The use of mechanical metamaterials in engineering applications is often limited because of uncertainty regarding their deformation behavior. This uncertainty necessitates large safety factors and assumptions about their behavior to be included in mechanical designs including metamaterials, which detracts from their greatest benefit, viz. their ultralight weight. In this study, a yield envelope was created for both a bending-dominated and a stretching-dominated cellular material topology to improve the understanding of the response of cellular materials under various load types and orientations. Experimental studies revealed that the shear strength of a cellular material is significantly lower than that predicted by Mohr’s criterion, necessitating a modification of the Mohr’s yield criterion for cellular materials. All topologies experienced tension–compression anisotropy and topology orientation anisotropy during loading, with the stretching-dominated topology experiencing the largest anisotropies.
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The Anisotropic Yield Surface of Cellular Materials
The use of mechanical metamaterials in engineering applications is often limited because of uncertainty regarding their deformation behavior. This uncertainty necessitates large safety factors and assumptions about their behavior to be included in mechanical designs including metamaterials, which detracts from their greatest benefit, viz. their ultralight weight. In this study, a yield envelope was created for both a bending-dominated and a stretching-dominated cellular material topology to improve the understanding of the response of cellular materials under various load types and orientations. Experimental studies revealed that the shear strength of a cellular material is significantly lower than that predicted by Mohr’s criterion, necessitating a modification of the Mohr’s yield criterion for cellular materials. All topologies experienced tension–compression anisotropy and topology orientation anisotropy during loading, with the stretching-dominated topology experiencing the largest anisotropies.
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- Award ID(s):
- 1834081
- NSF-PAR ID:
- 10403977
- Date Published:
- Journal Name:
- JOM
- ISSN:
- 1543-1851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Purpose Mechanical anisotropy associated with material extrusion additive manufacturing (AM) complicates the design of complex structures. This study aims to focus on investigating the effects of design choices offered by material extrusion AM – namely, the choice of infill pattern – on the structural performance and optimality of a given optimized topology. Elucidation of these effects provides evidence that using design tools that incorporate anisotropic behavior is necessary for designing truly optimal structures for manufacturing via AM. Design/methodology/approach A benchmark topology optimization (TO) problem was solved for compliance minimization of a thick beam in three-point bending and the resulting geometry was printed using fused filament fabrication. The optimized geometry was printed using a variety of infill patterns and the strength, stiffness and failure behavior were analyzed and compared. The bending tests were accompanied by corresponding elastic finite element analyzes (FEA) in ABAQUS. The FEA used the material properties obtained during tensile and shear testing to define orthotropic composite plies and simulate individual printed layers in the physical specimens. Findings Experiments showed that stiffness varied by as much as 22% and failure load varied by as much as 426% between structures printed with different infill patterns. The observed failure modes were also highly dependent on infill patterns with failure propagating along with printed interfaces for all infill patterns that were consistent between layers. Elastic FEA using orthotropic composite plies was found to accurately predict the stiffness of printed structures, but a simple maximum stress failure criterion was not sufficient to predict strength. Despite this, FE stress contours proved beneficial in identifying the locations of failure in printed structures. Originality/value This study quantifies the effects of infill patterns in printed structures using a classic TO geometry. The results presented to establish a benchmark that can be used to guide the development of emerging manufacturing-oriented TO protocols that incorporate directionally-dependent, process-specific material properties.more » « less
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