Prediction of the fatigue life of a notched body by the local stress-strain state. Part 1. Determination of stresses and strains in a notch under elastoplastic cyclic deformation

Fomichev, P. A.; Zvyagintsev, V. V.

doi:10.1007/bf02509850

Cited by 7 publications

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“…. The values of m and K correspond to high amplitudes of stresses exceeding the level of stresses at the salient point of the cyclic stress-strain diagram for D16AT alloy [9] and are of interest for the analysis of random loading. In [3], one can find the parameters of Eq.…”

Section: Comparative Analysis Of the Results Of Swanson's Experimentamentioning

confidence: 99%

“…In [9], one can find the cyclic deformation characteristics of D16AT alloy (an analog of 2024 alloy). For D16AT alloy, the values of the parameters of Eqs.…”

Section: Comparative Analysis Of the Results Of Swanson's Experimentamentioning

confidence: 99%

“…In view of relation (12) The results of numerous experimental investigations show [7][8][9] that the dependence of the mean amplitudes of strains on the amplitudes of stresses on logarithmic coordinates can be approximated by a straight (or broken) line. This means that the following equation is true:…”

mentioning

confidence: 99%

“…where W r * is the mean value of energy dissipated per loading cycle according to relation (9) for the amplitude of strains ε ar * .…”

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confidence: 99%

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Method for the evaluation of the service life under random loading based on the energy criterion of fatigue fracture

Fomichev

2008

Strength Mater

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We propose a method aimed at the assessment of the service life of structural elements under random loads based on the energy criterion of fatigue fracture and the model of cyclic deformation of materials after overloading. The possibility of determination of the maximum amplitude of stresses according to the number of loading cycles prior to fracture is substantiated. The results of evaluation of the service life under conditions of uniform stressed state are compared with the experimental data obtained by Swanson, Raikher spectral hypothesis of summation of defects, and linear hypothesis of summation. The dependence of the right-hand side of the linear hypothesis equation on the dispersion of the random loading process is established.Introduction. The service life of structural elements is, to a significant extent, determined by the spectrum of acting loads. In the stage of operation of a product, the loads are determined more precisely by recording the realizations of the force factor in time. The obtained realizations are processed by the methods of schematization of random processes. The methods of full cycles and "rain flow" are used especially extensively. The second method is often regarded as preferable because it allows one to form closed hysteresis loops. As a result of processing, we get the tables of differential repetition frequency of the loads characterizing the number of cycles of repetition of combinations of the amplitude and mean values. A method for the evaluation of the service life based on the energy fracture criterion was proposed for loads specified as indicated above in [1].In the stage of design, the loads can be found by the methods of statistical dynamics when the perturbing factor is analyzed in the probabilistic aspect. The random loading process is supposed to be stationary and normal with known spectral density and the distribution function of amplitudes of the force factor. In [2], a method for the evaluation of service life on the basis of the linear hypothesis of summation of fatigue defects is proposed within the framework of this approach. In [3], a hypothesis of spectral summation of defects is advanced and the comparison of the experimental and published data is realized. The results of calculations carried out according to the linear and spectral hypotheses either coincide or are sufficiently close. In [3], it is indicated that, for the Swanson experiment, the disagreement between the experimental data and numerical results is substantial. Indeed, in this case, the service life determined according to the numerical results is overestimated by about an order of magnitude.The aim of the present work is to develop a method aimed at the assessment of the service life under random loading realized under conditions of uniform stressed state on the basis of the energy approach to the process of fatigue fracture. Similar methods for the programmed, block, and biharmonic loads are proposed in [1,4,5].Theoretical Foundations. First, we consider some dependences typical of normal st...

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Section: Comparative Analysis Of the Results Of Swanson's Experimentamentioning

confidence: 99%

“…In [9], one can find the cyclic deformation characteristics of D16AT alloy (an analog of 2024 alloy). For D16AT alloy, the values of the parameters of Eqs.…”

Section: Comparative Analysis Of the Results Of Swanson's Experimentamentioning

confidence: 99%

mentioning

confidence: 99%

“…where W r * is the mean value of energy dissipated per loading cycle according to relation (9) for the amplitude of strains ε ar * .…”

mentioning

confidence: 99%

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Method for the evaluation of the service life under random loading based on the energy criterion of fatigue fracture

Fomichev

2008

Strength Mater

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“…The tests are performed until the specimen fails, and a relation between the number of cycles and the maximum nominal stress is found. The fatigue curves are approximated by exponential equations.The method of the fatigue life calculation by a local stress-strain state (SSS), which is based on the energy criterion for fatigue failure [2][3][4], makes it possible to theoretically predict the fatigue life till the formation of microcracks on the hole surface and macrocracks in the stress concentrator. For input data on the material properties this method uses cyclic deformation and fatigue characteristics as determined from the test results for smooth specimens.…”

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confidence: 99%

Substantiation of the predicted fatigue curve for structural elements of aluminum alloy

Fomichev

2011

Strength Mater

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The paper provides a more specific definition of the method for calculating fatigue life of aluminum alloy structural elements by a local stress-strain state in pulsating regular loading. The calculated results are compared to the test data for specimens with a free and filled holes and for lugs. Recommendations on the method application for calculating fatigue life by nominal stresses are given.Introduction. The method for calculating fatigue life by nominal stresses [1] is based on experimental fatigue curves for specimens with a free hole. These specimens with a ratio between the width and hole diameter B d = 6 have been standardized in aircraft industry. The stress concentration factor in elastic deformation is 2.6 for net stresses and 3.12 for gross stresses. The gross stresses are found without allowing for weakening of the specimen cross section near the hole. The hole diameter depends on the fasteners to be used and is usually 6 to 8 mm. Standard plate specimens were tested by means of a testing machine with pulsating loading. The fatigue curve plotted by the test results is called the basic curve. The fatigue life of structural elements is calculated by using an effective stress concentration factor which is determined either experimentally or by empirical relations based on test results for specimens with a free hole or for lugs. In specimens with a hole, the stress concentration is due to the stresses that pass round the hole. For lugs a contact problem of interaction between the bolt and the specimen is realized; a load is transmitted to the specimen via bearing stresses, the maximum stresses arise at the contact arc break points. The tests are performed until the specimen fails, and a relation between the number of cycles and the maximum nominal stress is found. The fatigue curves are approximated by exponential equations.The method of the fatigue life calculation by a local stress-strain state (SSS), which is based on the energy criterion for fatigue failure [2][3][4], makes it possible to theoretically predict the fatigue life till the formation of microcracks on the hole surface and macrocracks in the stress concentrator. For input data on the material properties this method uses cyclic deformation and fatigue characteristics as determined from the test results for smooth specimens.The objective of the present work is to specify the method for calculating fatigue life of aluminum alloy structural elements by the local SSS under pulsating regular loading and to provide recommendations for the method application to fatigue life calculation by normal stresses.The Method for Fatigue Life Calculation by Local SSS. The analysis for the pulsating regular loading case consists in the following.1. The Calculation of Local Notch-Tip Stresses and Strains at Maximum Nominal Stress s n max in a Loading Cycle. The local stress can be found through the solution of a nonlinear deformation problem by the finite-element method or by the refined Neuber formula [5]

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Fatigue life estimation of the overloaded notched components

Seifi

Mohammadi

2019

J Braz. Soc. Mech. Sci. Eng.

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Prediction of the fatigue life of a notched body by the local stress-strain state. Part 1. Determination of stresses and strains in a notch under elastoplastic cyclic deformation

Cited by 7 publications

References 4 publications

Method for the evaluation of the service life under random loading based on the energy criterion of fatigue fracture

Method for the evaluation of the service life under random loading based on the energy criterion of fatigue fracture

Substantiation of the predicted fatigue curve for structural elements of aluminum alloy

Fatigue life estimation of the overloaded notched components

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