arXiv subjects

Gregory C. Rutledge

Publications and source records attributed to Gregory C. Rutledge.

5 recordsLinked to original sources

arXiv2023

Large strain micromechanics of thermoplastic elastomers with random microstructures

Thermoplastic polyurethanes (TPU) are block copolymeric materials composed of plastomeric "hard" and elastomeric "soft" domains, by which they exhibit highly resilient yet dissipative large deformation features depending on volume fractions and microstructures of the two distinct domains. Here, we develop a new methodology to address the microscopic deformation mechanisms in TPU materials with highly disordered microstructures. We propose new micromechanical models for randomly dispersed (or occluded) as well as randomly continuous hard domains, each within a continuous soft structure as widely found in representative TPU materials over a wide range of volume fractions, v$_{\mathrm{hard}}$ = 26.9% to 52.2%. The micromechanical modeling results are compared to experimental data on the macroscopic large strain behaviors reported previously (Cho et al. 2017). We explore the role of the dispersed vs. continuous nature of the geometric features of the random microstructures on shape recovery and energy dissipation at the microstructural level in this important class of phase-separated copolymeric materials.

cond-mat.soft↗

arXiv2023

A polyurethane-urea elastomer at low to extreme strain rates

A finite strain nonlinear constitutive model is presented to study the extreme mechanical behavior of a polyurethane-urea well suited for many engineering applications. The micromechanically- and thermodynamically based constitutive model captures salient features in resilience and dissipation in the material at low to high strain rate. The extreme deformation features are further elucidated by laser-induced micro-particle impact tests for the material, where an ultrafast strain rate ($>10^6$ s$^{-1}$) incurs. Numerical simulations for the strongly inhomogeneous deformation events are in good agreement with the experimental data, supporting the predictive capabilities of the constitutive model for the extreme deformation features of the PUU material over at least 9 orders of magnitude in strain rates ($10^{-3}$ to $10^{6}$ s$^{-1}$).

cond-mat.soft↗

arXiv2020

Discretized Wiener-Khinchin theorem for Fourier-Laplace transformation: application to molecular simulations

The Wiener-Khinchin theorem for the Fourier-Laplace transformation (WKT-FLT) provides a robust method to calculate numerically single-side Fourier transforms of arbitrary autocorrelation functions from molecular simulations. However, the existing WKT-FLT equation produces two artifacts in the output of the frequency-domain relaxation function. In addition, these artifacts are more apparent in the frequency-domain response function converted from the relaxation function. We find the sources of these artifacts that are associated with the discretization of the WKT-FLT equation. Taking these sources into account, we derive the new discretized WKT-FLT equations designated for both the frequency-domain relaxation and response functions with the artifacts removed. The use of the discretized WKT-FLT equations is illustrated by a flow chart of an on-the-fly algorithm. We also give application examples of the discretized WKT-FLT equations for computing dynamic structure factor and wave-vector-dependent dynamic susceptibility from molecular simulations.

physics.comp-ph↗

arXiv2002

Multiresolution analysis in statistical mechanics. I. Using wavelets to calculate thermodynamic properties

The wavelet transform, a family of orthonormal bases, is introduced as a technique for performing multiresolution analysis in statistical mechanics. The wavelet transform is a hierarchical technique designed to separate data sets into sets representing local averages and local differences. Although one-to-one transformations of data sets are possible, the advantage of the wavelet transform is as an approximation scheme for the efficient calculation of thermodynamic and ensemble properties. Even under the most drastic of approximations, the resulting errors in the values obtained for average absolute magnetization, free energy, and heat capacity are on the order of 10%, with a corresponding computational efficiency gain of two orders of magnitude for a system such as a $4\times 4$ Ising lattice. In addition, the errors in the results tend toward zero in the neighborhood of fixed points, as determined by renormalization group theory.

physics.chem-ph↗

arXiv2002

Multiresolution analysis in statistical mechanics. II. The wavelet transform as a basis for Monte Carlo simulations on lattices

In this paper, we extend our analysis of lattice systems using the wavelet transform to systems for which exact enumeration is impractical. For such systems, we illustrate a wavelet-accelerated Monte Carlo (WAMC) algorithm, which hierarchically coarse-grains a lattice model by computing the probability distribution for successively larger block spins. We demonstrate that although the method perturbs the system by changing its Hamiltonian and by allowing block spins to take on values not permitted for individual spins, the results obtained agree with the analytical results in the preceding paper, and ``converge'' to exact results obtained in the absence of coarse-graining. Additionally, we show that the decorrelation time for the WAMC is no worse than that of Metropolis Monte Carlo (MMC), and that scaling laws can be constructed from data performed in several short simulations to estimate the results that would be obtained from the original simulation. Although the algorithm is not asymptotically faster than traditional MMC, because of its hierarchical design, the new algorithm executes several orders of magnitude faster than a full simulation of the original problem. Consequently, the new method allows for rapid analysis of a phase diagram, allowing computational time to be focused on regions near phase transitions.

physics.chem-ph↗