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About this book

Mechanics of Additive and Advanced Manufacturing, Volume 8 of the Proceedings of the 2018 SEM Annual Conference & Exposition on Experimental and Applied Mechanics, the eighth volume of eight from the Conference, brings together contributions to this important area of research and engineering. The collection presents early findings and case studies, including:

Fatigue & Fracture in AM Materials

Additively Manufactured Metals & Structures

AM Process Characterization

Processing & Mechanical Behavior of AM Materials

Dynamic Response of AM Materials

Additively Manufactured Polymers & Composites

Table of Contents


Chapter 1. Structure/Property Behavior of Additively Manufactured (AM) Materials: Opportunities and Challenges

The certification and qualification paradigms required for additively manufactured (AM) metals and alloys must evolve given the absence of any broadly accepted “ASTM- or DIN-type” AM certification/qualification processes or fixed AM-material produced specifications. This is in part due to the breath of the evolved microstructures produced across the spectrum of AM manufacturing technologies including powder bed and directed energy systems. Accordingly, design and microstructure optimization, manufacture, and thereafter implementation and insertion of AM-produced materials to meet the wide range of engineering applications requires detailed quantification of the structure/property behavior of AM-materials, across the spectrum of metallic AM methods, in comparison/contrast to conventionally-manufactured metals and alloys. The scope of this talk is a discussion of some present opportunities and challenges to achieving qualification and certification of AM produced metals and alloys for engineering applications.
George T. (Rusty) Gray, Veronica Livescu, Cameron Knapp, Saryu Fensin

Chapter 2. Fatigue Characterization of 3D-Printed Maraging Steel by Infrared Thermography

Fatigue performances of additively manufactured metals are affected by the high temperature gradients and high cooling rates occurring during laser beam melting. More generally, mechanical properties strongly depend on the process parameters (scan speed, laser power, laser spot size, etc.). The present study proposes a calorific analysis of the fatigue response of 3D-printed maraging steel from thermal measurements obtained by infrared (IR) thermography. Fatigue damage is indeed associated with heat production leading to material self-heating. Analysis of the thermomechanical response was performed in two steps: first, measurement of temperature maps on the specimen surface by IR camera; second, calculation of the calorific origin of the temperature changes by image processing based on the heat diffusion equation. Using specific thermal data acquisition conditions, the processing enabled us to extract the heat power density corresponding to the mechanical dissipation caused by fatigue. The study was performed on specimens featuring a specific geometry and printed with different process parameters. Distinguishing differences in the production of mechanical dissipation at the beginning of fatigue tests can be useful to determine relevant configurations for long-term fatigue durability.
Corentin Douellou, Xavier Balandraud, Emmanuel Duc

Chapter 3. Quasi-Static and Dynamic Fracture Behaviors of Additively Printed ABS Coupons Studied Using DIC: Role of Build Architecture and Loading Rate

This work deals with quasi-static and dynamic fracture behaviors of Additively Manufactured (AM) ABS coupons. In this research, planar specimens have been additively printed using a heated circular nozzle producing a continuous bead of 0.2 mm diameter and 0.2 mm layer thickness in the build directions. Of specific interest to this work is the role of two different print architectures namely 0/90° and ± 45° in-plane orientations. The local measurement of in-plane displacements are performed optically using DIC up to crack initiation and during growth in quasi-statically loaded 3-point bend specimens and impact loaded edge-notched specimens. The latter set of experiments are carried out using an instrumented Hopkinson pressure bar and an ultrahigh-speed digital camera. Significant differences in the engineering parameters and failure modes as a result of the build variables and loading rates are observed.
John P. Isaac, Hareesh V. Tippur

Chapter 4. Compression and Shear Response of 3D Printed Foam Pads

Polymeric porous materials have a wide range of applications. An important one in structural engineering is to use foams for cushioning or absorbing the kinetic energy from impact. Conventional foaming processes produce polymeric foams with disordered three-dimensional networks, which are dispersion in cell shape, size, etc. Since mechanical properties depend on the shape and structure of the cell, these foams are difficult to characterize and predict due to complexity and variation of cells. The new 3D printing fabrication method can now prepare components of foams with perfect regular array of cells. The printed foams potentially could be tuned or designed for application. In this study, foam pads of various porosities were printed using the same polymer. They all have a Body Centered Cubic (BCC) cell structured but with different span sizes. Experiments were conducted to characterize these foam pads in compression and shear, including off-axis loadings. The property of printing polymer was also characterized for analyzing the behaviors of these foam pads. Results are compared.
Wei-Yang Lu

Chapter 5. Mechanical Structure-Property Relationships for 2D Polymers Comprised of Nodes and Bridge Units

2D polymers have emerged as an infinitely-tailorable material with remarkable, tunable response and density-normalized mechanical properties far exceeding structural materials such as steel, high-performance fibers or reinforced composites. It is critical that the vast material design space of 2D polymers be mapped in order to achieve optimal mechanical performance, since hundreds of permutations of one class of 2D polymers known as covalent organic frameworks have already been synthesized in the decade since the introduction of these materials. To this end, this work establishes a general structure-property relationship for elastic modulus and strength for a common 2D polymer motif consisting of nodes linked by linear bridge polymer chains to form a two-dimensional network. The length of the bridge chains are parametrically varied to study the impact of chain compliance on stiffness and strength. The density-normalized isotropic strength of the graphene/polyethylene hybrid material known as graphylene begins at 0.015 GPa/kg·m3 (50% higher than that of perfect crystalline Kevlar®) and the density-normalized isotropic stiffness is 0.143 GPa/kg·m3 (31% higher than Kevlar®) and decreases non-monotonically with increasing bridge chain length. The mechanical response is mapped and correlated to the inherent molecular structure of these general 2D polymer as a framework for designing 2D polymer molecules for mechanical applications from the ground up.
Emil Sandoz-Rosado, Eric D. Wetzel

Chapter 6. Mechanical Behavior of Additively Manufactured Ti-6Al-4V Following a New Heat Treatment

Hydrogen sintering and phase transformation is a Ti-6Al-4V heat treatment process capable of normalizing the microstructure of bulk parts. The mechanical properties of these processed parts are comparable to that of wrought Ti-6Al-4V, which makes it attractive for use in manufacturing areas where the resulting microstructure is difficult to control, like powder metallurgy and additive manufacturing. To investigate the application space of this heat treatment, Ti-6Al-4V parts were printed from three different additive methods (DMLS, EBM, and cold spray) and their tensile properties were evaluated in both the as-printed and heat treated states. Due to the size of the printed parts, millimeter scale tensile specimens were used and care must be taken to ensure the reduced sample size still produces reliable results. Preliminary tension tests show that the heat treatment process normalizes the microstructure, closes porosity, and improves ductility.
Jonathan P. Ligda, Brady G Butler, Nathaniel Saenz, James Paramore

Chapter 7. Dynamic Thermal Softening Behavior of Additive Materials for Hybrid Manufacturing

Hybrid manufacturing involves both additive and subtractive (machining) processes to achieve the final product. Substantial differences can exist between the mechanical behavior of additively as-built materials compared to their wrought counterparts. As such, the use of wrought material properties for the simulation and optimization of the machining step in a hybrid manufacturing process may produce inaccurate results. The present work uses the NIST pulse-heated compression Kolsky bar to measure the dynamic behavior of both wrought and additively produced Inconel 625 and 17-4 PH stainless steel over a range of temperatures up to 1000 °C and at strain rates of 3000 s−1. The measurement results are correlated to underlying microstructural differences between additive and wrought materials that arise because of the differences between these material processing routes as described in the literature.
Steven Mates, Mark Stoudt, Gregor Jacob, Wilfredo Moscoso, Vis Madhavan

Chapter 8. Correlation Between Process Parameters and Mechanical Properties in Parts Printed by the Fused Deposition Modeling Process

Fused deposition modeling (FDM) represents one of the most common techniques for rapid prototyping and industrial additive manufacturing (AM). Optimizing the process parameters which significantly impact the mechanical properties is critical to achieving the ultimate final part quality sought by industry today. This work investigates the effect of different process parameters including nozzle temperature, printing speed, and print orientation on Young’s modulus, yield strength, and ultimate strength of the final part for two types of filament, namely, Poly Lactic Acid (PLA) and Acrylonitrile Butadiene Styrene (ABS). Design of Experiments (DOE) is used to determine optimized values of the process parameters for each type of filaments; also, a comparison is made between the mechanical properties of the parts fabricated with the two materials. The results show that Y-axis orientation presents the best mechanical properties in PLA while X-axis orientation is the best orientation to print parts with ABS.
Samuel Attoye, Ehsan Malekipour, Hazim El-Mounayri

Chapter 9. Mechanical Characterization of Cellulose Nanofibril Materials Made by Additive Manufacturing

Cellulose nanomaterials have high specific stiffness and strength, are optically transparent, and are biodegradable, making them an attractive building block for bulk materials. The overall dimensions of neat bulk cellulose nanofibril (CNF) materials is significantly limited by the development of residual stresses generated during the drying process, when the source CNF is 1.0 wt.% in water or less, or by agglomeration, when the source CNF is greater than 1.0 wt.%. Here, we overcome these issues by producing CNF films and structures by additive manufacturing (i.e., 3D printing) of a shear thinning aqueous CNF suspension onto hydrophobic substrates under controlled drying conditions. Films of enhanced thicknesses, greater than 80 μm, are achieved as a result of the multistep layer-by-layer manufacturing process. The mechanical properties of the resulting materials are characterized via nanoindentation and tensile testing. Nanoindentation is used primarily to map the mechanical properties and examine variations in properties spatially and through the thickness. Tensile testing, with strain measurement via digital image correlation, is used to characterize the bulk properties. Mechanical characterization is supported by additional characterization via atomic force, optical, and electron microscopy. This study demonstrates the ability to additively manufacture stiff, strong, uniform, and scalable cellulose nanofibril materials.
Lisa M. Mariani, John M. Considine, Kevin T. Turner

Chapter 10. Shock Propagation and Deformation of Additively-Manufactured Polymer Foams with Engineered Porosity

The propagation of shocks through additively-manufactured (AM) polymeric structures containing multiple length scales of engineered porosity is studied both experimentally and computationally. In this study, a single-stage light gas gun is used to impact cube-shaped specimens, 40 mm on a side, instrumented with photon Doppler velocimeter (PDV) light probes to capture free surface velocities and side-looking high-speed video to capture deformation history. A combined Eulerian-Lagrangian finite element (FE) model has been developed which reproduces the majority of the observed experimental trends, based on an independently-measured shock Hugoniot for the bulk AM polymer. After initial calibration, the FE model has been used to suggest candidate geometries for experimental investigation, based on the desired shock response. Geometries for structurally-efficient shock mitigation have been investigated. In a separate set of experiments, miniature (6 mm × 6 mm) square specimens have been impacted at the Dynamic Compression Sector at the Advanced Photon Source (APS), and imaged using x-ray Phase Contrast Imaging (PCI). This technique gives strong evidence for the propagation of discrete shocks within the engineered foam structures, in agreement with our models.
Jonathan E. Spowart, David Lacina, Christopher (Kit) Neel, Geoffrey Frank, Andrew Abbott, Brittany Branch

Chapter 11. Mechanical and Thermal Characterization of Fused Filament Fabrication Polyvinylidene Fluoride (PVDF) Printed Composites

Polyvinylidene fluoride (PVDF) is a polymer that offers a variety of desirable material properties. Its high resistance to corrosive acids and its capability to show piezoelectric behavior are some of these properties that are attractive to many industrial applications. Three-dimensional printing of PVDF is extremely difficult using fused filament fabrication processes due to the large coefficient of thermal expansion of homopolymer PVDF, which results in substantial component warping. In the present work, the effect of zirconium tungstate microparticles as a secondary phase within a PVDF matrix is experimentally studied. Viable printing parameters and the corresponding mechanical and thermal behavior of the PVDF composite structures based on digital image correlation tests are presented.
Niknam Momenzadeh, Carson M. Stewart, Thomas Berfield

Chapter 12. Influence of an Extreme Environment on the Tensile Mechanical Properties of a 3D Printed Thermoplastic Polymer

Inspired by the concept of deploying 3D printers into the field to produce parts on demand, the purpose of this study is to examine the effects of the environment on a 3D printing apparatus and its ability to produce consistent operative prints. The inelastic deformation behavior of Poly-lactic Acid, a biodegradable thermoplastic, 3D printed in extreme environments was investigated. The experimental program was specifically designed to explore the influence of ambient temperature (25–40 °C) during the printing process on the mechanical performance of the printed material. In order to understand the effects of the printing environment versus general exposure to extreme environments, samples were also printed at 25 °C and subsequently aged in an oven at temperatures ranging from 30 to 40 °C before mechanical testing. All mechanical testing was performed in standard laboratory temperature and humidity. The influence of the print temperature and oven aging on the elastic modulus, yield stress, strain energy, and tensile stress are all compared. In addition, the capacity to accumulate strain before failure is compared.
Jose Torres, Otito Onwuzurike, Amber J. W. McClung, Juan D. Ocampo

Chapter 13. A Framework for Estimating Mold Performance Using Experimental and Numerical Analysis of Injection Mold Tooling Prototypes

Additive Manufacturing (AM), 3D printing, rapid prototyping, or rapid tooling refer to a range of technologies that are capable of translating virtual CAD model data into physical model. It is executed in growing number of applications nowadays. A wide range of materials are currently being used to produce consumer products and production tools. AM has brought in revolutionary changes in traditional manufacturing practices. Yet, there are certain drawbacks that hinder its advancement at mass manufacturing. High cost associated with AM is one of them. Using 3D printed tooling can provide long-time cost effectiveness and better product quality. Additively manufactured injection molds can increase the cooling performance, reduce production cycle time, and improve surface finish and part quality of the final plastic product. Yet, manufacturers are still not using the printed molds for industrial mass production. Numerical analysis can provide approximation of such improved performance, but, factual experimental results are necessary to satisfy performance criteria of molds to justify the large investment into tooling for existing industries. In this research work, a desktop injection molding machine is used to evaluate performance of 3D printed molds to develop a cost and performance analysis tool. It serves as a baseline to predict the performance of molds in real-time mass manufacturing of consumer products. The analysis describes how appropriate the estimation can be from any simulation study of molds, how much the scaling down of tool and molding system can affect the prediction of actual performance, what correction factors can be used for better approximation of performance matrices. Several “scaled down” prototypes of injection molds have been used. They have design variations as: with or without cooling system, conformal or straight cooling channels, solid or lattice matrix, and metal or tough resin as the mold material. The molds are printed in in-house printing machines and can also be printed online with limited charges. This also provides an excellent demonstration of using inexpensive material and manufacturing process, such as resin to estimate the performance of highly expensive 3D printed stainless steel molds. The work encompasses a framework to reduce overall cost of implementing AM, by lowering time and monetary expenses during the research and development, and prototyping phases.
Suchana Jahan, Hazim El-Mounayri, Andres Tovar, Yung C. Shin

Chapter 14. Effect of Processing Parameters on Interlayer Fracture Toughness of Fused Filament Fabrication Thermoplastic Materials

Additive manufacturing by fused filament fabrication (FFF) is a promising method for rapid manufacturing of complex components for a wide variety of applications. FFF is often limited to non-structural and non-load bearing applications due to insufficient strength and stiffness of the end-material. This is particularly true in the direction of layer deposition, due to poor adhesion between FFF layers. Processing parameters such as extrusion temperature and print speed have been shown to have significant effect on the mechanical performance of FFF components, but these studies have often neglected interlayer properties. This work develops and experimental approach for quantifying the relationship between processing parameters and interlayer fracture toughness of FFF specimens. The processing parameters considered include extrusion and bed temperatures, extrusion speed, raster spacing, and cooling-fan speed. FFF test blocks were fabricated to identify which parameters would best optimize interlayer fracture toughness. To measure interlayer fracture toughness, unidirectional ABS double cantilever beam specimens were fabricated according to the parametric test matrix with guidance from the test block results. In situ full-field thermography was used to record the specimen thermal history during fabrication. X-ray computed tomography was used to determine the internal void resulting from varying the raster spacing. Finally, optical and SEM fractography was used to perform post mortem categorization of specimen fracture surfaces. The fracture toughness data measured in this study is used to develop an approach for rapid optimization of interlayer properties of FFF components.
Devin J. Young, Cara Otten, Michael W. Czabaj

Chapter 15. Forced-Response Verification of the Inherent Damping in Additive Manufactured Specimens

The laser powder bed fusion AM process has been used to manufacture beams with unique internal geometries that are capable of increasing inherent damping in a part. The concept of the internal design is to have densely packed, unfused powder pockets that dissipate energy via particle interaction. Four Inconel (IN) 718 beams have been tested and all demonstrated the capability to suppress vibration 10X more effectively than a fully fused beam. The mechanism presumed to dissipate energy and thus suppress vibration is the sliding of unfused particles. This mechanism has been associated with a crack opening under Mode II fracture. Based on this assumption, a proportional expression has been developed as a criterion for optimizing unfused powder locations for vibration suppression effectiveness and was validated with 3.175 mm thick beams. This study investigates five uniquely designed IN-718 beams created via the optimizing criterion to assess accuracy of the expression. The intent of this study is to investigate the predictability of the unfused pocket optimization criterion. The results of this study will lead to a more robust design criterion for more complex 3D structures with improved damping capability.
Onome Scott-Emuakpor, Tommy George, Brian Runyon, Bryan Langley, Luke Sheridan, Casey Holycross, Ryan O’Hara, Philip Johnson

Chapter 16. Computational and Experimental Characterization of 3D Printed Components by Fused Deposition Modeling

This paper presents the development of methodologies to understand the effects of process parameters in 3D printed components’ performance and geometrical characteristics, specifically distortions and residual stresses. Full-field-of-view noninvasive optical metrology methodologies and computational simulations outline the framework of this approach. We are developing computational models to predict the critical attributes of 3D printed parts by Fused Deposition Modeling (FDM). We are also designing particular testing artifacts with specific shapes and geometries to conduct Non-Destructive Testing (NDT) using full-field-of-view optical sensors, i.e., Digital Holographic Interferometry, Digital Image Correlation, and Digital Fringe Projection. These sensors can be utilized during and after fabrication for extraction of mechanical properties, identification of defects, and characterization of geometrical accuracies/distortions as a function of process parameters. The knowledge gained from NDT results is used for tuning our computational models. Representative results demonstrate the feasibility of the proposed computational-experimental approach for potential implementation into FDM processes in order to understand the interconnection between process parameters and part performance, which eventually will lead to improvements in the integrity, repeatability, and consistency of printed components and to reduced costs and optimized energy consumption.
Koohyar Pooladvand, Cosme Furlong

Chapter 17. Linking Thermal History to Mechanical Behavior in Directed Energy Deposited Materials

Additive manufacturing is a promising process that has the capability for process optimization and materials development of novel, multi-material and functional components of complex geometries due to the rapid and localized directional solidification of molten metallic alloys. Directed energy deposition, an additive manufacturing process that uses a high powered laser to melt blown metallic powder, introduces large gradients and sensitivity in thermal histories within a built component that lead to unique phase transformations, microstructures, residual stress and anisotropic mechanical behavior. Control of the overall mechanical behavior of DED-built components relies on control of thermal history at localized areas. Research at Northwestern University, in collaboration with Argonne National Laboratory, uses in-situ monitoring techniques such as infrared (IR) cameras, an IR two-wave pyrometer to monitor the melt pool, and a high-powered synchrotron to capture the phase change during build. Relationships between temperature, solidification rate and thermal gradient are made with the resulting microstructural characteristic and mechanical behavior at localized areas of each build. Linking thermal history to mechanical behavior of additively-built parts will lead to increased thermal control for optimal properties and open the door to alloy development.
Jian Cao
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