Biomechanics and modeling in mechanobiology, Jan 14, 2014
Nanomechanics of individual collagen fibrils govern the mechanical behavior of the majority of co... more Nanomechanics of individual collagen fibrils govern the mechanical behavior of the majority of connective tissues, yet the current models lack significant details. Majority of the current models assume a rod-shape molecule with homogenous mechanical properties. Recent X-ray crystallography revealed significantly different microstructures in the D-period of collagen microfibrils, markedly different from the conventionally assumed rod-shaped molecule. Motivated by this recent microstructure, the nanomechanics of hydrated collagen molecules are investigated through molecular dynamics simulations. The results reveal significant mechanical heterogeneity in individual collagen molecules, which is expected to significantly impact the biomechanics of collagen fibrils in healthy and diseased tissues.
Based on the molecular dynamics simulation and an elastic shell model, we investigated the intrin... more Based on the molecular dynamics simulation and an elastic shell model, we investigated the intrinsic loss under dynamic excitations in single walled carbon nanotube (SWCNT) due to the anelastic relaxation mechanism. We quantified the anelastic property of SWCNTs, i.e., the creep compliances, and showed them to be on the order of 1 (TPa-1) and sensitive to both the radius of SWCNT and the loading rate. Furthermore, our study showed that the time scale for a SWCNT to fully achieve its equilibrium elastic property through anelastic relaxation is on the order of nanosecond. This leads to significant intrinsic loss and damping for SWCNT resonators operating at the Gigahertz frequency range. Both the loss angle and quality (Q) factor of SWCNT were found to be strongly dependent on the load frequency. A dissipation peak and thus a low Q factor were observed in the Gigahertz frequency range. On the other hand, high Q factor and low dissipation were achieved in the range of low (< 0.001 GHz) excitation frequency. The predicted influence of load frequency on the Q factor is in good agreement with the recent experimental observations.
Journal of Engineering Materials and Technology, 2012
ABSTRACT We present a semi-analytical approach to study the energy dissipation in carbon nanotube... more ABSTRACT We present a semi-analytical approach to study the energy dissipation in carbon nanotube (CNT) beam oscillators under gigahertz excitation. The energy dissipation properties are quantified by the quality factor (Q factor) and associated anelastic properties. Our study reveals that the Q factor is related to the tube radius through an inverse relation for both single walled CNTs (SWCNTs) and multiwalled CNTs (MWCNTs) beam oscillators. At frequency close to the resonance range, significant energy dissipation is observed due to the activation of phonon modes that serve as a major mechanism for energy dissipation in SWCNTs. For MWCNTs, a registration dependent potential (RDP) is introduced to study the effect of intertube registration. Interlayer friction arising from the p bond overlap is shown to contribute significantly to the additional energy dissipation. Based on the extensive simulation studies, an analytical formula for estimating the Q factors of MWCNTs is proposed. Validation of the analytical prediction with the available experimental data yields a good agreement and quantifies the roles of different factors contributing to the energy dissipation through anelastic relaxation. [DOI:10.1115/1.4006506]
... the error is very small so that all results reduce to those under spherical indentation on a ... more ... the error is very small so that all results reduce to those under spherical indentation on a ... 6) leads to the following time-dependent displacement under a prescribed ar-bitrary indentation loading history in a ... where J(t) is the shear creep compliance at time t. The Poisson's ratio is ...
In this presentation, we discuss semi-analytical approaches to the visco-elastic properties of th... more In this presentation, we discuss semi-analytical approaches to the visco-elastic properties of the Carbon Nanotubes (CNTs) based on molecular dynamics (MD) simulation and continuum models. The viscoelastic properties of the CNTs defined in both the time and frequency domains have been obtained in terms of the creep compliance and the relaxation and complex modulus. The equilibrium visco-elastic properties were found to be strongly dependent on tube radius for both single-walled and multi-walled CNTs, while the chirality had no appreciable effect. For multi-walled CNTs, the interlayer interaction contributes significantly to the overall viscoelastic response. The time scale associated with the visco-elastic properties were found to be on the order of nanosecond. This time scale is reflected in the associated energy loss and damping mechanisms in CNT oscillators. From the computed visco-elastic properties, we further derived the quality factor Q for different tube geometries and load frequencies. We found that the Q factor is strongly influenced by the load frequency, in addition to the dependence on the tube radius. The predicted trends in terms of the dependence on the load frequency were further validated through comparison with experiments. The underlying mechanism for such trends was discussed in the context of thermoelastic theory.
Biomechanics and modeling in mechanobiology, Jan 14, 2014
Nanomechanics of individual collagen fibrils govern the mechanical behavior of the majority of co... more Nanomechanics of individual collagen fibrils govern the mechanical behavior of the majority of connective tissues, yet the current models lack significant details. Majority of the current models assume a rod-shape molecule with homogenous mechanical properties. Recent X-ray crystallography revealed significantly different microstructures in the D-period of collagen microfibrils, markedly different from the conventionally assumed rod-shaped molecule. Motivated by this recent microstructure, the nanomechanics of hydrated collagen molecules are investigated through molecular dynamics simulations. The results reveal significant mechanical heterogeneity in individual collagen molecules, which is expected to significantly impact the biomechanics of collagen fibrils in healthy and diseased tissues.
Based on the molecular dynamics simulation and an elastic shell model, we investigated the intrin... more Based on the molecular dynamics simulation and an elastic shell model, we investigated the intrinsic loss under dynamic excitations in single walled carbon nanotube (SWCNT) due to the anelastic relaxation mechanism. We quantified the anelastic property of SWCNTs, i.e., the creep compliances, and showed them to be on the order of 1 (TPa-1) and sensitive to both the radius of SWCNT and the loading rate. Furthermore, our study showed that the time scale for a SWCNT to fully achieve its equilibrium elastic property through anelastic relaxation is on the order of nanosecond. This leads to significant intrinsic loss and damping for SWCNT resonators operating at the Gigahertz frequency range. Both the loss angle and quality (Q) factor of SWCNT were found to be strongly dependent on the load frequency. A dissipation peak and thus a low Q factor were observed in the Gigahertz frequency range. On the other hand, high Q factor and low dissipation were achieved in the range of low (< 0.001 GHz) excitation frequency. The predicted influence of load frequency on the Q factor is in good agreement with the recent experimental observations.
Journal of Engineering Materials and Technology, 2012
ABSTRACT We present a semi-analytical approach to study the energy dissipation in carbon nanotube... more ABSTRACT We present a semi-analytical approach to study the energy dissipation in carbon nanotube (CNT) beam oscillators under gigahertz excitation. The energy dissipation properties are quantified by the quality factor (Q factor) and associated anelastic properties. Our study reveals that the Q factor is related to the tube radius through an inverse relation for both single walled CNTs (SWCNTs) and multiwalled CNTs (MWCNTs) beam oscillators. At frequency close to the resonance range, significant energy dissipation is observed due to the activation of phonon modes that serve as a major mechanism for energy dissipation in SWCNTs. For MWCNTs, a registration dependent potential (RDP) is introduced to study the effect of intertube registration. Interlayer friction arising from the p bond overlap is shown to contribute significantly to the additional energy dissipation. Based on the extensive simulation studies, an analytical formula for estimating the Q factors of MWCNTs is proposed. Validation of the analytical prediction with the available experimental data yields a good agreement and quantifies the roles of different factors contributing to the energy dissipation through anelastic relaxation. [DOI:10.1115/1.4006506]
... the error is very small so that all results reduce to those under spherical indentation on a ... more ... the error is very small so that all results reduce to those under spherical indentation on a ... 6) leads to the following time-dependent displacement under a prescribed ar-bitrary indentation loading history in a ... where J(t) is the shear creep compliance at time t. The Poisson's ratio is ...
In this presentation, we discuss semi-analytical approaches to the visco-elastic properties of th... more In this presentation, we discuss semi-analytical approaches to the visco-elastic properties of the Carbon Nanotubes (CNTs) based on molecular dynamics (MD) simulation and continuum models. The viscoelastic properties of the CNTs defined in both the time and frequency domains have been obtained in terms of the creep compliance and the relaxation and complex modulus. The equilibrium visco-elastic properties were found to be strongly dependent on tube radius for both single-walled and multi-walled CNTs, while the chirality had no appreciable effect. For multi-walled CNTs, the interlayer interaction contributes significantly to the overall viscoelastic response. The time scale associated with the visco-elastic properties were found to be on the order of nanosecond. This time scale is reflected in the associated energy loss and damping mechanisms in CNT oscillators. From the computed visco-elastic properties, we further derived the quality factor Q for different tube geometries and load frequencies. We found that the Q factor is strongly influenced by the load frequency, in addition to the dependence on the tube radius. The predicted trends in terms of the dependence on the load frequency were further validated through comparison with experiments. The underlying mechanism for such trends was discussed in the context of thermoelastic theory.
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