An Examination of the Low Strain Rate Sensitivity of Additively Manufactured Polymer, Composite and Metallic Honeycomb Structures

Abstract

The characterization of additively manufactured cellular materials, such as honeycombs and lattices, is crucial to enabling their implementation in functional parts. One of the characterization methods commonly employed is mechanical testing under compression. This work focuses specifically on the dependence of these tests to the applied strain rate during the test over low strain rate regimes (considered here as 10−6 to 10−1 s−1). The paper is limited to the study of strain the rate dependence of hexagonal honeycomb structures manufactured with four different additive manufacturing processes: one polymer (fused deposition modeling, or material extrusion with ABS), one composite (nylon and continuous carbon fiber extrusion) and two metallic (laser powder bed fusion of Inconel 718 and electron beam melting of Ti6Al4V). The strain rate sensitivities of the effective elastic moduli, and the peak loads for all four processes were compared. Results show significant sensitivity to strain rate in the polymer and composite process for both these metrics, and mild sensitivity for the metallic honeycombs for the peak load. This study has implications for the characterization and modeling of all mechanical cellular materials and makes the case for evaluation and if appropriate, inclusion, of strain rate effects in all cellular material modeling.

Investigations on Mechanical Properties of Lattice Structures with Different Values of Relative Density Made from 316L by Selective Laser Melting (SLM)

“…The first group is generally defined based on 2D topology designed with the use of various unit cell shapes and sizes, which are extruded in the third dimension. One of the well-known representatives of this material group is the honeycomb, which has been investigated in many scientific papers [39][40][41][42][43][44]. This group of structures requires different deformation processes depending on the applied loading orientation (in-plane or out-of-plane) [24,[45][46][47][48][49][50][51].…”

Bioinspired Honeycomb Core Design: An Experimental Study of the Role of Corner Radius, Coping and Interface

“…Out-of-plane compression test conditions including strain rates were taken from MIL-STD-401 [ 18 ]. Since these materials can be significantly strain rate sensitive even at relatively low strain rates [ 10 ], only one strain rate was examined for each test condition. ASTM D790 [ 20 ] was referenced for flexural strain rates for three-point bend testing as well as equations for calculating flexural properties.…”

“…admiring the geometry of their cells [ 1 ] to the mathematician Hales, who formally proved the “honeycomb conjecture” in a 2001 paper, showing once and for all that the hexagonal pattern was indeed the most efficient partitioning of two-dimensional space into equal areas [ 2 ]. The hexagonal cell has also inspired a wide range of engineering products, summarized in a review by Zhang et al [ 3 ], and been the subject of a great deal of analytical modeling [ 4 , 5 , 6 , 7 ], as well as computational and experimental study [ 8 , 9 , 10 ].…”

Fabrication of Ti-Alloy Powder/Solid Composite with Uniaxial Anisotropy by Introducing Unidirectional Honeycomb Structure via Electron Beam Powder Bed Fusion

“…Therefore, the peculiar deformation behavior of the porous specimen when compressed in the Y-axis was considered to be caused by the crushing of the local pores as the deformation progressed. The contribution of partial pore crushing to such deformation behavior has been reported in Al foam and various honeycomb structures made by additive manufacturing [31][32][33][34].…”

“…Because powders are isotropically packed and the bearing capacity of necked powder particles depends on the size of the neck [33], the stress in the powder part of the honeycomb pores is independent of the compressive direction. Therefore, the uniaxial anisotropy of the plateau stress depends on the anisotropy of the stress required to deform the solid wall.…”