Investigating the structure-property correlations of pyrolyzed phenolic resin as a function of degree of carbonization.

Carbon-carbon (C/C) composites are attractive materials for high-speed flights and terrestrial atmospheric reentry applications due to their insulating thermal properties, thermal resistance, and high strength-to-weight ratio. It is important to understand the evolving structure-property correlations in these materials during pyrolysis, but the extreme laboratory conditions required to produce C/C composites make it difficult to quantify the properties . This work presents an atomistic modeling methodology to pyrolyze a crosslinked phenolic resin network and track the evolving thermomechanical properties of the skeletal matrix during simulated pyrolysis.

Evolution of Physical, Thermal, and Mechanical Properties of Poly(methyl Methacrylate)-Based Elium Thermoplastic Polymer During Polymerization.

Elium-based thermoplastic composites are a key material for future use in the marine, wind energy, and automotive industries because of their recyclability and ease of manufacture. To optimize the processing of the Elium composites to yield optimal structural properties, computational process modeling can be used to relate processing parameters to residual stresses and material durability. The key ingredient for reliable and accurate process modeling is the evolution of physical, thermal, and mechanical properties during polymerization.

Implementing reactivity in molecular dynamics simulations with harmonic force fields.

The simulation of chemical reactions and mechanical properties including failure from atoms to the micrometer scale remains a longstanding challenge in chemistry and materials science. Bottlenecks include computational feasibility, reliability, and cost. We introduce a method for reactive molecular dynamics simulations using a clean replacement of non-reactive classical harmonic bond potentials with reactive, energy-conserving Morse potentials, called the Reactive INTERFACE Force Field (IFF-R).

LUNAR: Automated Input Generation and Analysis for Reactive LAMMPS Simulations.

Generating simulation-ready molecular models for the LAMMPS molecular dynamics (MD) simulation software package is a difficult task and impedes the more widespread and efficient use of MD in materials design and development. Fixed-bond force fields generally require manual assignment of atom types, bonded interactions, charges, and simulation domain sizes. A new LAMMPS pre- and postprocessing toolkit (LUNAR) is presented that efficiently builds molecular systems for LAMMPS.

Optimal Molecular Dynamics System Size for Increased Precision and Efficiency for Epoxy Materials.

Molecular dynamics (MD) simulation is an important tool for predicting thermo-mechanical properties of polymer resins at the nanometer length scale, which is particularly important for efficient computationally driven design of advanced composite materials and structures. Because of the statistical nature of modeling amorphous materials on the nanometer length scale, multiple MD models (replicates) are typically built and simulated for statistical sampling of predicted properties. Larger replicates generally provide higher precision in the predictions but result in higher simulation times.

A Micromechanical Study of Interactions of Cyanate Ester Monomer with Graphene or Boron Nitride Monolayer.

Polymer composites, hailed for their ultra-strength and lightweight attributes, stand out as promising materials for the upcoming era of space vehicles. The selection of the polymer matrix plays a pivotal role in material design, given its significant impact on bulk-level properties through the reinforcement/polymer interface. To aid in the systematic design of such composite systems, molecular-level calculations are employed to establish the relationship between interfacial characteristics and mechanical response, specifically stiffness.

Multiscale Process Modeling of Semicrystalline PEEK for Tailored Thermomechanical Properties.

Polyether ether ketone (PEEK) is a semicrystalline thermoplastic that is used in high-performance composites for a wide range of applications. Because the crystalline phase has a higher mass density than that of the amorphous phase, the evolution of the crystalline phase during high-temperature annealing processing steps results in the formation of residual stresses and laminate deformations, which can adversely affect the composite laminate performance. Multiscale process modeling, utilizing molecular dynamics, micromechanics, and phenomenological PEEK crystal kinetic laws, is used to predict the evolution of volumetric shrinkage, elastic properties, and thermal properties, as a function of crystalline phase evolution, and thus annealing time, in the 306-328 °C temperature range.

Evolution of Glassy Carbon Derived from Pyrolysis of Furan Resin.

Glassy carbon (GC) material derived from pyrolyzed furan resin was modeled by using reactive molecular dynamics (MD) simulations. The MD polymerization simulation protocols to cure the furan resin precursor material are validated via comparison of the predicted density and Young's modulus with experimental values. The MD pyrolysis simulations protocols to pyrolyze the furan resin precursor is validated by comparison of calculated density, Young's modulus, carbon content, sp carbon content, the in-plane crystallite size, out-of-plane crystallite stacking height, and interplanar crystallite spacing with experimental results from the literature for furan resin derived GC.

Simple and convenient mapping of molecular dynamics mechanical property predictions of bisphenol-F epoxy for strain rate, temperature, and degree of cure.

It is well-known that all-atom molecular dynamics (MD) predictions of mechanical properties of thermoset resins suffer from multiple accuracy issues associated with their viscoelastic nature. The nanosecond simulation times of MD simulations do not allow for the direct simulation of the molecular conformational relaxations that occur under laboratory time scales. This adversely affects the prediction of mechanical properties at realistic strain rates, intermediate degrees of cure, and elevated temperatures.

Scalable High Tensile Modulus Composite Laminates Using Continuous Carbon Nanotube Yarns for Aerospace Applications.

An approach is established for fabricating high-strength and high-stiffness composite laminates with continuous carbon nanotube (CNT) yarns for scaled-up mechanical tests and potential aerospace structure applications. Continuous CNT yarns with up to 80% degree of nanotube alignment and a unique self-assembled graphitic CNT packing result in their specific tensile strengths of 1.77 ± 0.

Probing the Influence of Surface Chemical Functionalization on Graphene Nanoplatelets-Epoxy Interfacial Shear Strength Using Molecular Dynamics.

In this work, a characterization study of the interfacial interaction between different types of graphene nanoplatelets and an epoxy matrix is computationally performed. To quantify the discrete mutual graphene-epoxy "interfacial interaction energy" (IIE) within the nanocomposite, molecular dynamics simulations with a reactive force field are performed on a localized model of the suggested nanocomposite. Pull-out molecular dynamics simulations are also performed to predict the interfacial shear strength between the two constituents.

Computational study of effect of radiation induced crosslinking on the properties of flattened carbon nanotubes.

Flattened carbon nanotubes (flCNTs) are a primary component of many carbon nanotube (CNT) yarn and sheet materials, which are promising reinforcements for the next generation of ultra-strong composites for aerospace applications. Significant improvements in the performance of CNT materials can be realized with improvements in the load transfer between flCNTs, which are generally oriented at different angles with respect to each other. An intriguing approach to improving the load transfer is irradiation-induced chemical crosslinking between adjacent flCNTs.

Accurate predictions of thermoset resin glass transition temperatures from all-atom molecular dynamics simulation.

To enable the design and development of the next generation of high-performance composite materials, there is a need to establish improved computational simulation protocols for accurate and efficient prediction of physical, mechanical, and thermal properties of thermoset resins. This is especially true for the prediction of glass transition temperature (), as there are many discrepancies in the literature regarding simulation protocols and the use of cooling rate correction factors for predicting values using molecular dynamics (MD) simulation. The objectives of this study are to demonstrate accurate prediction the with MD without the use of cooling rate correction factors and to establish the influence of simulated conformational state and heating/cooling cycles on physical, mechanical, and thermal properties predicted with MD.

Molecular Dynamics Modeling of Interfacial Interactions between Flattened Carbon Nanotubes and Amorphous Carbon: Implications for Ultra-Lightweight Composites.

Flattened carbon nanotubes (flCNTs) naturally form in many carbon nanotube-based materials and can exhibit mechanical properties similar to round carbon nanotubes but with tighter packing and alignment. To facilitate the design, fabrication, and testing of flCNT-based composites for aerospace structures, computational modeling can be used to efficiently and accurately predict their performance as a function of processing parameters, such as reinforcement/matrix cross-linking. In this study, molecular dynamics modeling is used to predict the load transfer characteristics of the interface region between the flat region of flCNTs (i.

Computational Modeling of Hybrid Carbon Fiber/Epoxy Composites Reinforced with Functionalized and Non-Functionalized Graphene Nanoplatelets.

The mechanical properties of aerospace carbon fiber/graphene nanoplatelet/epoxy hybrid composites reinforced with pristine graphene nanoplatelets (GNP), highly concentrated graphene oxide (GO), and Functionalized Graphene Oxide (FGO) are investigated in this study. By utilizing molecular dynamics data from the literature, the bulk-level mechanical properties of hybrid composites are predicted using micromechanics techniques for different graphene nanoplatelet types, nanoplatelet volume fractions, nanoplatelet aspect ratios, carbon fiber volume fractions, and laminate lay-ups (unidirectional, cross-ply, and angle-ply). For the unidirectional hybrid composites, the results indicate that the shear and transverse properties are significantly affected by the nanoplatelet type, loading and aspect ratio.

Mechanical Properties and Characterization of Epoxy Composites Containing Highly Entangled As-Received and Acid Treated Carbon Nanotubes.

Huntsman-Merrimack MIRALON carbon nanotubes (CNTs) are a novel, highly entangled, commercially available, and scalable format of nanotubes. As-received and acid-treated CNTs were added to aerospace grade epoxy (CYCOM 977-3), and the composites were characterized. The epoxy resin is expected to infiltrate the network of the CNTs and could improve mechanical properties.

Prediction of the Interfacial Properties of High-Performance Polymers and Flattened CNT-Reinforced Composites Using Molecular Dynamics.

The next generation of ultrahigh-strength composites for structural components of vehicles for manned missions to deep space will likely incorporate flattened carbon nanotubes (flCNTs). With a wide range of high-performance polymers to choose from as the matrix component, efficient and accurate computational modeling can be used to efficiently downselect compatible resins and provide critical physical insight into the flCNT/polymer interface. In this study, molecular dynamics simulation is used to predict the interaction energy, frictional sliding resistance, and mechanical binding of flCNT/polymer interfaces for epoxy, bismaleimide (BMI), and benzoxazine high-performance resins.

Wetting Simulations of High-Performance Polymer Resins on Carbon Surfaces as a Function of Temperature Using Molecular Dynamics.

Resin/reinforcement wetting is a key parameter in the manufacturing of carbon nanotube (CNT)-based composite materials. Determining the contact angle between combinations of liquid resin and reinforcement surfaces is a common method for quantifying wettability. As experimental measurement of contact angle can be difficult when screening multiple high-performance resins with CNT materials such as CNT bundles or yarns, computational approaches are necessary to facilitate CNT composite material design.

Multiscale Modeling of Epoxy-Based Nanocomposites Reinforced with Functionalized and Non-Functionalized Graphene Nanoplatelets.

The impact on the mechanical properties of an epoxy resin reinforced with pristine graphene nanoplatelets (GNP), highly concentrated graphene oxide (GO), and functionalized graphene oxide (FGO) has been investigated in this study. Molecular dynamics (MD) using a reactive force field (ReaxFF) has been employed in predicting the effective mechanical properties of the interphase region of the three nanocomposite materials at the nanoscale level. A systematic computational approach to simulate the reinforcing nanoplatelets and probe their influence on the mechanical properties of the epoxy matrix is established.

How to characterize interfacial load transfer in spiral carbon-based nanostructure-reinforced nanocomposites: is this a geometry-dependent process?

There is a great deal of attention given to spiral carbon-based nanostructures (SCBNs) because of their unique mechanical, thermal and electrical properties along with fascinating morphology. Dispersing SCBNs inside a polymer matrix leads to extraordinary properties of nanocomposites in diverse fields. However, the role of the interfacial mechanical properties of these nanocomposites remains unknown.

Simulating the effects of carbon nanotube continuity and interfacial bonding on composite strength and stiffness.

Molecular dynamics simulations of carbon nanotube (CNT) composites, in which the CNTs are continuous across the periodic boundary, overestimate the experimentally measured mechanical properties of CNT composites along the fiber direction. Since the CNTs in these composites are much shorter than the composite dimensions, load must be transferred either directly between CNTs or through the matrix, a mechanism that is absent in simulations of effectively continuous CNTs. In this study, the elastic and fracture properties of high volume fraction discontinuous carbon nanotube/amorphous carbon composite systems were compared to those of otherwise equivalent continuous CNT composites using ReaxFF reactive molecular dynamics simulations.

Modeling Skeletal Muscle Stress and Intramuscular Pressure: A Whole Muscle Active-Passive Approach.

Clinical treatments of skeletal muscle weakness are hindered by a lack of an approach to evaluate individual muscle force. Intramuscular pressure (IMP) has shown a correlation to muscle force in vivo, but patient to patient and muscle to muscle variability results in difficulty of utilizing IMP to estimate muscle force. The goal of this work was to develop a finite element model of whole skeletal muscle that can predict IMP under passive and active conditions to further investigate the mechanisms of IMP variability.

Comparing the Mechanical Response of Di-, Tri-, and Tetra-functional Resin Epoxies with Reactive Molecular Dynamics.

The influence of monomer functionality on the mechanical properties of epoxies is studied using Molecular Dynamics (MD) with the Reax Force Field (ReaxFF). From deformation simulations, the Young's modulus, yield point, and Poisson's ratio are calculated and analyzed. The results demonstrate an increase in stiffness and yield strength with increasing resin functionality.

A validated model of passive skeletal muscle to predict force and intramuscular pressure.

The passive properties of skeletal muscle are often overlooked in muscle studies, yet they play a key role in tissue function in vivo. Studies analyzing and modeling muscle passive properties, while not uncommon, have never investigated the role of fluid content within the tissue. Additionally, intramuscular pressure (IMP) has been shown to correlate with muscle force in vivo and could be used to predict muscle force in the clinic.