2024 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2024): Lattice Perforamce Prediction and Verification
Program Organizers: Joseph Beaman, University of Texas at Austin
Tuesday 8:00 AM
August 13, 2024
Room: 404
Location: Hilton Austin
Session Chair: Eric MacDonald, University of Texas at El Paso
8:00 AM
Experimental Characterization of Additively Manufactured Topologically Interlocked Tessellations: Matthew Ebert1; John Koithan1; Matt Pharr1; Vinayak Krishnamurthy1; 1Texas A&M University
We explore the mechanical behavior of additively manufactured topologically interlocked tessellations under bending and tensile loads. Topologically interlocked assemblies have a long history in architecture and provide unique properties, where an assembly of tiles is held in place by a peripheral force with no adhesive between neighboring pieces. We explore a special class of such assemblies composed of space-filling tiles, i.e., tiles with no empty space between any neighbors. Printing a system of such tiles results in a part that is strategically fractured to enable high energy absorption as determined by the area under the force-displacement curve. We hypothesize that increasing the intensity of interlocking will lead to higher energy absorption. We present a preliminary experimental study to test this hypothesis wherein we found that various topological interlocking methods allow for tuning of mechanical response under bending loading; by changing a few parameters, the flexural strength and ductility can change.
8:20 AM
Experimental Insights into Dynamic Behaviour Composite Lattice Structures: Piyapat Jameekornkul1; Ajit Panesar1; 1Imperial College London
This work presents insights into the dynamic response of composite lattice structures, essential for guiding designs and enhancing understanding in real-world applications, particularly in energy absorption during crash. Through drop weight impact experiments, the work shows the effect of impact conditions and lattice design on deformation behaviour and absorbed energy efficiency. Investigating design parameters of lattice structure, including functionally graded density, unit cell size, and print direction, enables a deeper understanding of lattice properties at higher strain rates. Additionally, the influence of fibre reinforcement in AM lattice is characterised through microscopy. This research demonstrates improvement in the dynamic deformation through composite metamaterials, offering insights for advanced engineering applications.
8:40 AM
Experimental Characterization of the Compression-compression Fatigue Performance in Flexible 3D Printed Honeycombs: Amador Chapa1; Enrique Cuan-Urquizo1; Pedro Urbina-Coronado1; 1Tecnológico de Monterrey
Cellular materials are gaining popularity as constituting materials of end-use products thanks to their tunable stiffness and energy absorption ability. Additive manufacturing technologies have allowed the fabrication of these porous materials with engineered topologies. Previous works have characterized the mechanical response of cellular materials, mainly under static loading scenarios; their fatigue behavior is a complex phenomenon, not yet well understood. In this work, we exploited the benefits of fused filament fabrication to build thermoplastic polyurethane honeycombs and characterize their properties under cyclic loading. Two different topologies (hexagonal and square) with same relative density were studied. A geometrical assessment was carried out on specimens to evaluate the accuracy of the selected fabrication process. Compression-compression fatigue tests resulted in the construction of accumulated strain per cycle plots and S-N curves. Our findings illustrated the comparative advantages between stretch- and bending-dominated honeycombs in terms of fatigue life performance.
9:00 AM Cancelled
Investigation of Material Interface Effect of Cellular Mechanical Interface in a Bi-Material Interlocking Structure for Additive Manufacturing: Sumit Paul1; Li Yang1; 1University of Louisville
This research focuses on the investigation of the effect of material contact interface characteristics on the cellular structure-based mechanical interlocking interface designs for bi-material structures, envisioned to be realizable by various additive manufacturing (AM) techniques such as material extrusion. Three arbitrarily selected different cellular designs were investigated, which include auxetic, body centered cubic (BCC), and octahedral lattices. Both experimental characterization and finite element analysis were performed in this study for comprehensive analysis. ANSYS was employed to introduce various material contact conditions for investigation, with material properties set based on experimental material results from material extrusion process. The findings of this study clearly suggest that the material interface characteristics not only exerts significant effects on the properties of the interlocking designs, but also exhibit potentials as a design parameter.
9:20 AM Cancelled
Assessing Structural Performance of Uniform, Graded, and Multi-Lattice AM Components Under Compression: Maxime Mermillod-Blondin1; Martha Baldwin1; Raquel Cosme1; Christopher McComb1; 1Carnegie Mellon University
Lattice structures are essential for lightweight and robust components in additive manufacturing (AM). The most common type are uniform lattices, which use a single lattice topology, however other lattice structure types offer more geometric and functional flexibility. For example, graded lattice structures vary density of a lattice throughout the part to achieve unique properties. Multi-lattice structures offer further flexibility, incorporating multiple lattice topologies within a single component. However, diverse lattice types necessitate thorough simulation and testing to achieve design objectives. Many studies experiment on either multi-lattice or graded structures, but do not compare them directly. Our research comprehensively tests uniform, graded, and multi-lattice structures under compression loading to evaluate mechanical behavior. In this work, we compare these structures in compression loading scenarios, examining key mechanical parameters such as stiffness, strength, and deformation characteristics. Our findings provide valuable insights into the mechanical behavior of lattice structures, offering guidance for their implementation.
9:40 AM Break
10:00 AM Cancelled
Component Level Comparison of On-machine Measurement to X-ray Computed Tomography of Octet Truss Lattices: Michael Juhasz1; G. Guss1; J. B. Forien1; N. Calta1; 1Lawrence Livermore National Laboratory
On-machine measurement (OMM)/in-situ monitoring is a feature available on almost all production laser powder bed fusion (LPBF) machines in some form. Another commonplace activity is performing x-ray computed tomography (xCT) on completed parts to identify defects and for quality assurance. This work seeks to highlight productive comparisons between OMM and xCT at the component level. The process is aided by Deep Learning/Machine Learning (ML/DL) through accelerated image processing and segmentation. Specifically, pyrometry and photodiode data gathered in-situ will be compared to ex-situ xCT data of octet truss lattices. It is from these comparisons that we will examine whether OMM data can predict the final shape of a completed part. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
10:20 AM
A Data Analytics Approach to Fatigue Crack Initiation Site Prediction in Cellular Materials Using Thermography: Tyler Smith1; Dhruv Bhate1; 1Arizona State University
Fatigue life prediction and crack initiation site localization of additively manufactured (AM) cellular metals is critical to designing fatigue tolerant components for enhanced structural performance. This study aims to demonstrate a novel method for predicting the location of fatigue crack initiation in AM metallic cellular materials which utilizes Infrared (IR) thermography to measure component surface temperature and predict crack initiation sites using data analytics. In this study, AM metallic honeycomb specimens were manufactured using Laser Powder Bed Fusion (LPBF) with Inconel 718. The specimens were tested under fully reversed low cycle fatigue conditions and data was collected with an IR camera at a framerate of 30fps. This data was analyzed using statistical data analytics methods to predict the location of crack initiation. The method developed was found to successfully predict the location of crack initiation prior to visible crack propagation.
10:40 AM Cancelled
Toward Fatigue Life Prediction of Multi-lattice Structures: Jiangce Chen1; Christopher McComb1; 1Carnegie Mellon University
Multi-lattice structures, made possible by additive manufacturing and characterized by diverse lattice configurations, provide substantial flexibility in meeting complex engineering requirements. This flexibility arises from the tunable physical properties of lattices achieved through a variety of geometries, topologies, and densities. However, despite these advantages, the fatigue behavior of such structures remains hard to predict and largely unexplored， impeding the widespread application of these advanced design and manufacturing methods due to reliability uncertainties. This paper aims to review current methods of fatigue life prediction, primarily tailored for smooth or uniform lattice structures. It also identifies the existing knowledge gaps and practical challenges inherent in predicting the fatigue life of multi-lattice structures, which exhibit variations in both micro- and meso-structural patterns. Moreover, we explore the opportunities present at the interaction of numerical simulation and machine learning for enabling high-fidelity and efficient simulations.
11:00 AM
An Investigation of Plastic Deformation of Periodic Cellular Structures Based on Analytical Modeling: Naresh Koju1; Li Yang1; 1University of Louisville
When coupled with complex boundary conditions, the mechanical characteristics of additively manufactured (AM) cellular structures deviate significantly from classic models, largely due to the local stress heterogeneity. This is particularly significant for properties driven by local behaviors, such as fracture and plasticity. Previously, full-scale analytical model of AM cellular structures based on elastic materials was established. However, with most structural applications non-brittle materials with plasticity are employed. Preliminary studies have shown that presence of plasticity further complicates their behaviors. To establish better understanding of plastic deformation behaviors under boundary-induced stress heterogeneity, this research employed stiffness matrix-based modeling and plastic hinge theory to investigate the compound material-geometry-plasticity relationships. Proposed models exhibited higher predictability on bending-dominated structures, while also suggested the need of further modeling development for stretching-dominated structures. Detailed experimental and modeling studies are carried out to evaluate the effect of non-elastic material behavior on mechanical performance and potential failure characteristics.
11:20 AM
Reconfigurable Lattice of Auxetic Backlash Structures for Shape-Changing Surfaces: Jacob Miske1; Jeffrey Lipton1; Adam Stevens2; 1Northeastern University; 2Oak Ridge National Laboratory Manufacturing Demonstration Facility
Shape-changing structures are used in robotics, wearable technology, and complex dynamic systems. Many of these structures rely on deformation of subcomponents to accomplish conformation to a desired shape within a configuration space. In this work, we present a method for designing many-linked mechanisms for building non-stressed, compliant structures. These lattice structures were printed on a set of FFF systems and demonstrate low cost of complexity with respect to conventional manufacturing methods. Additionally, we propose a method to determine the configuration space and kinematics of a flexible structure with variable degrees of freedom, useful for shape-changing robots. Using this framework, we show examplesof shape-changing structures that can be constructed with a Reconfigurable Lattice of Auxetic Backlash Structures (RLABS).
11:40 AM
Tensile and Fatigue Analysis of Functionally Graded Materials with Varying Concentrations Manufactured Using Material Extrusion: Suhas Alkunte1; Ismail Fidan2; Vivekanand Naikwadi2; Shamil Gudavasov2; 1Old Dominion University; 2Tennessee Tech University
This study employs material extrusion (MEX) technique, specifically a multi-material single extrusion system, to fabricate functionally graded materials (FGM) by blending PLA and TPU materials. This process introduces a gradient transition aimed at reinforcing the material interface. An array of concentration patterns, spanning from 20% to 80% by volume of FGM, undergoes systematic evaluation under both tensile and fatigue loading conditions. During fabrication, meticulous control is exercised over experimental parameters, encompassing stress level, stress ratio, and frequency. The characterization process entails a comparative analysis of the FGM interfaces. Results reveal a noteworthy enhancement in interface strength, irrespective of gradient alterations in material concentrations. This enhancement is particularly pronounced during the transition from softer to harder material constituents. The primary objective of this study is twofold: to elucidate the behavior of the material under tension-tension loading scenarios and to provide comprehensive insights into the intricacies of FGM interfaces