This article deals with the problem of predicting the brittle fracture of rocks and similar materials, which can also include frozen sandy soils. Such materials, due to the diversity of their conditions of origin, are characterized by natural heterogeneity at the micro-, meso-, and macro-levels, which makes it difficult to develop sufficiently universal criteria for their strength. Despite a number of known models and criteria of strength and fracture, the search for such criteria remains an urgent problem. In this paper, using the energy approach to the mathematical modeling of mechanical systems, the fracture criterion is justified, which differs from the known criteria that do not require integration to calculate the strain energy We and dissipation energy Wd. The well-known relation for the input energy W=We+Wd is used. The object of the study was the ratio of dW=dWe+dWd. The main research question concerned what the ratio of dWe and dWd would be at the point of brittle failure. The search for an answer to the question led to the justification of a differential energy criterion for the failure of brittle materials on the descending branch of the full stress–strain curve. It was found that the point of predicted fracture is determined by the equality σ=0.5 εEtangential (if there is an inflection point on the ascending branch) or σ=0.5 εEsecant_secant. The main result of the work was ascertaining the differential strength and fracture criteria of brittle materials in the form of inequalities and equations, which were oriented for application in engineering calculations. Examples of application of the developed criteria are given; their consistency with the experimental data known from the literature confirmed.
Underground laboratories provide a unique environment for various industries and are the perfect place for developing new technologies for mining, geophysical surveys, radiation detection as well as many other studies and measurements. Unfortunately working in underground excavations is associated with exposure to many hazards not encountered in the laboratories located on the surface. Water inflow, gas burst, roof fall and even seismic hazards translate into high accident rates in the underground mining industry across the globe. Therefore, to minimise the risk of serious accidents, a lot of research investigations related to the development of effective risk assessment procedures are being carried out. One of the initiatives aimed at improving the work safety in underground laboratories in the Baltic Sea Innovation Network project implemented under the Interreg Baltic Sea Region Programme. This study presents the process of compiling a database on hazards within underground laboratories. Finally, a proposal of unification of the procedure for risk assessment, including methods for determining the likelihood and potential impact of unwanted events has been developed.
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