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

Publisher Summary This chapter describes the mixed mode cracking in layered materials. There is ample experimental evidence that cracks in brittle, isotropic, homogeneous materials propagate such that pure mode I conditions are maintained at the crack tip. An unloaded crack subsequently subject to a combination of modes I and II will initiate growth by kinking in such a direction that the advancing tip is in mode I. The chapter also elaborates some of the basic results on the characterization of crack tip fields and on the specification of interface toughness. The competition between crack advance within the interface and kinking out of the interface depends on the relative toughness of the interface to that of the adjoining material. The interface stress intensity factors play precisely the same role as their counterparts in elastic fracture mechanics for homogeneous, isotropic solids. When an interface between a bimaterial system is actually a very thin layer of a third phase, the details of the cracking morphology in the thin interface layer can also play a role in determining the mixed mode toughness. The elasticity solutions for cracks in multilayers are also elaborated.

Mixed mode cracking in layered materials

Based on literature from the domains of organization science, marketing, accounting, and management information systems, this review article examines the theoretical basis of the information overload discourse and presents an overview of the main definitions, situations, causes, effects, and countermeasures. It analyzes the contributions from the last 30 years to consolidate the existing research in a conceptual framework and to identify future research directions.

The Concept of Information Overload: A Review of Literature from Organization Science, Accounting, Marketing, MIS, and Related Disciplines

Mother-of-pearl (nacre) is a platelet-reinforced composite, highly filled with calcium carbonate (aragonite). The Young modulus, determined from beams of a span-to-depth ratio of no less than 15 (a necessary precaution), is of the order of 70 GPa (dry) and 60 GPa (wet), much higher than previously recorded values. These values can be derived from ‘shear-lag’ models developed for platey composites, suggesting that nacre is a near-ideal material. The tensile strength of nacre is of the order of 170 MPa (dry) and 140 MPa (wet), values which are best modelled assuming that pull-out of the platelets is the main mode of failure. In three-point bending, depending on the span-to-depth ratio and degree of hydration, the work to fracture across the platelets varies from 350 to 1240 J m -2 . In general, the effect of water is to increase the ductility of nacre and increase the toughness almost tenfold by the associated introduction of plastic work. The pull-out model is sufficient to account for the toughness of dry nacre, but accounts for only a third of the toughness of wet nacre. The additional contribution probably comes from debonding within the thin layer of matrix material. Electron microscopy reveals that the ductility of wet nacre is caused by cohesive fracture along platelet lamellae at right angles to the main crack. The matrix appears to be well bonded to the lamellae, enabling the matrix to be stretched across the delamination cracks without breaking, thereby sustaining a force across a wider crack. Such a mechanism also explains why toughness is dependent on the span-to-depth ratio of the test piece. With this last observation as a possible exception, nacre does not employ any really novel mechanisms to achieve its mechanical properties. It is simply ‘well made’. The importance of nacre to the mollusc depends both on the material and the size of the shell. Catastrophic failure will be very likely in whole, undamaged shells which behave like unnotched beams at large span-to-depth ratios. This tendency is increased by the fact that predators act as ‘soft’ machines and store strain energy which can be fed into the material very quickly once the fracture stress has been reached. It may therefore be advantageous to have a shell made of an intrinsically less tough material which is better at stopping cracks (e. g. crossed lamellar). However, nacre may still be preferred for the short, thick shells of young molluscs, as these have a low span-to-depth ratio and can make better use of ductility mechanisms.

The Mechanical Design of Nacre

The Turn: Integration of Information Seeking and Retrieval in Context (The Information Retrieval Series)

A review of fracture mechanics and its relevance to designing with plastics is given. The basic philosophy of assuming the presence of flaws is developed, and the relevant equations are given. Data is presented for several polymers illustrating thickness and viscoelastic effects. A method of analysis for impact testing is then described together with some data. The unity of the data from a wide range of tests is emphasized.

Fracture Mechanics of Polymers

A general method is given for calculating the energy release rate G from the local values of bending moments and loads in a cracked laminate. This total value is then partitioned into mode I and II components. Examples are given of the analysis of several test geometries including both variable and constant ratio mixed mode tests. Solutions for compression failures with buckling are also given. Finally there is some discussion of specimen compliances and stability criteria for fixed load and fixed displacement.

On the calculation of energy release rates for cracked laminates

The present work has defined an adhesive fracture energy Ga for the peel testing of flexible laminates. The value of Ga characterises the fracture of the laminate and is considered to be a ‘geometry-independent’ parameter which reflects (i) the energy to break the interfacial bonding forces and (ii) the energy dissipated locally ahead of the peel front in the plastic or viscoelastic zone. We have shown that in order to determine this true adhesive fracture energy Ga that the following energy terms must be considered: (i) the stored strain-energy in the peeling arm, (ii) the energy dissipated during tensile deformation of the peeling arm, and (iii) the energy dissipated due to bending of the peeling arm. The analysis proposed yields quantitative expressions for these various energy dissipation terms and, in particular, considers the energy dissipated due to bending of the peeling arm. Another important feature of the analysis is the modelling of the region below the peel front as an elastic beam on an elastic foundation; such that the peeling arm does not act as a truly built-in beam and root rotation at the peel front is allowed. The analysis described in the present paper has been employed for four different laminates. The values of the local angle θ0 at the peel front from the theoretical calculations have been shown to be in excellent agreement with the experimentally measured values; a small-scale peel test rig having been built so that the peel test, as a function of applied peel angle θ, thickness h of peeling arm and rate of test, could be observed and photographed using a stereo-optical microscope. The value of the adhesive fracture energy Ga (i.e the ‘fully corrected’ value) for each laminate is indeed shown to be a ‘material parameter’.

The peeling of flexible laminates

Chapter Headings. Linear elastic fracture mechanics. Elastic-plastic fracture mechanics. Adhesion fracture mechanics. Delamination fracture mechanics.

Fracture Mechanics Testing Methods for Polymers, Adhesives and Composites

The idea of using visualization for document retrieval is introduced through a new paradigm for query response handling. The paradigm is based on parallel queries or points of interest . Each point of interest is defined by a number of key terms and a display position. Documents, represented by icons, are positioned in the display based on the frequency count of word matches in the document to key terms in the points of interest. This visualization method has been implemented through a visualization system called VIBE.

James G. Williams

Papers

Fracture Mechanics of Polymers

On the calculation of energy release rates for cracked laminates

The peeling of flexible laminates

Fracture Mechanics Testing Methods for Polymers, Adhesives and Composites

Visualization of a document collection: the vibe system