This critical review provides a processing-structure-property perspective on recent advances in cellulose nanoparticles and composites produced from them. It summarizes cellulose nanoparticles in terms of particle morphology, crystal structure, and properties. Also described are the self-assembly and rheological properties of cellulose nanoparticle suspensions. The methodology of composite processing and resulting properties are fully covered, with an emphasis on neat and high fraction cellulose composites. Additionally, advances in predictive modeling from molecular dynamic simulations of crystalline cellulose to the continuum modeling of composites made with such particles are reviewed (392 references).

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Cellulose nanomaterials review: structure, properties and nanocomposites

This work presents the analytic and experimental development of piezoelectric actuators as elements of intelligent structures, i.e., structures with highly distributed actuators, sensors, and processing networks. Static and dynamic analytic models are derived for segmented piezoelectric actuators that are either bonded to an elastic substructure or embedded in a laminated composite. These models lead to the ability to predict, a priori, the response of the structural member to a command voltage applied to the piezoelectric and give guidance as to the optimal location for actuator placement. A scaling analysis is performed to demonstrate that the effectiveness of piezoelectric actuators is independent of the size of the structure and to evaluate various piezoelectric materials based on their effectiveness in transmitting strain to the substructure. Three test specimens of cantilevered beams were constructed: an aluminum beam with surface-bonded actuators, a glass/epoxy beam with embedded actuators, and a graphite/epoxy beam with embedded actuators. The actuators were used to excite steady-state resonant vibrations in the cantilevered beams. The response of the specimens compared well with those predicted by the analytic models. Static tensile tests performed on glass/epoxy laminates indicated that the embedded actuator reduced the ultimate strength of the laminate by 20%, while not significantly affecting the global elastic modulus of the specimen.

Use of piezoelectric actuators as elements of intelligent structures

This paper provides an overview of recent progress made in the area of cellulose nanofibre-based nanocomposites. An introduction into the methods used to isolate cellulose nanofibres (nanowhiskers, nanofibrils) is given, with details of their structure. Following this, the article is split into sections dealing with processing and characterisation of cellulose nanocomposites and new developments in the area, with particular emphasis on applications. The types of cellulose nanofibres covered are those extracted from plants by acid hydrolysis (nanowhiskers), mechanical treatment and those that occur naturally (tunicate nanowhiskers) or under culturing conditions (bacterial cellulose nanofibrils). Research highlighted in the article are the use of cellulose nanowhiskers for shape memory nanocomposites, analysis of the interfacial properties of cellulose nanowhisker and nanofibril-based composites using Raman spectroscopy, switchable interfaces that mimic sea cucumbers, polymerisation from the surface of cellulose nanowhiskers by atom transfer radical polymerisation and ring opening polymerisation, and methods to analyse the dispersion of nanowhiskers. The applications and new advances covered in this review are the use of cellulose nanofibres to reinforce adhesives, to make optically transparent paper for electronic displays, to create DNA-hybrid materials, to generate hierarchical composites and for use in foams, aerogels and starch nanocomposites and the use of all-cellulose nanocomposites for enhanced coupling between matrix and fibre. A comprehensive coverage of the literature is given and some suggestions on where the field is likely to advance in the future are discussed.

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Review: current international research into cellulose nanofibres and nanocomposites

Hexagonal ferrites: A review of the synthesis, properties and applications of hexaferrite ceramics

The numerical implementation of the model of brittle fracture developed in Francfort and Marigo (1998. J. Mech. Phys. Solids 46 (8), 1319–1342) is presented. Various computational methods based on variational approximations of the original functional are proposed. They are tested on several antiplanar and planar examples that are beyond the reach of the classical computational tools of fracture mechanics.

Numerical experiments in revisited brittle fracture

Polymer matrix composites offer excellent properties such as high speci® c strength and stiffness, which make them attractive for many naval, aerospace, and automotive applications. Although they are candidate materials for many applicationswhere high strain rate loading is probable, little is known of the material responses to shock loading for most composite materials. Because mechanical properties vary signi® cantly with strain rate, the use of static properties in the analysis and design of structures that undergo dynamic loadings can, on one hand, lead to a very conservative overweight design or, on the other hand, can lead to designs that fail prematurely and unexpectedly. The use of dynamic material properties will ensure the design of composite structures, which are weight ef® cient and structurally sound when they are subjected to dynamic loads. A split Hopkinson pressure bar is used to obtain compressive mechanical properties of Cycom 5920/1583, an uniaxial cloth, E-glass/rubber toughened epoxy composite being used presently by the Electric Boat Division of General Dynamics for undersea structures. Yield stress, yield strain, ultimate stress, ultimate strain, andmodulus of elasticity values are presented and analyzed wherein the strain rates vary from 60 to 1150 s i 1 .

High Strain Rate Properties of Cycom 5920/1583

In shells, bending stresses in addition to the membrane stresses exist near each structural discontinuity (such as at edge supports, rings, stringers, holes, etc.) and each load discontinuity. This region is the “bending boundary layer”. In sandwich shells, mid-plane asymmetry can be employed to minimize these bending stresses. Governing equations for mid-plane asymmetric sandwich cylindrical shell subjected to axially symmetric loads are derived herein and solved. The solution involves a mid-plane asymmetry factor ϕ, defined herein such that for any asymmetric sandwich construction, -1 < ϕ < 1. Therefore, perturbation solutions are easily obtained using the solutions for the midplane symmetric cylindrical shell.

Theory for Midplane Asymmetric Sandwich Cylindrical Shells

A split Hopkinson pressure bar is used to obtain high-strain-rate, compressive mechanical properties of a uniweave AS4/3501-6 compositelaminate with and without reinforcement stitching in the through thickness. For both in-plane and out-of-plane directions, the compressive mechanical properties of yield stress, yield strain, ultimate strength, ultimate strain, and modulus of elasticity are determined for strain rates varying from 234 to 1216 s i 1 .

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Jack R. Vinson

Papers

High Strain Rate Properties of Cycom 5920/1583

Theory for Midplane Asymmetric Sandwich Cylindrical Shells

Through-Thickness Stitching Effects on Graphite/Epoxy High-Strain-Rate Compressive Properties

Minimum weight corrugated-core sandwich panels subjected to uniaxial compression☆

The natural vibrations of plates composed of composite materials