Observation methods in in-situ X-ray computed tomography (CT) of viscoelastic rubber can influence the evaluation of mechanical properties, even when image artifacts are negligible. Conventional intermittent CT measurements require repeated interruption of tensile deformation, during which stress relaxation inevitably occurs. Although the resulting displacement during holding may be sufficiently small to render motion artifacts in reconstructed images negligible, the accompanying time-dependent deformation can still affect the evaluation of mechanical properties, such as Young’s modulus. In this study, a compact tensile testing system with an ultra-slow loading capability was developed to enable continuous in-situ four-dimensional (4D) X-ray CT observation—integrating three-dimensional spatial imaging with the time dimension—at a constant tensile speed of 1.5 μm s -1 without interrupting tensile deformation. Continuous CT imaging experiments were conducted at a tensile speed of 1.5 μm s -1 , allowing submicron-resolution observation of internal deformation in rubber specimens. Comparative experiments between intermittent and continuous loading conditions revealed clear differences in the evaluated elastic modulus and stress response, confirming that stress relaxation during holding significantly affects the apparent mechanical properties in viscoelastic materials. These results demonstrate that, although intermittent CT observation can provide stable images under small-displacement conditions, continuous in-situ CT under ultra-slow tensile adopted in this study (1.5 μm s -1 ) loading minimizes method-dependent effects of stress relaxation, thereby enabling more mechanically and structurally consistent evaluation. This study experimentally clarifies an effect that is physically expected for viscoelastic materials but has not been explicitly demonstrated in in-situ CT studies on rubber. The results obtained provide a reliable basis for microstructure-informed mechanical evaluation of polymer materials. • Submicron tracking of rubber deformation via ultra-slow tensile loading. • Elastic modulus and stress differ under intermittent vs continuous loading. • Interrupted CT may underestimate stiffness due to viscoelastic relaxation. • Proposed 4D system enables consistent mechanical and structural evaluation.
MATSUBARA et al. (Fri,) studied this question.