Porous composite with negative thermal expansion obtained by photopolymer additive manufacturing

Abstract

Additive manufacturing (AM) could be a novel method of fabricating composite and porous materials having various effective performances based on mechanisms of their internal geometries. Materials fabricated by AM could rapidly be used in industrial application since they could easily be embedded in the target part employing the same AM process used for the bulk material. Furthermore, multi-material AM has greater potential than usual single-material AM in producing materials with effective properties. Negative thermal expansion is a representative effective material property realized by designing a composite made of two materials with different coefficients of thermal expansion. In this study, we developed a porous composite having planar negative thermal expansion by employing multi-material photopolymer AM. After measurement of the physical properties of bulk photopolymers, the internal geometry was designed by topology optimization, which is the most effective structural optimization in terms of both minimizing thermal stress and maximizing stiffness. The designed structure was converted to a three-dimensional STL model, which is a native digital format of AM, and assembled as a test piece. The thermal expansions of the specimens were measured using a laser scanning dilatometer. The test pieces clearly showed negative thermal expansion around room temperature.

Lightweight Mechanical Metamaterials with Tunable Negative Thermal Expansion

“…2(c) and 2(d) and 4(b), the effective negative thermal expansion of the unit cell can be tuned over a factor of 3, from −1.57 × 10 −5 to −4.06 × 10 −5 K −1 by varying the copper volume concentration from 2% to 10%, and from −1.78 × 10 −5 to −3.85 × 10 −5 K −1 by varying the length of beam BC. The negative thermal expansion is in a reasonable range compared with the existing theoretical studies and experimental demonstrations of NTE lattices [7][8][9][10][11][12][13][14][15][16][17][18][19]. To the best of our knowledge, the current work is the first experimental demonstration that shows large tunability of negative thermal expansion in three dimensions in microlattice structures.…”

“…Based on this principle, a number of theoretical designs for NTE structures have been proposed to achieve these effects [7][8][9][10][11][12]. However, the existing experimental validation of NTE effects by using microarchitected structures has been limited to structures with two-dimensional layouts [13][14][15][16][17][18][19], while the experimental realization of three-dimensional negative expansion remains elusive [13,15]. This is primarily due to the difficulty in fabricating three-dimensional composite lattices with multiple material constituents and highly sophisticated geometric connections.…”

“…This is primarily due to the difficulty in fabricating three-dimensional composite lattices with multiple material constituents and highly sophisticated geometric connections. In addition, existing NTE structures are built with only limited material choices so that the NTE cannot be well tuned over a large range of temperatures [13][14][15][16][17][18][19].…”

Length scale and manufacturability in density-based topology optimization

“…Topology optimization for additive manufacturing has been demonstrated in a large number of articles [25], [137] and recently for multi material designs in [52], [136]. One of the issues is the post processing step for designs obtained using pure SIMP approach, i.e., the physical density is modeled using the filtered design field and posses gray regions.…”

Lattice structure design with topology optimization and additive manufacturing

“…( Gibson and Ashby, 1997;) 3D (Gibson et al, 2015) (Brandl et al, 2010;Lantada and Morgado, 2012) (SLM) (EBM) (DED) SLM EBM EBM SLM (Murr et al, 2010;Murr et al, 2012) (Bendsøe and Sigmund, 2003) (Guedes and Kikuchi, 1990) ( , 1999) (Gardan and Schneider, 2015;Koizumi et al, 2016;Rezaie et al, 2013;Takezawa et al, 2015;Takezawa et al, 2017) EBM 2.…”