Analysis of deformation of the filled elastomer in mesoscopic scale was investigated with 3-D FEM (Finite Element Analysis). Combination of 3-D TEMT (Transmission Electron Micro Tomography) and Voxel-FEM enables us to reconstruct mesoscopic scale 3-D image and calculate 3-D strain distribution. To the first approximation, the calculated stress-strain behavior shows a good agreement with the experimental results. The strain concentration over 200% can be seen between carbon black aggregates, even if the overall strain is only 15%. The rubber occluded by carbon black aggregates can also be observed. The virtual rubber model constructed with perfectly dispersed fillers was also calculated. This shows less overall stress than that of the actual filled model reconstructed with 3-D TEMT image. It is found that the occluded rubber can behave as a hard domain and is an important factor of the filler reinforcement effect on rubber.

The three-dimensional (3D) morphology of particulate fillers embedded in a rubbery matrix was examined by transmission electron microtomography (TEMT). Two types of nanofillers, i.e., carbon black (CB) and silica (Si) nanoparticles, were used as the nanofillers. Although the CB and Si nanoparticles were difficult to distinguish by conventional transmission electron microscopy (TEM), they appeared different by TEMT; the CB and Si nanoparticles appeared to be hollow and solid particles in the cross-sectional images of the TEMT 3D reconstruction, respectively, demonstrating that TEMT itself provided a unique particle-discriminative function. The nanoparticles were found to form aggregates in the matrix. It is intriguing that each aggregate was made of only one species; not a single aggregate contained both the CB and Si nanoparticles. A particle-packing algorithm was developed to estimate the positions of each primary nanoparticle inside the aggregates.

Nanoparticle-filled rubber under tensile deformation was observed in situ by transmission electron microscopy (TEM), and the spatial distributions of the local maximum and minimum principal strains (ε max and ε min ) under tensile deformation were determined experimentally for the first time. The local ε max showed that deformation behavior depends heavily on the local structures and their spatial arrangements. Additionally, greatly deformed rubbery regions were found to appear along a network consisting of silica aggregates (silica-aggregate network). The distribution of the local ε min revealed the reorganization mechanisms of the internal hierarchical structures. The finite element method (FEM) was then applied to a series of TEM images under tensile deformation to simulate the structural changes, principal strains, and von Mises stress. The simulated morphology and ε max were in excellent agreement with the experimentally obtained morphology and strain. The distribution of the simulated von Mises stress, obtainable only from the FEM based on the experimental results, revealed that large stress propagates along the silica-aggregate network parallel to the tensile direction, suggesting that the silica-aggregate network may be primarily responsible for providing mechanical strength to the nanoparticle-filled rubber under deformation. Since the stress concentrates along the silica-aggregate networks, cavities appeared along these "stress pathways." The present study would pave the way to understanding the microscopic factors determining the macroscopic mechanical properties of rubber nanocomposites mainly used for automobile tires and seismic isolation rubber.

Silica is widely used in passenger tire treads to improve the balance between wet traction and rolling resistance, compared to the balance achieved when the filler is strictly carbon black. Improvement in wet traction with silica is attributed to the difference in energy loss encountered at high frequencies. The energy loss difference is deduced from the difference in shift factors, determined by time temperature superposition in viscoelastic testing of silica compounds compared to carbon black compounds. Further investigation indicated that some mineral fillers other than silica showed similar behavior. Thus, some mineral fillers could improve tire wet traction without adverse effects on other tire performance traits.

An in situ straining holder capable of tensile deformation and high-angle tilt for electron tomography was developed for polymeric materials. The holder has a dedicated sample cartridge, on which a variety of polymeric materials, such as microtomed thin sections of bulk specimens and solvent-cast thin films, can be mounted. Fine, stable control of the deformation process with nanoscale magnification was achieved. The holder allows large tensile deformation (≃800 μm) with a large field of view (800 × 200 μm before the deformation), and a high tilt angle (±75°) during in situ observations. With the large tensile deformation, the strain on the specimen can be as large as 26, at least one order of magnitude larger than the holder's predecessor. We expect that meso- and microscopic insights into the dynamic mechanical deformation and fracture processes of polymeric materials can be obtained by combining the holder with a transmission electron microscope equipped with an energy filter. The filter allows zero-loss imaging to improve the resolution and image contrast for thick specimens. We used this technique to study the deformation process in a silica nanoparticle-filled isoprene rubber.