Study On Speckle Patterns Made By UV Inkjet Printing On Surface Of Specimen

Digital image correlation method is an attractive non-contact full-field measurement method in modern mechanics measurement technology.Due to its simple measurement equipment,low measurement environment requirements,and non-contact nature of the entire field,it is widely used in scientific research and engineering.In the digital image correlation method,the speckle patterns play a very important role in the deformation measurement as a carrier for carrying the deformation information of the test piece.The quality of the speckle patterns have a very important influence on the calculation accuracy of the digital image correlation method and the consistency of the calculation results.For the first time,this paper proposes a method of directly printing the optimized digital speckle patterns on the surface of the test piece using the UV inkjet printing method.This method can completely eliminate the influence of human subjective factors on the quality of the speckle field,and has important significance for the implementation of the speckle patterns standardization.The article proposed a UV inkjet printing speckle patterns production process: First,the use of acrylic paint coating,after the coating is dry,through a domestically modified UV flatbed printer to optimize the digital speckle patterns in the test piece surface production.In order to measure the accuracy of the UV flatbed printer on the coating surface,a two-dimensional microscopic image measurement system was set up to test the area,roundness,and positioning accuracy of the micron-sized printing ink dots.Finally,ink dot edge printing was measured.The root-mean-square error is 0.1±0.012 mm,and the average circularity of ink dots is 0.85.In order to determine the minimum particle size of speckle that can be replicated by this UV flatbed printer,based on the simulation principle of the circular distributed speckle patterns,a method of evaluating the print quality of the circular distributed speckle patterns is proposed.The steps are:(1)Select the sparse speckle array as the test object(to avoid overlap between points);(2)Binarize the image using the adtapttresh function based on image edge and grayscale segmentation;(3)Use the roundness and area ratio(independent speckle area/independent speckle print area),Spot print quality is evaluated.When both evaluation index values are greater than 95%,the speckle patterns requirements for speckle size,duty cycle,and randomness can be satisfied during the printing process.It was determined that the minimum diameter required for the copying of the digital speckle patterns by this retrofit UV printer was 1 mm.Static noise experiment,small deformation field measurement experiment,and four-point bend measurement experiment were used to test the frequency distribution histogram,the accuracy of strain field measurement,and the deformation of the whole field in the noise distribution of the printed speckle patterns under static conditions,small deformation,and large deformation,respectively.Consistency.Experiments show that the digital speckle patterns produced by this process has good adhesion and shear resistance to the surface of the specimen.The speckle patterns has obvious anti-noise ability compared with the traditional speckle field,can represent the whole field deformation with high precision and high reliability,and has a high degree of consistency in the performance of the whole field.This also proves the rationality of the print quality evaluation method for circular distributed speckle field.