Complexities of Capturing Large Plastic Deformations Using Digital Image Correlation: A Test Case on Full-Scale Pipe Specimens

Abstract

Abstract This paper identifies the challenges associated with using digital image correlation (DIC) measurements for full-scale bending tests that result in large deformations, and it describes techniques to address these challenges. Full-scale bend tests experimentally determine the strain capacity of line pipe, which is a critical parameter in strain-based design and assessment. DIC is a preferred measurement technique for these tests as it provides non-contact, full-field measurements of the pipe deformation over time. The primary challenges identified in using DIC for full-scale, large-deformation pipe testing relate to the speckle pattern, imaging system, and DIC performance measurement. A series of procedure and equipment improvements have been developed to address each of these challenges and to help improve the overall accuracy of the measurement system. The successful implementation of the DIC technique is illustrated through a recent full-scale pipe bend test of a 4.45-metre-long section of 24-inch diameter, X65 pipe. The pipe was subjected to severe bending (up to a 51° bend angle), resulting in the formation of a self-contact buckle. The test was monitored using four DIC systems (each system consisting of stereo cameras) incorporating the recommended procedure and equipment improvements identified herein. The DIC results were validated against conventional strain gauges.