| Among the deformation measurement methods,three-dimensional digital image correlation method is widely used in engineering survey because of its non-contact,good environmental adaptability and simple experimental device.There are two kinds of existing three-dimensional digital image correlation systems: dual camera imaging system and single camera imaging system.The blind area will emerge in the traditional dual camera system when observing narrow space.The imaging system combined with spectroscopic device and single camera will reduce the image resolution,and the color industrial camera has high requirements for light source.In practical engineering measurement,The commonly used correlation algorithms are more suitable for measuring continuous deformable.For discontinuous deformation,virtual strain will appear in direct calculation.Therefore,this paper develops a coaxial dual camera three-dimensional digital image correlation method to realize the whole field deformation measurement in a narrow space,and proposes the partition inverse sequence calculation and strain gauge-guided partial derivative of radial basis function to realize the high-precision strain calculation during discontinuous deformation.The main research contents are as follows:1.A coaxial dual-camera three-dimensional measurement system is composed of a camera and a beam splitter.The optical path model of the system was established,and the specific steps of measuring deformation were introduced.In the rigid body displacement experiment,the measured values of coaxial method and the traditional dual camera methods were compared with the actual displacement respectively,and the relative error of coaxial method is within 2%.In the profiles reconstruction experiment,the absolute error of the measurement results of the coaxial method is less than 0.04 mm compared with the traditional dual camera,which meets the accuracy requirements and can be used for actual measurement.2.An image matching based partition inverse sequence calculation method is proposed in this study.The final deformed image is selected as a reference image and the displacement of the collected images is calculated from back to front.Two or more areas of interest are identified along the crack boundary prior to calculation.The positive displacement distribution can be obtained by adding and subtracting the displacement field in the reverse order calculation of each region,and then the final displacement field can be obtained by summing all regions.In addition,the strain distribution is obtained by the strain gauge-guided partial derivative of a radial basis function method,the shape parameters are obtained from the strain gauge data,and then the strain field is obtained by strain calculation based on partial derivative method based on radial basis function.Four point bending experiment of aluminum alloy beam were conducted to verify the validity and accuracy of these two algorithms.Moreover,the proposed methods were applied to evaluate the strain distributions at the crack tip of a cast iron beam,and its applicability in dealing with discontinuous deformation is further verified.3.The full field strain distribution of the inner wall of four different honeycomb structures(with and without panels)in quasi-static compression were measured by coaxial threedimensional digital image correlation method.The mechanical behavior their under out-ofplane compression were analyzed and the the strain distribution between the outer side wall and the inner side wall were compared.The compressive strength of honeycomb structures were successfully predicted by using the theoretical model of composite overall failure,and the deformation process was simulated by finite element calculation,which is in good agreement with the experimental results.Meanwhile,The coaxial dual camera three-dimensional measurement system is combined with hypercentric lens and applied to the defect detection of the inner wall of the pipeline,and determined the location of defects in the pipeline through the strain distribution of the inner wall,which proves that it has good practical application value. |
