PSI - Issue 32

A.M. Ignatova et al. / Procedia Structural Integrity 32 (2021) 79–86 Author name / StructuralIntegrity Procedia 00 (2019) 000 – 000

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and determination of consumer properties of armor barrier materials (Dubrovina, 2012; Naimark O.B. et al. 2000; Stavrogin A.Net al., 1985). In theoretical and fundamental studies, research of behavior of brittle materials under diverse types of loads can be important to gain a deeper insight into various aspects of rigid body dynamics, but mostly in terms of description of “self - organized criticality” phenomenon (Davydova М.М.et al., 2013; Damaskinskaya E.E. and Kadomtsev A.G., 2015; Makarov P.V. and Eremin M.P., 2013; Makarov P.V., 2010; PushcharovskyD.Yu., 1986). Brittle destruction under static loading is quite extensively studied; multiple sources (Barenblatt G.I.,1964; Makarov P.V. et al., 2005; Ignatova A.M. et al., 2012;) confirm that it is accompanied by dynamic emergence of a certain amount of macrofractures and subsequent fragmentation into large, visually identifiable splinters. Research by Ignatova A.M. et al. (2013) also shows that at the pre-destruction stage, some brittle materials can exhibit fractoemission – a phenomenon which suggests that during static loading, microdisperse fragments (50 to 400 µm) of the material exfoliate from its surface without forming major fractures. Destruction of brittle materials under high velocity dynamic impact is also accompanied by fracturing and fragmentation, but with one substantial difference. Under dynamic loads, the deformation and destruction mechanism is determined by local dissipative processes, the material becomes zoned, temperature and pressure change at the boundaries of local volumes depends on the distance from the loading point, which results in growth of interfacial stresses. As a result of such localization of impact energy, a certain volume of material is destroyed, with emergence of ultra- and microdisperse fragments, which is not typical of static loads, whereas the remaining (peripheral) part is being destroyed and fragmented following the mechanism alike to the one in static loads (Ignatova A.M., 2019). Parameters of fragmentation as a phenomenon occurring in a material under external physical effect depend on the parameters of the material itself (hardness, density, Young’s modulus etc.), on parameters of the effect (type of effect, force, velocity, periodicity etc.) and on the form factor of the sample under effect. Besides, parameters of destruction and fragmentation of brittle materials are significantly influenced by presence of constraints. So, in it is shown (Astafurov S.V. et al., 2017; StefanovYu.P. et al., 2005) that under static effects, brittle materials exposed to compressive lateral stresses manifest phenomena typical of inelastic behavior; in particular, shear bands are known to emerge. Change in the destruction behavior of brittle materials depending on the increase of the characteristic value of compressive volumetric stresses is referred to as brittle-to-ductile transition. Fragmentation behavior of brittle materials under non-constrained and constrained dynamic loading is presently understudied. It is known, however, that for some brittle materials, such as glass- and mica-crystalline materials (Ignatova A.M. et al., 2021) used as elements of armor installations, lateral compression is inherent to use in protective structures. In previous research byArtemov A.O. (2012), it has been established that the angle of collision between the mica crystalline material and the accelerated projectile significantly affects fragmentation parameters. It has been shown that the least destruction occurs at an angle of 30º, and the greatest at an angle of 90º. This is because an impact at 30º facilitates rebound and change of the projectile’s trajectory (fig. 1).

Fig. 1. Scheme of impact at a sample of brittle material with a steel ball at an angle of 30º in an experiment for rebound conditions identification.