Visualization of Buckling on Thin-walled Cylindrical Shell by Digital Image Correlation Method

The problem of buckling stability is very important in thin-walled cylindrical shell structure. In order to investigate the buckling phenomena, digital image correlation (DIC) method was applied in this experiment. The specimens have a thickness of 0.131mm and the ratio of external diameter (R0) to thickness (H) R0/H is 252. Due to its curved and thin walled elements, measurement of displacement and strains by using the traditional methods is difficult, because there is not enough space for sticking necessary torsion gauges to measure the out-of-plane behaviour, even if it is possible, the rigidity of the gauge itself will have an effect on the buckling strength. However, by using the optical image correlation method, the problem is solved. DIC method is an optical instrument which utilizes the full-field and non-contact measurement to gauge the three-dimensional displacement and strains on materials and structural parts. In this paper three dimensional digital image correlation system is applied to observe the buckling generation process in details and make a record of the surface displacement during the compression test by using two high resolution digital cameras, then the test data are analyzed and compared by a special correlation technique which can determine the surface displacements of cylindrical shells and it is shown in colour contour in full-field region. The buckling strengths obtained by the theoretical and experimental methods are compared and discussed in this paper. The experimental study shows that the buckling strength of theoretical value is much higher than that of experimental one, because the buckling strength is highly dependent on the imperfections.