Complex Rheology in Particle-Laden Composite Materials

2003 ◽  
Author(s):  
Rekha R. Rao ◽  
Douglas B. Adolf ◽  
Lisa A. Mondy
Keyword(s):  
Composite Materials ◽  
Constitutive Equation ◽  
Particle Concentration ◽  
Model System ◽  
Fiber Spinning ◽  
Hysteretic Behavior ◽  
Manufacturing Processes ◽  
Colloidal Systems ◽  
Couette Viscometer ◽  
Epoxy Systems

The rheology of curing composite materials is important to many manufacturing processes. At Sandia, we work with particle-filled epoxy systems for a variety of applications. One particular system, designated as “459,” exhibits complex, counter-intuitive rheological dependence on temperature, flow history and particle-concentration. Despite the particles being relatively large (10 μm), 459 exhibits shear-thinning hysteretic behavior reminiscent of colloidal systems. It is hypothesized that the thixotropy arises from reaction of the 459 curative with the surface of the particulates. Under certain conditions, the addition of filler offsets the effect of epoxy polymerization on the viscosity, resulting in a viscosity that is constant with time. For this reason, we have developed an experimental model system that can be used to separate the effects of particle aggregation from the effects of cure on the viscosity. We have done experiments with this model suspension to determine its time-dependent response in step shear. In addition, we are working on a computational model that can be used to predict the behavior of the aggregating suspension. Preliminary modeling efforts focus on using a generalized Newtonian constitutive equation that relates the viscosity to the local aggregate concentration, defined by a dimensionless structure factor, to capture the time-dependence. Results from this constitutive equation are presented and compared to the experimental data from step-shear experiments in a Couette viscometer. Modeling results are also presented for a transient fiber spinning problem where the free surface evolves as the viscosity develops over time.

Fiber symmetry

2017 ◽  
Author(s):  
David J. Steigmann
Keyword(s):  
Composite Materials ◽  
Constitutive Equation ◽  
Transversely Isotropic ◽  
Fiber Reinforced ◽  
Fiber Reinforced Materials ◽  
Reinforced Materials

This chapter develops the general constitutive equation for transversely isotropic, fiber-reinforced materials. Applications include composite materials and bio-elasticity.

Migration and Settling of Particulates in Filled Epoxies

2003 ◽  
Author(s):  
Lisa Mondy ◽  
Rekha Rao ◽  
Eric Lindgren ◽  
Amy Sun ◽  
Robert Lagasse ◽  
...  
Keyword(s):  
Particle Concentration ◽  
Particle Migration ◽  
Polymerization Reaction ◽  
Temperature Dependent ◽  
Filled Polymers ◽  
Post Test ◽  
Manufacturing Applications ◽  
Microscopy Data ◽  
Suspension Model ◽  
Epoxy Systems

Manufacturing applications for filled polymers include encapsulation of microelectronics and injection molding of composite parts. Predictive tools for simulating these manufacturing processes require knowledge of time- and temperature-dependent rheology of the polymer as well as information about local particle concentration. The overall system rheology is highly dependent on the particle concentration. The local particle concentration can change due to gravity, convection and shear-induced migration. For the epoxy systems of interest, an extent of reaction can be used to track the degree of cure. We couple the curing model with a diffusive flux suspension model [Zhang and Acrivos 1994] to determine the particle migration. This results in a generalized Newtonian model that has viscosity as a function of temperature, cure and concentration. Using this model, we examine settling of the particulate phase in both flowing and quiescent curing systems. We focus on settling in molds and flow in wide-gap counter-rotating cylinders. The heat transfer, including the exothermic polymerization reaction, must be modeled to achieve accurate results. The model is validated with temperature measurements and post-test microscopy data. Particle concentration is determined with x-ray microfocus visualization or confocal microscopy. Agreement between the simulations and experimental results is fair.

THE DIFFERENTIAL CONSTITUTIVE EQUATION AND MODEL OF ABALONE NACRE BY NANOINDENTER

2013 ◽  
Vol 13 (06) ◽  
pp. 1340011
Author(s):  
ZHIJUN ZHANG ◽  
HONLEI JIA ◽  
JIYU SUN ◽  
MINGZE LING ◽  
YUEMING WANG ◽  
...  
Keyword(s):  
Composite Materials ◽  
Constitutive Equation ◽  
Self Assembly ◽  
Mechanical Performance ◽  
Viscoelastic Behavior ◽  
Laminated Composite ◽  
Medical Apparatus ◽  
Assembly Method ◽  
Multiple Length Scales ◽  
Laminated Composite Materials

Nacre has a complex hierarchical microarchitecture that spans over multiple length scales from nanoscale to macroscale. Its structures are optimized leading to extraordinary mechanical performance and energy absorption. Nacre's special characteristics of the self-assembly method have attracted the interest of material scientists to develop laminated composite materials, molecular scale self-assembly and biomineralization. Nanoindentation testing can determine a material's anisotropic properties through a single indentation. In the present study, nanoindentation stress–strain curves were used to characterize the complete mechanical behavior of nacre of abalone shell. A differential constitutive equation was developed with time-dependent spring constants k and viscosities η. Furthermore, to describe the complex viscoelastic behavior of abalone nacre, a descriptive representation of the linear viscoelasticity law for the multilayer matrix was formulated. A qualitative model for the relationship between nacre structure and mechanical properties of nacre may help develop bionic composite materials for micro-aircraft, bionic tribology, bionic medical apparatus and bionic organs (tissue engineering).

scholarly journals Epoxyorganosilane Finishing Compositions for Fibrous Fillers of Thermosetting and Thermoplastic Binders

Polymers ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 59
Author(s):  
Alexey V. Shapagin ◽  
Natalia A. Gladkikh ◽  
Arkadiy A. Poteryaev ◽  
Valentina Yu. Stepanenko ◽  
Uliana V. Nikulova ◽  
...  
Keyword(s):  
Free Energy ◽  
Composite Materials ◽  
Surface Free Energy ◽  
Materials Science ◽  
Sessile Drop ◽  
Inert Atmosphere ◽  
Energy Characteristics ◽  
Urgent Task ◽  
Wide Range ◽  
Epoxy Systems

The development of universal finishing compositions for fibers of various natures is an urgent task for polymer composite materials science. The developed finishes can be used for the fiber reinforcement of polymer matrices with a wide range of surface free energy characteristics. Epoxy systems modified with diaminesilane in a wide concentration range were examined by optical interferometry, FTIR spectroscopy, DSC and the sessile drop technique. It was shown that the partial curing of epoxy resin by diaminesilane at room temperature under an inert atmosphere, followed by contact with air, leads to a significant increase of the surface free energy of the system. Varying the concentration of diaminesilane allows us to effectively regulate the surface free energy of the composition. This makes it possible to use fibers finished with epoxyaminosilane compositions in composite materials based on a various thermosetting and thermoplastic binders with a surface tension of up to 75 mJ/m2.

scholarly journals A Review on Developments in Manufacturing Process and Mechanical Properties of Natural Fiber Composites

2021 ◽  
Vol 2 (01) ◽  
pp. 13-23
Author(s):  
Md. Maruf Billah ◽  
Md. Sanaul Rabbi ◽  
Afnan Hasan
Keyword(s):  
Mechanical Properties ◽  
Composite Materials ◽  
Natural Fiber ◽  
Fiber Composite ◽  
Synthetic Fiber ◽  
Manufacturing Processes ◽  
Manufacturing Cost ◽  
Mechanical And Thermal Properties ◽  
Natural Fiber Composite ◽  
Fiber Composite Materials

From the last few decades, the study of natural fiber composite materials has been gaining strong attention among researchers, scientists, and engineers. Natural fiber composite materials are becoming good alternatives to conventional materials because of their lightweight, high specific strength, low thermal expansion, eco-friendly, low manufacturing cost, nonabrasive and bio-degradable characteristics. It is proven that natural fiber is a great alternative to synthetic fiber in the sector of automobiles, railway, and aerospace. Researchers are developing various types of natural fiber-reinforced composites by combining different types of natural fiber such as jute, sisal, coir, hemp, abaca, bamboo, sugar can, kenaf, banana, etc. with various polymers such as polypropylene, epoxy resin, etc. as matrix material. Based on the application and required mechanical and thermal properties, numerous natural fiber-based composite manufacturing processes are available such as injection molding, compression molding, resin transfer molding, hand lay-up, filament welding, pultrusion, autoclave molding, additive manufacturing, etc. The aim of the paper is to present the developments of various manufacturing processes of natural fiber-based composites and obtained mechanical properties.

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