Multiscale Modeling of Polymer Materials at Cryogenic and Elevated Temperatures (original) (raw)
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International Journal of Plasticity, 2015
A visco-hyperelastic constitutive model, based on an original approach initially developed by (Billon, 2012) and applied to amorphous rubbery polymers for a one-dimensional formalism, was extended in this study to three-dimensional constitutive equations based on a thermodynamic framework. The model was applied to a semi-crystalline polyamide polymer, PA66. The experiments included tension and shear testing coupled with synchronized digital image correlation and infrared measurements device for capturing the time, temperature, and stress state dependence, as well as the complex thermomechanical coupling exhibited by the material under large deformation. A notion of equivalent strain rate (based on the timetemperature principle superposition) was also introduced to show its capability to build master curves and therefore decrease the number of testing needed to build a material database. The model is based on the Edward Vilgis theory (1986) and accounts for chains network reorganization under external loading through the introduction of an evolution equation for the internal state variable, η, representing the degree of mobility of entanglement points. The model accounting for the equivalent strain rate notion was calibrated using master curves. The thermomechanical model agreed well with the experimental mechanical and temperature measurements under tension and shear conditions. The approach developed in this study may open a different way to model the polymer behavior.
Molecular dynamics simulations of uniaxial deformation of thermoplastic polyimides
Soft Matter, 2016
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Prediction of Mechanical Properties of Polymers with Various Force Fields
46th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 2005
The effect of force field type on the predicted elastic properties of a polyimide is examined using a multiscale modeling technique. Molecular Dynamics simulations are used to predict the atomic structure and elastic properties of the polymer by subjecting a representative volume element of the material to bulk and shear finite deformations. The elastic properties of the polyimide are determined using three force fields: AMBER, OPLS-AA, and MM3. The predicted values of Young's modulus and shear modulus of the polyimide are compared with experimental values. The results indicate that the mechanical properties of the polyimide predicted with the OPLS-AA force field most closely matched those from experiment. The results also indicate that while the complexity of the force field does not have a significant effect on the accuracy of predicted properties, small differences in the force constants and the functional form of individual terms in the force fields determine the accuracy of the force field in predicting the elastic properties of the polyimide.
Multiscale Constitutive Modeling of Polymer Materials
2006
My sincere thanks to Prof. Gregory Odegard, for advising me on issues throughout the program; to Prof. Ranjit Pati, Prof. Spandan Maiti and Prof. Reza Yassar for their valuable guidance and for being on my dissertation committee. I am grateful to all my colleagues at Computational Mechanics and Materials Research Laboratory (CMMRL) and Prof. Pati's Laboratory for their support and assistance at various stages of this research. Most importantly, I will always be indebted to my family for their support and encouragement to pursue my dreams. Finally, I would like to express my appreciation for all the readers of this manuscript, who I hope will find it useful and carry on the work with same dedication and integrity I have valued in all the above mentioned people. This research was jointly sponsored by National Aeronautics and Space Administration under grants NNL04AA85G and the National Science Foundation under grant DMI-0403876. Multiscale Modeling Computational Chemistry Computational Mechanics Quantum Mechanics Micromechanics Structural Mechanics Nanomechanics Length scale (m) Discrete molecular structure Continuous material structure Time scale (sec)
Influence of representative volume element size on predicted elastic properties of polymer materials
Modelling and Simulation in Materials Science and Engineering, 2009
Molecular dynamics (MD) simulations and micromechanical modeling are used to predict the bulk-level Young's modulus of polycarbonate and polyimide polymer systems as a function of representative volume element (RVE) size and force field type. The bulk-level moduli are determined using the predicted moduli of individual finite-sized RVEs (microstates) using a simple averaging scheme and an energy-biased micromechanics approach. The predictions are compared to experimental results. The results indicate that larger RVE sizes result in predicted bulk-level properties that are in closer to the experiment than the smaller RVE sizes. Also, the energy-biased micromechanics approach predicts values of bulk-level moduli that are in better agreement with experiment than those predicted with simple microstate averages. Finally, the results indicate that negatively-valued microstate Young's moduli are expected due to nanometer-scale material instabilities, as observed previously in the literature.
The Journal of Chemical Physics, 2009
Isothermal compression of poly ͑dimethylsiloxane͒, 1,4-poly͑butadiene͒, and a model Estane ® ͑in both pure form and a nitroplasticized composition similar to PBX-9501 binder͒ at pressures up to 100 kbars has been studied using atomistic molecular dynamics ͑MD͒ simulations. Comparison of predicted compression, bulk modulus, and U s − u p behavior with experimental static and dynamic compression data available in the literature reveals good agreement between experiment and simulation, indicating that MD simulations utilizing simple quantum-chemistry-based potentials can be used to accurately predict the behavior of polymers at relatively high pressure. Despite their very different zero-pressure bulk moduli, the compression, modulus, and U s − u p behavior ͑including low-pressure curvature͒ for the three polymers could be reasonably described by the Tait equation of state ͑EOS͒ utilizing the universal C parameter. The Tait EOS was found to provide an excellent description of simulation PVT data when the C parameter was optimized for each polymer. The Tait EOS parameters, namely, the zero-pressure bulk modulus and the C parameter, were found to correlate well with free volume for these polymers as measured in simulations by a simple probe insertion algorithm. Of the polymers studied, PDMS was found to have the most free volume at low pressure, consistent with its lower ambient pressure bulk modulus and greater increase in modulus with increasing pressure ͑i.e., crush-up behavior͒.
Thermal properties of bulk polyimides: insights from computer modeling versus experiment
Soft Matter, 2014
Due to the great importance for many industrial applications it is crucial from the point of view of theoretical description to reproduce thermal properties of thermoplastic polyimides as accurate as possible in order to establish "chemical structure-physical properties" relationships of new materials. In this paper we employ differential scanning calorimetry, dilatometry, and atomistic molecular dynamics (MD) simulations to explore whether the state-of-the-art computer modeling can serve as a precise tool for probing thermal properties of polyimides with highly polar groups. For this purpose the polyimide R-BAPS based on dianhydride 1,3-bis(3 0 ,4-dicarboxyphenoxy)benzene (dianhydride R) and diamine 4,4 0 -bis(4 00aminophenoxy)biphenyl sulphone) (diamine BAPS) was synthesized and extensively studied. Overall, our findings show that the widely used glass-transition temperature T g evaluated from MD simulations should be employed with great caution for verification of the polyimide computational models against experimental data: in addition to the well-known impact of the cooling rate on the glass-transition temperature, correct definition of T g requires cooling that starts from very high temperatures (no less than 800 K for considered polyimides) and accurate evaluation of the appropriate cooling rate, otherwise the errors in the measured values of T g become undefined. In contrast to the glass-transition temperature, the volumetric coefficient of thermal expansion (CTE) does not depend on the cooling rate in the low-temperature domain (T < T g ) so that comparison of computational and experimental values of CTE provides a much safer way for proper validation of the theoretical model when electrostatic interactions are taken into account explicitly. Remarkably, this conclusion is most likely of generic nature: we show that it also holds for the commercial polyimide EXTEM™, another polyimide with a similar chemical structure.
Use of Mechanical Modeling To Study Multiphase Polymeric Materials
Macromolecules, 2001
Viscoelastic properties of several multiphase polymeric materials were investigated in connection with their morphologies. Both mechanical modeling and mechanical spectrometry were used as tools for extracting information about morphology, molecular mobility, and interfacial interactions in such heterogeneous systems. The use of self-consistent mechanical models in direct and reverse modes was shown to be of interest for in depth discussion of the possibilities and limitations of the theoretical mechanical approach in the understanding of experimental dynamic mechanical data of complex polymeric materials. Christensen and Lo's model was used in direct mode to highlight mechanical coupling effects in binary thermoset/thermoplastic polymer blends. It was shown that the magnitude of these effects between phases in such blends, as in composite materials, depends not only on mechanical properties and relative content of each phase but also on the geometric arrangement of the polymeric phases. Furthermore, a new way of presenting experimental dynamic mechanical data and simulations resulting from direct mechanical approach, was also proposed as a qualitative, well-suited probe of morphology of multicomponent polymeric materials. The models of Christensen and Lo and of Herve and Zaoui were both used in reverse mode. It was demonstrated that such a new approach for mechanical modeling allows the extraction of the actual viscoelastic properties of one phase among others in multiphase polymeric materials. That is of particular interest for investigating the actual properties of the interfacial area in such complex systems, whose experimental in situ detection and characterization remain problem.
2001
The objective of this paper is to discuss and present the results of an experimental study that considers the effects of crosslink density, molecular weight and temperature on the viscoelastic behavior including physical aging of an advanced polymer. Five distinct variations in crosslink density were used to evaluate the differences in mechanical performance of an advanced polyimide. The physical aging behavior was isolated by conducting sequenced, short-term isothermal creep compliance tests in tension. These tests were performed over a range of sub-glass transition temperatures. The material constants, material master curves and physical aging-related parameters were evaluated as a function of temperature crosslink density and molecular weigh using time-temperature and time-aging time superposition techniques.