Kumar A et al. (2022), Energy Absorption and Stiffness of Thin and Thi...

ECB-ART-50385

Materials (Basel) 2022 Mar 25;157:. doi: 10.3390/ma15072441.

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Energy Absorption and Stiffness of Thin and Thick-Walled Closed-Cell 3D-Printed Structures Fabricated from a Hyperelastic Soft Polymer.

Kumar A , Collini L , Ursini C , Jeng JY .

Abstract
This study analyses the energy absorption and stiffness behaviour of 3D-printed supportless, closed-cell lattice structures. The unit cell design is bioinspired by the sea urchin morphology having organism-level biomimicry. This gives rise to an open-cell lattice structure that can be used to produce two different closed-cell structures by closing the openings with thin or thick walls, respectively. In the design phase, the focus is placed on obtaining the same relative density with all structures. The present study demonstrates that closure of the open-cell lattice structure enhances the mechanical properties without affecting the functional requirements. Thermoplastic polyurethane (TPU) is used to produce the structures via additive manufacturing (AM) using fused filament fabrication (FFF). Uniaxial compression tests are performed to understand the mechanical and functional properties of the structures. Numerical models are developed adopting an advanced material model aimed at studying the hysteretic behaviour of the hyperelastic polymer. The study strengthens design principles for closed-cell lattice structures, highlighting the fact that a thin membrane is the best morphology to enhance structural properties. The results of this study can be generalised and easily applied to applications where functional requirements are of key importance, such as in the production of lightweight midsole shoes.

PubMed ID: 35407774
PMC ID: PMC8999644
Article link: Materials (Basel)

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References [+] :

Ashby, The properties of foams and lattices. 2006, Pubmed

	Figure 13. Experimental and numerical radial dilatation of specimens.
	Figure 1. The biomimetic local closed-cell lattice structure based on SU morphology (a) SU morphology (b) primitive patch (c) primitive patch developed by boundary equation (d) surface generation on the boundary equation and mirroring of this surface patch for final design in Creo (e) final design of supportless open-cell lattice structure in Creo parametric (f) closed-cell designed by closing the openings of the open-cell lattice structure.
	Figure 2. Designed model (a) open-cell lattice (b) thin-walled closed-cell lattice (c) thick-walled closed-cell lattice.
	Figure 3. Four parameters considered within design for additive manufacturing and post-processing (a) minimum feature size (b) minimum wall thickness (c) minimum overhang angle (d) minimum bridge length.
	Figure 4. AM using MEX process: (a) thick-wall closed-cells; (b) thin-wall closed-cells; (c) open-cells. The arrow represents the build direction.
	Figure 5. FE models of open, thin- and thick-walled closed unit cells.
	Figure 6. Schematic of numerical calculation of absorbed energy.
	Figure 7. Experimental and Ogden model (N = 2) behaviour for the employed TPU.
	Figure 8. SEM images of the TPU layer deposition in both longitudinal direction (LD) and transversal directions (TD) (a) open-cell LD direction no defects are observed (b) thin-wall LD under-extrusion layer deposition is observed (c) thick-wall LD no defects are observed (d) in open-cell TD random micro-pores encircled with red colour is observed (e) continuous micro-pore encircled in red colour are seen in thin-wall TD (f) In thick-wall TD too micro-pores are observed.
	Figure 9. Images obtained during compression testing of all printed lattice structures.
	Figure 10. Experimental load-displacement curves.
	Figure 11. Unit cells 30% deformed: Von Mises equivalent stress, Principal and compressive strains ε22. The deformation behaviour of open (a), thin (b) shows barrelling, whereas thick wall (c) negative barrelling effect is seen.
	Figure 12. Experimental and numerical results.
	Figure 14. Strain in ribs and walls at the intrados and extrados of the cell structures.
	Figure 15. Comparison of bending load in the ribs and walls of the structures.