In-situ measurement of dynamic micro X-ray CT and dynamic mechanical analysis for rubber materials

Abstract

Observing the internal state that takes place during deformation is essential for comprehending the mechanical properties of polymeric materials like rubber. For the effective utilization of rubber in damping applications, it is imperative to comprehend the relationship between the loss factor and microstructure. In an earlier study, we developed a dynamic X-ray CT technique tailored for damping materials subjected to tensile amplitude and proposed a method to directly evaluate the internal deformation behavior under dynamic conditions. However, owing to the technical constraints of the shaker employed for dynamic X-ray computed tomography, key variables such as vibration frequency and amplitude could not be incorporated into the analysis. Additionally, it has not been possible to simultaneously measure dynamic viscoelasticity and dynamic micro X-ray CT in situ.In this study, we developed an experimental system that enables simultaneous measurement of dynamic mechanical properties and dynamic X-ray computed tomography (CT). This system facilitates in-situ investigation of internal deformation behavior and the loss factor in rubber materials, allowing for the assessment of variations in loss factors at the micro-scale. We examined the differences between styrene butadiene rubber (SBR) and natural rubber (NR) as base materials and investigated the influence of shape, and particle size of ZnO on the dynamic behavior of SBR composites. Dynamic X-ray computed tomography (CT) was conducted at excitation frequencies of 1 and 2 Hz, excitation amplitudes corresponding to 1% and 1.25% of the inter-chuck distance of the specimens, and a spatial resolution of 0.5 µm. Local strains were extracted from the 3D reconstructed images, and both the local strain amplitudes and their histograms were assessed as characteristics of dynamic behavior. The results indicated that the effect of varying the excitation frequency between 1 and 2 Hz was minimal for the SBR. Additionally, the median value of local strain amplitudes shifted in relation to the magnitude of the excitation amplitude. When comparing base materials (SBR and NR) with significantly different loss factors, no discernible differences were observed in the histograms of local strain amplitudes. The histograms did vary based on the formulation conditions of the SBR microparticle composite, although the loss factor remained unchanged. This lack of change in the loss factor can be attributed to the minimal impact of the particulate composites on the inherent loss factor of pure SBR. Importantly, the study successfully achieved multimodal and simultaneous measurements using dynamic mechanical analysis and dynamic micro X-ray CT.