Hierarchical honeycombs with tailorable properties

Ajdari, Amin; Jahromi, Babak Haghpanah; Papadopoulos, Jim; Nayeb-Hashemi, Hamid; Vaziri, Ashkan

doi:10.1016/j.ijsolstr.2012.02.029

Cited by 278 publications

(134 citation statements)

References 30 publications

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“…3D printing provides a geometric design freedom unrivalled by traditional manufacturing methods, coupled with the increased accessibility of this technology in recent years, this has allowed the creation of honeycombs with dual-material structures [5], structural hierarchy [6][7][8] and graded density [9]; these topological complexities all have the potential to enhance and tailor the energy absorbing capabilities of honeycombs. Much of the work in this field has focused on exploring the behaviour of rigid 3D printed honeycombs [6][7][8][9]; such structures subject to large compressive loads would fail by crushing and brittle fracture, preventing energy recovery or reuse. In order to utilise the advances in our understanding of honeycomb design in applications such as vibration isolation and personal protection equipment, it is necessary that the next generation of honeycomb structures be 3D printed from highly elastic, hard wearing materials.…”

Section: Introductionmentioning

confidence: 99%

3D printed polyurethane honeycombs for repeated tailored energy absorption

Bates¹,

2016

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. AbstractFused filament fabrication (FFF) 3D printing of thermoplastic polyurethanes (TPUs) offers a unique capability to manufacture tailorable, flexible cellular structures which can be designed and optimised for specific energy absorbing applications. This paper describes the first application of this methodology in the creation and experimental analysis of 3D printed cellular structures, which are capable of undergoing repeated compressions to densification without failure. A parametric study has been undertaken, capturing the energy absorbing capability of hexagonal arrays manufactured from two types of TPU, with relative densities 0.18-0.49. Arrays were subject to compressions at strain rates 0.03-0.3s -1 and were capable of absorbing energies over the range of 0.01-0.34J/cm 3 , before recovering elastically. Critically, samples attained a maximum energy absorbing 'efficiency' of 0.36, which is comparable to that of traditional expanded closed cell polyurethane foams. The energy absorption behaviour of all structures was found to be dependent on strain rate and cell orientation with respect to the compression direction. This study shows the clear potential of FFF 3D printing for the creation of a new breed of cellular architectures, which are not constrained by existing manufacturing principles, offering the designer the capability to create resilient architectures specifically tailored to operational applications and environmental conditions. Keywords: Cellular structures, thermoplastic polyurethane, 3D printing, energy absorption Introduction:

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Section: Introductionmentioning

confidence: 99%

3D printed polyurethane honeycombs for repeated tailored energy absorption

Bates¹,

2016

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“…By adjusting the side length and side thickness of the small replacement hexagons, a rich class of structures is created. First and second iterations of such hierarchical honeycombs with uniform wall thickness were recently shown to provide up to two and 3.5 times the specific stiffness of the regular honeycomb of the same density [32].…”

Section: Resultsmentioning

confidence: 99%

“…Figure 2b shows the free body diagram of the unit cell, where external forces F at an angle θ from the vertical are applied to the tips of the two oblique beams with thickness t o , and the reaction force 2F sin(θ) is applied to the horizontal beam. Owing to the 180 • rotational symmetry of adjacent unit cells sharing an oblique member, those oblique-beam tips (midpoints of the underlying hexagon edges) are also moment-free (see [32] for further discussion). Because force F is applied to vertical and horizontal unit cell projected areas √ 3L/2 and 3L/2, respectively, macroscopic normal stresses in the x-and y-directions, denoted by S x and S y , respectively, can be obtained from …”

Section: Hierarchical Honeycombs: Basic Unit-cell Relationsmentioning

confidence: 99%

Self-similar hierarchical honeycombs

et al. 2013

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Hierarchical structures are observed in nature, and can be shown to offer superior efficiency. However, the potential advantages of structural hierarchy are not well understood. We extensively explored a bending-dominated model material (i.e. transversely loaded hexagonal honeycomb) which is susceptible to improvement by simple iterative refinement that replaces each three-edge structural node with a smaller hexagon. Using a blend of analytical and numerical techniques, both elastic and plastic properties were explored over a range of loadings and iteration parameters. A wide variety of specific stiffness and specific strengths (up to fourfold increase) were achieved. The results offer insights into the potential value of iterative structural refinement for creating low-density materials with desired properties and function.

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“…Although there have been a number of attempts to create 3D printed cellular structures with tailorable stress-strain and energy absorbing behaviour [5][6][7], much of the work has focused on the printing of brittle structures and attempts to create structures with hyperelastic behaviour via polyjet 3D printing produced samples fragile in nature which fractured during the removal of support material [8]. In order to create hyperelastic, durable structures, fused filament fabrication (FFF) 3D printing is used as it allows the use of thermoplastic polyurethane (TPU), a material known to have excellent impact properties and abrasion resistance [9].…”

Section: Introductionmentioning

confidence: 99%