[S08P] PM-P

[S08P-05] On Selective Rupture in and around Weak Zones

*Koji UENISHI¹, Shoya SHIOIRI¹, Masanao SEKINE¹ (1. Univ. of Tokyo)

We have been investigating, experimentally as well as numerically, the quasi-static and dynamic rupture behavior in brittle solids containing mechanically weak zones. The weak zones, representing geological fault planes, may not only be interfaces of layered solid media but also consist of sets of small-scale cracks distributed in some specific areas of the brittle solids. So far, we have considered, for example, deflection or bifurcation of rupture propagation at an interface (Uenishi, Proc. Mat. Sci., 2014) and the effect of the existence of weak zones on acceleration and deceleration of rupture propagation (Uenishi et al., SSJ Fall Meeting, 2019; Uenishi and Nagasawa, SSJ Fall Meeting, 2020, 2021, Proc. Struct. Integr., 2022, Mech. Adv. Mater. Struct., 2022). However, in the previous study, weak zones, preset in model solid specimens by a digitally controlled laser cutter, often stretch from the free surfaces of the specimens and therefore, ruptures tend to be initiated at these free surfaces. In this work, in order to exclude this "surface effect" of the specimen on rupture initiation, we preset a weak zone only at the very center of a model rectangular photoelastic polycarbonate specimen. As before, the weak zone itself consists of small-scale cracks that are parallel to each other and have some dip angle. Using a high-speed digital video camera, we experimentally observe the effect of the dip angle on the initiation and extension of ruptures in the model specimens that are externally loaded by a tensile testing machine quasi-statically at a constant strain rate. We show that depending on the dip angle, rupture can be really selective. If the weak zone dips vertically (dip angle 90 degrees) and the quasi-static load acts normal to each small-scale crack surface inside the weak zone, as suggested by Uenishi and Nagasawa (SSJ Fall Meeting, 2021), the sudden spatial change of crack density in the specimen, i.e. the edge of the weak zone, serves as a large-scale plane of weakness or an interface and the rupture is initiated and extends along this virtual interface, namely, along the edge of the weak zone. In this case, the rupture moves "around" the weak zone, and the weak zone itself will not be damaged. It the weak zone is less inclined with a smaller dip angle, the rupture is initiated "inside" the weak zone and will damage and divide the weak zone. This selective rupture behavior, "inside" or "around" the weak zone, can be roughly explained, at least qualitatively, through stress intensity factors and stress distributions near the tips of the effective (virtual) large-scale crack associated with (the small-scale cracks inside) the weak zone.

Acknowledgements: The research has been financially supported by the Japan Society for the Promotion of Science (JSPS) through the "KAKENHI: Grant-in-Aid for Scientific Research (C)" Program under grant number 23K04021.