Why are tensile cracks suppressed under dynamic loading?—Transition strain rate for failure mode

Abstract

Mechanical properties of rocks under dynamic loading are significantly different from those under quasi-static loadings. This difference is driven by more fundamental mechanical principles of materials at failure and will influence subsequent macroscale cracking behaviour. Understandings on this fundamental mechanism, however, are still controversial significantly. This paper tries to provide a feasible explanation of the underlying connections between the rate-dependent strength and the cracking behaviours. Open-flaw marble specimens, which provide good stress concentration at possible fracture initiation and material homogeneity, have been investigated experimentally and mathematically. We observe that experimentally the tensile strength is more sensitive to strain rate than the compressive strength. Meanwhile, tensile cracks are suppressed under dynamic loading, and shear cracks appear first along the flaw boundary. We incorporate the “localized strain rate effect” concept into the analytical study and propose the “transition strain rate” as a watershed for the different fracturing behaviours under quasi-static and dynamic loadings. This model successfully explains why the tensile cracks are suppressed in rocks under dynamic loadings, while quasi-statically, the stress distribution nonuniformity would suggest otherwise cracking behaviours. The well-correlation between the experimental and modelling results indicates that the model can be introduced to quantitatively analyse more complex macroscopic problems involving high strain rates in material science, geology and civil engineering.