Fracture in heterogeneous materials: experimental and theoretical studies

Abstract

The kinetics of fracture in stressed heterogeneous materials is investigated in a differentiated way using the parameter Δt, the interval between single or multiple (cooperative) microfracture events recorded by acoustic emission (AE) responses. The patterns of fracture nucleation and growth, which is a statistic process, are controlled by the heterogeneity of deforming material. There are two important aspects revealed by the study: 1) structural heterogeneity of materials causes uneven distribution of stress in loaded solids and thus creates local zones of microstress and ensuing microfracture in the overstressed zones; 2) AE measurements and microseismic monitoring are applicable to prediction of fracture by locating its source and thus allows predicting related hazard in mines, tunnels, bridges, nuclear-power plants, and other important engineering objects.

Migrations of Released Seismic Energy in Various Geodynamic Conditions

“…Можно предположить, что сейсмичность проявляется в ослабленных зонах земной коры, где уже подготовлены условия для реализации сейсмических событий разной силы. Такими зонами могут являться зоны динамического влияния разломов, зоны сопряжения тектонических структур, области перемычек, где создаются высокие локальные напряжения за счет гетерогенности геологической среды [Kuksenko, Makhmudov, 2017], а также зоны высокого градиента напряжений между областями повышенных и пониженных напряжений (зоны метастабильного состояния) [Rebetsky, 2007]. Процесс накопления напряжений, приводящий к землетрясениям, складывается из нарастания напряжений за счет тектонической нагрузки (в том числе от движения литосферных плит) и передачи напряжений из соседних областей [Rogers, Dragert, 2003], например от сильного, умеренного события или от роя землетрясений, что иногда сопровождается миграцией кластеров толчков разной силы.…”

Methodological aspects of studying the parameters of elastic waves and controlling the standard form of acoustic emission in the field

“…Equally oriented faults create the anisotropy of the medium, while microcracks form a network of small heterogeneities, determining the absorbing properties of the medium. The assessment of the geomechanical stability [1][2][3] and the safety of operation of various large-scale underground structures [4][5][6], such as tunnels and liquefied gas tanks, remains relevant [7,8], since the conclusions about the current geomechanical and geodynamic problems provided by mining research institutes state [9][10][11]that the tasks of ensuring safety and timely detection of critical situations that arise during the development of deposits and underground spaces remain not fully resolved. New methods and computer technologies make it possible to assess the stress-strain state in rock masses [12][13][14], but one of the widely used methods for such assessment is the acoustic emission (AE) method [15][16][17] , which studies the process of the initial stages of destruction (initiation and accumulation of microscopic cracks) [18] in various materials, such as rocks [19,20], building materials [21], composites [22].…”

Nanotechnologies of Strength Control of Materials

“…Strength assessment is not possible without an understanding of the fracture processes [20][21][22][23][24][25][26] and their relationship to the material state and residual resource. The statistical approach [27] to the evaluation of acoustic emission signals sometimes gives a false idea of the material state [28,29].…”