Microstructure investigations on two different aluminum wrought alloys after very high cycle fatigue

Schwerdt, Daniela; Pyttel, Brita; Berger, Christina; Oechsner, Matthias; Kunz, Ulrike

doi:10.1016/j.ijfatigue.2013.01.004

Cited by 14 publications

(9 citation statements)

References 10 publications

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“…A similar observation is made in [22] where fatigue crack initiation in non-heat treated Al6082 occur most frequently at interior sites in the material where no particles or other features are present. Internal fatigue crack initiation sites, which do not show evidence of particle inclusions, are also observed in wrought Al6082-T5 in [42]. In the latter study, fatigue cracks are found to initiate at single grains with high Schmid factors and which are exposed to significant local plastic slip.…”

mentioning

confidence: 61%

“…Such inclusions are also observed in forged Al6082 in [20] and in cast Al6082 in [35]. In contrast, particle inclusions or fatigue crack initiation due to particles could not be detected in the high-cycle fatigue experiments on wrought Al6082-T5 studied in [42]. Second-phase particles with sizes typically around 2 µm were found in the material presently under consideration.…”

Section: Methodsmentioning

confidence: 84%

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Crystal plasticity modeling of microstructure influence on fatigue crack initiation in extruded Al6082-T6 with surface irregularities

Hallberg

Ås

Skallerud

2018

International Journal of Fatigue

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The influence of surface roughness and microstructure heterogeneities in the vicinity of macroscopic stress concentrations are investigated by crystal plasticity simulations. It is shown that in the extruded Al6082-T6 alloy under consideration, twin grain boundaries and other highly misoriented grain interfaces, which constitute significant barriers to plastic slip, provide internal domains in the material where initiation of fatigue damage is more likely to occur than at the stress concentrations which are due to the surface roughness. In addition, the microstructure influence on the appearance of stress gradients is found to be significant. Further, the present study indicates that frequently used fatigue initiation parameters (FIP) such as the locally accumulated plastic strain or stored energy may be insufficient to identify fatigue crack initiation. Such parameters should be complemented or replaced by other FIP which take additional characteristics of the microstructure into account. This is exemplified in the present study by employing two additional FIPs, based on a modified Fatemi-Socie critical-plane parameter and on the Dang Van criterion, respectively.

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mentioning

confidence: 61%

Section: Methodsmentioning

confidence: 84%

Crystal plasticity modeling of microstructure influence on fatigue crack initiation in extruded Al6082-T6 with surface irregularities

Hallberg

Ås

Skallerud

2018

International Journal of Fatigue

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“…Due to this influence of the testing technique on the material and hence on the fatigue behaviour it is especially in the VHCF regime necessary to get a deep understanding of the influencing factors: the material, the testing method and the test frequency Although the different influences can be described in principle, it is not yet possible to quantify them with regard to fatigue strength. This makes the direct comparison of results from various sources more dif- [45] ficult. Thereby the role of current research projects is given a greater importance [46][47][48].…”

Section: Resultsmentioning

confidence: 99%

“…Thus here too, the decrease in fatigue strength results from the localized changes in the microstructure in correlation with the localized micromechanical properties. For example, a large grain that has in comparison as its surrounding matrix a different orientation and a higher Schmid factor could be a possible microstructural inhomogeneity, Figure 5 [45]. Here localized slip can occur even at low stress amplitudes, resulting in the initiation of a crack.…”

Section: Crack Formation In the Interiormentioning

confidence: 99%

“…Here localized slip can occur even at low stress amplitudes, resulting in the initiation of a crack. EN AW-6056-T6 is a further example of a precipitation hardened wrought aluminium alloy which shows crack formation in the inner of the specimen as well as the appearance of cleavage-like planes from a fractographic perspec- [42] tive, starting from the transition from the HCF to the VHCF regime, Figure 6 [45]. In this case, crack initiation and propagation occurs at precipitate free zones (PFZ) both along grain boundaries as well as along the {101}-planes with lined β 00 -precipitates.…”

Section: Crack Formation In the Interiormentioning

confidence: 99%

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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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Very High Cycle Fatigue

Zimmermann

2017

Handbook of Mechanics of Materials

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Microstructure investigations on two different aluminum wrought alloys after very high cycle fatigue

Cited by 14 publications

References 10 publications

Crystal plasticity modeling of microstructure influence on fatigue crack initiation in extruded Al6082-T6 with surface irregularities

Crystal plasticity modeling of microstructure influence on fatigue crack initiation in extruded Al6082-T6 with surface irregularities

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

Very High Cycle Fatigue

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