| Strain and stress are the core parameters to characterize the mechanical properties of rock.Rock strain measurement is mainly realized by contact measurement methods such as the resistive strain gauge method,fiber Bragg grating method,and extensometer test.The contact strain measurement method is easily affected by factors such as the on-site measurement environment,measurement scale,temperature,and the bonding effect of the observed object,and it is often difficult to achieve high-precision measurement in practical applications.Digital Photographic Deformation Measurement(DPDM)is a large-scale,reusable,high-precision,full-field non-contact deformation measurement method.However,limited by the current camera resolution,achieving higher precision strain measurement is difficult.Therefore,this thesis proposes a micro-DPDM-based resolution doubling rock strain measurement method,which realizes the strain measurement of rock two-dimensional plane and three-dimensional curved surface.The main research conclusions are as follows:(1)Proposed a resolution-doubling strain measurement algorithm based on micro-DPDM,and developed a resolution doubling strain measurement image acquisition device,which increased the resolution of the camera by more than 8 times,forming a resolution based on micro-DPDM Ratio multiplication rock strain measurement method,the 2D plane strain measurement accuracy of this method is verified by tensile and compression tests,and the maximum strain measurement error is less than 20 με.(2)Based on the basic principles of digital photography deformation measurement,the influence of speckle quality,ambient light,image noise,and calculation window size on digital photography deformation measurement is analyzed.A speckle quality evaluation method based on image resolution histogram shape and the average gray gradient was obtained,the optimal ambient light conditions for image acquisition and the optimal calculation window size for image analysis in this study were determined,and the standard for median filter denoising was formed Image preprocessing methods.(3)A resolution-doubling rock strain measurement and analysis process based on microDPDM was formed,and the rock surface deformation and strain distribution characteristics of rock compression tests of different lithologies were analyzed.The uniaxial compression test of red sandstone was designed,and the resolution multiplied rock 3D surface strain measurement based on micro-DPDM was realized.The test results showed that the maximum strain measurement error of this method’s 3D surface strain measurement was less than 150 με,compared with ordinary 3D digital photography.The strain measurement error of deformation measurement is reduced by 2.7 times.The research work of this thesis proposes an effective research idea for improving the accuracy of DPDM strain measurement,and accordingly proposes a method and image acquisition device that can realize rock 2D plane and 3D curved surface strain measurement,which is beneficial to micro DPDM The method is more widely used in the field of rock deformation measurement.There are 59 illustrations,4 tables and 103 references in this thesis. |
