The features of steel surface hardening with high energy heating by high frequency currents and shower cooling

The paper examines the process of surface hardening of steel 45 with the help of high energy heating by high frequency currents with simultaneous shower water cooling. We theoretically justified and experimentally proved a possibility of liquid phase forming in the course of heating not on the surface, but in the depth of the surface layer

ASSESSMENT OF CRACKING RESISTANCE OF CELLULAR CONCRETE PRODUCTS UNDER MOISTURE AND CARBONISATION DEFORMATIONS WITH STRESS RELAXATION

Objectives. On the basis of the experimental, theoretical and field studies, an engineering calculation method was developed for assessing the cracking resistance of external enclosing constructions made of cellular concrete, with the maximum gradient development of moisture and carbonisation forced deformations along their thickness, taking into account the relaxation of the shrinkage stresses. In this regard, the aim of the work is to provide technological measures at the manufacturing stage in order to increase the operational cracking resistance of the construction's outer surface layers by reducing the moisture and carbonation shrinkage of cellular concrete by introducing a large or fine porous aggregate in calculated amounts.Methods. A number of analytical equations were applied to establish the dependence of the shrinkage of heavy concrete of conventional hardness on the amount of aggregate introduced and its elasticity modulus, water-cement ratio and cement consumption, as well as the concrete's moisture content.Results. Knowing the volumes of the structural aggregate and the cellular concrete mass, as well as their modulus of elasticity, the shrinkage reduction factor of the cellular concrete was calculated with the addition of a lightweight porous aggregate. Subsequently, the shrinkage deformations of concrete in the surface layer of the outer enclosing construction, maximising crack resistance due to moisture exchange and carbonation influences under operating conditions, were defined, taking into account the relaxation of tensile stresses due to creep of concrete.Conclusion. Theoretical calculations, based on the recommended method of assessing the cracking resistance of cellular concrete enclosing constructions under moisture exchange and carbonisation processes, taking into account the relaxation of shrinkage stresses, showed that in order to exclude the appearance of cracks in wall panels 280 mm thick made of 700 kg/m3 gas ash concrete with elasticity modulus of 2500 MPa, it is necessary to have 70-80% of keramzite or granulated slag, and 50-60% of stone crumb (granite or marble crushed stone) of the volume of cellular concrete in the surface layer of 30-50 mm

REGULATION OF SEISMIC LOAD ON BUILDINGS SEISMIC DEVICES

The issues of regulation of seismic loads on structures using kinematic supports of highstrength concrete on the impregnated coarse aggregate and seismic isolation bearings Belleville. The results of experimental studies related to the obtaining of a new coarse aggregate and construction of seismic isolation bearings. Addresses the issues of interaction forces in thehemispherical supports vibration process

A novel operando approach to analyze the structural evolution of metallic materials during friction with application of synchrotron radiation

In this study, we describe an experimental setup and a new approach for operando investigation of structural evolution of materials during wear and friction. The setup is particularly suited for testing various friction pairs, including those in which both rubbing bodies are made of metals. The developed device allows circumventing the problems related to significant scattering of X-rays produced by metals and makes it possible using “real samples” in synchrotron beamlines operating in reflection mode. To demonstrate the capabilities of the device and the proposed new approach, an iron-based massive sample was subjected to thousands of friction cycles using a cemented carbide pin. The material was probed with synchrotron X-ray radiation within a few milliseconds after leaving the friction zone. The results of the microstructural and structural analysis, as well as results obtained from diverse mathematical models, allowed us to evaluate several features, including gradual accumulation of defects, microstructural refinement, dislocation density changes, surface layer oxidation, as well as several other phenomena caused by the dry sliding friction process. Mainly, it was possible to conclude that the process of wear occurred due to the cooperative action of oxidation and plastic deformation, which began during the first cycle of frictional interaction and was manifested in increasing the dislocation density, whose type was changed gradually during testing. The number of defects quickly reached a threshold value and subsequently fluctuated around it due to periodically repeated processes of defect accumulation and stress relaxation resulting from material wear. It was also observed that friction led to the quick formation of a mechanically mixed layer, consisting of the sample material and a mixture of two types of iron oxide – hematite and magnetite. The delamination of this layer was probably the primary wear mechanism

Interaction between Fe66Cr10Nb5B19 metallic glass and aluminum during spark plasma sintering

In the area of metal matrix composites, novel reinforcing options are currently being evaluated. Particles of amorphous alloys present an interesting possibility to reinforce soft metals. In the present work, the interaction between Fe66Cr10Nb5B19 metallic glass and aluminum during spark plasma sintering (SPS) was studied for the first time. In order to trace the phase and microstructural changes upon sintering, mixtures containing 20 vol% and 50 vol% of metallic glass were subjected to SPS at 500–570 °C. After SPS at 500 °C, no reaction layer between the metallic glass particles and aluminum was observed. After SPS at 570 °C, a reaction layer containing Fe2Al5 and FeAl3 formed around the Fe-based cores. The Vickers hardness of composites obtained from mixtures containing 20 vol% Fe66Cr10Nb5B19 at 540 °C was 75 HV and increased to 280 HV after sintering at 570 °C due to the formation of thicker reaction layers at the interface. The hardness of the composite sintered from the mixture containing 20 vol% Fe66Cr10Nb5B19 at 570 °C was between the values predicted by Reuss and Voigt models. Comparison of results of SPS of the powder mixtures with those of SPS of a pre-compacted pellet and electric current-free annealing suggests that local heating at the interface caused by interfacial resistance may be an important factor influencing the reaction advancement at the interface and the formation of Al-containing intermetallic

Composites of copper and cast iron fabricated via the liquid: In the vicinity of the limits of strength in a non-deformed condition

In this study, the effect of copper on the structure and properties of cast iron is discussed. The experimental samples, with copper content from 0.09 wt% to 14.2 wt%, were synthesized in an induction furnace. The structure of the samples was characterized using light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The influence of copper on the volume fraction of graphite and pearlite, and its interlamellar spacing and the tendency of the composites to form a white iron structure are discussed. In particular, precipitation of s-copper was investigated. For a better understanding of the structural evolution, the isoplethal section of 3 wt% C in the Fe-Cu-C phase diagram was calculated. The hardness, tensile strength, friction coefficient and wear resistance of the composites were measured. The addition of copper leads to hardening and strengthening of the composites. However, at a high copper content, the strength of alloys decreases due to the formation of a brittle white iron structure. Copper has a positive effect on the friction coefficient and reduces wear resistance by promoting the formation of ledeburite.111sciescopu

CHOICE THEORY OF CREEP DEFORMATION FOR EVALUATION OF LONG FINE-GRAINED AUTOCLAVED AERATED CONCRETE IN VIEW OF FACTORS CARBONIZATION

Experimental data on the effect of the age of autoclaved aerated concrete with and without carbonation factor to change its physical and mechanical characteristics, as well as by the amount of creep deformation and degree of reversibility. It was found that the solution of applied problems creep theory for structures of autoclaved aerated concrete, in accordance with their carbonation from the effects of atmospheric carbon dioxide, it is necessary to use the theory of elastic-creeping body on the basis of function creep measures in the form proposed by prof. S.V. Alexandrovsky

CRACK RESISTANCE AND DURABILITY OF PRESTRESSED WALL PANELS CONSTRUCTED FROM CELLULAR CONCRETE

Objectives The aim of the studyis to develop ways to increase the crack resistance and durability of prestressed wall panels made of cellular concrete.Method A complex study was carried out at the stage of factory manufacturing of two-module, aerated concrete wall panels with prestressed rods of class A-III reinforcing steel, 10 mm in diameter, located in the middle of the panel in the longitudinal and transverse directions.Results It was found that the total stress losses in straining rods prior to casting of the aerated concrete mix, connected with stress relaxation in the reinforce and with deformations of the headings of the straining rods in the gripping jaws, the steel mould deformations, as well as the losses after the panel exit from the autoclave during the transfer of force to the concrete, are 15-20% of the initial level. At the same time, depending on the dimensions of the straining rods, the length of the strain transfer zone was in the range of 150 to 250 mm. A study of the effect of pre-compression on the closure of possible technological cracks in concrete test panels showed that, due to biaxial compression of concrete, new cracks do not appear when they work on bending and stretching (during the decking and transportation). Moreover, initial cracks that sometimes can appear during the autoclave processing become closed.Conclusion Comparative tests of prestressed and typical panels for short-term load in accordance with GOST 8829-94 requirements indicate a significant increase in their rigidity and crack resistance, as well as the shear strength of their bridge part. The design of straining reinforcing rods with the end transverse anchor in the form of a horseshoe, together with attached flat welded frameworks made of Vr-I wire with a diameter of 5 mm, which are installed along the contour of the window openings of the test panels, ensure its reliable adhesion to cellular concrete and effective anchoring in the panel's body until the end of its useful life. Biaxial prestressed reinforcement by single rods in combination with conventional frame reinforcement opens up possibilities for the production of external wall panels from non-autoclaved cellular concrete with ordinary heat treatment, instead of ceramsite concrete panels