MODELING OF STRESS-DEFORMED STATE OF BENDED REINFORCED CONCRETE ELEMENTS IN ZONES OF CLEAN AND TRANSVERSE BEND

The article deals with the analysis of the stress-strain state (SSS) of a bent reinforced concrete element in zones of pure and transverse bending. It is assumed that a bent element in the process of loading (after the formation of normal and oblique cracks) is divided into blocks, united by uncracked concrete and reinforcement that has adhesion to concrete. SSS was formed using the results of experimental studies of special prototypes in the PC “Lira-SAPR”. A fi nite element model of a prototype has been developed in the form of a reinforced concrete rectangular beam loaded with two identical concentrated forces in the span. By the method of successive approximations, the process of formation and formation of a system of cracks is realized, with which the beam is divided into blocks during loading. The results of calculating the fi nite element model and their comparison with experimental data are presented.

Thermal fracture of functionally graded thermal barrier coatings with pre-existing edge cracks and multiple internal cracks imitating a curved interface

This work is devoted to the problem of thermal fracture of a functionally graded coating on a homogeneous substrate (FGC/H) with an emphasis on the analysis of a special system of cracks that simulates a curved interface. The FGC/H structure contains the pre-existing crack system in the FGC, both edge cracks (which are often seen in FGC/H structures) and internal cracks. The stress intensity factors are calculated. (Generally, both Mode I and Mode II are nonzero.) Then, using the appropriate fracture criterion for mixed-mode fracture conditions, the crack propagation direction (so-called fracture angles) and critical loads, when this propagation is initiated, are determined. The application of fracture criteria requires knowledge of the fracture toughness near the crack tips. Thus, it is assumed that the fracture toughness of an FGC, as well as other material properties, continuously varies through the thickness of the coating. For multiple cracks, it is also important to know the weakest crack that starts to propagate first, and the initial direction of this growth. Therefore, the main attention is paid to the evaluation of the fracture angles for the cracks for different parameters of the FGC/H structure. Both cases of a homogeneous semi-infinite medium with a system of cracks imitating a curved interface and FGC/H structures with identical crack systems are studied.

On the Application of the Method of Hypersingular Integral Equations to Solving Problems for an Elastic Plane with a Collinear System of Cracks

In the present paper, using the method of hypersingular integral equations, based on the formulas of the inversion of the corresponding singular integral equations, the exact quadrature solution of the classical problems of the mechanics of an elastic plane with a collinear system of cracks is constructed. The elastic plane is in a state of antiplane deformation or plane deformation; in case of antiplane deformation, crack edges are symmetrically loaded by tangential forces, while in case of plane deformation, they are again loaded symmetrically but by normal forces. Mixed boundary-value problems for an elastic half-plane equivalent to these problems are formulated. Under plane deformation, the mixed boundary-value problem for an elastic half-plane is discussed as well when the plane boundary is reinforced by two similar and symmetrically located semi-infinite stringers between which a system of an arbitrarily final number of stringers is situated. It is considered that the stringers are absolutely rigid for expansion and compression and absolutely flexible for bending. A particular case of two similar symmetrically located cracks is considered more in detail. In this case, the exact solution to the problem is also constructed by the method of Chebyshev orthogonal polynomials.

Evaluation of Cracking Patterns in Cement Composites—From Basics to Advances: A Review

The structure and the development degree of a cracking pattern has a key impact on the durability of cement composites. This literature review focuses on the four most important aspects related to the evaluation of the surface cracking patterns, i.e., the process of formation, propagation and evolution of cracks into a branched system of cracks from the point of view of the fracture mechanics; the detection techniques of the cracking patterns on the surface of cement composites, where the tools of computer image analysis are the most used; parameters which can quantify the development degree and morphology of the cracks system; and also the influence of a cracking pattern on the functional features of cement composites. The studies described so far indicate the necessity of continuous development of this research area, because the knowledge of key relationships between the cracking patterns and functional properties of a cement composite is necessary to estimate the degree of material degradation. Researchers agree that the works carried out in the field of evaluation of the cracking patterns, to a large extent, contributes to the development of non-destructive testing methods in the field of cement composites technology.

Amphibole and biotite of melanocratic rocks from the Ural granitic massifs: composition, relationship, petrogenetic consequences

Research subject. The article discusses the features of the relationship between biotite and amphibole on the example of magmatogene melanocratic rocks from a number of granitoid massifs of the Urals. These rocks form xenoliths and synplutonic intrusions of the calc-alkaline series of normal alkalinity: gornblenditam, gabbro, diorite, quartz diorite. They are composed of amphibole, acidic or middle plagioclase, in a subordinated quanitity they contain clinopyroxene, biotite, potassium feldspar, quartz.Materials and methods. The composition of the minerals of melanocratic rocks was determined on a JSM-6990LV electron microscope with an EDC-adapter of INCA Energy 450 X-Max 80 in the Geoanalytical Center of the IGG Ural Branch of the Russian Academy of Sciences.Results and conclusions. Wide variations in amphibole compositions and narrow biotite variations caused by exchange processes between the mineral and postmagmatic fluid are shown. The phenomenon of replacement of early magmatic amphibole with biotite is substantiated by the presence of a gap in the crystallization temperatures of minerals, indicating a lack of physicochemical equilibrium between them. Their structural relationships confirm the development of biotite as a result of the replacement of amphibole in accordance with the competent and incompetent phase boundaries. In the first case, the structural packets of biotite are embedded along the silicon-oxygen chains of amphibole, which is expressed in the parallelism of the (001) plane of biotite with the (100), (110) planes of amphibole. In the second case, the development of biotite occurs irregularly, inheriting the system of cracks in amphibole. The distribution of Mg/Fe between biotite and early magmatic amphibole was studied, showing that the magnesia value of biotite is higher than that of amphibole replaced by it. Inverse ratios of magnesia value occur between biotite and post-magmatic amphibole. The equality of the magnesia values of both minerals may reflect the conditions of subsolidus equilibration of the compositions. The problem of choosing amphibole compositions for calculating the PTparameters of the formation of massifs in the Earth crust is considered.

The Yarkon-Taninim Aquifer (Judea Group Israel): What Radiocarbon Can Tell

ABSTRACTRadiocarbon (14C) conclusively demonstrates that the very important Yarkon-Tanininm aquifer, named after the two springs where the drainage presumably occurs, is in actuality two distinct aquifers—Upper and Lower. The springs have higher 14C activities than the exploitation wells that surround them (all drilled into the Upper aquifer). The springs are situated at faults that allow the Lower aquifer water to rise due to its higher pieziometric head and drain along with the Upper aquifer. The Lower aquifer water flows rapidly along a path that includes a karstic system. The Upper aquifer flows more slowly, primarily through a system of cracks in the carbonate aquifer. The Upper aquifer groundwater in the Beer-Sheba extension flows northwards at approximately ~4–7 m/yr.