Abstract

The initial local dynamic fracture is an important stage of deformation process which defines the macroscopic strength of brittle materials. Nucleation and development of initial sources of damage is closely associated with the local structural instabilities of dynamic deformation process. In their scale, the structural instabilities belong to mesoscale, which supposes that experimental study of the response of material on shock loading should also be carried out at the mesoscale. In the present work, the results of studying the dynamic fracture of typical brittle material, gabbro-diabase, are presented. The goal of research was a determination of the criterions for nucleation of localized structural instabilities as sources of initial stage of dynamic fracture. Shock tests of specimens were performed under uniaxial strain conditions (plane collision) by using light gas gun of 37mm bore diameter. The gabbrodiabase under investigation has the following characteristics: density ρ=3,05g/сm3 and sound velocity Cl=6,25cm/s. The specimens for shock tests were in the form of parallelepiped of 52mm in size and 12.2mm in thick. They were polished and covered with aluminum layer of 25μm, which provides a mirror reflection of laser beam of interferometer from the free surface of target. The local probing of the free surface velocity of target (opposite to loaded surface) by using interferometric technique allows to determine the criterion for initial stage of damage [1,2]. The time resolved free surface velocity profiles were registered with the velocity interferometer, the laser beam of which was focused on the free surface of target up to 60-70μm, so all the local strength characteristics inferred from the velocity profile concerns to mesoscale.