Journal: Journal of Applied Mechanics

Abbreviation

J. appl. mech.

Publisher

American Society of Mechanical Engineers

Journal Volumes

ISSN

0021-8936
1528-9036

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2013 - 201952020 - 20244
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Publications1 - 9 of 9
  • The deflection limit of slab-like topologically interlocked structures
    Item type: Journal Article
    Ullmann, Silvan; Kammer, David S.; Feldfogel, Shai (2024)
    Journal of Applied Mechanics
    Topologically Interlocked Structures (TIS) are structural assemblies that achieve stability and carrying capacity through the geometric arrangement of interlocking blocks, relying solely on contact and friction forces for load transfer. Unlike beam-like TIS, whose deflection never exceeds the height of the blocks, the deflection of slab-like TIS often does. Yet, the upper limit of deflection of slab-like TIS, a key parameter defining their loading energy capacity, remains unexplored. Here, we establish a theoretical upper bound for the deflection capacity of slab-like TIS and outline a systematic design strategy to approach this upper bound. This strategy is based on engineering the contact interfaces such that the non-central blocks are more engaged in the structural response, leading to a more global and holistic deformation mode with higher deflections. We demonstrate the application of this strategy in a numerical case study on a typical slab-like TIS and show that it leads to a 350% increase in deflection, yielding a value closer to the upper bound than previously reported in the literature. We find that the resulting deflection mode engages all the blocks equally, avoids localized sliding modes, and resembles that of monolithic equivalents. Lastly, we show that the strategy not only maximizes TIS' deflection capacity but also its loading energy capacity.
  • Elastic-Plastic Wave Propagation in Uniform and Periodic Granular Chains
    Item type: Journal Article
    Burgoyne, Hayden A.; Daraio, Chiara (2015)
    Journal of Applied Mechanics
    We investigate the properties of high-amplitude stress waves propagating through chains of elastic–plastic particles using experiments and simulations. We model the system after impact using discrete element method (DEM) with strain-rate dependent contact interactions. Experiments are performed on a Hopkinson bar coupled with a laser vibrometer. The bar excites chains of 50 identical particles and dimer chains of two alternating materials. After investigating how the speed of the initial stress wave varies with particle properties and loading amplitude, we provide an upper bound for the leading pulse velocity that can be used to design materials with tailored wave propagation.
  • Linking Internal Dissipation Mechanisms to the Effective Complex Viscoelastic Moduli of Ferroelectrics
    Item type: Journal Article
    Wojnar, Charles S.; Kochmann, Dennis M. (2017)
    Journal of Applied Mechanics
  • Nonlinear Poro-Elastic Model for Unsaturated Porous Solids
    Item type: Journal Article
    Carmeliet, Jan; Derome, Dominique; Dressler, Martin; et al. (2013)
    Journal of Applied Mechanics
    A nonlinear poroelastic constitutive model for unsaturated porous materials is formulated based on a higher order formulation of free energy including mechanical and moisture contributions and the coupling between moisture and mechanics. This orthotropic model leads to the explicit formulation of the dependence of the compliance, moisture capacity, and coupling coefficient on stress and liquid pressure. The nonlinear poroelastic material properties can be easily determined from mechanical testing at different moisture content and free swelling/sorption tests. An academic example illustrates the capacity of the proposed model to describe nonlinear moisture dependent elasticity, stress dependent sorption, and swelling, also called mechano-sorption and moisture expel during mechanical loading. Two materials are analyzed in detail: wood and Berea sandstone. The poroelastic model shows a good agreement with measurements. Different moisture dependence of the elastic properties is found, with wood showing a more complex moisture/mechanical interaction. Berea sandstone is found to show an important nonlinear elastic behavior dependent on stress, similar in dry and wet conditions.
  • Topology Optimization of Graded Truss Lattices Based on On-the-Fly Homogenization
    Item type: Journal Article
    Telgen, Bastian; Sigmund, Ole; Kochmann, Dennis M. (2022)
    Journal of Applied Mechanics
    We introduce a computational framework for the topology optimization of cellular structures with spatially varying architecture, which is applied to functionally graded truss lattices under quasistatic loading. We make use of a first-order homogenization approach, which replaces the discrete truss by an effective continuum description to be treated by finite elements in a macroscale boundary value problem. By defining the local truss architecture through a set of Bravais vectors, we formulate the optimization problem with regards to the spatially varying basis vectors and demonstrate its feasibility and performance through a series of benchmark problems in 2D (though the method is sufficiently general to also apply in 3D, as discussed). Both the displacement field and the topology are continuously varying unknown fields on the macroscale, and a regularization is included for well posedness. We argue that prior solutions obtained from aligning trusses along the directions of principal stresses are included as a special case. The outlined approach results in heterogeneous truss architectures with a smoothly varying unit cell, enabling easy fabrication with a tunable length scale (the latter avoiding the ill-posedness stemming from classical nonconvex methods without an intrinsic length scale).
  • Multiscale Mass-Spring Model for High-Rate Compression of Vertically Aligned Carbon Nanotube Foams
    Item type: Journal Article
    Thevamaran, Ramathasan; Fraternali, Fernando; Daraio, Chiara (2014)
    Journal of Applied Mechanics
    We present a one-dimensional, multiscale mass-spring model to describe the response of vertically aligned carbon nanotube (VACNT) foams subjected to uniaxial, high-rate compressive deformations. The model uses mesoscopic dissipative spring elements composed of a lower level chain of asymmetric, bilateral, bistable elastic springs to describe the experimentally observed deformation-dependent stress–strain responses. The model shows an excellent agreement with the experimental response of VACNT foams undergoing finite deformations and enables in situ identification of the constitutive parameters at the smaller lengthscales. We apply the model to two cases of VACNT foams impacted at 1.75 ms−1 and 4.44 ms−1 and describe their dynamic response.
  • Beam-like topologically interlocked structures with hierarchical interlocking
    Item type: Journal Article
    Koureas, Ioannis; Pundir, Mohit; Feldfogel, Shai; et al. (2023)
    Journal of Applied Mechanics
    Topologically interlocked materials and structures, which are assemblies of unbonded interlocking building blocks, are promising concepts for versatile structural applications. They have been shown to exhibit exceptional mechanical properties, including outstanding combinations of stiffness, strength, and toughness, beyond those achievable with common engineering materials. Recent work has established a theoretical upper limit for the strength and toughness of beam-like topologically interlocked structures. However, this theoretical limit is only attainable for structures with unrealistically high friction coefficients; therefore, it remains unknown whether it is achievable in actual structures. Here, we demonstrate that a hierarchical approach for topological interlocking, inspired by biological systems, overcomes these limitations and provides a path toward optimized mechanical performance. We consider beam-like topologically interlocked structures that present a sinusoidal surface morphology with controllable amplitude and wavelength and examine the properties of the structures using numerical simulations. The results show that the presence of surface morphologies increases the effective frictional strength of the interfaces and, if well-designed, enables us to reach the theoretical limit of the structural carrying capacity with realistic friction coefficients. Furthermore, we observe that the contribution of the surface morphology to the effective friction coefficient of the interface is well described by a criterion combining the surface curvature and surface gradient. Our study demonstrates the ability to architecture the surface morphology in beam-like topological interlocked structures to significantly enhance its structural performance.
  • Modeling of Flexible Beam Networks and Morphing Structures by Geometrically Exact Discrete Beams
    Item type: Journal Article
    Lestringant, Claire; Kochmann, Dennis M. (2020)
    Journal of Applied Mechanics
  • Stiffness and strength of hexachiral honeycomb-like metamaterials
    Item type: Journal Article
    Tancogne-Dejean, Thomas; Karathanasopoulos, Nikolaos; Mohr, Dirk (2019)
    Journal of Applied Mechanics
    Two-dimensional hexachiral lattices belong to the family of honeycomb-like mechanical metamaterials such as triangular, hexagonal, and kagome lattices. The common feature of this family of beam-based metamaterials is their six-fold rotational symmetry which guarantees their (transversely-) isotropic elastic response. In the case of hexachiral lattices, a single geometric parameter may be introduced to control the degree of chirality such that the elastic Poisson's ratio can be adjusted between 0.33 and −0.8. Detailed finite element simulations are performed to establish the structure–property relationships for hexachiral lattices for relative densities ranging from 1% to 45%. It is shown that both the Young's and shear moduli are always lower for hexachiral structures than for optimal lattices (triangular and kagome). This result is in line with the general understanding that stretching-dominated architectures outperform bending-dominated architectures. The same conclusions may be drawn from the comparison of the tensile yield strength. However, hexachiral structures provide a lower degree of plastic anisotropy than stretching-dominated lattices. Furthermore, special hexachiral configurations have been identified that exhibit a slightly higher shear yield strength than triangular and kagome lattices, thereby presenting an example of bending-dominated architectures outperforming stretching-dominated architectures of equal mass. Tensile specimens have been additively manufactured from a tough PLA polymer and tested to partially validate the simulation results.
Publications1 - 9 of 9