Image‐based inertial impact test for viscoelastic constitutive identification: A digital replica for error quantification

Polymers find widespread use in applications where they are subjected to impact loading. Therefore, understanding the time dependence of their mechanical response is critical to the design of structures subjected to these high strain rate environments. However, characterising these materials on microsecond time scales has proven challenging. Traditional experimental techniques rely on satisfying a number of limiting assumptions and typically do not provide direct measurements of the material parameters. Here, we propose a novel implementation of the image‐based inertial impact (IBII) test to extract viscoelastic constitutive parameters on these microsecond time scales using the stress gauge implementation of the virtual fields method. We validate the experiment using a digital replica approach in which the constitutive parameters are first extracted on a finite element model of an IBII test on a viscoelastic material. The finite element data are then used to synthetically deform computer‐generated grid images, which are then polluted with grey‐level noise to simulate the images that would be captured in a real‐life experiment. These images are processed identically to a physical experiment, and the identification is repeated using the full‐field displacements extracted from the computer‐generated images to determine the ideal processing parameters. Parameter identification was found to strongly depend on the processing parameters used to extract the kinematic fields from full‐field images, emphasising the need for computational validation before attempting a physical experiment to extract constitutive parameters. The IBII experimental method was found to be capable of simultaneously identifying the bulk modulus and the shear modulus along with their associated time constant.