| As the most active and outstanding non-contact,full-field optical technique,digital image correlation(DIC)has been widely used in scientific research and industrial fields due to its simple optical setup,low environmental vulnerability,wide measuring range and the ability to measure more physical quantities.By tacking the randomly distributed speckle,DIC can obtain information of the tracked object and further calculated its fullfield deformation.Thus,speckle is the basis factor of DIC,which will affect the measuring accuracy,computational efficiency,and stabilities of DIC results.Therefore,the comprehensive evaluation of speckle quality,design and optimization of the digital speckle pattern(DSP),and fabrication of optimized DSP will contribute to the standardization of DIC,in details,will reduce computational errors,improve the computational efficiency and enhance the stability of DIC measurements.In order to realize the standardization of DIC,this paper is devoted to the optimization design and fabrication of the DSPs.In the optimization design of the DSPs,first of all,formulas of the DSPs were built according to the features of traditional artificial speckles.The built DSPs are vectorgraph and binary.Based on the principle of camera imaging,three imaging models of the built DSPs were given.In order to evaluate the quality of the DSPs,a comprehensive method was proposed based on the inverse Gauss-Newton iterative algorithm,where the root mean square error(RMSE)of the sub-pixel displacements,and the boxplot of the iterative cycles of the inverse Gauss-Newton iterative algorithm were the measure of speckle accuracy and computational efficiency,respectively.Through the comprehensive optimization of three imaging models and multiple parameters of DSPs,an single-radius optimized DSP with features of random factor of 0.3,radius of 2,and black-white ratio 1:1 was suggested and demonstrated to have the best accuracy and efficiency.By comparison and analysis of the optimized DSP with a series of artificial speckles,the optimized one was demonstrated to have the superiority of calculation accuracy,efficiency and consistency.In the aspect of DSP fabrication,a "copy" of the optimized DSP by directly print or indirectly transfer DSPs to tested surfaces was proposed to obtain stable DSP field instead of common uncertain techniques,such as spray paint,brush,etc.The portable water transfer printing(WTP)technique to transfer DSP for DIC was introduced and demonstrated by measuring uniform and large deformations.UV lithography was adopted to directly print the DSPs on plane surface for DIC measuring,and the printed DSPs were verified to be more accurate.To enhance the application of multiple DSPs fabrication techniques,WTP and UV lithography,with some other techniques including heat transfer printing,photosensitive seal,etc.were further discussed in terms of precision and regions to be measured.Non-invasive,three-dimensional(3D)full-field surface deformation measurements of the human body are important for biomedical investigations.In this paper,we proposed a 3D non-invasive,full-field body sensor using optimized DSPs and improved WTP for surface deformation monitoring of the human body in vivo based on stereo digital image correlation(stereo-DIC).The proposed stereo-DIC-based body sensor were applied in measuring pulses for Traditional Chinese Medicine(TCM)and pulse wave velocity(PWV)for human carotid artery,which demonstrated that stereo-DIC-based body sensor using optimized DSPs and improved WTP would have wide application prospect.Due to the controllable characteristics of DSPs,applications of DSPs in mechanical performances of materials will contribute to high quality and stable results.As some large structures and multicamera test that traditional techniques cannot obtain good speckles,DSPs also have the unique superiority.These applications of DSPs and standardizations of DSP will further promote the development of DIC in more scientific and industrial fields.At the same,this study is of great significance to promote the standardization of DIC measurement. |
