Collective modes in the microshear ensemble as a mechanism of the failure wave

Abstract

Results of theoretical and experimental study of failure wave phenomena are presented. A description of the failure wave phenomenon was proposed in terms of a self-similar solution for the microshear density. The mechanisms of failure wave generation and propagation were classified as a delayed failure with the delay time corresponding to the time of excitation of self-similar blow-up collective modes in a microshear ensemble. Experimental study of the mechanism of the failure wave generation and propagation was carried out using a fused quartz rod and included the Taylor test with high-speed framing. The results obtained confirmed the "delayed" mechanism of the failure wave generation and propagation.Introduction. The phenomenon of a failure wave in brittle materials has been the subject of intensive study during the last two decades [1-3]. The term "failure wave" was introduced by Galin and Cherepanov [4] as the limit case of damage evolution, where the number of microshears is large enough for the determination of the front with a characteristic group velocity. This front separates the structured material from the failed area. Rasorenov et al. [1] were the first to observe the phenomenon of delayed failure behind an elastic wave in glass. Such a wave was introduced by Brar and Bless in [5], where the concept of a fracture wave was discussed to explain the nature of the elastic limit. A failure wave appeared in shocked brittle materials (glasses, ceramics) as a particular failure mode in which they lose strength behind the propagating front. Generally, the interest to the failure wave phenomenon is initiated by the still open problem of physical interpretation of traditionally used material characteristics such as the Hugoniot elastic limits, dynamic strength, and relaxation mechanism of elastic precursor.Qualitative changes in silicate glasses behind the failure wave, e.g., an increase in the refractive index, allowed Gibbons and Ahrens (1971) to qualify this effect as the structural phase transformation. These results stimulated Clifton [6] to propose a phenomenological model in which the failure front was assumed to be a propagating phase boundary. According to this model, the mechanism of failure wave nucleation and propagation results from the local densification followed by shear failure around the inhomogeneities triggered by the shock.Using high-speed photography, Paliwal et al.[7] obtained real-time data on the damage kinetics during dynamic compressive failure of a transparent AlON. The results suggest that final failure of the AlON under dynamic loading was due to the formation of a damage zone with unstable propagation of the critical crack.Statistical Model. The description of the failure wave phenomenon was proposed by Naimark et al. [8,9] after analyzing the damage localization dynamics in terms of a self-similar solution for the microshear density. This solution describes qualitative changes in the microshear density kinetics that allows defining failure waves as a specific ("slow dynamics") ...