Frequency dependent deformation reversibility during cyclic loading

ABSTRACT

High-frequency testing (HFT) is useful for accelerated fatigue testing of conventional materials that typically serve under low-frequency loading conditions, as well as for the assessment of the robustness of microelectromechanical systems which typically experience high-frequency service conditions. Using discrete dislocation dynamics, we attempt to elucidate the effect of loading frequency on the reversibility of cyclic deformation. We demonstrate that the HFT induces a higher fraction of reversible cyclic deformation because of a larger portion of elastic/anelastic deformation due to limited dislocation mobility, and a higher degree of reversibility in plastic deformation owing to the less occurrence of cross-slip.

IMPACT STATEMENT

Dislocation-based frequency effects on high-cycle deformation reversibility in metals are elucidated. Hysteresis energy is shown to dissipate even under ideal, damage-free conditions, contrary to popular assumptions of energy-based fatigue models.

GRAPHICAL ABSTRACT

KEYWORDS:

• Dislocation mobility
• deformation reversibility
• high-frequency cyclic loading
• fatigue damage

Acknowledgements

The support provided by the U.S. National Science Foundation (NSF OIA-1541079) and the Louisiana State Board of Regents (LEQSF(2013-16)-RD-B-01) is acknowledged. The support provided by the Office of Research and Economic Development and the Department of Mechanical and Industrial Engineering, Louisiana State University is greatly appreciated. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Los Alamos National Laboratory, an affirmative action equal opportunity employer, is operated by Los Alamos National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy under contract DE-AC52-06NA25396.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Shuai Shao http://orcid.org/0000-0002-4718-2783

Jian Wang http://orcid.org/0000-0001-5130-300X

Notes

1 Quotation marks are used here to signify the reversible nature of plastic deformation during high-frequency cyclic loading. In monotonic loading, plastic deformation is commonly perceived to be irreversible after unloading. In cylic loading under low frequencies, as will be demonstrated in this paper, are not truly reversible since wall dislocations are left behind.

2 In reality, the time scale of the cross-slip event is sensitive to temperature but generally varies from a fraction to several nanoseconds, which agrees with the cross-slip time scale considered in our simulations. For instance, it has been demonstrated that the time scale for annihilation of two screw dipoles in Cu due to cross-slip is from ∼0.005 ns to ∼5 ns, over a temperature range of 225K to 375K [37].

Additional information

Funding

This work was supported by Los Alamos National Laboratory: [grant number DE-AC52-06NA25396]; Louisiana Board of Regents: [grant number LEQSF(2013-16)-RD-B-01]; National Science Foundation: [grant number NSF OIA-1541079].