Removing thermal error from DVC measurements with laboratory x-ray CT

The acquisition of high-fidelity volume images using x-ray CT is crucial for achieving accurate internal full-field deformation measurements using digital volume correlation (DVC). However, the self-heating effect of x-ray CT devices inevitably induces slight and continual thermal drift of the x-ray source during volumetric imaging. This drift gives rise to geometric distortions in the reconstructed volume images, leading to substantial errors in displacement and strain results detected by DVC. To address this issue, an easy-to-implement and effective reference ball correction (RBC) method is proposed in this work. The RBC method utilizes a fixed reference ball to record and track the thermal drift from projection images, allowing for accurate reconstruction of undistorted volume images and fundamental correction of thermal-induced errors in DVC measurements. For validation, both simulated and real tests, including rescan and uniaxial compression tests on a foam copper sample, were conducted. Experimental results demonstrate the accuracy, efficacy and practicality of the RBC method. As the RBC method corrects the thermal errors through restoring high-fidelity volume images rather than compensating for deformation fields, it significantly outperforms the existing reference sample compensation method in correcting thermal errors in both displacement and strain measurements. The RBC methods is especially suitable for DVC applications requiring high measurement accuracy.