Digital Image Correlation Method And Experimental Investigation On Damage And Failure Of Material

The study of rock damage and failure is an important basic science issue in solidmechanics, geotechnical engineering and mechanical engineering. Experimentaltechniques play a key role on deeper investigation of rock damage and fracture.Digital image correlation (DIC) is a practical and effective optical metrology forfull-filed deformation measurement with the advantages of simple experimental setup,high resolution and strong environmental adaptability. In this work, some technicalproblems in DIC calculation, such as error analysis, parameter selection of algorithmhave been analyzed and discussed, and it has been utilized to investigate the damageevolution of rock. The topic of this thesis has important scientific significance andengineering backgroundMeasurement errors of displacement and strain in2D-DIC have been discussed.Through simulated image and numerical experiments, considering several variationswhich are the quality of image, noise, shape function matching process, the influenceof shape function and selection of subset size have been discussed. The determinationof strain fields based on displacement components obtained via2D-DIC is subject toseveral errors that originate from various sources. Considering the influence ofdisplacement function and window size of strain calculation, the optimal selection ofsubset size has been studied by numerically deformed images. Multi-plane DICsystem, for measuring deformation of surfaces of prismatic specimen, has beenestablished. This system has been successfully used in the uniaxial compression testsof sandstones.A3D-DIC system, including Software and hardware devices, has been established.Simulated speckle images with different qualities were generated by a simplifiedcamera model to analyze the influence of subset size selection and the angle betweenthe two cameras on matching errors and measurement accuracy of3D globalcoordinates. A temporal matching technique which includes series of images has beenpresented to measure the large deformation of crack tip of rubber. The3D deformationfields have been obtained by the present method to study the deformation behavior ofcrack tip field.Damage evolution and crack propagation of rock have been investigated by DIC method. To investigate deformation and failure process of rock under different loadingconditions, uniaxial compression and indentation tests were performed. Experimentalresults show that the damage distributes diffusely in rock at early loading stage andbecomes increasingly concentrated with the loading which causes the nucleation ofthe crack, propagation of the crack leads to the eventual failure of the specimen.Based on the statistical analysis of strain fields, damage factor and localization factorare presented to describe damage evolution. The combined use of two factors can wellrepresent the damage evolution of rock under compression. The damage evolutionprocess rock under cyclic uniaxial compression has been also studied, the influence ofloading cycles on damage evolution and crack nucleation have been analyzed.