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).

/pdf/cellulose-nanomaterials-review-structure-properties-and-2z8x922p3v.pdf

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.

/pdf/review-current-international-research-into-cellulose-vduhai1vrx.pdf

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

: The report presents the development of rational methods of structural optimization for flat, corrugated core (single truss core) and web-core sandwich panels under two loading conditions: in-plane shear loads, and combined uniaxial compression and in-plane shear loads. These methods provide a means by which minimum weight structures can be designed for a given load index, plate width, length, and face and core materials. The methods developed can be used as a means of rational material selection by comparing weights of optimum construction for various material systems as a function of applied load index. The methods are sufficiently general to account for orthotropic or isotropic face and core materials and various boundary conditions. Design procedures are given in detail for the design engineer to use.

https://apps.dtic.mil/dtic/tr/fulltext/u2/656056.pdf

Structural optimization of flat, corrugated core and web-core sandwich panels under in-plane shear loads and combined uniaxial compression and in-plane shear loads

: Methods of analysis are developed to provide the stresses (both bending and membrane) and deformations in specially orthotropic circular cylindrical shells subjected to localized loads. An accurate shell theory is employed which includes the effects of orthotropy and transverse shear deformation. The governing differential equations are obtained, and are transformed into a set of algebraic equations through expanding all displacements, rotations, and the localized loading in a doubly infinite series in the shell coordinates. A computer program is formulated, and included, to perform numerical calculations easily using the analytic solutions. Comparisons and design curves are made for large variations in orthotropy which cover all known composite materials. Various sizes and shapes of localized loadings are systematically explored and reported. The various curves and tables presented can be used directly in design through interpolation. The computer program is included to permit the handling of any additional cases. (Author-PL)

Stresses in Circular Cylindrical Shells of Composite Materials Subjected to Localized Loads

Preliminary Design of Piezo-activated Composite Sandwich Fins for Projectile Maneuverability

Consider any elastic body with a constant coefficient of thermal expansion, α, in the units of in/in/°F, or equivalent, at a uniform temperature wherein the body is assumed to be free of thermal stresses and strains. If the body is free to deform, and the temperature is raised slowly to a temperature of T degrees from the stress free temperature, the thermal strains produced at any material point can be written as 

$$ {\varepsilon_{{ij}}}_{{th}} = \alpha \Delta T\left( {{x_i}} \right){\delta_{{ij}}} $$

(5.1)

where x 1 are the coordinate directions, and δ ij is the Kronecker delta (δ ij = 1 for i = j, δ ij = 0 for i ≠ j). It should be noted that thermal strains are purely dilatational (i = j); thermal shear strains do not exist.

Thermal Stresses in Plates

Shells involve thin walled elastic bodies wherein one dimension is considerably smaller than the other two, but in which the midsurface is curved in at least one direction. Thus, to describe a shell succinctly, curvilinear coordinates must be employed. This causes considerable complications in the mathematical descriptions and operations, not existing in the same equations posed in a Cartesian coordinate system. It would be proper to introduce the subject of shell theory by preceding it with a course in topology. However, in what follows, the description of mathematics involving curvilinear coordinates is given, sufficient only to derive the general shell equations. In no way is the presentation rigorous or inclusive. Other texts such as Malvern (Reference 1.1) and Sokolnikoff [1.2] should be consulted by those who wish to learn more.

Jack R. Vinson

Papers

Structural optimization of flat, corrugated core and web-core sandwich panels under in-plane shear loads and combined uniaxial compression and in-plane shear loads

Stresses in Circular Cylindrical Shells of Composite Materials Subjected to Localized Loads

Preliminary Design of Piezo-activated Composite Sandwich Fins for Projectile Maneuverability

Thermal Stresses in Plates

Curvilinear Coordinate Systems