Fracture Process of Mechanically Interlocked Ductile Glass Under Uniaxial Tension

A unique toughening mechanism in ductile glass was elucidated by multiscale in situ structural analysis. A brittle glass of a cyclic oligosaccharide derivative was significantly toughened by a small amount of a polymer that penetrated the molecular cavity. In situ scanning electron microscopy and synchrotron X-ray scattering under uniaxial tension revealed strain-induced nanovoid formation and growth accompanied by molecular-level structural changes. Nanovoids were widely formed in the sample before yielding, and then, they clustered into a disk-shaped slit a few micrometers in size and perpendicular to the tensile direction. Owing to the strain concentration through necking, the slit formed by the nanovoid cluster was widely opened in the tensile direction to form fibrils and then became stabilized, whereas the craze in a conventional polymer glass generally splits under a small strain. After the initial glass structure maintained by interactions between the homogeneously dispersed cyclic components collapsed, a high strain was applied to the polymers. The transfer of polymers through the cavity led to the conversion to another structure that had a shorter distance between the main components and a high molecular orientation. Because the reconstructed structure was considerably harder than the initial structure, this strain-induced hardening delocalized the strain at the fibrils and tips of the slits, leading to stable propagation of necking. This mechanism is similar to that of transformation-induced plasticity in advanced ductile steels. The results suggest that intuitive molecular designs focusing on the unique structural changes in mechanically interlocked glass are promising for creating advanced hard and ductile glasses.