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

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

The Effect of Selected Technological Parameters of Laser Cutting on the Cut Surface Roughness

The theoretical part of the paper presents some basics of the laser cutting technology and principles. The characteristics of the CO2 laser beam and the parameters entering the laser cutting process are described. The conventionally used material – S235JR steel, method of its laser cutting and the effect of process technological parameters on the cut area characteristics are presented as well. Experimental investigations were performed on samples made of the S235JR steel, with application of different laser cutting technological parameters, while observing the surface roughness Rz and Ra. Roughness results are displayed as images of the scanned cutting surface geometry and graphically for each sample, with comparison between the individual test samples. Effects of the position of the laser beam focus point, the cutting speed and assist gas pressure on the cut surface roughness are analyzed. It was concluded that the laser cutting parameters impose significant influence on the cut surface quality

Uniaxial tension of drying sieves

Although the literature contains numerous studies that have been developed to describe the nonlinear behavior of drying sieves' operation, there are no papers in this which report deeper investigation of the drying sieve behavior when exposed to tension and thermo stabilization. The aim of this paper is to provide insight into the elastoplastic behavior of the thermo stabilized and not stabilized sieves subjected to the tensile force. Within this work both theoretical and experimental investigations were performed. The sieves were joined by using a spiral. In separate experiments tests of wire base and weft of the weave mesh were performed, both for thermo stabilized and not thermo stabilized sieves, sieves joining and the sieve thermo stabilization itself. It was established that the thermo stabilization of sieves provides for stability of sieves' dimensions and that open thermo stabilized drying sieve exhibits better mechanical properties and exploitation characteristics then the sieves joining. [Projekat Ministarstva nauke Republike Srbije, br. ON174004: Micromechanics criteria of damage and fracture and br. TR 32036: Development of software for solving the coupled multi-physical problems

Tribological Behaviour of the Sucaslide Diamond-like Carbon Coating

Tribological behaviour of the Sucaslide diamond-like carbon coating applied to low-alloy steel was studied in this research. Experimental work included the determination of the chemical composition and the evaluation of the microstructure of both the base material and the Sucaslide coating. The methods used in the research were dilatometry and energy dispersive x-ray analysis, mechanical properties measurements, and wear resistance and scratch tests. From the results obtained in experiments, the authors concluded that the Sucaslide DLC coating has very good sliding and abrasion-resistant properties. With regard to these facts, it is possible to recommend the Sucaslide DLC coating for application to the low-alloy steel used in the bearing industry

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

Analiza kvalitete Al-Cu spoja ostvarenog zavarivanjem trenjem

This paper outlines the bases of the friction welding process, especially when it comes to friction welding of different materials. This was illustrated on an example of friction welding of aluminum and copper, which is often applied in electrical engineering. The analysis of influential parameters was conducted based on the data obtained by an experiment, since the data on this topic are very seldom in the available literature.Ovaj članak daje osnove procesa zavarivanja trenjem, naročito kada je u pitanju zavarivanje trenjem različitih materijala. To je ilustrirano na primjeru zavarivanja trenjem aluminija i bakra, koji se često primjenjuje u elektrotehnici. Analiza utjecajnih parametara provedena je na temelju podataka dobivenih eksperimentom jer su podaci o ovoj temi vrlo rijetko u dostupnoj literaturi