Potential ambiguity in the determination of the plastic strain range component in LCF testing

Kandil, F.A.

doi:10.1016/s0142-1123(99)00103-6

Cited by 23 publications

(23 citation statements)

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“…As was shown in [28,43], the difference between the Δε in and Δε p values defined by relation (5) is insignificant under low-cycle loading and increases to 10% and more in passing to high-cycle loading.…”

mentioning

confidence: 65%

“…The kinetics of the variation of those characteristics under low-cycle loading was studied in [43,44].…”

mentioning

confidence: 99%

“…5[43], where Δσ σ = 2 a is the stress range per cycle, Δε ε = 2 a is the total strain range per cycle, Δε ε Distribution of stresses over the material grains (a) and "energy intensities" over plastically deformed volumes (plastic strain per cycle determined by the formulas…”

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confidence: 99%

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Nonlocalized Fatigue Damage of Metals and Alloys. Part 1. Inelasticity, Investigation Methods, and Results

Troshchenko

2005

Strength Mater

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Analysis of data presented in the literature and results of unique studies revealed that nonlocalized fatigue damage of metals and alloys, which manifests itself in the initiation and propagation of a large number of microcracks distributed arbitrarily in the bulk of the material, can be considered with the use of the characteristics of inelastic deformation such as inelastic strain and inelastic strain energy per cycle. The author studied the nature of the material inelasticity and methods of its investigation. Analysis has been made of the hysteresis loop shape, width, and area, as well as of the main regularities of inelastic deformation of metals and alloys.Keywords: nonlocalized fatigue damage, inelastic strain, inelastic strain energy.Introduction. The process of fatigue of metals and alloys can be divided into two stages: the stage of nonlocalized fatigue damage and that of localized fatigue damage where the process of fatigue is defined by the propagation of the dominant crack that leads to final fracture.As numerous investigations showed, the stage of the fatigue crack initiation is longer lasting than the stage of its propagation. Figure 1 shows the results of generalization of some of those investigations performed in [1], which are presented in the form of the relation between the ratio of the number of cycles to the initiation of a fatigue crack of length about 0.05 mm under axial loading of smooth specimens from various materials to the number of cycles to fracture and the number of cycles to fracture.It is seen that under high-cycle fatigue, which corresponds to the number of cycles to fracture equal to 10 5 and more, the stage of the fatigue crack initiation accounts for more than 90% of the total number of cycles to fracture.In the case of the fatigue fracture in the presence of stress concentration, fretting, etc., the stage of crack initiation is of shorter duration, yet it remains dominating.The size of a fatigue crack corresponding to the transition from the stage of nonlocalized to the stage of localized fatigue damage depends on the material structure, the level of acting stresses, loading regime, stress state type, and other factors. The size of such a crack generally decreases with increasing strength of the alloy and increases in torsion as compared with tension-compression [2,3].Thus, in [3] for steel 45 (σ u = 516 MPa) it is shown that, at stresses equal to the fatigue limit for the test duration 10 7 cycles, the size of the maximum crack in tension-compression and in torsion is 0.05 and 0.17 mm, respectively, and for 12KhN3A steel of higher strength (σ u = 950 MPa), it is 0.03 and 0.08, respectively. These crack dimensions are close to those used for plotting the relation in Fig. 1.

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“…The kinetics of the variation of those characteristics under low-cycle loading was studied in [43,44].…”

mentioning

confidence: 99%

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Nonlocalized Fatigue Damage of Metals and Alloys. Part 1. Inelasticity, Investigation Methods, and Results

Troshchenko

2005

Strength Mater

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“…Therefore, the conventional method of calculating the plastic and elastic components of strain cannot be used because it would yield incorrect values since, depending on the hysteresis, the tensile unloading tangent could find negative values of plastic strain. Therefore, the extent of hysteresis at half-life was determined by the mean stress, as shown in Figure 19 [KANDIL, 1999]. Note that the distance db corresponds to the plastic strain amplitude, the horizontal distance ac corresponds to the total strain amplitude, and the vertical distance ac corresponds to the stress amplitude; E 1 is the modulus of elasticity in tensile unloading, and E 2 is the modulus of elasticity in compressive unloading.…”

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Thermomechanical and Isothermal Fatigue Behavior of Gray Cast Iron for Automotive Brake Discs

Maluf¹,

Moreto²,

Angeloni³

et al. 2011

New Trends and Developments in Automotive System Engineering

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“…O efeito de um entalhe sobre a resistência à fadiga varia consideravelmente com o material e a geometria do entalhe (MCEVILY et al, 2008). O fator de concentração de tensão em fadiga possui um papel muito importante na estimativa da vida em fadiga e da resistência à fadiga das estruturas (WEIXING et al, 1995 , 1992;EYLON et al, 1994;BANIA, 1994). Ligas Ti-β são aquelas cujo teor de estabilizadores beta faz com que a temperatura de início da martensita seja inferior à temperatura ambiente, dando ao material, a capacidade de reter 100% da fase β após a têmpera.…”

Section: Efeito Da Concentração De Tensãounclassified

Estudo do comportamento em fadiga de alto ciclo da liga Ti-13V-11Cr-3AI

Nascimento¹

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Estudo do comportamento em fadiga de alto ciclo da liga Ti -13V -11Cr -3Al The Ti- alloys are a promising group of titanium alloys in terms of processing, properties and potential applications. In order to achieve the optimum balance between strength and toughness it is necessary, besides determining a proper composition in the alloy design, to obtain suitable microstructures by means of thermo-mechanical process and heat treatment. This study aimed to assess the high cycle fatigue behavior of Ti-13V-11Cr-3Al alloy, a high-strength alloy intended for use in the aerospace industry. The material was received in the form of bars with 7.6 mm in diameter, whose microstructure comprises elongated grains and whose mechanical properties combines high tensile strength (1,479 MPa), and reasonable ductility (true strain fracture equal to 0.217). The material was heat treated in two conditions: vacuum annealing at 750C for 1 h with slow cooling, and flash 650C salt bath for 6 min with subsequent water quenching. The study was based on obtaining  / N curves through by rotary bending (R = -1) fatigue tests employing cantilever beam specimens. For each microstructural condition, two  / N curves were obtained, the former with smooth samples and the latter employing specimens with geometric stress concentrators (notches), to evaluate the notch sensitivity of this alloy in both microstructural conditions. The material subjected to flash treatment showed greater dispersion and lower fatigue strength compared to annealed; however also showed lower notch sensitivity at long life (10 6 cycles). The study was complemented by fractographics analysis to identify the fracture initiation points. LORENA

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Potential ambiguity in the determination of the plastic strain range component in LCF testing

Cited by 23 publications

References 3 publications

Nonlocalized Fatigue Damage of Metals and Alloys. Part 1. Inelasticity, Investigation Methods, and Results

Nonlocalized Fatigue Damage of Metals and Alloys. Part 1. Inelasticity, Investigation Methods, and Results

Thermomechanical and Isothermal Fatigue Behavior of Gray Cast Iron for Automotive Brake Discs

Estudo do comportamento em fadiga de alto ciclo da liga Ti-13V-11Cr-3AI

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