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

Many applications of structural materials involving composites include impact or dynamic loading in a humid environment. Composite materials are known to degrade when subjected to humid conditions, and therefore the humidity confounds the difficulty of determining the high strain rate behavior of composites. Several researchers have found that water absorption by composites causes degradation of matrix dominated quasi-static properties. However, very little is known of the effect of absorbed moisture on the high strain rate properties of polymer matrix composites, that are useful in the automotive, aerospace, and naval applications of composite structures. A Split-Hopkinson Pressure Bar facility is used herein to study the effect of absorbed moisture in high strain rate tests (200–1200/s) of a unidirectional IM7/8551-7 graphite/epoxy composite. The study includes dry, medium, and saturated moisture conditions. The tests show significant variation of high strain rate properties from static properties, and the reasons are identified. In addition, a better understanding of the effect of the matrix and fiber/matrix interface on the high strain rate properties of composites is achieved.

Determination of moisture effects on impact properties of composite materials

Results obtained as part of a design study regarding a non-circular pressurized sandwich fuselage cross section are presented. The originating problem is associated with preliminary studies for the “Global Range Transport” envisaged by the “New World Vistas” program of the United States Air Force. The modeling and analysis is conducted using a high-order sandwich theory formulation in which the elastic response of each face laminate is accounted for, including bending-stretching coupling, and including the transverse flexibility of the core material. The paper includes a presentation of the high-order sandwich theory approach adopted for the analysis of the fuselage section, including the formulations for flat and curved sandwich panels. The paper is concluded by presentation of the results of a parametric study, which includes the effects on the structural response of varying the sandwich panel mid-plane asymmetry, the core properties, and the radius of curvature of the fuselage cross section corners.

Analysis and Parametric Study of Non-Circular Pressurized Sandwich Fuselage Cross Section Using a High-Order Sandwich Theory Formulation

Analytical methods are developed by which web-core sandwich panels can be designed with minimum weight while retaining their structural integrity (i.e., structurally optimum) for a given load index, panel length and width, and specified face and web materials. These methods also provide a means for rational material selection through the comparison of weights of the minimum weight construction for various material system as a function of load index, and an assessment of weight penalties associated with the use of commercially available thicknesses. The methods account for both isotropic and orthotropic face and core material as well as various boundary conditions. Numerical results clearly show the weight savings associated with the use of second generation composite materialssuch as boron-epoxy and graphite-epoxy.

Minimum weight web-core sandwich panels subjected to uniaxial compression.

In the design of composite material structures, components must be joined in such a manner that the overall structure retains its structural integrity while performing its intended function, subjected to loads (static and dynamic) and environment (temperature, humidity).

Joining of Composite Material Structures

Methods of analysis have been developed that provide the means to determine whether a ballistic impactor of known shape, mass, and striking velocity will penetrate a given thin-walled composite material structure and if it does, what the residual velocity of the impactor will be. The methods developed require performing penetration experiments at two striking velocities (with suitable replicates for statistical purposes) for any given composite structural target. From this minimum number of tests, one can predict the penetration, nonpenetration, and residual velocity of an impact at other striking velocities. This provides a dramatic reduction in the amount of expensive testing required to study penetration due to ballistic impact. It also provides a less expensive and less time-consuming means to select the best material system and structural configuration to resist ballistic impact. Finally, it shows that the physics of ballistic impact and the penetration phenomena is modeled satisfactorily. These methods also accurately predict the ballistic limit.

Jack R. Vinson

Papers

Determination of moisture effects on impact properties of composite materials

Analysis and Parametric Study of Non-Circular Pressurized Sandwich Fuselage Cross Section Using a High-Order Sandwich Theory Formulation

Minimum weight web-core sandwich panels subjected to uniaxial compression.

Joining of Composite Material Structures

Ballistic Impact of Thin-Walled Composite Structures