All Things ANSYS 043: Optimize Materials Knowledge & Applications with ANSYS Granta pt. 1

 

Published on: August 12th, 2019
With: Eric Miller, Ward Rand, & John Perek
Description:  

In this episode your host and Co-Founder of PADT, Eric Miller is joined by Ward Rand, one of PADT’s other Co-Founders, and John Perek, Principal Materials Engineer at Honeywell Aerospace to discuss the introduction of Granta to the ANSYS product line, its benefits for materials selection & analysis, and thoughts the Honeywell team has had since implementing it into their workflow.

If you would like to learn more about what’s available in this latest release check out PADT’s webinar on ANSYS Granta here: https://bit.ly/3001IFA

If you have any questions, comments, or would like to suggest a topic for the next episode, shoot us an email at podcast@padtinc.com we would love to hear from you!

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Fluids Updates in ANSYS 2019 R2 – Webinar

ANSYS CFD goes beyond qualitative results to deliver accurate quantitative predictions of fluid interactions and trade-offs. These insights reveal unexpected opportunities for your product — opportunities that even experienced engineering analysts can miss.

Products such as ANSYS Fluent, Polyflow, and CFX work together in a constantly improving tool kit that is developed to provide ease of use improvements for engineers simulating fluid flows and it’s impacts on physical models.

Join PADT’s Simulation Support and Application Engineer, Sina Ghods, for a look at what is new and improved for fluids-related tools in ANSYS 2019 R2. This presentation includes updates regarding:

A new fluent experience

Parallel Mosaic-enabled meshing

Discrete Phase Modeling

Creating high-quality meshes for complex models

Transient elasticity for fluid structure interaction

And much more

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All Things ANSYS 035 – The History of ANSYS: An Interview with Dr. John Swanson, author of the original program & founder of ANSYS Inc.

 

Published on: April 22nd, 2019
With: Eric Miller, Ted Harris, & Dr. John Swanson
Description:  

In this episode your host and Co-Founder of PADT, Eric Miller is joined by PADT’s Ted Harris for a very special interview for users of ANSYS software, Dr. John Swanson. Dr. Swanson is known as the founder of “Swanson’s Analysis Systems” in 1970; the company that would later be known to the public as ANSYS Inc. He also wrote the original ANSYS program in his home, and since leaving the company has gone on the work in philanthropy and alternative energy.

A John Fritz Medal winner, and member of the National Academy of Engineering, John is considered an authority and pioneer in the application of Finite Element methods to engineering.

We are incredibly thankful that John was able to join us for this interview, and we hope you enjoy learning a little bit about the history of ANSYS from the founder himself.

If you have any questions, comments, or would like to suggest a topic for the next episode, shoot us an email at podcast@padtinc.com we would love to hear from you!

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Analyze, Visualize, and Communicate – What’s New With EnSight In ANSYS 2019 R1 – Webinar

Effective prototyping in today’s day and age requires not only an understanding of your product’s capabilities but also those of the environment it operates in, and how said environment impacts its use.

Engineers are finding that it is no longer possible to ignore the interactions between fluids and the structures that surround them, as they strive to optimize their product’s performance. 

EnSight helps you visualize coupled fluid-structure interaction data to gain the insights you need; providing a highly effective environment regardless of the complexity of the situation and the simulation being run. After exploring your data, EnSight can also be used to create a high quality visual representation to effectively communicate your results, thanks to the ability to place your model in immersive environments, add realistic lighting conditions, and so much more. 

Join PADT’s CFD Team Lead Engineer, Clinton Smith as we explore the capabilities of this tool, and take a look at what’s new in ANSYS 2019 R1, including updates on:

  • Parallel Fluent to Parallel Ensight capabilities
  • Transnational visual symmetry
  • EnVision handling of multi-panel display
  • And much more

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Simulate Multibody Dynamics More Accurately with ANSYS Motion – Webinar

As mechanical systems continue to get more advanced and interconnected, there is an ever growing need for tools that can accurately analyze the impacts of various forces on the entirety of the system. Mechanical systems often contain complex assemblies of interconnected parts undergoing large overall motion, and thus require engineering simulation for optimal design.

Tools that produce multibody dynamics solutions are better able to account for these components and thus provide more accurate results quicker than running simulations of each component individually. 

One of the latest offerings from ANSYS Inc. is designed to do just that.

ANSYS Motion is a third generation engineering solution based on an advanced multibody dynamics solver. It enables fast and accurate analysis of rigid and flexible bodies and gives accurate evaluation of physical events through the analysis of the mechanical system as a whole. ANSYS Motion uses four tightly integrated solving schemes: rigid body, flexible body, modal and mesh-free EasyFlex. This gives the user unparalleled capabilities to analyze systems and mechanisms in any desired combination.

Join PADT’s Senior Staff Technologist, Jim Peters for a look at how this tool works, along with a deeper dive into its benefits and capabilities, including:

  • Multiple Advanced Toolkits
  • Various Application Areas
  • Accurate Boundary Conditions
  • Easy Interface with Other Software
  • Tightly Integrated Multi-body & Structural Analysis Solvers
  • And Much More

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All Things ANSYS 032 – What’s New in ANSYS Mechanical: Updates Made in 2019 R1

 

Published on: March 11th, 2019
With: Eric Miller & Ted Harris
Description:  

PADT’s Simulation Support Manager, Ted Harris for a discussion on what updates have been made available in the 2019 R1 version on ANSYS Mechanical. Listen as they discuss the various capabilities and applications for this new release, along with what makes these updates so significant.

Want to learn more about what to expect in ANSYS Mechanical 2019 R1? Check out PADT’s webinar covering everything you need to know about the tool’s latest update.

Watch here: https://bit.ly/2SSntmd

If you have any questions, comments, or would like to suggest a topic for the next episode, shoot us an email at podcast@padtinc.com we would love to hear from you!

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Gone Skiing: Aerodynamics – Does It Matter Which Way Your Skis Are Pointing On Your Roof Rack?

I was on the gondola up at Keystone for night-skiing a week ago, after a long day at Beaver Creek, because the last thing I am going to do at 3:00 pm is try to make it back to Denver, as everyone knows it’s hardly more than a parking lot at that point. As it gets later, there’s nothing like a solo gondola ride, however, a solo ride would stop this story right about now.

On the gondola, I overheard a conversation where one gentleman was discussing how he was unable to open the hatch of his vehicle when his skis are in his roof rack. That’s fair, I know older WRX wagons with the spoiler would not be able to open with skis on the roof no matter what, so I figured that was the case. It turns out, that was NOT the case. The reason his hatch would not open was that he orients the skis with the tails forward because it is ‘more aerodynamic’ that way… I was skeptical, but held my tongue, knowing that I had the tools at my disposal to investigate!

I decided to make a model that would allow me to simulate various conditions to get to the bottom of this. My initial hypothesis is that the addition of the ski rack and crossbars is what has the largest effect on aerodynamics, and orientation of the skis probably has a negligible effect after that. As a side note, I am solely concerned with aerodynamics in this case, and am not worrying about the amount of the ski’s base material that is exposed for a given orientation. I am of the mindset that tree trunks and hidden rocks on the mountain are more of a danger to your bases than small rocks on the highway anyway. If you are waiting to comment, “Just get a roof box!”, I understand as I own both a box and a rack at this point, and they both have their advantages, and I will not be exploring the aerodynamics of a box…

…yet…

I was able to start by finding some faceted geometry of a Subaru Forester online (I’m from Colorado, can you tell?) and was able to import that into ANSYS Spaceclaim. Once in Spaceclaim, I was able to edit the faceted geometry to get nice exterior panel surfaces, which I then combined to get a single clean faceted exterior for the car.


Faceted Forester Geometry (Equipped with factory side rails)

After that, I used Spaceclaim to generate the remainder of the rack and skis, including crossbars, a ski rack, and a pair of skis (Complete with the most detailed bindings you have ever seen!). I made a combined part of the crossbars, rack, and skis for each one of my orientations, as this allows me to report the forces on each combined part during the simulation.


Added CAD geometry for the crossbars, ski rack, and a pair of skis

For the simulation, I used ANSYS Discovery Live, the newest tool from ANSYS that allows for instant and interactive design exploration. This tool lets me actively add my CAD geometry and shows results in realtime. I was able to start with just the car and then add and swap my ski/rack geometry with simple button clicks. With traditional simulation tools, I would have needed to create a mesh for each one of these cases, analyze them one at a time, and the post-process and compare results after the fact. After launching Discover Live, it’s as easy as selecting the type on analysis I want to run.

The various types of solutions that can be done in ANSYS Discovery Live. For the purpose of this blog, I am using ‘Wind Tunnel’

Once I have selected ‘Wind Tunnel’ for my solution, I can select my geometry, and then am prompted for the direction of flow, as well as selecting the ‘floor’ of my domain. Once that is done, results show up on the screen instantly. I only needed to modify the flow velocity to ~65 mph. I am most interested in the force on the faces of the combined crossbars, rack, and skis in each orientation, so I created Calculations for each one, which is done by simply selecting the part and using the popup toolbar to create the graph.

Popup toolbar allows for the quick creation of solution calculations

I was already off and running. I ran each one of the cases until the force plot had become steady.

Car Only
Skis Tips Forward Orientation

Skis Tails Forward Orientation

Seeing that the force results for the Tips Forward vs. Tails Forward cases were very similar, I decided I should also run a ‘Bases Up’ Orientation, even though I STRONGLY advise against this, as UV wrecks the base material of your skis/snowboard.

Ski Bases Up and Tips Forward Orientation

In addition to the contour plot shown in the images above, you can also use emitters to show streamlines and particle flow, which also give some pretty neat visualizations.

Streamlines shown on the Tips Forward orientation

Particle Emitter shown on the Tips Forward orientation

The graph plots show values for the Total Y Force for Tips Foward, Tails Forward, and Bases Up orientations to be 37.7 N, 39.1 N, and 37.1 N, respectively. Using Discovery Live, I was able to quickly run all 3 of these simulations, showing that there is not a major difference in the forces on the ski rack between the three orientations. So, put the skis on the roof in the direction that makes life easiest for you, and keep those bad boys paired to protect your bases from the sun, because splitting them isn’t going to help with aerodynamics anyway!

Next steps would be taking a specific case and running in 2D, then 3D, in ANSYS Fluent.

All Things ANSYS 028 – A Year in Review: Predictions for ANSYS in 2019

 

Published on: January 7th, 2019
With: Eric Miller, Joe Woodward, & Ted Harris
Description:  

In this episode your host and Co-Founder of PADT, Eric Miller is joined by PADT’s Simulation Support Manager Ted Harris, and Specialist Mechanical Engineer Joe Woodward, for a discussion on their predictions for ANSYS in 2019, and a look back at our predictions from 2018.

If you have any questions, comments, or would like to suggest a topic for the next episode, shoot us an email at podcast@padtinc.com we would love to hear from you!

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All Things ANSYS 020 – Modeling Flow & Heat Transfer with Flownex

 

Published on: September 10th, 2018
With: Eric Miller, Luke Davidson, Vincent Britz, and Farai Hetze
Description: In this episode your host and Co-Founder of PADT, Eric Miller is joined by Luke Davidson and Vincent Britz of M-Tech, and Farai Hetze from CFX-Berlin, for an interview on the what Flownex is, it’s capabilities for modeling flow and heat transfer, and how it works with ANSYS products. All that, followed by an update on news and events in the respective worlds of ANSYS and PADT.

If you have any questions, comments, or would like to suggest a topic for the next episode, shoot us an email at podcast@padtinc.com we would love to hear from you!

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Updates and Enhancements in ANSYS Mechanical 19.1 – Webinar

Don’t miss this informative presentation – Secure your spot today!
Register Here

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Discover the strength of structural and modal analysis in ANSYS Discovery Live – Webinar

 

Join PADT’s Simulation Support Application Engineer Doug Oatis, for a free webinar including an exploration of the static structural and modal capabilities available within ANSYS Discovery Live, followed by a live demo of the tool as it relates to both application areas.

Don’t miss this informative presentation – Secure your spot today!
If this is your first time registering for one of our Bright Talk webinars, simply click the link and fill out the attached form. We promise that the information you provide will only be shared with those promoting the event (PADT).

You will only have to do this once! For all future webinars, you can simply click the link, add the reminder to your calendar and you’re good to go!

Assembly Modeling with ANSYS

In my previous article, I wrote about how you get what you pay for with your analysis package.  Well, buckle up for some more…but this time we’ll just focus on handling assemblies in your structural/thermal simulations.  If all you’re working on are single components, count yourself lucky.  Almost every simulation deals with one part interacting with another.  You can simplify your boundary conditions a bit to make it equivalent, but if you have significant bearing stresses, misalignments, etc…you need to include the supporting parts.  Better hope your analysis package can handle contact…

Image result for get what you pay for

First off, contact isn’t just for structural simulations.  Contact allows you to pass loads across difference meshes, meaning you don’t need to create a conformal mesh between two parts in order to simulate something.  Here’s a quick listing on the degrees of freedom supported in ANSYS (don’t worry…you don’t need to know how to set these options as ANSYS does it for you when you’re in Workbench):

image

You can use contact for structural, thermal, electrical, porous domain, diffusion, or any combination of those.  The rest of this article is going to focus on the structural side of things, but realize that the same concepts apply to essentially any analysis you can do within ANSYS Mechanical..

First, it’s incredibly easy to create contact in your assembly.  Mechanical automatically looks for surfaces within a certain distance from one another and builds contact.  You can further customize the automated process by defining your own connection groups, as I previous wrote about.  These connection groups can create contact between faces, edges, solids bodies, shell bodies, and line bodies.

image

Second, not only can you create contact to transfer loads across different parts, but you can also automatically create joints to simulate linkages or ‘linearize’ complicated contacts (e.g. cylindrical-to-cylindrical contact for pin joints).  With these joints you can also specify stops and locks to simulate other components not explicitly modeled.  If you want to really model a threaded connection you can specify the pitch diameter and actually ‘turn’ your screw to properly develop the shear stress under the bolt head for a bolted joint simulation without actually needing to model the physical threads (this can also be done using contact geometry corrections)

image Look ma, no threads (modeled)!

image

If you’re *just* defining contact between two surfaces, there’s a lot you simulate.  The default behavior is to bond the surfaces together, essentially weld them closed to transmit tensile and compressive loads.  You also have the ability to let the surfaces move relative to each other by defining frictionless, frictional, rough (infinite coefficient of friction), or no-separation (surfaces don’t transmit shear load but will not separate).

image

Some other ‘fancy’ things you can do with contact is simulate delamination by specifying adhesive properties (type I, II, or III modes of failure).  You can add a wear model to capture surface degradation due to normal stress and tangential velocity of your moving surfaces.  You can simulate a critical bonding temperature by specifying at what temperature your contacts ‘stick’ together instead of slide.  You can specify a ‘wetted’ contact region and see if the applied fluid pressure (not actually solving a CFD simulation, just applying a pressure to open areas of the contact interface) causes your seal to open up.

image

Now, it’s one thing to be able to simulate all of these behaviors.  The reason you’re running a finite element simulation is you need to make some kind of engineering judgement.  You need to know how the force/heat/etc transfers through your assembly.  Within Mechanical you can easily look at the force for each contact pair by dragging/dropping the connection object (contact or joint) into the solution.  This will automatically create a reaction probe to tell you the forces/moments going through that interface.  You can create detailed contour plots of the contact status, pressure, sliding distance, gap, or penetration (depending on formulation used).

image

image

Again, you can generate all of that information for contact between surface-to-surface, surface-to-edge, or edge-to-edge.  This allows you to use solids, shells, beams, or any combination you want, for any physics you want, to simulate essentially any real-world application.  No need to buy additional modules, pay for special solvers, fight through meshing issues by trying to ‘fake’ an assembly through a conformal mesh.  Just import the geometry, simplify as necessary (SpaceClaim is pretty awesome if you haven’t heard), and simulate it.)

For a more detailed, step-by-step look at the process, check out the following video!


PADT Startup Spotlight – The Speed of Simulation

The Speed of Simulation  with Velox Motorsports

With thoroughly engineered components including the use of Finite Element Analysis (FEA), thermodynamics, heat transfer, and Computational Fluid Dynamics (CFD), PADT Startup Spotlight Velox Motorsports strives to produce aftermarket parts that can effectively outperform the factory components.

Join Velox Co-Owners Eric Hazen and Paul Lucas for a discussion on what they use ANSYS simulation software for and how they have benefited from it’s introduction into their manufacturing process.

This webinar will focus on two projects within which the engineers at Velox have see the impact of ANSYS, including:

Using Finite Element Analysis (FEA) to reverse engineer a Subaru fork, find the cause of failure and develop an improved replacement part.

Using Computational Fluid Dynamics (CFD) to rub a shape sensitivity study on Nissan GT R strakes, and develop a replacement that increases down-force without significantly increasing drag.

Modeling 3D Printed Cellular Structures: Approaches

How can the mechanical behavior of cellular structures (honeycombs, foams and lattices) be modeled?

This is the second in a two-part post on the modeling aspects of 3D printed cellular structures. If you haven’t already, please read the first part here, where I detail the challenges associated with modeling 3D printed cellular structures.

The literature on the 3D printing of cellular structures is vast, and growing. While the majority of the focus in this field is on the design and process aspects, there is a significant body of work on characterizing behavior for the purposes of developing analytical material models. I have found that these approaches fall into 3 different categories depending on the level of discretization at which the property is modeled: at the level of each material point, or at the level of the connecting member or finally, at the level of the cell. At the end of this article I have compiled some of the best references I could find for each of the 3 broad approaches.

1. Continuum Modeling

The most straightforward approach is to use bulk material properties to represent what is happening to the material at the cellular level [1-4]. This approach does away with the need for any cellular level characterization and in so doing, we do not have to worry about size or contact effects described in the previous post that are artifacts of having to characterize behavior at the cellular level. However, the assumption that the connecting struts/walls in a cellular structure behave the same way the bulk material does can particularly be erroneous for AM processes that can introduce significant size specific behavior and large anisotropy. It is important to keep in mind that factors that may not be significant at a bulk level (such as surface roughness, local microstructure or dimensional tolerances) can be very significant when the connecting member is under 1 mm thick, as is often the case.

The level of error introduced by a continuum assumption is likely to vary by process: processes like Fused Deposition Modeling (FDM) are already strongly anisotropic with highly geometry-specific meso-structures and an assumption like this will generate large errors as shown in Figure 1. On the other hand, it is possible that better results may be had for powder based fusion processes used for metal alloys, especially when the connecting members are large enough and the key property being solved for is mechanical stiffness (as opposed to fracture toughness or fatigue life).

Fig 1. Load-displacement curves for ULTEM-9085 Honeycomb structures made with different FDM toolpath strategies

2. Cell Level Homogenization

The most common approach in the literature is the use of homogenization – representing the effective property of the cellular structure without regard to the cellular geometry itself. This approach has significantly lower computational expense associated with its implementation. Additionally, it is relatively straightforward to develop a model by fitting a power law to experimental data [5-8] as shown in the equation below, relating the effective modulus E* to the bulk material property Es and their respective densities (ρ and ρs), by solving for the constants C and n.

homogenizationeqn

While a homogenization approach is useful in generating comparative, qualitative data, it has some difficulties in being used as a reliable material model in analysis & simulation. This is first and foremost since the majority of the experiments do not consider size and contact effects. Secondly, even if these were considered, the homogenization of the cells only works for the specific cell in question (e.g. octet truss or hexagonal honeycomb) – so every new cell type needs to be re-characterized. Finally, the homogenization of these cells can lose insight into how structures behave in the transition region between different volume fractions, even if each cell type is calibrated at a range of volume fractions – this is likely to be exacerbated for failure modeling.

3. Member Modeling

The third approach involves describing behavior not at each material point or at the level of the cell, but at a level in-between: the connecting member (also referred to as strut or beam). This approach has been used by researchers [9-11] including us at PADT [12] by invoking beam theory to first describe what is happening at the level of the member and then use that information to build up to the level of the cells.

membermodeling
Fig 2. Member modeling approach: represent cellular structure as a collection of members, use beam theory for example, to describe the member’s behavior through analytical equations. Note: the homogenization equations essentially derive from this approach.

This approach, while promising, is beset with some challenges as well: it requires experimental characterization at the cellular level, which brings in the previously mentioned challenges. Additionally, from a computational standpoint, the validation of these models typically requires a modeling of the full cellular geometry, which can be prohibitively expensive. Finally, the theory involved in representing member level detail is more complex, makes assumptions of its own (e.g. modeling the “fixed” ends) and it is not proven adequately at this point if this is justified by a significant improvement in the model’s predictability compared to the above two approaches. This approach does have one significant promise: if we are able to accurately describe behavior at the level of a member, it is a first step towards a truly shape and size independent model that can bridge with ease between say, an octet truss and an auxetic structure, or different sizes of cells, as well as the transitions between them – thus enabling true freedom to the designer and analyst. It is for this reason that we are focusing on this approach.

Conclusion

Continuum models are easy to implement and for relatively isotropic processes and materials such as metal fusion, may be a good approximation of stiffness and deformation behavior. We know through our own experience that these models perform very poorly when the process is anisotropic (such as FDM), even when the bulk constitutive model incorporates the anisotropy.

Homogenization at the level of the cell is an intuitive improvement and the experimental insights gained are invaluable – comparison between cell type performances, or dependencies on member thickness & cell size etc. are worthy data points. However, caution needs to be exercised when developing models from them for use in analysis (simulation), though the relative ease of their computational implementation is a very powerful argument for pursuing this line of work.

Finally, the member level approach, while beset with challenges of its own, is a promising direction forward since it attempts to address behavior at a level that incorporates process and geometric detail. The approach we have taken at PADT is in line with this approach, but specifically seeks to bridge the continuum and cell level models by using cellular structure response to extract a point-wise material property. Our preliminary work has shown promise for cells of similar sizes and ongoing work, funded by America Makes, is looking to expand this into a larger, non-empirical model that can span cell types. If this is an area of interest to you, please connect with me on LinkedIn for updates. If you have questions or comments, please email us at info@padtinc.com or drop me a message on LinkedIn.

References (by Approach)

Bulk Property Models

[1] C. Neff, N. Hopkinson, N.B. Crane, “Selective Laser Sintering of Diamond Lattice Structures: Experimental Results and FEA Model Comparison,” 2015 Solid Freeform Fabrication Symposium

[2] M. Jamshidinia, L. Wang, W. Tong, and R. Kovacevic. “The bio-compatible dental implant designed by using non-stochastic porosity produced by Electron Beam Melting®(EBM),” Journal of Materials Processing Technology214, no. 8 (2014): 1728-1739

[3] S. Park, D.W. Rosen, C.E. Duty, “Comparing Mechanical and Geometrical Properties of Lattice Structure Fabricated using Electron Beam Melting“, 2014 Solid Freeform Fabrication Symposium

[4] D.M. Correa, T. Klatt, S. Cortes, M. Haberman, D. Kovar, C. Seepersad, “Negative stiffness honeycombs for recoverable shock isolation,” Rapid Prototyping Journal, 2015, 21(2), pp.193-200.

Cell Homogenization Models

[5] C. Yan, L. Hao, A. Hussein, P. Young, and D. Raymont. “Advanced lightweight 316L stainless steel cellular lattice structures fabricated via selective laser melting,” Materials & Design 55 (2014): 533-541.

[6] S. Didam, B. Eidel, A. Ohrndorf, H.‐J. Christ. “Mechanical Analysis of Metallic SLM‐Lattices on Small Scales: Finite Element Simulations versus Experiments,” PAMM 15.1 (2015): 189-190.

[7] P. Zhang, J. Toman, Y. Yu, E. Biyikli, M. Kirca, M. Chmielus, and A.C. To. “Efficient design-optimization of variable-density hexagonal cellular structure by additive manufacturing: theory and validation,” Journal of Manufacturing Science and Engineering 137, no. 2 (2015): 021004.

[8] M. Mazur, M. Leary, S. Sun, M. Vcelka, D. Shidid, M. Brandt. “Deformation and failure behaviour of Ti-6Al-4V lattice structures manufactured by selective laser melting (SLM),” The International Journal of Advanced Manufacturing Technology 84.5 (2016): 1391-1411.

Beam Theory Models

[9] R. Gümrük, R.A.W. Mines, “Compressive behaviour of stainless steel micro-lattice structures,” International Journal of Mechanical Sciences 68 (2013): 125-139

[10] S. Ahmadi, G. Campoli, S. Amin Yavari, B. Sajadi, R. Wauthle, J. Schrooten, H. Weinans, A. Zadpoor, A. (2014), “Mechanical behavior of regular open-cell porous biomaterials made of diamond lattice unit cells,” Journal of the Mechanical Behavior of Biomedical Materials, 34, 106-115.

[11] S. Zhang, S. Dilip, L. Yang, H. Miyanji, B. Stucker, “Property Evaluation of Metal Cellular Strut Structures via Powder Bed Fusion AM,” 2015 Solid Freeform Fabrication Symposium

[12] D. Bhate, J. Van Soest, J. Reeher, D. Patel, D. Gibson, J. Gerbasi, and M. Finfrock, “A Validated Methodology for Predicting the Mechanical Behavior of ULTEM-9085 Honeycomb Structures Manufactured by Fused Deposition Modeling,” Proceedings of the 26th Annual International Solid Freeform Fabrication, 2016, pp. 2095-2106

The Additive Manufacturing Cellular Solids Research Landscape

I am writing this post after visiting the 27th SFF Symposium, a 3-day Additive Manufacturing (AM) conference held annually at the University of Texas at Austin. The SFF Symposium stands apart from other 3D printing conferences held in the US (such as AMUG, RAPID and Inside3D) in the fact that about 90% of the attendees and presenters are from academia. This year had 339 talks in 8 concurrent tracks and 54 posters, with an estimated 470 attendees from 20 countries – an overall 50% increase over the past year.

As one would expect from a predominantly academic conference, the talks were deeper in their content and tracks were more specialized. The track I presented in (Lattice Structures) had a total of 15 talks – 300 minutes of lattice talk, which pretty much made the conference for me!

In this post, I wish to summarize the research landscape in AM cellular solids at a high level: this classification dawned on me as I was listening to the talks over two days and taking in all the different work going on across several universities. My attempt in this post is to wrap my arms around the big picture and show how all these elements are needed to make cellular solids a routine design feature in production AM parts.

Classification of Cellular Solids

First, I feel the need to clarify a technicality that bothered me a wee bit at the conference: I prefer the term “cellular solids” to “lattices” since it is more inclusive of honeycomb and all foam-like structures, following Gibson and Ashby’s 1997 seminal text of the same name. Lattices are generally associated with “open-cell foam” type structures only – but there is a lot of room for honeycomb structures and close-cell foams, each having different advantages and behaviors, which get excluded when we use the term “lattice”.

CellularSolids
Figure 1. Classification of Cellular Solids [Gibson & Ashby, 1997]

The AM Cellular Solids Research Landscape

The 15 papers at the symposium, and indeed all my prior literature reviews and conference visits, suggested to me that all of the work in this space falls into one or more of four categories shown in Figure 2. For each of the four categories (design, analysis, manufacturing & implementation), I have listed below the current list of capabilities (not comprehensive), many of which were discussed in the talks at SFF. Further down I list the current challenges from my point of view, based on what I have learned studying this area over the past year.

AMcellular
Figure 2. AM Cellular Solid Research Landscape

Over the coming weeks I plan to publish a post with more detail on each of the four areas above, summarizing the commercial and academic research that is ongoing (to the best of my knowledge) in each area. For now, I provide below a brief elaboration of each area and highlight some important research questions.

1. Representation (Design)

This deals with how we incorporate cellular structures into our designs for all downstream activities. This involves two aspects: the selection of the specific cellular design (honeycomb or octet truss, for example) and its implementation in the CAD framework. For the former, a key question is: what is the optimum unit cell to select relative to performance requirements, manufacturability and other constraints? The second set of challenges arises from the CAD implementation: how does one allow for rapid iteration with minimal computational expense, how do cellular structures cover the space and merge with the external skin geometry seamlessly?

2. Optimization (Analysis)

Having tools to incorporate cellular designs is not enough – the next question is how to arrange these structures for optimum performance relative to specified requirements? The two most significant challenges in this area are performing the analysis at reasonable computational expense and the development of material models that accurately represent behavior at the cellular structure level, which may be significantly different from the bulk.

3. Realization (Manufacturing)

Manufacturing cellular structures is non-trivial, primarily due to the small size of the connecting members (struts, walls). The dimensions required are often in the order of a few hundred microns and lower, which tends to push the capabilities of the AM equipment under consideration. Additionally, in most cases, the cellular structure needs to be self-supporting and specifically for powder bed fusion, must allow for removal of trapped powder after completion of the build. One way to address this is to develop a map that identifies acceptable sizes of both the connecting members and the pores they enclose. For this, we need robust ways of monitoring quality of AM cellular solids by using in-situ and Non-Destructive techniques to guard against voids and other defects.

4. Application (Implementation)

Cellular solids have a range of potential applications. The well established ones include increasing stiffness-to-weight ratios, energy absorption and thermal performance. More recent applications include improving bone integration for implants and modulating stiffness to match biological distributions of material (biomimicry), as well as a host of ideas involving meta-materials. The key questions here include how do we ensure long term reliability of cellular structures in their use condition? How do we accurately identify and validate these conditions? How do we monitor quality in the field? And how do we ensure the entire life cycle of the product is cost-effective?

So What?

I wrote this post for two reasons: I love to classify information and couldn’t help myself after 5 hours of hearing and thinking about this area. But secondly, I hope it helps give all of us working in this space context to engage and communicate more seamlessly and see how our own work fits in the bigger picture.

A lot of us have a singular passion for the overlapping zone of AM and cellular solids and I can imagine in a few years we may well have a conference, an online journal or a forum of some sort just dedicated to this field – in fact, I’d love to assess interest in such an effort or an equivalent collaborative exercise. If this idea resonates with you, please connect with me on LinkedIn and drop me a note, or send us an email (info@padtinc.com) and cite this blog post so it finds its way to me.