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 existing analysis methods for laminated composite material structural components assume structural integrity between laminae and predict load carrying capabilities considerably higher than those sometimes obtained experimentally. These methods do not include the means to determine accurately the interlaminar shear and normal stresses, which can cause premature structural failure. Methods of analysis are presented herein for a laminated circular cylindrical shell composed of generally orthotropic materials subjected to arbitrary axially symmetric loadings. Elastic shell theory, including transverse shear deformation, is utilized. By treating each lamina individually, in conjunction with imposing stress and displacement boundary conditions between laminae, the governing equations for the individual laminae are combined, yielding the interlaminar shear and normal stresses as explicit dependent variables. A parametric study for a generally othotropic circular cylindrical shell, subjected to a uniform pressure with both clamped and simple supported end boundary conditions is presented. Variables include laminate geometry, fiber orientation, stacking sequence and material properties. The solutions obtained provide insight into the interlaminar stress fields of shells with any number of plies, and provide a baseline for finite element and finite difference solutions for the same problem. A computer program has been formulated to expedite calculations with the analytical solution.

Interlaminar stresses in laminated cylindrical shells of composite materials

: Recent experiments have shown that significant improvements can be made in the structural efficiency of single lap joints through several modifications Tests have been conducted in which the adherends were linearly tapered from full panel thickness to practically zero thickness over the length of the bondline in the load direction Further, tests were conducted to examine the effects of introducing small grooves on the adhesive side of the adherends, perpendicular to the load direction Similarly, grooves only over the thicker half of the tapered adherend were investigated, because these grooves do introduce stress concentrations In each case, significant improvements in joint efficiency were made under either static or fatigue loadings Additionally, specific observations are made pertaining to the residual strain effect due to joint fabrication on the fatigue life of strain effect due to joint fabrication on the fatigue life of the joint Second, studies were made on the effects of using hybrid adherends and their effect on joint efficiency

The Analysis and Design of Composite Material Bonded Joints.

Cylindrical bending of a sandwich panel assembly consisting of straight and curved sections is considered. The sandwich assembly is statically determinate, loaded by a uniform pressure and possibly by forces and moments at its edges. The influence of the change of geometry upon the stresses and displacements at the transition zone between the different panel sections is investigated. An exact asymptotic mathematical model based on a number of small parameters is derived. The model assumes the faces of the sandwich panels to be thin elastic beams obeying the Kirchhoff-Love assumptions, while the isotropic core is treated as a 2-D elastic medium. An asymptotic expansion technique is exploited to derive analytical estimate formulae for calculating the deformation and stress distribution characteristics at the critical sections of the assembly. A numerical example illustrates the applicability of the derived formulae, and the validity of the proposed approach is demonstrated through comparison with FEM calcul...

Asymptotic analysis for the curved/straight sandwich panel junctions

The results of an experimental program are given which provide quantitative and reproducible shear property data for many of the present and promising adhesives for use in bonded joints in composite material structures. The experiments employ a composite material test specimen in which the adhesive material is in a film configuration, typical of bonded joints, rather than measuring bulk adhesive properties. Because both the flexural and in-plane stiffnesses of the glass-epoxy adherends of the test piece are extremely large (> 106) compared to a parameter proportional to the shear and extensional modulus of the adhesive film, the adhesive film is virtually in a state of constant shear stress with negligible normal stresses. The details of the shear test piece have been published previously. The adhesives tested were those recommended by the major adhesive manufacturers, those selected by NASA Langley in the civil aviation program, and those utilized in the USAF PABST program. The data reported includes the ultimate shear stress, initial shear modulus, and elongation to failure, both mean values and standard deviations, for specimens made by the adhesive manufacturer and the University of Delaware.

Shear Properties of Promising Adhesives for Bonded Joints in Composite Material Structures

Comparative Study of Two Different Conceptual Design Principles for Non-Circular Pressurized Sandwich Fuselage Sections Using a High-Order Sandwich Theory Formulation

Jack R. Vinson

Papers

Interlaminar stresses in laminated cylindrical shells of composite materials

The Analysis and Design of Composite Material Bonded Joints.

Asymptotic analysis for the curved/straight sandwich panel junctions

Shear Properties of Promising Adhesives for Bonded Joints in Composite Material Structures

Comparative Study of Two Different Conceptual Design Principles for Non-Circular Pressurized Sandwich Fuselage Sections Using a High-Order Sandwich Theory Formulation