Experimental Characterization of Long Slender Structures Using DIC

ABSTRACT

High‐strain composite deployable structures have been developed for systems such as solar arrays, camera masts, or solar sailing propulsion elements. Composite booms in such applications are often flattened and then rolled into a small footprint for low‐packaged volume for launch prior to deployment in space. Long, slender composite booms have a strong nonlinear response; hence, Earth‐based experimental tests with gravity offloading methods are required for prediction validation. Gravity offloading is achieved by suspending the booms vertically and applying distal end (tip) loads to represent a specific loading and boundary condition in a potential solar sailing application. Three‐dimensional digital image correlation (3D‐DIC), along with other measurement techniques, was used to obtain strain and displacement along the length of a 7.5‐m subscale composite triangular, rollable, and collapsible (TRAC) boom in preparation for full scale testing of a 30‐m boom. However, incorporating 3D‐DIC as a primary measurement tool on long, slender, high‐aspect‐ratio boom structures present significant challenges. Such challenges included (1) small, correlated area due to high aspect ratio, specimen geometry, and loss of spatial resolution due to field of view and anticipated displacement, (2) limited standoff distance due to test facility constraints, (3) coordinate system alignment of multiple DIC systems along the length of the boom, (4) nodal mesh extraction for adequate test and analysis correlation, and (5) measurement comparison between DIC and other instrumentation used such as fibre optic strain sensing (FOSS) and laser displacement tracking. The contents of the proposed paper will focus on techniques and methods for overcoming the previously mentioned challenges associated with applying 3D‐DIC to long, slender boom structures. Results from subscale tests along with lessons learned will be discussed.