A normalized method for determining the influence on the fixed joints tightness using the technology of the sealing surface job

On the basis of metallographic analysis and test results of samples of welded junctions of aluminum alloys AMg6 and D16T, made by friction stir welding, for static stretching, it is shown that destruction occurs in the zone of thermo-mechanical action for the AMg6 alloy and in the zone of thermal influence for the D16T alloy. At the same time, the dependence of the temporary resistance value of the welded junction on the state of the seam weld face has not been revealed. Tests for low-cycle fatigue have shown that the endurance limit is clearly dependent on the amount of seam weld face roughness. The value of the roughness of the seam weld face for the studied alloys has been determined, in which the nature of the fracture during the low-cycle fatigue test changes from multi-stage to single-stage.

Influence of titanium and zirconium on structure and heat-resistance of low-carbon iron-aluminium alloys

The paper considers the effect of introducing ferroalloys containing titanium and zirconium on the structure and heat-resistance of low-carbon ferroalloys. Theoretically and experimentally, it has been proven that addition of 1.0 mass. % of titanium and 0.1 mass. % of zirconium to a low-carbon iron-aluminum melt containing 12 – 14 mass. % of aluminum, grinds its structure increasing temporary resistance and heat-melting. Titanium and zirconium are strong carbide-forming elements. When introduced into a low-carbon iron-aluminium alloy, they form a large number of crystallization centers, thus affecting its microstructure, allowing to get shredded and more equal grain compared to an alloy without additive. This in turn increases the strength limit of processed alloy. In addition, the use of titanium as a modifying additive in a low-carbon ferroalloy allows increasing its heatresistance, which exceeds several times the heat-resistance of famous chrome-nickel steel of 20Kh23N18 grade. As a result, a new technology for obtaining titanium and zirconium was developed based on research of the effect of their modifying additives on the structure and heat-resistance of low-carbon iron-aluminum alloys.

Investigation of plastic properties of AISI 316l steel by method of registration of macrolocalization fields

Selective laser melting is one of the modern methods of manufacturing parts in the production of machine-building equipment, a special place is occupied by complex technological processes used in the manufacture of high-load units of pneumatic-hydraulic system from heat-resistant alloys. The research was carried out on samples made of powder material - stainless steel AISI 316L martensite class. Metallographic studies showed that the density of the sample is 99.83%, the structure of the samples is a martensitic structure of equilibrium constructed tracks. Tests to determine the mechanical properties were performed in accordance with ISO 6892 on an INSTRON test machine. From the tensile diagram it was found that the yield strength was 376.56 MPa, the maximum point of temporary resistance of the sample - 615, 40 MPa 319 seconds after the start of the test. The control of the surface roughness was performed using a BioBase device. The working area of the tensile sample consisted of two areas: a roughness area of 5 μm, which accounted for 80% of the working part of the sample (zones A and Б) and 20% of the working part of the sample (zone Б), the roughness was 17 μm. According to the results of microstructure studies and studies by the method of registration of macrolocalization fields of the working zone of the samples, it was found that the destruction began from the surface of the samples from microconcentrators due to different roughness. It is established that the surface and subsurface layer with increased roughness in comparison with the main body has a smaller elongation by 10.84%. From microstructural studies of the working zone in the area of the gap, it was found that the destruction began from the surface of the samples between zones A and Б. During the research in zone A and Б, one of the concentrators of the gap was detected. As a result of the study, it was found that the destruction began with the surface of the samples and the place of change of its roughness. The mechanism of deformation of the sample from AISI 316L steel is shown, the scheme of extraction of tail sections of tracks and crack propagation in the conditions of tensile testing of the sample is constructed.

Research of non-metal composite basalt reinforcement of periodic profile and prospects of its use

Introduction. The results of research of physical and mechanical characteristics of non-metallic composite basalt reinforcement obtained by researchers, in particular, the shear strength of basalt reinforcement, coupling of basalt reinforcement to concrete, leaching of basalt fiber, durability of structures reinforced with non-metallic composite basalt reinforcement.Problem Statement. In the road industry, the main part of the costs for repair and restoration of reinforced concrete structures of bridges and overpasses is associated with corrosion of metal reinforcement. The use of non-metallic armature is a promising fundamental solution to this problem. Technical characteristics allow to apply basalt armature for road construction, at strengthening of bridges, for enclosing designs, in the designs which are exposed to aggressive environments.The effect of the use of basalt reinforcement is obtained, in particular, from reducing the cost of construction through the use of reinforcement of smaller diameter (hereinafter Ø) compared to metal while providing the necessary strength characteristics, reducing the weight of structures with such reinforcement. Also, due to the absence of certain types of corrosion of the armature during operation, the durability of the structure increases, reduce or eliminate certain types of repair work.However, the use of non-metallic composite basalt reinforcement of periodic profile, made of basalt fibers, designed for reinforcement of concrete structures of transport structures, is constrained by the lack of a sufficient number of research results of the characteristics of such reinforcement. On the basis of such researches it will be necessary, further, to make changes in norms on designing, standards on test methods, etc.Purpose. Investigate the armature of one of the main manufacturers, which were manufactured at the time of the study in Ukraine. Determine the geometric dimensions, mass, color, temporary resistance, elongation after rupture of the basalt reinforcement of the periodic profile with a diameter of 6 mm, 10 mm. To process the results of tests of physical and mechanical characteristics of non-metallic composite basalt reinforcement of periodic profile with a diameter of 6 mm, 10 mm, analysis of test results. Develop, based on the conclusions of the analysis of test results, proposals for the requirements for non-metallic composite basalt reinforcement for public transport structures.Materials and methods. Experimental studies of physical and mechanical characteristics of basalt reinforcement of periodic profile type A, nominal diameter 6 mm, 10 mm, manufactured according to TU U V.2.7-25.2-34323267-001, in particular, the curvature of the bar, surface quality, color of reinforcement, inner diameter reinforcement, temporary resistance, elongation after breaking.Results. As a result of researches it is established that curvature of a bar, quality of a surface, color of armature correspond to TU U V.2.7-25.2-34323267-001. The inner diameter of the valve, for individualbars, exceeds the permissible deviations within 0.3 mm in accordance with TU U V.2.7-25.2-34323267-001, DSTU B V.2.7-312:2016. However, as a result of the analysis of the obtained mechanical characteristics it was found that such deviations do not significantly affect the values of the mechanical characteristics of the tested samples (they are not less than necessary).However, in the future, when using basalt reinforcement, it is necessary to check such reinforcement for compliance with the requirements of DSTU B B.2.7-312:2016 and compliance must be ensured.Determined for basalt reinforcement temporary resistance, elongation after breaking, respectively: for Ø 6 mm ― 1 105 MPa and 2,13 %; for Ø 10 mm ― 1 068 MPa and 2,10 %.Conclusions1. Analysis of research on non-metallic composite reinforcement has shown that in recent years, scientists have paid considerable attention to reinforcement, as they see the prospect of its widespread use in the future. Studies of basalt reinforcement have shown that it has high strength, low density, has sufficient resistance to alkaline environment.2. As a result of researches of armature with a diameter of 6 mm and 10 mm it is established that curvature of a bar, quality of a surface, color of armature correspond to TU U V.2.7-25.2-34323267-001, DSTU B V.2.7-312:2016. The inner diameter of the valve, for individual bars, exceeds the permissible deviations within 0.3 mm (according to TU U V.2.7-25.2-34323267-001 and DSTU B B.2.7-312:2016). However, as a result of the analysis of the obtained mechanical characteristics it was found that such deviations do not significantly affect the values of the mechanical characteristics of the tested samples (they are not less than necessary). However, in the future, when using basalt reinforcement, it is necessary to check such reinforcement for compliance with the requirements of DSTU B V.2.7-312:2016 and compliance must be ensured.3. Defined for basalt reinforcement temporary resistance, elongation after breaking, respectively: for Ø 6 mm ― 1105 MPa and 2,13 %; for Ø 10 mm ― 1068 MPa and 2,10 %.4. The strain corresponding to the maximum static tensile load (Pmax) before the failure of basalt reinforcement samples was set when testing the reinforcement sample Ø 6 mm and is near 1153 MPa, which corresponds to the tensile strength of high-strength steel reinforcement class A-1000. The relative elongation of the basalt reinforcement δ is in the range from 2,0 % to 2,3 %, and is proportional to the δof the reinforcement A-1000, which is equal to 2,0 %.5. The results of tests for static loads show high performance characteristics of basalt reinforcement Ø 6 mm and Ø 10 mm, which is a prerequisite for the use of the tested reinforcement in the construction of transport facilities.Keywords:reinforcement, basalt, basaltoplastic, test, diameter, research, bridge, periodic profile, size, series, transport structure, characteristic.

Engineering assessment of minimum fatigue life for given probability of its non-exceedance

Object and purpose of research. This paper discusses structural materials under cyclic load. The purpose is to determine the minimum fatigue life corresponding to a certain non-exceedance probability of this value. Materials and methods. The study was performed on three structural materials: steel 15ХМ, steel 08Kh18N10Т and titanium alloy PТ-7М. Initial estimate of fatigue life distribution parameters relied on the data about guaranteed maximum and minimum values of temporary resistance and relative cross-section tapering. The assessment was performed as per a common curve “conditionally elastic stress amplitude versus number of cycles to failure” taking into account the mechanical prop-erties of given material. The values of minimum fatigue life were obtained as per two different methods: statistical simulation of the random values following the Weibull distribution law and the analytical expression for probability density of the lows for given distribution function of random value and fixed scope of sampling. Main results. The lows yielded by statistical simulation are more conservative than those yielded by the analytical formula. The margin in terms of the number of cycles to failure stipulated as 10 in several regulatory documents seems to be somewhat unsubstantiated. This margin is too great in the low-cycle domain and too small in the high-cycle one. Conclusion. This paper postulates the existence of guaranteed maximum and minimum values for mechanical properties of structural materials, namely temporary resistance and relative cross-section tapering. These values were applied to well-known analytical curves of fatigue, which finally yielded possible variation ranges for fatigue life at various amplitudes of conditionally elastic reduced stresses, assuming the existence of a certain shift in the sensitivity limit of fatigue life distribution. These data were further used to establish standard deviations and mathematical expectations for the number of cycles to failure.

Features of structure and properties formation in welded joints made of A500C and B500C strength classes reinforcing steels

In the manufacture of welded reinforcing mesh, rolled products of various strength classes are used. High requirements for mechanical properties and structural condition are imposed on welded joints. Connections must provide a set of operational properties. This article presents the results of studies of the structure and mechanical properties of welded joints of reinforced rolled products of strength classes A500C and B500C, performed by spot welding. It is established that the weld (core) of A500C strength class steel is characterized by the presence of a layer of cast metal (hardness 180–190 HV) with slag inclusions. In the heat-affected zone, widmanstett ferrite and bainite — like structures with a hardness of 251–268 HV are observed. The temporary breaking resistance of A500C steel joints is 322–350 MPa. It is shown that the welded joint of steel of strength class B500C does not have a clear division into structural zones. Similar bainite structures in the form of batch formations are observed in the seam and the heat-affected zone. The hardness of the metal of the welded joint is in the range from 205 to 241 HV, and the level of temporary resistance is 510–525 MPa. It is established that the probable cause of premature failure of welded joints of A500C steel is the presence of large slag formations in the metal seam (core). This may be due to insufficient cleaning and preparation of the weld site. Particles of scale and other contaminants fall into the molten metal of the core and "freeze" in it, forming slag inclusions. Cavities filled with slag reduce the cross-section of the seam and as a result significantly weaken it. In addition, slag inclusions are additional stress concentrators and act as a source of destruction when an external load is applied. For the manufacturer of reinforcing nets, it is proposed, as a technological recommendation, to use additional tools for cleaning the welding site in the form of metal brushes or abrasive tools with additional surface degreasing.

The study of the microstructure and mechanical properties of low carbon steel, microalloying by boron

The paper presents the results of the study of non-metallic inclusions, the structure and mechanical properties of low carbon steel, microalloying by boron. The study of the amount and composition of nonmetallic inclusions showed that with the introduction of boron the volume fraction of oxide and oxysulfide inclusions increases and the volume fraction of sulfide inclusions significantly decreases. At the same time, the alloying of steel with boron increases to 99.7% the proportion of inclusions with a size of no more than 5 microns against 80.6% in the metal without boron. In the metal with boron, nonmetallic inclusions larger than 10 μm are absent, while in the metal without boron their share is 13.6%. Studies have shown that in a metal containing 0.011% boron, independent boron-containing inclusions were not detected. Boron was not detected in the composition of the studied nonmetallic inclusions. In all samples, steel nonmetallic inclusions are represented mainly by oxide, oxysulfide and sulfide inclusions. In the boron-free steel, a small amount of perlite is present along with the ferritic phase. Steel microalloying by boron is accompanied by the formation of a dispersed ferrite-bainite structure, which consists of fine-grained ferrite with bainite sites with a tendency to form bainite strips along the rolling direction. The microhardness of ferrite and perlite in steel without boron does not exceed an average of 180 and 214 HV10, respectively. It is noted that the presence of boron in steel in an amount of 0.011% increases the microhardness of ferrite to 260 HV10 and bainite to 335 HV10. The mechanical properties of hot-rolled steel with a thickness of 10 mm from boron-containing low-alloyed steel, due to the predominant formation of small rounded inclusions with a size of no more than 5 microns and the formation of a fine ferrite-bainite structure, are characterized by enhanced strength properties with preservation of plastic characteristics. The absolute values of the yield strength and temporary resistance of steel with boron reach 575 and 650 MPa, respectively. With such strength properties of metal, high plastic characteristics are preserved. Rolled steel without boron is characterized by reduced to 540 and 610 MPa tensile strength and temporary resistance, respectively.

Structure and properties of 17G1S-U low-carbon pipe steel microalloyed by boron

The results of analysis of the influence of boron microalloying on structure and properties of 17G1S-U pipe steel are given in the paper. Studies of metal structure were performed by electron microscopy and local X-ray spectral analysis. It has been established that metal containing 0.006 % of boron is characterized by an increased volume concentration to 0.029 % of oxide (OS) and oxysulfide (OSB) inclusions, whose content in metal without boron reaches 0.006 %. Separate sulphide inclusions (CB), whose concentration does not exceed 0.004 % against 0.029 % in a metal without boron, containing 0.01 % S is practically absent in the metal with boron containing 0.003 % S. The microalloying of pipe steel by boron has ensured the preferential formation of small nonmetallic inclusions, evenly distributed in the volume of metal. The proportion of nonmetallic inclusions with size less than 2 (rm is 76.1 %, whereas in steel without boron it is only 58.5 %. In this case, large nonmetallic inclusions of more than 10 rm are practically absent in the sample with boron. Their share does not exceed 0.6 %, which is 22 times less than their amount in the sample without boron. The structure of the sample without boron consists mainly of ferrite and a small amount of perlite, and the sample with boron is represented by a dispersed ferritic-bainitic structure. Increasing the microhardness of both ferrite and pearlite 80 and 100 HV10, respectively, is observed by adding boron to steel. The mechanical properties of 10 mm hot rolled metal from boron-containing 17G1S-U pipe steel are characterized by increased strength properties with preservation of plastic characteristics, due to the formation of predominantly small nonmetallic inclusions and a finely dispersed ferritic-bainitic structure. The absolute values of the yield stress and the time resistance of pipe steel containing in mass %: 0.006 B and 0.003 S are achieved without heat treatment at 585 and 685 MPa, respectively, and meet the X80 strength class, while retaining sufficiently high plastic characteristics. The pipe steel without boron containing 0.01 % of S belongs to the X70 strength class and is characterized by tensile strength lowered to 540 and 610 MPa and a temporary resistance, respectively.

Combinations of Respiratory Chain Inhibitors Have Enhanced Bactericidal Activity against Mycobacterium tuberculosis

ABSTRACT As an obligate aerobe, Mycobacterium tuberculosis uses its electron transport chain (ETC) to produce energy via oxidative phosphorylation. This pathway has recently garnered a lot of attention and is a target for several new antimycobacterials. We tested the respiratory adaptation of M. tuberculosis to phenoxyalkylbenzimidazoles (PABs), compounds proposed to target QcrB, a component of the cytochrome bc 1 complex. We show that M. tuberculosis is able to reroute its ETC to provide temporary resistance to PABs. However, combination treatment of PAB with agents targeting other components of the electron transport chain overcomes this respiratory flexibility. PAB in combination with clofazimine resulted in synergistic killing of M. tuberculosis under both replicating and nonreplicating conditions. PABs in combination with bedaquiline demonstrated antagonism at early time points, particularly under nonreplicating conditions. However, this antagonistic effect disappeared within 3 weeks, when PAB-BDQ combinations became highly bactericidal; in some cases, they were better than either drug alone. This study highlights the potential for combination treatment targeting the ETC and supports the development of PABs as part of a novel drug regimen against M. tuberculosis.

ASSESSMENT OF RANGES OF POSSIBLE CHANGE OF TEMPORARY RESISTANCE OF CAST IRON WITH LAMELLAR AND FLAKED GRAPHITE ON THEIR HARDNESS

The analysis of ranges of possible change of temporary resistance of sB of castings from ductile and gray cast iron is carried out. The analytical description of ranges of change of sВ depending on casting BH hardness is developed. It is shown that the range of change of sВ of pig-iron castings, wider in comparison with steel, with the measured hardness of BH is caused variations of forms and the amount of graphite inclusions at the considered classes of cast iron and influence of thickness of a wall of casting from gray cast iron on dependence of sВ (HB). The result is intended for determination of the guaranteed casting size sВ without her destruction, when there is no information on sВ of check test pieces.