT图像相似度随着轴向荷载不断增大而逐渐降低。在整个三轴加载过程中,CT图像的相似度绝对差均值表现出两个明显的变化阶段:缓慢增加阶段和快速增加阶段。分形维数可以定量描述裂隙演化,受载样品破坏过程中分形维数主要经历了缓慢减小、缓慢增大和快速增大3个阶段。

The computed tomography(CT)scanning test during the destruction of coal rock specimens can achieve visual characterization of the internal fracture structure of coal rock specimens.However,during the loading process,the displacement and deformation of the specimens will cause positioning errors in the CT scanning layers,which will affect the accuracy of the test results.To solve this problem,the image similarity retrieval technique was utilized to retrieve the most similar CT images of the loaded specimens under different stress levels,to more accurately describe the fracture evolution law of the loaded coal samples.The results show that during the triaxial compressive damage process,the stress-strain curve of the specimen is divided into five distinct phases,the initial compression-density phase,the linear-elastic deformation phase,the plastic yielding phase,the peak damage phase,and the residual deformation phase.The image retrieval technique based on the perceptual Hash algorithm can accurately identify and locate CT images with the highest similarity in different stress stages,and CT image similarity decreases with increasing axial load.Throughout the triaxial loading process,the mean absolute difference in similarity of CT images shows two distinct stages of change:a slowly increasing stage and a rapidly increasing stage.The fractal dimension can quantitatively describe fracture evolution,and the fractal dimension mainly experienced three stages of slow decrease,slow increase,and rapid increase during the damage process of loaded samples.