Interfacial crack behavior in the stationary temperature field conditions

The brittle coatings, made of different materials, when subjected to elevated temperatures and in the heat exchange conditions, are susceptible to delamination. Those coatings, as well as thin films, can be used for various therm insulating deposits, e.g. in turbines of thermal power plants. Due to environmental temperature change, in layers made of materials having different thermal expansion coefficients, appear thermal stresses. In this paper driving forces causing delamination of one layer from the other are analyzed i.e. the interfacial fracture in the two-layered, bi-material sample. This analysis was limited to considering the sample behavior when exposed to the stationaiy temperature field. The energy release rate G, which is the driving force for this interfacial fracture, is changing with temperature and that variation is increasing with increase of the temperature difference between the environment and the sample. Analysis of this relation, between the G variation and temperature difference, can be used to predict the maximal temperature difference, which the two-layered sample can be subjected to, without appearance of delamination between layers

Fundamental Problems of Modeling the Fracture Processes in Concrete II: Size Effect and Selection of the Solution Approach

AbstractTheory of concrete fracture, despite all the efforts of numerous researchers, still did not provide the clear answer to the problem of modeling the fracture processes of concrete. Three well known theories are at hand: fracture mechanics, plasticity theory and mechanics of continuous damages. The fundamental assumptions, those theories are based on, do not completely correspond to the nature of concrete. They all are confronted with numerous problems, out of which the four are fundamental: damages micromechanics, damages localization, size effects and the dilemma when to apply the phenomenological and when the micromechanical approach to considering this problem. In this paper are considered the last two of those problems: size effect (scaling laws) and decision making what would be the best way in solving problems of modeling the fracture processes in concrete and concrete structures

Interfacial crack behavior in the stationary temperature field conditions

The brittle coatings, made of different materials, when subjected to elevated temperatures and in the heat exchange conditions, are susceptible to delamination. Those coatings, as well as thin films, can be used for various therm insulating deposits, e.g. in turbines of thermal power plants. Due to environmental temperature change, in layers made of materials having different thermal expansion coefficients, appear thermal stresses. In this paper driving forces causing delamination of one layer from the other are analyzed i.e. the interfacial fracture in the two-layered, bi-material sample. This analysis was limited to considering the sample behavior when exposed to the stationaiy temperature field. The energy release rate G, which is the driving force for this interfacial fracture, is changing with temperature and that variation is increasing with increase of the temperature difference between the environment and the sample. Analysis of this relation, between the G variation and temperature difference, can be used to predict the maximal temperature difference, which the two-layered sample can be subjected to, without appearance of delamination between layers

Influence of temperature on behavior of the interfacial crack between the two layers

In this paper is considered a problem of the semi-infinite crack at the interface between the two elastic isotropic layers in conditions of the environmental temperature change. The energy release rate needed for the crack growth along the interface was determined, for the case when the two-layered sample is cooled from the temperature of the layers joining down to the room temperature. It was noticed that the energy release rate increases with the temperature difference increase. In the paper is also presented the distribution of stresses in layers as a function of the temperature and the layers' thickness variations. Analysis is limited to the case when the bimaterial sample is exposed to uniform temperature

Estimate of a power distributor life span based on the fracture mechanics criteria

Dimensioning of pressure vessels can be done according to various criteria, the basic one being the safety against the fracture by splashing. In this paper two methods for this dimensioning procedure are presented. The first one is based on application of the classical mechanics while the second one uses the fracture mechanics principles. Both methods were applied for checking the exploitation properties and capability of a vapor distributor in a power plant. Based on the in-situ measured damages and calculations by both methods, it was concluded that the vapor distributor could be further used as a part of the boiler installation in the local power plant. The second criterion, based on the application of the fracture mechanics principles, provided more reliable results than the first one, based on the classical mechanics

Estimate of a power distributor life span based on the fracture mechanics criteria

Dimensioning of pressure vessels can be done according to various criteria, the basic one being the safety against the fracture by splashing. In this paper two methods for this dimensioning procedure are presented. The first one is based on application of the classical mechanics while the second one uses the fracture mechanics principles. Both methods were applied for checking the exploitation properties and capability of a vapor distributor in a power plant. Based on the in-situ measured damages and calculations by both methods, it was concluded that the vapor distributor could be further used as a part of the boiler installation in the local power plant. The second criterion, based on the application of the fracture mechanics principles, provided more reliable results than the first one, based on the classical mechanics

Some Aspects of the Three-Dimensional Interface Cracks Analysis

Many problems of interfacial cracks are three dimensional in nature. Three-dimensional cracks at an interface of the two materials are analysed in this paper. For a crack at an interface, the stress intensity factors, load phase angle and energy release rate depend on elastic characteristics of two bonded materials and on geometry and the load conditions of a bimaterial sample. Influence of Dundurs\u27 parameters on stress intensity factors, load phase angle and energy release rate for different bi-material combinations and for the quarter-circular corner crack are discussed in this paper. Results show that elastic properties of materials constituting the interface have significant influence on behaviour of the 3D interface crack. Mode I stress intensity factor KI increases when the crack front approaches the free surface, while KII remains almost constant having the highest values between 10° and 80°, what results in high values of the load phase angle. The KIII stress intensity factor is zero in the symmetry plane, while its value increases as the crack front approaches free surfaces. The energy release rate diagrams show that the crack of a quarter circular front propagates faster closer to free surfaces than in the middle what means that the crack front would have the tendency of straightening

Selection of the Optimal Window Type and Orientation for the Two Cities in Serbia and One in Slovakia

The necessity of having windows on any building’s façade is not questionable. However, not every window is suitable for any building. The selection of an adequate window must include the analysis of various factors—the most important ones are the type of window (e.g., single or double glazing); filling gas in cavities (e.g., air, argon or some other gas); and placing, i.e., orientation of a window on a façade (facing north, south, or east, etc.). The research presented in this paper is dealing with the calculation of the window thermal loading for the cities of Kragujevac and Bor in Serbia and Žilina in Slovakia. These three cities were selected because they belong to different climate regions, according to the Köppen–Geiger climatic classification. The first two cities in Serbia belong to the same region Cf with difference only in the category of summer—Kragujevac Cfa and Bor Cfb—while the third city—Žilina in Slovakia—belongs to the Dfb region. The calculated thermal loading through the window was obtained as a sum of the thermal loading due to the heat conduction and thermal loading due to the solar radiation. The objective was to find the optimal window construction and orientation of a building’s façade for each of these cities, by varying the type of the window, its frame material and the filling gas. The results show that for the first two cities in Serbia, there is a difference in the window frame material in the optimal window construction, while for the third city (Žilina in Slovakia), the results are the same as for the second city (Bor in Serbia) despite the fact that they belong to different climate regions (Cfb and Dfb, respectively). These results support the fact that the climate affects the optimal window construction for any city/region in the world

Analysis of work-related injuries in mining industry in Serbia

The mining industry in Serbia has an important place in the country's economic development. Bearing in mind that the number of injuries that occur in the mining industry is unacceptably high, occupational safety and health is a challenge that existing and future mines will have to deal with. Studying injuries in mining, it was noticed that injuries requiring an absence from work for more than three days (especially fatal ones) are diametrically different in relation to the cause and manner of events related to injuries for which an absence from work is not necessary. In this research, authors focused on injuries that were characterized as ones requiring an absence from work. The statistical analysis of work-related injuries in mining is presented, as well as analysis of the direct causes of injuries, which are described as unsafe conduct of employees, unsafe conduct of company's management and/or unsafe working environment. In relation to classification of causes of injuries, a recommendation on what needs to be changed in order to remedy this situation in Serbia is given

Influence of the 3D interface crack front shape on the fracture parameters

Mechanical properties of multi-layer materials are often restrained by the strength of the interface between the constituting materials. Interface is frequently a spot of the crack initiation and delamination usually starts at corners. The singular stress field corresponds to interface destruction and depends on characteristics of materials and the shape of the corner. The growth of an interfacial crack, from the straight angle along the joint plane between the two long plates made of different materials, for various shapes of the crack front, is considered in this paper