2023 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2023): Applications: Lattices and Cellular II
Program Organizers: Joseph Beaman, University of Texas at Austin
Tuesday 8:15 AM
August 15, 2023
Room: Salon B
Location: Hilton Austin
Session Chair: Jack Beuth, Carnegie Mellon University
8:15 AM
Experimental and Numerical Investigations on Dynamic Mechanical Properties of TPMS Structures: Deepak Kumar Pokkalla1; Jier Wang2; Brandon Turner White3; Ryan Spencer3; Ajit Panesar2; Seokpum Kim1; Uday Vaidya3; 1Oak Ridge National Laboratory; 2Imperial College London; 3University of Tennessee
Triply Periodic Minimal Surface (TPMS) lattice structures have been of increasing interest due to their light weighting, enhanced mechanical properties, and energy absorption characteristics for automotive and biomedical applications. With the advent of additive manufacturing and geometric modeling software, TPMS lattices with complex geometries can be realized. In this work, several TPMS lattice structures were fabricated using fused filament fabrication (FFF) and characterized through a combination of experimental and numerical investigations. Although lightweight TPMS lattices are beneficial for their impact absorption capability, most of the existing works are limited to quasi-static compression and dynamic impact tests are rarely performed. The current study investigates the stress-strain and energy absorption characteristics of TPMS lattices through drop tower testing and numerical modeling. Finite element modeling for TPMS lattices is carried out with experimental validation. The mechanical properties, deformation, and failure mechanisms of TPMS lattices under dynamic impact are summarized for potential future applications.
8:35 AM
Behavior of Additively Manufactured Plate-lattice Structures in Quasi-static, Dynamic, and Ballistic Testing: Joseph Berthel1; Yayati Jadhav1; Chunshan Hu1; Rahul Panat1; Jack Beuth1; Amir Barati Farimani1; 1Carnegie Mellon University
The manufacturing of complex lattice structures is made possible through additive manufacturing. Among the different possible lattice topologies, plate lattices have attracted attention for ballistic impact applications because of their potential for high energy absorption at low relative weights. Here, we manufacture and study different plate lattice topologies in three different mechanical tests: quasi-static compression, Split Hopkinson Pressure Bar dynamic compression, and ballistic impact. Plate lattice samples were manufactured using laser powder bed fusion, where plate lattice topology and volume fraction were varied. Stress-strain behaviors were extracted from compression testing and specific energy absorptions were calculated. Specific energy absorptions and ballistic penetration resistances were compared to determine the effect of plate lattice topology and volume fraction. Finite element simulations of the mechanical tests were also performed and compared to experimental test results.
8:55 AM
Out-of-plane Mechanical Properties of Additively Manufactured Fractal Reinforced Structures: Mario Martinez Magallanes1; Enrique Cuan-Urquizo1; Erick Ramírez-Cedillo1; Armando Roman-Flores1; 1Tecnológico de Monterrey
Architected materials are an emergent kind of materials that gain their physical properties from their rationally designed micro-structures. They are normally conformed by regular unit-cells repetition, but other variations, such as hierarchal, aperiodic, and graded arrangements have also been explored as well. Here we propose an approach consisting of using fractal geometry to control the mechanical response of the metamaterials. We designed a set of 11 different arrangements based on the self-filling Hilbert fractal, the set consisted of 3 different iteration orders at 3 different matching relative densities, and two other graded arrangements. The samples were fabricated using a Micro-LCD 3D-printer and tested under out-of-plane loads. The test was performed using a texturometer with a spherical probe impregnated with red paint to characterize the conformability of the samples. Force and displacement were recorded to compare the mechanical response of the samples against the fractal parameters and obtain the structure-property relation.
9:15 AM
Experimental Characterization of the Mechanical Properties of 3D Printed Bézier-based Lattice Beams: Alberto Alvarez Trejo1; Enrique Cuan-Urquizo1; Armando Roman-Flores1; 1Tecnologico de Monterrey
Architected materials are widely used in additive manufacturing to reduce weight. The controlled arrangement of material allows to tailor their mechanical properties by tuning their geometrical parameters. A parametrization based on cubic Bézier curves is employed here to generate lattice-beams by changing the position of a free control point. Two topologies with the same volume fraction and base curve for the lattice constituent elements at different positions are studied and compared. Lattice beams are manufactured via Fused Filament Fabrication of polylactic acid. The effective stiffness and yield stress of these lattice-beams is analyzed experimentally using three-point bending tests. Adjusting the control point location leads to tailoring the effective mechanical properties of the lattice-beams. This methodology leads to the synthesis of architected topologies with customized mechanical properties.
9:35 AM
Strength Enhancement of cellular structures through selective reinforcement of elements based on analytical modeling: Naresh Koju1; Li Yang1; 1University of Louisville
This work investigate the strength enhancement of cellular structures via individual element thickness optimization based on the analytical model for critical elements. In order to focus on the investigation of the enhancement method, a rather simplified perfectly elastic material property was assumed, and an analytical model was utilized to identify the critical element of a number of cellular structure designs. Stepwise element thickness enhancement was utilized to investigate the effectiveness of overall strength enhancement. The results indicate that the strength of cellular structures can be improved by selectively reinforcing critical elements. In addition, the enhanced cellular structures also exhibit altered fracture failure characteristics that could potentially be exploited for more application objectives.
9:55 AM Break
10:25 AM
3D Printing of Passive Microfluidic Flow Mixers using Triply Period Minimal Surface Microlattice Structures: Mazher Mohammed1; 1Loughborough University
Microfluidics are miniaturised devices useful for precision fluid handling phases when conducting a range of chemical reactions or biological processes. Such devices operate at micrometre length scales, where laminar flow dominates and so interactions are limited to diffusion between the flowing liquid interfaces unless flow is made turbulent to induce mixing. Passive mixers are desirable for this task as they comprise geometrical features which can be incorporated during the fabrication of such devices. Designs largely remain planar due to traditional microfluidic manufacturing being conducted with 2.5D fabrication processes. Additive Manufacturing now allows for passive mixers to now be realised in true 3D but have seen limited investigation. This study explores the efficacy of several miniaturised Triply Period Minimal Surface micro-lattice structures, formed within microfluidic channels as turbulence inducing structures for increased mixing. We explore several lattice designs and report on their efficacy for mixing reactions conducted during continuous flow conditions.
10:45 AM
Tailoring Anisotropic Material Properties of Hierarchical Lattice Structures through Strut Diameter and Orientation Variations: Implications for 3D-printed Ti6Al4V Lattices: Ata Babazadeh Naseri1; Jason Ye1; Benjamin Fregly1; C. Fred Higgs1; 1Rice University
Functional grading of strut diameters and orientations within hierarchical lattice structures (HLSs) offers the potential to achieve complex mechanical properties, including material anisotropy. However, the extent to which the desired anisotropy can be materialized in 3D-printed HLSs remains unclear. Here, we report on the experimental characterization of anisotropic mechanical properties in 3D-printed HLSs manufactured using Ti6Al4V alloy. Four anisotropic HLS designs were created by varying strut diameters or orientations on an 8-by-8-by-8 array, and 21 samples were fabricated and tested in two principal directions. Digital image correlation was used to record the deformations. We found that strut orientations were slightly more effective than strut diameters in generating stiffness anisotropy. However, statistical significance could not be established for the stiffness due to variations within samples of the same design. In contrast, the effective yield strength exhibited significant anisotropy. Our findings provide guidance for tailoring the material properties of 3D-printed HLSs.
11:05 AM
Building Equation-based Lattice Structures using Large Minimum Feature Size AM Processes: Joseph Bartolai1; Joseph Fisher1; Simon Miller1; 1Pennsylvania State University
This work discusses the challenges of 3D printing equation-based lattice structures where the ratio of wall thickness to AM process minimum feature size is quite small. Lattice structures are typically constructed with unit cell sizes where the AM minimum feature size is much smaller than that of the lattice’s structural thickness. This is not always possible for certain AM processes (e.g., DED, WAAM) at unit cell sizes and volume fractions where a lattice would be most beneficial. Results of this study include: a design space within which fabrication of a lattice structure is possible with a large minimum feature size AM process; modifications necessary to ensure a lattice structure is producible; and simulated changes to unit cell mechanical properties based on these geometric modifications. Work presented explores the Gyriod and D-surface equation-based lattices using Material Extrusion AM (MEX) and discusses the lessons learned and extension for Directed Energy Deposition.
11:25 AM
Quasistatic Energy Absorption in Aperiodic Cellular Materials: Irving Ramirez-Chavez1; Mandar Shinde1; Dhruv Bhate1; 1Arizona State University
Cellular materials have been used for decades for their energy absorbing properties. These have typically been either honeycombs or open cell foams, the former representing a periodic distribution of cells, the latter a stochastic one. Recently however, several studies have demonstrated the potential for additively manufactured cellular materials as energy absorbers, but the majority of them have been focused on periodic cellular designs. In this work, we present a classification of aperiodic cellular materials, followed by a discussion of studies that examined the influence of aperiodicity on the energy absorption properties, for three types of modifiers: hybridization, perturbation, and gradation. These experimental and numerical studies were conducted on honeycombs and surface-based cellular structures under quasistatic compression. Our findings suggest that aperiodicity does occasionally benefit energy absorption behavior, but that these benefits depend on how the underlying cellular topology and the aperiodicity influence the failure patterns that develop during compression.