Aerospace series. Test methods for metallic materials. Constant amplitude force-controlled high cycle fatigue testing

During technical operation, high performance materials are partially exposed to high frequency cyclic loading conditions. Furthermore, the small strains in the very high cycle fatigue (VHCF)-regime lead to accumulative damage which causes crack initiation related to an appropriate local deformation leading to final fatal fracture. At the same time, quite high requirements with regard to high number of cycles without any damage are demanded for many applications. Fields of application of these light-weight, but expensive materials, are e.g. in the automobile industry (e.g. engine blocks, cylinder heads, brakes).The fatigue behavior of Al-matrix composites (Al-MMCs) reinforced by alumina particles (15 vol.% Al2O3) or short fibers (20 vol.% Saffil), respectively, was already intensively studied in the LCF and HCF range. The present study is focusing on investigations in the very high cycle fatigue regime at stress amplitudes up to 140 MPa to reach fatigue life of about 1010 cycles. All experiments were carried out using an ultrasonic fatigue testing device under symmetric loading conditions (R=-1). Fatigue tests were accompanied by in situ thermography measurements to record the temperature of the whole specimen and to find “hot spots” indicating changes in microstructure and therefore the initiation or growth of cracks. Moreover, the resonant frequency as well as the damage parameter were evaluated to determine the beginning of damage. For a better understanding of the damage mechanism (matrix decohesion, matrix failure or failure of reinforcement) all fractured surfaces were investigated by scanning electron microscopy. The combination of these methods contributes to a better understanding of the underlying mechanism of damage in aluminum-matrix-composites.

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Very High Cycle Fatigue Testing under Spectrum Loading for Endurance Limit Structural Design

Journal of the American Helicopter Society ◽

10.4050/jahs.65.012008 ◽

2020 ◽

Vol 65 (1) ◽

pp. 1-7

Author(s):

David T. Rusk ◽

Robert E. Taylor ◽

Bruce A. Pregger ◽

Luis J. Sanchez

Keyword(s):

Fatigue Test ◽

Test Data ◽

High Cycle Fatigue ◽

Fatigue Testing ◽

Crack Nucleation ◽

Peak Stress ◽

Material Behavior ◽

Cycle Fatigue ◽

Very High Cycle Fatigue ◽

Very High

A program has recently concluded that generated fatigue test data for the influence of a rotorcraft main rotor blade root bending spectrum (Helix) on the crack nucleation mechanisms in 7075-T651 aluminum. High-frequency tests were performed that generated spectrum fatigue failures out to nearly 109 cycles. Fractographic examination showed a distinct change in crack nucleation from slip initiated to inclusion-initiated cracking as the spectrum peak stress level was increased. Spectrum life predictions were made using three different baseline constant-amplitude S-N curves, one using a traditional rotorcraft original equipment manufacturer fitting methodology, one using the high-cycle fatigue (HCF) portion of a strainlife curve, and one that was fitted to S-N data with test lives out to 3×108 cycles. The spectrum life prediction using the S-N curve that properly modeled material behavior in the very high cycle fatigue regime provided a good correlation to the spectrum fatigue test data. Predictions using the other S-N curves were highly conservative.

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Recent Advances in Very High Cycle Fatigue Behavior of Metals and Alloys—A Review

Metals ◽

10.3390/met10091200 ◽

2020 ◽

Vol 10 (9) ◽

pp. 1200

Author(s):

Ashutosh Sharma ◽

Min Chul Oh ◽

Byungmin Ahn

Keyword(s):

Crack Initiation ◽

High Cycle Fatigue ◽

Fatigue Testing ◽

Fatigue Behavior ◽

Simulation Studies ◽

Cycle Fatigue ◽

Future Directions ◽

Very High Cycle Fatigue ◽

Ultrasonic Fatigue ◽

Very High

We reviewed the research and developments in the field of fatigue failure, focusing on very-high cycle fatigue (VHCF) of metals, alloys, and steels. We also discussed ultrasonic fatigue testing, historical relevance, major testing principles, and equipment. The VHCF behavior of Al, Mg, Ni, Ti, and various types of steels were analyzed. Furthermore, we highlighted the major defects, crack initiation sites, fatigue models, and simulation studies to understand the crack development in VHCF regimes. Finally, we reviewed the details regarding various issues and challenges in the field of VHCF for engineering metals and identified future directions in this area.

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Fatigue life time modelling of Cu and Au fine wires

MATEC Web of Conferences ◽

10.1051/matecconf/201816506002 ◽

2018 ◽

Vol 165 ◽

pp. 06002

Author(s):

Golta Khatibi ◽

Ali Mazloum-Nejadari ◽

Martin Lederer ◽

Mitra Delshadmanesh ◽

Bernhard Czerny

Keyword(s):

Fatigue Life ◽

Strain Rate ◽

High Cycle Fatigue ◽

Fatigue Testing ◽

Low Cycle Fatigue ◽

Load Ratio ◽

Life Time ◽

Material Model ◽

Cycle Fatigue ◽

Rate Dependency

In this study, the influence of microstructure on the cyclic behaviour and lifetime of Cu and Au wires with diameters of 25μm in the low and high cycle fatigue regimes was investigated. Low cycle fatigue (LCF) tests were conducted with a load ratio of 0.1 and a strain rate of ~2e-4. An ultrasonic resonance fatigue testing system working at 20 kHz was used to obtain lifetime curves under symmetrical loading conditions up to very high cycle regime (VHCF). In order to obtain a total fatigue life model covering the low to high cycle regime of the thin wires by considering the effects of mean stress, a four parameter lifetime model is proposed. The effect of testing frequency on high cycle fatigue data of Cu is discussed based on analysis of strain rate dependency of the tensile properties with the help of the material model proposed by Johnson and Cook.

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