Gigacycle Fatigue in Mechanical Practice

Bathìas, Claude; Paris, Paul C.

doi:10.1201/9780203020609

Cited by 346 publications

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“…To predict the number of cycles to initiate a fatigue crack from an inclusion, several models are used more or less successfully. 1 In the gigacycle fatigue range, the integration of Paris' law 3−5 allows one to predict the number of cycles in the fish-eye growth and obtain the number of cycles at crack initiation. As the crack initiation appears, a short crack around the defect propagates followed by a long crack.…”

Section: Introductionmentioning

confidence: 99%

Fatigue crack initiation detection by an infrared thermography method

Wagner

Ranc

Bathìas

et al. 2009

Fatigue Fract Eng Mat Struct

103

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A B S T R A C T In this paper, the study of the temperature variation during fatigue tests was carried out on different materials (steels and aluminium alloys). Tests were performed at ambient temperature using a piezoelectric fatigue system (20 kHz). The temperature field was measured on the surface of the specimen, by means of an infrared camera. Just at the beginning of the test, it was observed that the temperature increased, followed by a stabilization which corresponds to the balance between dissipated energy associated with microplasticity and the energy lost by convection and radiation at the specimen surface and by conduction inside the specimen. At the crack initiation, the surface temperature suddenly increases (whatever the localization of the initiation), which allows the determination of the number of cycles at the crack initiation and the number of cycles devoted to the fatigue crack propagation. In the gigacycle fatigue domain, more than 92% of the total life is devoted to the initiation of the crack.So, the study of the thermal dissipation during the test appears a promising method to improve the understanding of the damage and failure mechanism in fatigue and to determine the number of cycles at initiation.Keywords infrared pyrometry; number of cycles at crack initiation; temperature recording; very high cycle fatigue. N O M E N C L A T U R Eb = burger vector E = Young's modulus K eff = effective stress intensity factor K = stress intensity factor σ = stress amplitude σ y = yield stress σ y = cyclic yield stress

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Section: Introductionmentioning

confidence: 99%

Fatigue crack initiation detection by an infrared thermography method

Wagner

Ranc

Bathìas

et al. 2009

Fatigue Fract Eng Mat Struct

103

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“…The result is a longer crack propagation life in ultrasonic fatigue tests and an increase in fatigue life until failure. In relation to the total fatigue life in the VHCF regime the difference caused by crack propagation should be classified as minor, as the proportion of long crack growth to total fatigue life is minor [18].…”

Section: Influence Of the Testing Methodsmentioning

confidence: 99%

“…The cracks in the inner of the specimen can initiate at inclusions or at other microstructural inhomogeneities [18]. The term "matrix failure" or "nondefect failure" is used in the literature where no inhomogeneity in the microstructure at the area of crack formation in the inner of the specimen can be detected in metallographic examinations of the fracture surface [30,31].…”

Section: Influence Of the Strain Ratementioning

confidence: 99%

Fatigue at high number of cyclic loads: Testing methods and failure mechanism

Schneider¹,

Schwerdt²,

Wuttke³

et al. 2015

Mat.-wiss. u. Werkstofftech

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A significant proportion of machinery and equipment is operated up to a number of cycles greater 10 8 , which is in the range of conventionally fatigue limit design. For materials with a face-centred cubic crystal lattice and for high-strength steels with a body-centred cubic crystal lattice fatigue failures were observed even in the Very High Cycle Fatigue (VHCF) regime of load-cycles greater N = 10 7 . To reduce the testing time in the VHCF regime, one possibility is to perform the tests at a higher frequency. In addition to the typical servo-hydraulic testing machines or resonant fatigue testing machine with test frequencies up to f = 400 Hz, ultrasonic fatigue testing machines with frequencies up to f = 20 kHz were used. In different comparative investigations it was shown that the testing method has a significant influence on fatigue life and fatigue strength. In this paper the influence of the testing method and test frequency on fatigue behaviour in the VHCF regime is presented using the example of steels and aluminium alloys and different hypotheses for the decrease in fatigue strength in this area are discussed.Keywords: VHCF / test frequency / testing method / ultrasonic fatigue testing machine / failure mechanism Eine Vielzahl von Maschinen und Anlagen werden bis zu Zyklenzahlen von mehr als 10 8 , also im klassischen dauerfesten Auslegungsbereich, betrieben. Bei Werkstoffen mit kubisch-flächenzentriertem Kristallgitter sowie hochfesten Stähle mit kubisch-raumzentriertem Gitter sind auch noch im Bereich sehr hoher Zyklenzahlen N > 10 7 , dem sogenannten Very High Cycle Fatigue Bereich (VHCF), Brüche zu beobachten. Eine Möglichkeit zur Reduzierung der Prüfzeiten im VHCF-Bereich ist die Durchführung der Prüfung bei höheren Frequenzen. Neben den typischen servohydraulischen Prüfmaschinen oder Resonanzprüfmaschinen mit Prüffrequenzen bis zu f = 400 Hz kommen auch Ultraschallschwingprüfsysteme mit Frequenzen von f = 20 kHz zum Einsatz. In verschiedenen vergleichenden Untersuchungen konnte festgestellt werden, dass die Prüfmethode einen signifikanten Einfluss auf die Lebensdauer sowie die Schwingfestigkeit hat. Der Beitrag stellt Einflüsse der Prüf-methode und der Prüffrequenz auf das Ermüdungsverhalten im VHCF-Bereich am Beispiel von Stählen und Aluminiumlegierungen vor und diskutiert verschiedene Hypothesen zum Abfall der Schwingfestigkeit in diesem Bereich.

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“…In the gigacycle range, fatigue failures have been observed to originate from interior defects. [38][39][40] Typical surface defects includes machining marks, corrosion pits and non-metallic inclusions or pores located close to or at the surface.…”

Section: Block Maximum Methodsmentioning

confidence: 99%

Non‐local stress approach for fatigue assessment based on weakest‐link theory and statistics of extremes

Wormsen

Sjödin

Härkegård

et al. 2007

Fatigue Fract Eng Mat Struct

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A B S T R A C T In the present paper a non-local stress approach for fatigue assessment based on weakestlink theory and statistics of extremes is presented. It is a non-local stress approach in the sense that it takes the complete stress field into account rather than just the highest local stress. The statistical distribution of fatigue strength data from smooth standard specimens serves as a starting point for the computation of the probability of fatigue failure of a mechanical component under cyclic loading. The probability of fatigue failure can be obtained by post-processing results from a standard finite element stress analysis. It is shown that the non-local stress approach can be linked to the probability of finding the fatigue critical defect in the most highly stressed volume of the component. A numerical procedure is presented that is fully compatible with the results from a standard finite element stress analysis. It is further shown how the fatigue strength distribution can be transformed into a fatigue life distribution by using Basquin's equation. Finally, the nonlocal stress approach is used for predicting the fatigue limit of several specimens and predictions are compared with test results.Keywords block maximum method; effective stress amplitude; defects; finite element analysis; finite-element post-processor; statistics of extremes; surface effect; stress field; volume effect; weakest-link model. N O M E N C L A T U R E A = surface areaA 0 = reference surface area a = 'intrinsic' crack length a 0 = scale parameter in the generalized extreme value distribution a * 0 = characteristic largest defect size a crit = critical defect size B = Basquin coefficient b σ , b n = Weibull exponent G(a) = generalised extreme value distribution FEA = finite element analysis |J| = Jacobian determinant l = gauge length m = Basquin exponent n = number of cycles n = element face normal N = fatigue life (random variable) N * 0 = characteristic fatigue life N = element shape functions Correspondence: A. Wormsen.

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Gigacycle Fatigue in Mechanical Practice

Cited by 346 publications

References 0 publications

Fatigue crack initiation detection by an infrared thermography method

Fatigue crack initiation detection by an infrared thermography method

Fatigue at high number of cyclic loads: Testing methods and failure mechanism

Non‐local stress approach for fatigue assessment based on weakest‐link theory and statistics of extremes

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