Compressive properties of auxetic structures produced with direct 3D printing

Abstract

In the presented paper, three types of auxetic structures were produced with direct 3D printing and their compressive mechanical properties were tested. Samples were prepared from acrylic material suitable for high-resolution direct printing. Three different structures exhibiting in-plane and volumetric negative strain-dependent Poisson's ratio were selected for the analysis: two-dimensional missing-rib cut, two-dimensional inverted (re-entrant) honeycomb and three-dimensional inverted (re-entrant) honeycomb. The samples were subjected to quasi-static compression, from which stress-strain relationships were established. For a proper strain evaluation, digital-image correlation was applied to measure full-field displacements on the sample surfaces. From the displacement fields, true strain/true stress curves were derived for each sample. Furthermore, for each structure a three-dimensional FE model was developed using beam elements and subjected to identical loading conditions. Then, experimentally obtained stress-strain relationships were compared with numerically obtained results. For all the tested auxetic structures, the compressive behaviour was predicted well by the FE models. This demonstrates that parametric FE models can be used to tune the design parameters of the structures with a negative Poisson's ratio to optimize their overall properties. Keywords: auxetics, cellular materials, quasi-static testing, finite-element method V prispevku so predstavljene tri vrste struktur materialov z negativnim Poissonovim razmerjem, ki so proizvedene z neposrednim tridimenzionelnim tiskanjem. Preizku{ene so bile njihove mehanske lastnosti pri stiskanju. Vzorci so bili pripravljeni iz akrilnih materialov, ki so primerni za visoko resolucijsko neposredno tiskanje. Za analizo so bile izbrane tri razli~ne strukture, ki prikazujejo negativno odvisno Poissonovo razmerje v ravnini in v prostoru: dvodimenzionalni prerez z manjkajo~im rebrom, dvodimenzionalni obrnjeni (navznoter usmerjeni) vzorec satovja in tridimenzionalni obrnjeni (navznoter usmerjeni) vzorec satovja. Vzorci so bili izpostavljeni kvazi-stati~nem stiskanju pri katerem smo ugotavljali razmerja sileraztezek. Za primerno oceno sile obremenitve je bila uporabljena metoda korelacije digitalne slike in s tem izmerjeni odmiki na povr{ini vzorcev. Glede na te odmike so bile za vsak vzorec izpeljane dejanske obremenitvene krivulje. Nadalje je bil za vsako strukturo izdelan tridimenzionalni FE model, z uporabo matemati~nega modela podpornih struktur in izpostavljen identi~nim pogojem obremenitve. Nato smo primerjali eksperimentalno pridobljena razmerja med silo in obremenitvijo, z ra~unsko pridobljenimi rezultati. S pomo~jo primerjalnih diagramov sile in raztezka lahko ugotovimo, da FE modeli dobro napovedujejo obna{anje pri stiskanju vseh preizku{enih struktur z negativnim Poissonovim razmerjem. To prikazuje mo`nost uporabe parametri~nih FE modelov za prilagoditev zasnovnih parametrov struktur z negativnim Poissonovim razmerjem za optimiziranje njihovih splo{nih lastn...

Numerical Modelling of Compressive Characteristics of Auxetic Structures

“…As can be seen at the resulting diagrams in Figure 5, the relative Young's modulus is in both cases proportional to the relative density of the structure and the curves have very similar trend for both loading modes. The acquired diagrams have similar trend to such diagrams for conventional porous solids [2]. However, the values are lower than values estimated for conventional foams with open cells e.g.…”

“…Similarly to conventional porous solids, auxetic structures have the potential to absorb relatively high amount of deformation energy especially due to significant stress plateau, which occurs after yield point [2]. However, the simulations in this study were performed only in a limited deformation range with only a linearelastic material model and thus this phenomenon can not be observed.…”

“…For example, their relatively low specific weight and thus high specific strength, make them suitable for applications requiring mass reduction and simultaneous high energy absorption [1]. However, for constructions subjected to extreme ways of loading such as high strain-rate impacts or blasts, compressive properties of conventional metal foams are insufficient [2]. Thus, alternative materials are sought and investigated.…”

Compressive Properties of Auxetic Structures With Controlled Stiffness of Strut Joints

“…Three-dimensional inverted honeycomb was selected which exhibits auxetic behaviour in all three dimensions. Design of the tested auxetic structure was based on our previous study [6], in which first preliminary results were presented. Only entirely auxetic structures were used in contrary to the planar auxetics.…”

Preprocessing of Hopkinson Bar Experiment Data: Filter Analysis

“…Selective laser sintering (SLS) method was used for production of the samples and manufacturing was performed using (a) (b) Figure 3. 2D missing-rib auxetic structure the AM250 system (Renishaw, UK) by sintering the 316L-0407 powdered austenitic steel [4]. Structure with missing-rib unit-cell geometry (i.e.…”