A method of fatigue testing of thin-sheet materials in plane bending at high loading frequencies

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A. G. Trapezon UDC 669.15:539.43 Within the framework of the proposed scheme of an accelerated evaluation of strength of base material-coating compositions under cyclic loading, we show the necessity of its comprehensive realization by experimental and theoretical methods. The use of a high-frequency method for this purpose is substantiated by the example of the proposed experimental procedure. On the basis of the relationships for calculating residual stresses obtained in this work, a calculation model for predicting cyclic strength has been developed. We show its applicability for a preliminary evaluation of the durability of the base material-coating systems and for refinement of the hardening coating technology.Introduction. Methods of depositing hardening coatings are finding an increasing use for improving the load-carrying capacity of structural elements. The experience showed that the fatigue strength of the base material-coating composition is the most important quality criterion for hardening coatings. Therefore, accelerated evaluation of this characteristic is considered to be an immediate and decisive task, particularly at the stage of developing and refining the processes of formation and deposition of coatings. A special feature of the base material-coating compositions is the presence of residual stresses (σ res ) in the coating and in the upper layer of the base material (base), which may play an important role in hardening (or softening) of the load-bearing structural elements. Consideration of σ res when evaluating cyclic strength, just as strength in general, is therefore necessary as one of the prerequisites for ensuring the required level of the service properties of coated structural elements. The coating thickness is an important factor; its magnitude influences both the σ res value and the strength characteristics, which depend on the structural and mechanical parameters of the coating. The latter are directly related to the specific features of the coating technology: the process duration, temperature, chemical composition, etc. It is apparent that when developing a base-coating system with the aim to optimize it by considering all the problem factors, an experimental method will be the most reliable for checking the obtained results. Thus, when determining the fatigue strength of materials with thin-film coatings on specimens subjected to flexural vibrations, with some initial conditions being fulfilled [1], consideration of σ res , specific features of the technological process, surface and structural effects takes place automatically and the fatigue strength is presented in the form of various values of endurance limits (σ −1 ). Experimental determination of σ −1 requires much time and money. For this reason, along with the problem of accelerating this process, an alternative task is to construct appropriate calculation models.It is evident that the calculation methods do not allow one to consider fully the great number of factors that influence the σ −1 value. Thus, for instance, ...

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confidence: 79%

“…where k is the vibration mode factor determined by the method described in [2], E is the Young's modulus of the base material, and H is the specimen thickness. Loading scheme for a specimen tested in fatigue: (1) vibrator; (2) specimen with a coating;…”

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confidence: 99%

To the method of accelerated evaluation of fatigue of metals with hardening coatings

Trapezon

2009

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“…Usage of the most easily manufactured rectangular prismatic specimens of constant cross section in combination with high loading frequency ensured accelerated and costeffective testing. The choice of the required dimensions of resonant specimens, calculation of fracture stresses and fatigue testing practice using this procedure are described elsewhere [7,8].…”

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confidence: 99%

Effect of the deposition and thickness parameters of titanium nitride (TiN) coatings on the fatigue strength

Trapezon

Lyashenko

2010

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669.15:539.43 The effect of vacuum-plasma coatings of titanium nitride (TiN) on the fatigue strength of titanium VT1-0 is investigated in terms of the coating deposition and thickness parameters. The analysis of the obtained results is performed with the goal of improving the required fatigue strength of the base material-coating composition. It is shown that in all the investigated cases, TiN coatings enhance the fatigue strength. The optimum range of coating thicknesses is established, in which the change in the deposition conditions influences slightly the fatigue limit. A satisfactory agreement is noted between the experimental and calculated values of fatigue limits obtained using the calculation model earlier proposed by the authors. The principal possibility of essential increasing the fatigue strength has been discussed and confirmed in the case of formation of ultra-thin coatings under well-defined conditions of their deposition.Introduction. Surface hardening of engineering components through the use of vacuum plasma coatings has a number of economic, ecological and manufacturing advantages. These coatings obtained by the physical vapor deposition (PVD) method combined with the ion bombardment-assisted deposition (IBAD) during the condensation of the metal plasma are applied to components using an industrially produced "Bulat"-type deposition system [1]. When producing vacuum plasma coatings with the use of this type of equipment, it is possible to easily vary the parameters of the manufacturing process, such as medium pressure, arc current intensity, gas (N, O 2 , Ar, etc.) supply time, composition of the gas atmosphere, deposition rate, and temperature, which offers a real possibility of optimizing the process for producing coatings with different properties, in particular, the strength properties.In this paper, the influence of vacuum plasma coatings of titanium nitride (TiN) on the fatigue resistance of titanium VT1-0 is investigated in terms of the deposition and coating thickness parameters. The analysis of the results obtained is performed based on the statement of the problem and objectives of the investigation.Problem Statement. Real processes accompanying the formation of coatings are of a complex nature. Depending on the energy-based parameters of the coating deposition process, these may influence the change in the chemical-structural composition and its related physico-mechanical characteristics. Thus, aside from the titanium δ-nitride TiN, coatings of TiN can contain a certain amount of α-Ti and titanium ε-nitride (Ti 2 N) to form solid

“…Diagram of π 1 vs. H 1 plotted by the results of investigation for the bending case: T =°20 C {(1) AMg6[17,28]; (2) D20[17]; (3) VT8[20,24]; (4) MLT1[22]; (5) 20Kh15N3MA[21]; (6) OT4-1[11]; (7) AMg6-BM[11]; (8) VD17[19]; (9) steel 45[10,12,14,15,23,26]; (10) 40KhNMA[12]; (11) steel 35[25]; (12) steel 40Kh[14,16,26];(13) high-strength cast iron[10,23]; (14) AV[23]; (15) 34KhN1M[27]; (16) 12Kh1MF[13]; (17) 15Kh1M1F[13];(18) 1Kh18N12T[13];(19) steel 50[14]; (20) steel 40[14];(21)1Kh17N2Sh [16]; (22) ÉI612 [16]; (23) ÉI437B [16]; (24) ÉI726 [18]; (25) Kh18N10T [28]}; T =°300 C {(26) 12Kh1MF; (27) 1Kh18N12T; (28) 15Kh1M1F; (29) VT8 [13, 24]}; T =°400 C {(30) VT8; (31) VT3-1 [24]}; T =°450 C {(32) VT8 [24]}; T =°550 C {(33) ZhS6-K; (34) ÉI893; (35) ÉI787 [30]}; T =°600 C {(36) 12Kh1MF; (37) 1Kh18N12T; (38) 15Kh1M1F; (39) ZhS6-K; (40) ÉI612 [13, 16, 29]}; T =°650 C {(41) ÉI726; (42) ZhS6-K; (43) ÉI893; (44) ÉI787 [18, 30]}; T =°700 C {(45) ÉI473B [16]}; T =°800 C {(46) ZhS6-K [29]}; T =°900 C {(47) ZhS6-K [29]}; T =°950 C {(48) ZhS6-K [29]}; T =°1000 C {(49) ZhS6-K [29]}. A, B, C, D -data groups…”

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confidence: 99%

Endurance assessment for structural elements at engineering stage

Fedorenko¹,

Luk'yanov²

2007

The paper demonstrates a possibility to assess endurance (high-cycle fatigue) of a structural element allowing for its geometry, material properties, and type of loading. An analytical relation is derived, where the parameters representing the endurance of a structural element are given in combination (i.e., in the form of dimensionless quantities) rather than individually. The proposed method is implemented numerically and the results obtained are compared to some available published data.Introduction. One of the most critical tasks a design engineer faces is to assess endurance (high-cycle fatigue) of a structure at the design stage. The available methods of solving this problem, which were developed based on the physical [1], statistical [2], and phenomenological [3] approaches, fail to provide a possibility to allow for an element's geometry, material properties, fabrication techniques, and type of loading over a wide range of their variation. The present work involves the well-known method of dimensional analysis [4]. It enables us to consider the parameters, which have an effect on an element's endurance, not individually but in combinations, by arranging these parameters in dimensionless sets (complexes π i ). Based on these complexes, an analytical relation (hereinafter, the relation) is derived to assess endurance of a structural element.Results and Discussion. For the purpose of deriving the above-mentioned relation, we selected the parameters in view of the known physical concepts of endurance of structural elements (in this case, of metal materials) under cyclic loading. The number of the parameters chosen can have an influence on the endurance assessment accuracy. To derive the relation, we consider the bending and tension-compression fatigue test results for standard [5] and nonstandard specimens. The last-mentioned ones have some of their geometrical parameters deviating from the standard requirements [5].Since the tests were carried out in the cyclic loading mode, we have added the parameters involved in the differential equation for vibration of a bar [6]: stiffness EI (where E is the material's elastic modulus and I is the moment of inertia of the element's cross-section at the maximum stress location), material specific weight γ ρ = g