Comparative identificational characteristic of artificial leather with embossed surface damages caused by airgun pistol pellets with different head end forms

Background: Authors of this article have made a comparative identificational description of artificial leather damage caused by air gun pistol pellets with different head end forms. Aim: This study aimed to provide a comparative identification characteristic of injuries caused by shots from an air pistol MP-53 M on artificial leather with a raised surface and a textile net glued to the wrong side at different angles and from different distances by bullets with different head end shapes (hemispherical, flat round, and conical). Used: Air pistol MP-53M, bullets with different head end shape, a fragment of black artificial leather with an embossed surface, and a textile mesh glued to the wrong side. Shots were fired at close range, 50 and 100 cm at angles of 30, 45, 60, and 90. The prevailing forms of damage (defects) of artificial skin, characteristic of bullets with a hemispherical, conical, and flat rounded head end, dependence of the form of damage (defect) on the distance of the shot, and the angle of entry of the bullet into the material. Conclusion: A comparative study showed that the form of damage to the material depends on the head end shape of bullets. Moreover, intragroup differences were found in the damage due to the distance of the shot and angle of entry of the bullet into the material in groups of bullets with the same head end shape.

Capacity of roller mill for cement grinding

Engineering for the cement industry is part of the heavy industry. The cement industry is the main supplier of raw materials for the production of concrete and reinforced concrete. For grinding cement, two types of mills are used - ball and roller. Recent decades have proven the great effectiveness of a vertical roller mill for grinding raw materials. Its effectiveness, combined with the implementation of drying, grinding and separation in one unit, gives it an undeniable advantage over a ball mill. This explains the significant increase in the share of roller mills in the cement mill market. The grinding process in such mills occurs due to abrasion, respectively, in the process of work wear of the rubbing parts of the mill occurs. The work evaluated the performance of a mill with smooth disk rolls. During the study, the cause of the destruction of the sectors of the mill produced by FLSmidth, operating in the Russian Federation, was identified. The study revealed the causes of the destruction of the details of the roller mill: with the simultaneous impact of the workload and the displacement of the sectors resulting from intensive wear, the total equivalent stresses exceed the value of the endurance limit under cyclic loading. Therefore, the accumulation of fatigue damage to the material, the formation and growth of cracks, which adversely affects the performance of the mill. A number of measures have been proposed to increase the operability of mills of this design.

ASSESSMENT OF THE IN HOMOGENEITY OF THE PHYSICO-MECHANICAL PROPERTIES OF PARTS OF AEROSPACE ENGINEERING OBTAINED BY SELECTIVE LASER MELTING

The article considers the problem of assessing the damage and heterogeneity of a material obtained by selective laser melting. To study these characteristics, it is planned to adapt a new method of ultra-jet diagnostics, developed at the Bauman Moscow State Technical University. Its feature is the ability to assess the damage to the material and its technological memory, i.e. conditions, modes and factors that influenced the formation of the structure and operational characteristics in the process of manufacturing parts by selective laser melting. The article compares traditional control methods and the method of ultra-jet diagnostic, which, as studies have shown, will expand the arsenal of applied monitoring and diagnostics, which is extremely important for critical parts of aerospace technology. The experiments were conducted on special samples and witness samples obtained from materials widely used in the manufacture of spacecraft. The most important result of the research was the conclusion about the relationship between the variability of the parameters of the surface micro relief due to the process of hydroerosion under the action of a high-speed jet of water and structurally inhomogeneous, physically anisotropic material obtained by the selective laser melting technology.

Magnetic Metal Memory in the Assessment of the Technical Condition of Crane Girders for the Needs of Safety

With the passage of time of exploitation of means of technological transport, their degradation takes place and the threat to operational safety increases. The source of development of fatigue damages of gantry crane girders are areas of stress concentration caused by loads. The subject of the publication is to determine the possibility of diagnosing potential damage sites of the overhead travelling crane (girders) by magnetic metal memory (MPM). As a result of the test with the use of the TSC-7M-16 ferrite magnetometer, stress concentration areas were determined in which processes leading to the reduction of material strength or damage to the material structure may take place. Residual tangential magnetic field distributions and normal components of their gradients were determined. A magnetogram database for the needs of girder diagnostics was created.

STRUCTURAL FEATURES OF DAMAGES ACCUMULATION IN CONDITIONS OF COMBINED CYCLIC LOADING

A significant part of the elements of machines and structures along with stationary fatigue is subjected to combined impacts of low-cycle and multi-cycle fatigue loading in operation. The physical nature of their fracture in these conditions depends on the ratio of the mode parameters and entails the necessity of advanced research. The predominance of this or that process determines the nature of the damage accumulation which leads to the destruction. Under such conditions, i.e., preliminary cyclic elastoplastic deformation followed by subsequent fatigue loading, the material subjected to preliminary loading at the first stage can be considered the "new material" with the new properties acquired upon cyclic elastoplastic loading which then undergoes further fatigue loading at the second stage. Hence, at the second stage, the new properties of the material are determined by the level of structural changes and damages earlier accumulated in the material. In this case, the damage to the material is considered on the basis of the well-known statement about the staging character of plastic flow, two main processes, i.e., shear, caused by the interaction of dislocations, and destructuring, attributed to violation of the continuity or integrity of the metal. Experimental studies of changes in the durability of cyclically hardened and cyclically softened steel specimens at different levels of preliminary elastoplastic deformation with varying number of cycles and amplitudes of preliminary elastoplastic strain showed the occurrence of an additional damage to the material when combination of loading modes leads to change in the fatigue durability at the subsequent stage of the basic multi-cycle loading. It is shown that correlation between changes in the fatigue durability and structural state of the material, caused by accumulated damage upon preliminary overloads, and, moreover, those changes can be characterized by the ratio of plastic and destructive strains as a Q-factor of the material.

Sandwich Panel Manufacturing Method In Form of Test Specimens For Ship Construction

Sandwich panel as a composite materials require special method of manufacture, to produce the best of physical condition. This study give the manufacturing process of sandwich panel for the purpose of testing the strength of material. Sandwich panel created with molding method for simplify the process of work and can be repeated if a failure occurs. Saveral failures occur in creating process until preparation specimen process that are influenced by saveral things, such as damage caused by the temperature of the sun, difference in viscosity between the layers of the conditions faceplate (smooth and rough), and the method of cutting the sandwich panel which requires cutting methods at low temperatures and does not produce the high vibration to avoid damage to the material before material strength test were performed.

Influence of acid mediums on degradation and adherence of streptococcus mutans to a indirect dimethacrylate-based polymeric matrix

Objectives: Dental biofilm can be formed in greater quantities and on rough surfaces. Biofilm maturation has clinical implications because the presence of pathogenic microorganisms. This study verified surface degradation and bacterial adherence to Resilab Master® after immersion in acid solutions. Material and Methods: The specimens (diameter=10 mm ⁄ thickness = 2 mm) were stored in deionized water for 7 days, and divided into immersion groups (n=10): Coca Cola, G1; H2OH lemon refrigerant, G2; phosphoric acid, G3; and citric acid, G4; immersed for 7 days. Mass (g) was analyzed with a digital scale, and Ra roughness (μm) by readouts on specimen surfaces using a roughness meter. Three specimens of the groups were analyzed by SEM(deionized water – control). Five specimens of the groups were introduced into test tubes with Streptococcus mutansand glucose. Results: They were incubated at 37ºC/24h. Results: Increase in roughness (G1.T0=0.2209, G1.TF=0.2262; G2.T0=0.1705, G2.TF=0.1756; G3.T0=0.1848, G3.TF=0.2276; G4.T0=0.1694, G4.TF=0.1905) showing no significant differences (signal test, p>0.05). Loss of mass, being significant (Student’s-t test p>0.05) for Groups G1 (G1.T0=0.3560, G1.TF=0.3535) and G3 (G3.T0=0.3594, G3.TF=0.3532). Adherence of Streptococcus mutansforming colonies was observed on the surface degraded (UFC/mg): 3.83 x 104, G1; 2.83 x 104, G2; 4.67 x 104, G3; 3.67 x 105, G4 showing no significant differences among the groups (Kruskal-Wallis test, p>0.05). Conclusions: The acid solutions caused damage to the material surface with loss of matter, intensifying bacterial colonization. Solutions with the same pH and type of acid, but different compositions, showed no significant differences on indirect polymeric matrix degradation.

Structural Performance of Pultruded Composites under Elevated Temperatures

One of the major limitations for wider use of pultruded fiber reinforced polymeric (PFRP) composites in the civil engineering sector has been their behavior under elevated temperature and ultimately fire. This limitation arises not only due to the reduction in mechanical properties at high temperatures, including increased propensity to creep, but also due to limitations on the continuous working temperature causing permanent damage to the material as a result of thermal and oxidative degradation. Significant gains in property retention at high temperatures with crystalline polymers have been derived from the incorporation of fibrous reinforcement, but the development of new polymer matrices is the key for further elevation of the useful temperature range. This paper presents summary results of a research project focused on characterizing the viscoelastic behavior of commercially-produced, off-the-shelf unidirectional PFRP materials subjected to elevated temperature environments.