On imperfect KUBC with view toward experimental homogenisation

This study investigates the use of imperfect Kinematic Uniform Boundary Conditions (KUBC) in experimental setups to measure the effective stiffness of architectured materials. To this aim, a numerical model simulates various experimental configurations: the number of grips applying the discretized KUBC, their compliance and clearance, etc. Simulations are conducted on bulk, periodic, and quasi-periodic specimens to understand the interactions between the grips and the mesostructures. The paper compares results from this Experimental KUBC (E-KUBC) to classical numerical KUBC to assess accuracy. Errors from E-KUBC are typically within 2–5%, but can significantly rise for some specimen design choices. The study identifies design guidelines to mitigate these errors, including adding notches to lower the stiffness of the specimen boundary and avoiding matching the specimen pattern with machine one. Quasi-periodic structures tend to be less sensitive to these issues. Overall, E-KUBC setups can yield accurate stiffness measurements if carefully implemented.