A coupled MD-FE methodology to characterize mechanical interphases in polymeric nanocomposites: pseudo-experimental data

readme.txt

Abstract:
(from [1])

This contribution introduces an unconventional procedure to characterize spatial profiles of elastic and inelastic properties inside polymer interphases around nanoparticles. Interphases denote those regions in the polymer matrix whose mechanical properties are influenced by the filler surfaces and thus deviate from the bulk properties. They are of particular relevance in case of nano-sized filler particles with a comparatively large surface-to-volume ratio and hence can explain the frequent observation that the overall properties of polymer nanocomposites cannot be determined by classical mixing rules, which only consider the behavior of the individual constituents.

Interphase characterization for nanocomposites poses hardly solvable challengesto the experimenter and is still an unsolved problem in many cases. Instead of real experiments, we perform pseudo experiments using our recently developed Capriccio method, which is an MD-FE domain-decomposition tool specifically designed for amorphous polymers. These pseudo-experimental data then serve as input for a typical inverse parameter identification. With this procedure, spatially varying mechanical properties inside the polymer are, for the first time, translated into intuitively understandable profiles of continuum mechanical parameters.

As a model material, we employ silica-enforced polystyrene, for which our procedure reveals exponential saturation profiles for Young’s modulus and the yield stress inside the interphase, where the former takes about seven times the bulk value at the particle surface and the latter roughly triples. Interestingly, hardening coefficient and Poisson’s ratio of the polymer remain nearly constant inside the interphase. Besides gaining insight into the constitutive influence of filler particles, these unexpected and intriguing results also offer interesting explanatory options for the failure behavior of polymer nanocomposites.

Contact:

Maximilian Ries
Institute of Applied Mechanics
Friedrich-Alexander-Universiät Erlangen-Nürnberg
Egerlandstr. 5
91058 Erlangen

License:

Creative Commons Attribution 4.0 International

Context:

Data set supplementing  journal paper:
[1] Ries, M.; Possart, G.; Steinmann, P. & Pfaller, S., "A coupled MD-FE methodology to characterize mechanical interphases in polymeric nanocomposites," International Journal of Mechanical Sciences, Elsevier, 2021, 106564.

This dataset contains the results of a multiscale study on polystyrene-silica nanocomposites using an atomistic-continuum coupling approach. 120 polystyrene samples, each containing 2 nano-sized silica particles are subjected to uniaxial tension. Here we use coarse-grained molecular dynamics (MD) domain embedded into a larger finite element (FE) region. These two resolutions are coupled in a concurrent multiscale fashion using the so-called Capriccio method. We observe the deformation state of the MD and FE domain, as well as the relative displacement of the two nanoparticles with respect to each other. Based on this pseudo-experimental data, we derive the material properties (Young's modulus, Poisson's ratio, yield stress, hardening) of the interphase forming in the proximity of the nanoparticles in [1].

A more detailed description of the used methods can be found in Ries et al.  [1].

Content:

The attached text file contains the following quantities (columns) for all samples (rows):

sample: [initial nanoparticle distance]-ID

d0_NP: initial distance of nanoparticles in nm

rot_x: rotation of nanoparticles with respect to x-axis in degree

d_NP: distance of nanoparticles in nm (after equilibration)

Elements: number of finite elements

Element_warnings: number of element warnings by Abaqus

LS: loadstep 1-6

eps_NP(LS): tensile strain of nanoparticles in loadstep LS in %

eps_MD(LS): tensile strain of MD domain in loadstep LS in %

eps_NP_MD(LS): tensile strain of nanoparticles normalized to eps_MD(LS) in loadstep LS

eps_FE(LS): tensile strain of FE domain in loadstep LS in %

eps_NP_FE(LS): tensile strain of nanoparticles normalized to eps_FE(LS) in loadstep LS

eps_NP_FE(LS): tensile strain of nanoparticles normalized to eps_FE(LS) in loadstep LS

u_max(LS): maximum displacement of FE nodes in load step LS in nm

F_ext(LS):  external force in load step LS in E-11 N