Mechanically Modulated Strain-Induced Crystallization around Crack Tips in Nanofiller-Reinforced Elastomers.

Understanding how materials respond to extreme local deformation is critical for advancing soft material design. In elastomers that combine nanofiller reinforcement with strain-induced crystallization (SIC), we reveal the interplay of these mechanisms near crack tips by integrating microscale digital image correlation with scanning wide-angle X-ray diffraction. By analyzing over 15,000 diffraction patterns, we mapped local strain and crystallinity fields. Nanofillers significantly expand the SIC-active zone by nearly an order of magnitude and considerably reduce the crystallization onset strain from 130 to 65%. However, the strain amplification typically induced by fillers diminishes as the crack tip is approached, indicating a mechanical compensation effect. This spatial modulation reflects a dynamic balance among local crystallinity, deformation, and filler-mediated stress transfer. We identify a dual-slope strain singularity linked to crystallinity gradients and quantify an empirical correlation between crystallinity and the major principal strain throughout the SIC-active region. These findings show that SIC-generated crystallites serve as in situ reinforcements, mitigating strain concentrations and enhancing damage tolerance. Our results provide mechanistic insights into SIC-driven toughening in filled elastomers and offer guiding principles for designing soft materials with superior mechanical robustness.