Length-scale and strain rate-dependent mechanism of defect formation and fracture in carbon nanotubes under tensile loading

High damping capacity is one of the prominent properties of NiTi shape memory alloy (SMA), having applications in many engineering devices to reduce unwanted vibrations. Recent experiments demonstrated that, the hysteresis loop of the stress-strain curve of a NiTi strip/wire under a tensile loading-unloading cycle changed non-monotonically with the loading rate, i.e., a maximum damping capacity was obtained at an intermediate strain rate (ε.critical). This rate dependence is due to the coupling between the temperature dependence of material’s transformation stresses, latent-heat release/absorption in the forward/reverse phase transition and the associated heat exchange between the specimen and the environment. In this paper, a simple analytical model was developed to quantify these thermo-mechanical coupling effects on the damping capacity of the NiTi strips/wires under the tensile loading-unloading cycle. We found that, besides the material thermal/mechanical properties and specimen geometry, environmental condition also affects the damping capacity; and the critical strain rate ε.criticalfor achieving a maximum damping capacity can be changed by varying the environmental condition. The theoretical predictions agree quantitatively with the experiments.

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Atomistic Simulations of Strain Rate Dependent Deformation Behavior at Continuum Timescales

MRS Proceedings ◽

10.1557/proc-976-0976-ee01-05 ◽

2006 ◽

Vol 976 ◽

Author(s):

Vikas Tomar

Keyword(s):

Monte Carlo ◽

Strain Rate ◽

Defect Formation ◽

Interatomic Potential ◽

Md Simulations ◽

Strain Rates ◽

Cu Nanowires ◽

Rate Dependent ◽

Fundamental Reason ◽

Dependent Strain

AbstractA majority of computational mechanical analyses of nanocrystalline materials or nanowires have been carried out using classical molecular dynamics (MD). Due to the fundamental reason that the MD simulations must resolve atomic level vibrations, they cannot be carried out at the timescale of the order of microseconds. Additionally, MD simulations have to be carried out at very high loading rates (∼108 s−1) rarely observed in experiments. In this investigation, a modified Hybrid Monte Carlo (HMC) method that can be used to analyze time-dependent (strain rate dependent) atomistic mechanical deformation of nanostructures at continuum timescales is established. In this method there is no restriction on the size of MD timestep except that it must be such that to ensure a reasonable acceptance rate between consecutive Monte-Carlo (MC) time-steps. For the purpose of comparison HMC analyses of Cu nanowires deformation at two different strain rates (108 s−1 and 109 s−1) (each with three different timesteps 2 fs, 4fs, and 8 fs) are compared with the analyses based on MD simulations at the same strain rates and a MD timestep of 2 fs. As expected, the defect formation is found to be strain rate dependent. In addition, HMC with timestep of 8 fs correctly reproduces defect formation and stress-strain response observed in the case of MD with 2 fs (for the interatomic potential used 2 fs is the highest MD timestep). Simulation time analyses show that by using HMC a saving of the order of 4 can be achieved bringing the atomistic analyses closer to the continuum timescales.

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Strain rate-dependent mechanical behavior of quasi-unidirectional E-glass fabric reinforced polypropylene composites under off-axis tensile loading

Polymer Testing ◽

10.1016/j.polymertesting.2018.05.033 ◽

2018 ◽

Vol 69 ◽

pp. 276-285 ◽

Cited By ~ 5

Author(s):

Zhanyu Zhai ◽

Bingyan Jiang ◽

Dietmar Drummer

Keyword(s):

Strain Rate ◽

Mechanical Behavior ◽

Tensile Loading ◽

Glass Fabric ◽

Polypropylene Composites ◽

Rate Dependent

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A method for analyzing nanomechanical deformation of nanocrystalline Ni at higher timesteps than is possible in classical molecular dynamics

MRS Proceedings ◽

10.1557/proc-978-0978-gg06-03 ◽

2006 ◽

Vol 978 ◽

Author(s):

Vikas Tomar

Keyword(s):

Molecular Dynamics ◽

Monte Carlo ◽

Strain Rate ◽

Defect Formation ◽

Interatomic Potential ◽

Md Simulations ◽

Classical Molecular Dynamics ◽

Rate Dependent ◽

Nanocrystalline Structures ◽

Defect Nucleation

AbstractA majority of computational mechanical analyses of nanocrystalline materials have been carried out using classical molecular dynamics (MD). Due to the fundamental reason that the MD simulations must resolve atomic level vibrations, they cannot be carried out at the timescale of the order of microseconds. Additionally, MD simulations have to be carried out at very high loading rates (∼108 s−1) rarely observed in experiments. In this investigation a modified Hybrid Monte Carlo (HMC) method that can be used to analyze time-dependent (strain rate dependent) atomistic mechanical deformation of nanocrystalline structures at higher timescales than currently possible using MD is established. In this method there is no restriction on the size of MD timestep except that it must be such that to ensure a reasonable acceptance rate between consecutive Monte-Carlo (MC) time-steps. For the purpose of comparison HMC analyses of a nanocrystalline Ni sample at a strain rate of 109 s−1 with three different timesteps, viz. 2 fs, 4fs, and 8 fs, are compared with the analyses based on MD simulations at the same strain rate and a MD timestep of 2 fs. MD simulations of nanocrystalline Ni reproduce the defect nucleation and propagation results as well as strength values reported in the literature. In addition, HMC with timestep of 8 fs correctly reproduces defect formation and stress-strain response observed in the case of MD simulations with permissible timestep of 2 fs (for the interatomic potential used 2 fs is the highest MD timestep). Simulation time analyses show that by using HMC a saving of the order of 4 can be achieved bringing the atomistic analyses closer to the continuum timescales.

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