PSI - Issue 32

Anatoly M. Bragov et al. / Procedia Structural Integrity 32 (2021) 340–344 Author name / Structural Integrity Procedia 00 (2019) 000–000

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mechanical properties at different types of stress-strain state and strain rates is necessary for reliable modeling of dynamic processes and predicting the limiting state of structures. To date, there are a large number of publications about the behavior of brittle media under dynamic loading, for example Bragov et al. (2013, 2015, 2017, 2019), Brara and Klepaczko (2007), Schuler et al. (2006), Smirnov et al. (2020), Thomas and Sorensen (2017), Tran et al. (2016), Xu et al. (2011), etc. Nevertheless, a large number of conferences and symposia are held in Russia and abroad at which the problems of the dynamic strength of structural materials are discussed. This indicates the presence of unsolved problems in the designated area. Among these problems are the poorly studied principles of changing energy characteristics under impacts. In this regard, the presented study reveals the experimentally observed features of the energy absorption of sand-lime brick under dynamic loading. The results of the tests carried out by the Kolsky method were deformation diagrams at different strain rates which were used to determine the specific energy intensity of the studied material. Empirical patterns of changes of energy characteristics with an increase of the strain rate which were noted earlier at dynamic tests of other brittle media have been revealed. 2. Test procedure and used samples Dynamic tests before fracture of sand-lime brick samples were carried out by the Kolsky method using a split Hopkinson bar described by Kolsky (1949). The recommendations related to the ratio of the geometric dimensions of the samples and the lubrication of the ends of the measuring bars were followed at preparation for testing. A comparison of the sum of the incident and reflected pulse with the transmitted pulse was made. This showed the equality of the forces acting on the left and right on the sample and homogeneity of the stress-strain state of it in experiments. Cylindrical specimens with a diameter of 20 mm and a length of 10 mm were made from sand-lime bricks of grade 150 (15 MPa) for testing. The manufacturing technology of the samples included the following operations. First, plates with a thickness of 10 mm were cut from the bricks on a stone-cutting machine with a diamond disc and then cylindrical samples for experiments were drilled from these plates on a drilling machine by a diamond-coated crown. At the same time, certain difficulties arose with the manufacture of high-quality samples, since its edges were often chipped when drilling. 3. Test procedure and used samples The specimens were loaded by compression pulses with different strain rates determined by the speed of the striker accelerated in the barrel of a gas gun. For each loading mode, 3-4 tests were performed, the results of which were then averaged.

Figure 1. Average dynamic deformation diagrams of the sand-lime brick