Subcritical Crack Growth in Soda‐Lime Glass under Combined Modes I and III Loading

Abstract

Fracture and subcritical crack‐growth characteristics under combined Modes I and III loading were studied using the modified compact tension (CT) specimens of soda‐lime glass. The combined mode load was applied to the specimen in the direction β with respect to the initial crack. By superposition of Mode III, the advancing crack begins to rotate at an angle Ψ to the initial crack plane, which nearly maximizes the Mode I stress intensity factor KI(Ψ), and the crack continues to propagate in the same direction. In this case, unlike combined Modes I and II, the crack breaks into multiple partial fronts, and ligamentary bridging forms fracture lances when these segmented cracks are held together. The crack velocity da/dt was plotted versus the maximum Mode I stress intensity factor KI(Ψ) for combined Modes I and III loading. The da/dt values are initially high, and the crack growth tends to be discontinuous compared with the result for pure Mode I. The subcritical crack growth seems to occur when the KI value for the initial crack reaches a certain value. The da/dt‐KI(Ψ) curves for combined Modes I and III lie roughly on the same curve as that for pure Mode I as the crack growth increases.