Fibrous mesoporous polymer monoliths: macromolecular design and enhanced photocatalytic degradation of aromatic dyes

A bottom-up design provides polymer monoliths comprising two monomers that form mesoporous, compressible, random fiber networks, as in marine sponges.

Electromechanical Coupling of Isotropic Fibrous Networks with Tailored Auxetic Behavior Induced by Water-Printing under Tension

Understanding the electromechanical coupling of auxetic materials offers unique opportunities to enhance the sensitivity of piezoresistive sensors. Reports on the auxetic behavior of random fiber networks have been relatively scarce...

Understanding extensibility of paper: Role of fiber elongation and fiber bonding

The tensile tests of individual bleached softwood kraft pulp fibers and sheets, as well as the micro-mechanical simulation of the fiber network, suggest that only a part of the elongation potential of individual fibers is utilized in the elongation of the sheet. The stress-strain curves of two actual individual pulp fibers and one mimicked classic stress-strain behavior of fiber were applied to a micromechanical simulation of random fiber networks. Both the experimental results and the micromechanical simulations indicated that fiber bonding has an important role not only in determining the strength but also the elongation of fiber networks. Additionally, the results indicate that the shape of the stress-strain curve of individual pulp fibers may have a significant influence on the shape of the stress-strain curve of a paper sheet. A large increase in elongation and strength of paper can be reached only by strength-ening fiber-fiber bonding, as demonstrated by the experimental handsheets containing starch and cellulose microfi-brils and by the micromechanical simulations. The key conclusion related to this investigation was that simulated uniform inter-fiber bond strength does not influence the shape of the stress-strain curve of the fiber network until the bonds fail, whereas the number of bonds has an influence on the activation of the fiber network and on the shape of the whole stress-strain curve.

Homogenized elastic response of random fiber networks based on strain gradient continuum models

The purpose of this work is to develop anisotropic strain gradient linear elastic continuum models for two-dimensional random fiber networks. The constitutive moduli of the strain gradient equivalent continuum are assessed based on the response of the explicit network representation in so-called windows of analysis, in which each fiber is modeled as a beam and the fibers are connected at crossing points with welded joints. The principle of strain energy equivalence based on the extension to the strain gradient of the Hill–Mandel macro homogeneity condition is employed to identify the classical and strain gradient moduli, based on the application of a sequential set of polynomial displacements on windows of analysis of different sizes. The scaling of the first- and second-order moduli with network parameters, such as network density and the ratio of fiber bending to axial stiffness, is determined. We observe a similar dependency of classical and strain gradient moduli on the same network parameters. The internal length scales associated with the gradient coefficients of the constitutive equation are also defined in terms of the network parameters. The strain gradient moduli prove to be size-independent in the affine regime, and they converge toward a size-independent value in the non-affine deformation regime after a rescaling of physical dimensions by the window size. The obtained results show that the strain gradient moduli scale uniformly with the square of the magnitude of the strain gradients applied to the window of analysis.