The mechanical behavior of athermal random fiber networks embedding particulate inclusions is studied in this work. Composites in which the filler size is comparable with the mean segment length of the network are considered. Inclusions are randomly distributed in the network at various volume fractions, and cases in which fibers are rigidly bonded to fillers and in which no such bonding is imposed are studied separately. In the presence of inclusions, the small strain modulus increases, while the ability of the network to strain stiffen decreases relative to the unfilled network case. The reinforcement induced by fillers is most pronounced in sparse networks of floppier filaments that deform in the bending-dominated mode in the unfilled state. As the unfilled network density or the bending stiffness of fibers increases, the effect of filling diminishes rapidly. Fillers lead to a transition from the soft, bending-dominated, to the stiffer, stretching-dominated, deformation mode of the network, a transition which is primarily responsible for the observed overall reinforcement. The confinement, i.e., the restriction on network kinematics imposed by fillers, causes this transition. These results provide a justification for the observed difference in reinforcement obtained in sparsely versus densely cross-linked networks at a given filling fraction and provide guidance for the further development of network-based materials.
Many materials of everyday use are fibrous and their strength is important in most applications. In this work we study the dependence of the strength of random fiber networks on structural parameters such as the network density, cross-link density, fiber tortuosity, and the strength of the inter-fiber cross-links. Athermal networks of cellular and fibrous type are considered. We conclude that the network strength scales linearly with the cross-link number density and with the cross-link strength for a broad range of network parameters, and for both types of networks considered. Network strength is independent of fiber material properties and of fiber tortuosity. This information can be used to design fiber networks for specified strength and, generally, to understand the mechanical behavior of fibrous materials.
Mycelium, the root structure of fungi, grows naturally as a biodegradable filamentous material. This unique material has highly heterogeneous microstructure with pronounced spatial variability in density and exhibits strongly non-linear mechanical behavior. In this work we explore the material response in compression, under cyclic deformation, and develop an experimentally-validated multiscale model for its mechanical behavior. The deformation localizes in stochastically distributed sub-domains which eventually percolate to form macroscopic bands of high density material. This is reflected in the stress-strain curve as strain softening. Cycling at fixed macroscopic strain leads to deformation history dependence similar to the Mullins effect. To capture this behavior, we use a two-scale model. At the micro-scale, a random fiber network is used, while at the macroscale the spatial density fluctuations are captured using a stochastic continuum model. The density-dependent local constitutive behavior is defined by the microscale model. An empirical damage model is incorporated to account for the experimentally observed cyclic softening behavior of mycelium. The model is further validated by comparison with a separate set of experimental results.
Link- https://doi.org/10.1016/j.matdes.2018.09.046
50 day free access link - https://authors.elsevier.com/c/1Xpyiy3ZwvtIQ
We study the mechanical behavior of mycelium composites reinforced with biodegradable agro-waste particles. In the composite, the mycelium acts as a supportive matrix which binds reinforcing particles within its filamentous network structure. The compressive behavior of mycelium composites is investigated using an integrated experimental and computational approach. The experimental results indicate that the composite mimics the soft elastic response of pure mycelium at small strains and demonstrates marked stiffening at larger strains due to the densification of stiff particles. The composite also exhibits the characteristic stress softening effect and hysteresis under cyclic compression previously observed for pure mycelium. To gain further insight into the composite behavior, a three dimensional (3D) finite element model based on numerical homogenization technique, is presented.
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Mohammad Refatul Islam, Catalin Picu - Journal of Applied Mechanics, 2018
Fiber-based materials are prevalent around us. While microscopically these systems resemble a discrete assembly of randomly interconnected fibers, the network architecture varies from one system to another. To identify the role of the network architecture, we study here cellular and fibrous random networks in tension and compression, and in the context of large strain elasticity. We observe that, compared to cellular networks of same global parameter set, fibrous networks exhibit in tension reduced strain stiffening, reduced fiber alignment, and reduced Poisson's contraction in uniaxial tension. These effects are due to the larger number of kinematic constraints in the form of cross-links per fiber in the fibrous case. The dependence of the small strain modulus on network density is cubic in the fibrous case and quadratic in the cellular case. This difference persists when the number of cross-links per fiber in the fibrous case is rendered equal to that of the cellular case, which indicates that the different scaling is due to the higher structural disorder of the fibrous networks. The behavior of the two network types in compression is similar, although softening induced by fiber buckling and strain localization is less pronounced in the fibrous case. The contribution of transient interfiber contacts is weak in tension and important in compression.
Article link- http://appliedmechanics.asmedigitalcollection.asme.org/article.aspx?arti...
Connective tissue mechanics is highly non-linear, exhibits a strong Poisson effect and is associated with significant collagen fiber re-arrangement. Although the general features of the stress-strain behavior in tension and compression and under uniaxial, biaxial and shear loading have been discussed extensively, especially from the macroscopic perspective, the Poisson effect and the kinematics of filaments have received less attention. In general, the relationship between the microscopic fiber network mechanics and the macroscopic experimental observations remains poorly defined. The objective of the present work is to provide additional insight into this relationship. To this end, results from models of random collagen networks are compared with experimental data on reconstructed collagen gels, mouse skin dermis and the human amnion. Attention is devoted to the mechanism leading to the large Poisson effect observed in experiments. The effect of fiber tortuosity on network mechanics is also discussed. A comparison of biaxial and uniaxial loading response is performed. Such model validation is essential since these can be used to evaluate parameters important in tissue mechanics which are not accessible experimentally.
link : http://biomechanical.asmedigitalcollection.asme.org/article.aspx?article...
Our Mechanics of Materials Group at Eindhoven University of Technology, Netherlands, in association with Materials innovation institute M2i, has two openings for talented PhD students in the field of multiscale mechanics of materials. They are part of a project on multiscale hygro-mechanics of paper. The industrial background of the project is in inkjet-printing. One opening is on experimental characterisation and the other on multiscale computational modelling.
For exceptionally suited young doctors we may consider changing the positions into PostDoc positions.
More information can be found via the following links, via which candidates may also directly apply. Remaining questions may be directed to me (R.H.J.Peerlings@tue.nl).
http://www.m2i-careers.nl/job-opportunities/jobDetails/Eindhoven/52/PhD-...
http://www.m2i-careers.nl/job-opportunities/jobDetails/Eindhoven/53/PhD-...