Roy L. McCullough

Bio: Roy L. McCullough is an academic researcher from University of Delaware. The author has contributed to research in topics: Fiber & Heat generation. The author has an hindex of 21, co-authored 53 publications receiving 1504 citations.

An Analysis of Mechanisms Governing Fusion Bonding of Thermoplastic Composites

Abstract: A number of mechanisms have been proposed in the literature as contributors to the strength development at the polymer-polymer interface during fusion bonding of thermoplastic composites. Of these, healing and intimate contact emerge as fundamental mechanisms governing bonding. Intimate contact refers to the development of the amount of surface area that is physically contacted at the interface at any time, and healing describes the migration of polymer chains across the interface in intimate contact.This work provides a new theoretical development of a coupled bonding model that accounts for variability in initiation time for healing due to growth in the area in intimate contact. The generalized coupled bonding model is valid for any set of processing conditions and reduces to the proper controlling mechanism as dictated by the process. Analysis revealed a key dimensionless group, Q, that captures the coupled nature of the mechanisms governing fusion bonding. By evaluating Q, which is a function of mater...

Characterization of nanoscale property variations in polymer composite systems: 1. Experimental results

Abstract: A technique utilizing the indenting capabilities of the atomic force microscope is used to evaluate local changes in the response of polymer composite systems near the fiber-matrix interface. Room temperature and elevated temperature indentation response is measured for several model composite systems. Results of indentation studies are compared to finite element model predictions to understand the influence of interphase properties on the measured responses. For sized fiber systems, unexpected property variations are observed, leading to the discovery of a possible interphase formation mechanism in these systems. q 1998 Published by Elsevier Science Ltd. All rights reserved.

Behavior of discontinuous fiber composites: Fiber orientation

Abstract: The behavior of polymeric materials reinforced by discontinuous. Descriptors for the planar and axial orientation distributions are discussed. Predictions of micromechanical models and experimental data are presented to illustrate the influence of orientation state upon elastic constants, thermal coefficients of expansion and tensile strength. Results are presented for the notched strength and compressive creep behavior of the glass/phenolic composite of two orientation states. Finally, the implications of these results upon the design of elements molded of discontinuous fiber composites are discussed.

Orientation Behavior of Fibers in Concentrated Suspensions

Abstract: A mathematical model is developed to predict the orientation distribution function of rigid fibers in concentrated suspensions. The model contains a phenomenological term to account for interactions between fibers. Predictions of the model are tested against experiments in simple shear flow, using suspensions of nylon monofilaments in silicone oil. The results compare favorably for steady-state distributions, though the theory predicts a more rapid approach to steady state than actually occurs. The model predicts, and experiments show, that fiber orientation is not reversible when the flow is reversed. The model is useful for predicting the effects of processing on fiber orienta tion in short fiber composites.

Carbon nanotube/carbon fiber hybrid multiscale composites

Abstract: Carbon nanotubes were grown directly on carbon fibers using chemical vapor deposition. When embedded in a polymer matrix, the change in length scale of carbon nanotubes relative to carbon fibers results in a multiscale composite, where individual carbon fibers are surrounded by a sheath of nanocomposite reinforcement. Single-fiber composites were fabricated to examine the influence of local nanotube reinforcement on load transfer at the fiber/matrix interface. Results of the single-fiber composite tests indicate that the nanocomposite reinforcement improves interfacial load transfer. Selective reinforcement by nanotubes at the fiber/matrix interface likely results in local stiffening of the polymer matrix near the fiber/matrix interface, thus, improving load transfer.

Models proposed to explain the electrical conductivity of mixtures made of conductive and insulating materials

Abstract: The electrical conductivity of mixtures of conductive and insulating materials is reviewed In general, the conductivity of such mixtures increases drastically at a certain concentration of the conductive component, the so-called percolation concentration Among the parameters influencing the percolation concentration, the filler distribution, filler shape, filler/matrix interactions and the processing technique are the most important ones On the basis of these parameters, different models have been proposed aimed at the prediction of the conductivity or the percolation concentration It will be shown here that statistical, geometric or thermodynamic models explain the conductivity behaviour of specific mixtures on the basis of insufficient assumptions However, the conductivity seems to be predictable with the help of structure-oriented models