| 1. |
- Borodulina, Svetlana
(author)
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Micromechanics of Fiber Networks
- 2016
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Doctoral thesis (other academic/artistic)abstract
- The current trends in papermaking involve, but are not limited to, maintaining the dry strength of paper material at a reduced cost. Since any small changes in the process affect several factors at once, it is difficult to relate the exact impact of these changes promptly. Hence, the detailed models of the network level of a dry sheet have to be studied extensively in order to attain the infinitesimal changes in the final product.In Paper A, we have investigated a relation between micromechanical processes and the stress–strain curve of a dry fiber network during tensile loading. The impact of “non-traditional” bonding parameters, such as compliance of bonding regions, work of separation and the actual number of effective bonds, is discussed. In Paper B, we studied the impact of the chemical composition of the fiber cell wall, as well as its geometrical properties, on the fiber mechanical properties using the three-dimensional model of a fiber with helical orientation of microfibrils at a range of different microfibril angles (MFA). In order to accurately characterize the fiber and bond properties inside the network, via statistical distributions, microtomography studies on the handsheets have been carried out. This work is divided into two parts: Paper C, which describes the methods of data acquisition and Paper D, where we discuss the extracted data. Here, all measurements were performed at a fiber level, providing data on the fiber width distribution, width-to-height ratio of isotropically oriented fibers and contact density. In the last paper, we utilize data thus obtained in conjunction with fiber morphology data from Papers C and D to update the network generation algorithm in order to produce more realistic fiber networks. We also successfully verified the models with the help of experimental results from dry sheets tested under uniaxial tensile tests. We carry out numerical simulations on these networks to ascertain the influence of fiber and bond parameters on the network strength properties.
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| 2. |
- Linvill, Eric
(author)
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3-D Forming of Paper Materials
- 2017
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Doctoral thesis (other academic/artistic)abstract
- Paper materials have a long history of use as a packaging material, although traditional paper-based packaging is limited in its shape, complexity, and design. In order to better understand the deformation and failure mechanisms during 3-D forming, two experimental studies of paper materials have been conducted. Furthermore, constitutive modeling combined with explicit finite element modeling have been validated against numerous experimental setups and utilized to develop further understanding of 3-D forming processes.Two experimental studies were necessary to further investigate and model the 3-D formability of paper materials. The combined effect of moisture and temperature on the uniaxial mechanical properties of paper was investigated, providing new insights into how moisture and temperature affect both the elastic and plastic properties of paper materials. Furthermore, the in-plane, biaxial yield and failure surfaces were experimentally investigated in both stress and strain space, which gave an operating window for 3-D forming processes as well as input parameters for the constitutive models.The constitutive modeling of paper materials and explicit finite element modeling were directed towards two 3-D forming processes: deep drawing and hydroforming. The constitutive models were calibrated and validated against simple (typically uniaxial) mechanical tests, and the explicit finite element models (which utilize the developed constitutive models) were validated against 3-D forming experiments. Hand-made papers with fibers partially oxidized to dialcohol cellulose, which has greater extensibility than typical paper materials, was furthermore characterized, modeled, and 3-D formed as a demonstration of the potential of modified paper fiber products for 3-D forming applications.
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| 3. |
- Agrawal, Vishal, et al.
(author)
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An efficient isogeometric/finite-difference immersed boundary method for the fluid–structure interactions of slender flexible structures
- 2024
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In: Computer Methods in Applied Mechanics and Engineering. - : Elsevier BV. - 0045-7825 .- 1879-2138. ; 418
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Journal article (peer-reviewed)abstract
- In this contribution, we present a robust and efficient computational framework capable of accurately capturing the dynamic motion and large deformation/deflection responses of highly-flexible rods interacting with an incompressible viscous flow. Within the partitioned approach, we adopt separate field solvers to compute the dynamics of the immersed structures and the evolution of the flow field over time, considering finite Reynolds numbers. We employ a geometrically exact, nonlinear Cosserat rod formulation in the context of the isogeometric analysis (IGA) technique to model the elastic responses of each rod in three dimensions (3D). The Navier–Stokes equations are resolved using a pressure projection method on a standard staggered Cartesian grid. The direct-forcing immersed boundary method is utilized for coupling the IGA-based structural solver with the finite-difference fluid solver. In order to fully exploit the accuracy of the IGA technique for FSI simulations, the proposed framework introduces a new procedure that decouples the resolution of the structural domain from the fluid grid. Uniformly distributed Lagrangian markers with density relative to the Eulerian grid are generated to communicate between Lagrangian and Eulerian grids consistently with IGA. We successfully validate the proposed computational framework against two- and three-dimensional FSI benchmarks involving flexible filaments undergoing large deflections/motions in an incompressible flow. We show that six times coarser structural mesh than the flow Eulerian grid delivers accurate results for classic benchmarks, leading to a major gain in computational efficiency. The simultaneous spatial and temporal convergence studies demonstrate the consistent performance of the proposed framework, showing that it conserves the order of the convergence, which is the same as that of the fluid solver.
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