ANSYS Startup Roadshow Kickoff – CEI Phoenix

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Can’t make it? Keep an eye out as we will be hosting events in other locations as the roadshow continues on!

In the meantime, click here for more information on the ANSYS Startup Program.

Machine & Fuel Efficiency – Industry Application

As it progresses, we here at PADT would like to share some examples of companies working within the five topics that this campaign focuses on (Advanced Electrification, Machine & Fuel Efficiency, Effective Lightweighting, Thermal Optimization, and Aerodynamic Design) in order to give you a better idea as to how they can be applied within the industry.

Machine & Fuel Efficiency – Volvo States Up to 50% Fuel Efficiency Gain Possible with Prototype Electric Hybrid Loader

During its Xploration Forum in Eskilstuna, Sweden last week, Volvo Construction Equipment gave customers, the international press, government representatives and academics an exclusive look at the prototype LX1 electric hybrid machine, which can deliver up to a 50% improvement in fuel efficiency.

Want to learn more? Click Here for more information on how ANSYS simulation software can benefit companies working in the field of Machine & Fuel Efficiency.

Join PADT in exploring the impact of breakthrough energy innovation as well as how ANSYS simulation solutions can be used to help combat the challenges that this area presents. Fill out the registration form to receive additional information on each topic, along with updates regarding the release of various webinars as the campaign progresses.

ANSYS Breakthrough Energy Innovation Campaign – Machine & Fuel Efficiency

Information regarding the next topic in the Breakthrough Energy Innovation Campaign has been released, covering machine and fuel efficiency, and how ANSYS simulation software can be used to help solve a variety of issues related to this topic, as well as optimize the performance of all system components as they work together.

Additional content regarding machine and fuel efficiency can be viewed and downloaded here.

This is the second topic of a campaign that covers five main topics:

  1. Advanced Electrification 
  2. Machine & Fuel Efficiency
  3. Effective Lightweighting
  4. Thermal Optimization
  5. Aerodynamic Design

Information on each topic will be released over the course of the next few months as the webinars take place.

Sign Up Now to receive updates regarding the campaign, including additional information on each subject, registration forms to each webinar and more.

We here at PADT can not wait to share this content with you, and we hope to hear from you soon.

Modeling 3D Printed Cellular Structures: Challenges

In this post, I discuss six challenges that make the modeling of 3D printed cellular structures (such as honeycombs and lattices) a non-trivial matter. In a following post, I will present how some of these problems have been addressed with different approaches.

At the outset, I need to clarify that by modeling I mean the analytical representation of material behavior, primarily for use in predictive analysis (simulation). Here are some reasons why this is a challenging endeavor for 3D printed cellular solids – some of these reasons are unique to 3D printing, others are a result of aspects that are specific to cellular solids, independent of how they are manufactured. I show examples with honeycombs since that is the majority of the work we have data for, but I expect that these ideas apply to foams and lattices as well, just with varying degrees of sensitivity.

1. Complex Geometry with Non-Uniform Local Conditions

I state the most well-appreciated challenge with cellular structures first: they are NOT fully-dense solid materials that have relatively predictable responses governed by straightforward analytical expressions. Consider a dogbone-shaped specimen of solid material under tension: it’s stress-strain response can be described fairly well using continuum expressions that do not account for geometrical features beyond the size of the dogbone (area and length for stress and strain computations respectively). However, as shown in Figure 1, such is not the case for cellular structures, where local stress and strain distributions are non-uniform. Further, they may have variable distributions of bending, stretching and shear in the connecting members that constitute the structure. So the first question becomes: how does one represent such complex geometry – both analytically and numerically?

non-uniform-strain
Fig 1. Honeycomb structure under compression showing non-uniform local elastic strains [Le & Bhate, under preparation]

2. Size Effects

A size effect is said to be significant when an observed behavior varies as a function of the size of the sample whose response is being characterized even after normalization (dividing force by area to get stress, for example). Here I limit myself to size effects that are purely a mathematical artifact of the cellular geometry itself, independent of the manufacturing process used to make them – in other words this effect would persist even if the material in the cellular structure was a mathematically precise, homogeneous and isotropic material.

It is common in the field of cellular structure modeling to extract an “effective” property – a property that represents a homogenized behavior without explicitly modeling the cellular detail. This is an elegant concept but introduces some practical challenges in implementation – inherent in the assumption is that this property, modulus for example, is equivalent to a continuum property valid at every material point. The reality is the extraction of this property is strongly dependent on the number of cells involved in the experimental characterization process. Consider experimental work done by us at PADT, and shown in Figure 2 below, where we varied both the number of axial and longitudinal cells (see inset for definition) when testing hexagonal honeycomb samples made of ULTEM-9085 with FDM. The predicted effective modulus increases with increasing number of cells in the axial direction, but reduces (at a lower rate) for increasing number of cells in the longitudinal direction.

This is a significant challenge and deserves a full form post to do justice (and is forthcoming), but the key to remember is that testing a particular cellular structure does not suffice in the extraction of effective properties. So the second question here becomes: what is the correct specimen design for characterizing cellular properties?

sizeeffect
Fig 2. Effective modulus under compression showing a strong dependence on the number of cells in the structure [Le & Bhate, under preparation]

3. Contact Effects

In the compression test shown in the inset in Figure 2, there is physical contact between the platen and the specimen that creates a local effect at the top and bottom that is different from the experience of the cells closer the center. This is tied to the size effect discussed above – if you have large enough cells in the axial direction, the contribution of this effect should reduce – but I have called it out as a separate effect here for two reasons: Firstly, it raises the question of how best to design the interface for the specimen: should the top and bottom cells terminate in a flat plate, or should the cells extend to the surface of contact (the latter is the case in the above image). Secondly, it raises the question of how best to model the interface, especially if one is seeking to match simulation results to experimentally observed behavior. Both these ideas are shown in Figure 3 below. This also has implications for product design – how do we characterize and model the lattice-skin interface? As such, independent of addressing size effects, there is a need to account for contact behavior in characterization, modeling and analysis.

contact
Fig 3. Two (of many possible) contact conditions for cellular structure compression – both in terms of specimen design as well as in terms of the nature of contact specified in the simulation (frictionless vs frictional, for example)

4. Macrostructure Effects

Another consideration related to specimen design is demonstrated in an exaggerated manner in the slowed down video below, showing a specimen flying off the platens under compression – the point being that for certain dimensions of the specimen being characterized (typically very tall aspect ratios), deformation in the macrostructure can influence what is perceived as cellular behavior. In the video below, there is some induced bending on a macro-level.

5. Dimensional Errors

While all manufacturing processes introduce some error in dimensional tolerances, the error can have a very significant effect for cellular structures – a typical industrial 3D printing process has tolerances within 75 microns (0.003″) – cellular structures (micro-lattices in particular) very often are 250-750 microns in thickness, meaning the tolerances on dimensional error can be in the 10% and higher error range for thickness of these members. This was our finding when working with Fused Deposition Modeling (FDM), where on a 0.006″ thick wall we saw about a 10% larger true measurement when we scanned the samples optically, as shown in Figure 4. Such large errors in thickness can yield a significant error in measured behavior such as elastic modulus, which often goes by some power to the thickness, amplifying the error. This drives the need for some independent measurement of the manufactured cellular structure – made challenging itself by the need to penetrate the structure for internal measurements. X-ray scanning is a popular, if expensive approach. But the modeler than has the challenge of devising an average thickness for analytical calculations and furthermore, the challenge of representation of geometry in simulation software for efficient analysis.

Fig 4. (Clockwise from top left): FDM ULTEM 9085 honeycomb sample, optical scan image, 12-sample data showing a mean of 0.064″ against a designed value of 0.060″ – a 7% error in thickness

6. Mesostructural Effects

The layerwise nature of Additive Manufacturing introduces a set of challenges that are somewhat unique to 3D Printed parts. Chief among these is the resulting sensitivity to orientation, as shown for the laser-based powder bed fusion process in Figure 5 with standard materials and parameter sets. Overhang surfaces (unsupported) tend to have down-facing surfaces with different morphology compared to up-facing ones. In the context of cellular structures, this is likely to result in different thickness effects depending on direction measured.

Fig 5. 3D Printed Stainless Steel Honeycomb structures showing orientation dependent morphology [PADT, 2016]
For the FDM process, in addition to orientation, the toolpaths that effectively determine the internal meso-structure of the part (discussed in a previous blog post in greater detail) have a very strong influence on observed stiffness behavior, as shown in Figure 6. Thus orientation and process parameters are variables that need to be comprehended in the modeling of cellular structures – or set as constants for the range of applicability of the model parameters that are derived from a certain set of process conditions.

Figure
Fig 6. Effects of different toolpath selections in Fused Deposition Modeling (FDM) for honeycomb structure tensile testing  [Bhate et al., RAPID 2016]

Summary

Modeling cellular structures has the above mentioned challenges – most have practical implications in determining what is the correct specimen design – it is our mission over the next 18 months to address some of these challenges to a satisfactory level through an America Makes grant we have been awarded. While these ideas have been explored in other manufacturing contexts,  much remains to be done for the AM community, where cellular structures have a singular potential in application.

In future posts, I will discuss some of these challenges in detail and also discuss different approaches to modeling 3D printed cellular structures – they do not always address all the challenges here satisfactorily but each has its pros and cons. Until then, feel free to send us an email at info@padtinc.com citing this blog post, or connect with me on LinkedIn so you get notified whenever I write a post on this, or similar subjects in Additive Manufacturing (1-2 times/month).

Advanced Electrification – Industry Application

As it progresses, we here at PADT would like to share some examples of companies working within the five topics that this campaign focuses on (Advanced Electrification, Machine & Fuel Efficiency, Effective Lightweighting, Thermal Optimization, and Aerodynamic Design) in order to give you a better idea as to how they can be applied within the industry.

Advanced Electrification – Additional components of vehicle electrification

Manufacturers of electric vehicles are finding additional ways to reduce electric loads by any means necessary, often in ways you wouldn’t think of at first.

Engineers on the eBooster® team in Kirchheimbolanden, Germany (Image credit: BorgWarner)

Want to learn more? Click Here for more information on how ANSYS simulation software can benefit companies working in the field of Advanced Electrification.

Join PADT in exploring the impact of breakthrough energy innovation as well as how ANSYS simulation solutions can be used to help combat the challenges that this area presents. Fill out the registration form to receive additional information on each topic, along with updates regarding the release of various webinars as the campaign progresses.

Machine & Fuel Efficiency – Industry Application

As it progresses, we here at PADT would like to share some examples of companies working within the five topics that this campaign focuses on (Advanced Electrification, Machine & Fuel Efficiency, Effective Lightweighting, Thermal Optimization, and Aerodynamic Design) in order to give you a better idea as to how they can be applied within the industry.

Machine & Fuel Efficiency – Infiniti unveils its Twin-Turbo VC-T Engine at the PMS 2016

Infiniti Motor Company gave a tech briefing on a new remarkable engine at the Paris Motor Show 2016. The VC-T Engine is the world’s first production-ready compression ratio machine. It will be available from

All you need to know about Infiniti's Twin Turbo V6 Engine

Want to learn more? Click Here for more information on how ANSYS simulation software can benefit companies working in the field of Machine & Fuel Efficiency.

Join PADT in exploring the impact of breakthrough energy innovation as well as how ANSYS simulation solutions can be used to help combat the challenges that this area presents. Fill out the registration form to receive additional information on each topic, along with updates regarding the release of various webinars as the campaign progresses.

Advanced Electrification – Industry Application

As it progresses, we here at PADT would like to share some examples of companies working within the five topics that this campaign focuses on (Advanced Electrification, Machine & Fuel Efficiency, Effective Lightweighting, Thermal Optimization, and Aerodynamic Design) in order to give you a better idea as to how they can be applied within the industry.

Advanced Electrification – Regenerative energy harvesting in 48V mild hybrids

48V mild hybrids are incremental improvements to conventional internal combustion engine vehicles so they can handle four times the current and store four times as much electricity.

Image result for Regenerative energy harvesting in 48V mild hybrids Read more at: http://www.energyharvestingjournal.com/articles/9959/regenerative-energy-harvesting-in-48v-mild-hybrids

Want to learn more? Click Here for more information on how ANSYS simulation software can benefit companies working in the field of Advanced Electrification.

Join PADT in exploring the impact of breakthrough energy innovation as well as how ANSYS simulation solutions can be used to help combat the challenges that this area presents. Fill out the registration form to receive additional information on each topic, along with updates regarding the release of various webinars as the campaign progresses.

ANSYS How To: Result Legend Customization and Reuse

ansys-mechanical-custom-legend-0A user was asking how to modify the result legend in ANSYS Mechanical R17 so Ted Harris put together this little How To in PowerPoint:

padt_mechanical_custom_legend_r17.pdf

It shows how to modify the legend to get just what you want, how to save the settings to a file, and then how to use those seettings again on a different model.  Very simple and Powerful.

ansys-mechanical-custom-legend-1

 

 

ansys-mechanical-custom-legend-2

Advanced Electrification – Industry Application

As it progresses, we here at PADT would like to share some examples of companies working within the five topics that this campaign focuses on (Advanced Electrification, Machine & Fuel Efficiency, Effective Lightweighting, Thermal Optimization, and Aerodynamic Design) in order to give you a better idea as to how they can be applied within the industry.

Advanced Electrification – Hybrid Cost Advantage

One of the world’s leading experts in the electrification of cars says that hybrid technology has already reached price parity with diesel, and that this trend is likely to continue as the cost of diesel cars goes up due to tougher regulations.

Satoshi Ogiso at his office in Kariya, Jpana (Photo; Bertel Schmitt)

Want to learn more? Click Here for more information on how ANSYS simulation software can benefit companies working in the field of Advanced Electrification.

Join PADT in exploring the impact of breakthrough energy innovation as well as how ANSYS simulation solutions can be used to help combat the challenges that this area presents. Fill out the registration form to receive additional information on each topic, along with updates regarding the release of various webinars as the campaign progresses.

 

ANSYS Breakthrough Energy Innovation Campaign – Advanced Electrification

Information regarding the first topic in the Breakthrough Energy Innovation Campaign has been released, covering advanced electrification and how ANSYS simulation software can be used to help solve a variety of issues related to this topic, as well as provide significant competitive advantages.

Additional content regarding advanced electrification can be viewed and downloaded here.

This is the first topic of a campaign that covers five main topics:

  1. Advanced Electrification
  2. Machine & Fuel Efficiency
  3. Effective Lightweighting
  4. Thermal Optimization
  5. Aerodynamic Design

Information on each topic will be released over the course of the next few months as the webinars take place.

Sign Up Now to receive updates regarding the campaign, including additional information on each subject, registration forms to each webinar and more.

We here at PADT can not wait to share this content with you, and we hope to hear from you soon.

Jet Engines to Golf Clubs – Phoenix Area ANSYS Users Share their Stories

ansys-padt-skysong-conference-1There is nothing better than seeing the powerful and interesting way that other engineers are using the same tools you use.  That is why ANSYS, Inc. and PADT teamed up on Thursday to hold an “ANSYS Arizona Innovation Conference”  at ASU SkySong where users could come to share and learn.

The day kicked off with Andy Bauer from ANSYS welcoming everyone and giving them an update on the company and some general overarching direction for the technology.  Then Samir Rida from Honeywell Aerospace gave a fantastic keynote sharing how simulation drive the design of their turbine engines.  As a former turbine engine guy, I found it fascinating and exciting to see how accurate and detailed their modeling is.

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Next up was my talk on the Past, Present, and Future of simulation for product development.  The point of the presentation was to take a step back and really think about what simulation is, what we have padt-ansys-innovation-az-2016-pptbeen doing, and what it needs to look at in the future.  We all sort of agreed that we wanted voice activation and artificial intelligence built in now.  If you are interested, you can find my presentation here: padt-ansys-innovation-az-2016.pdf.

After a short break ANSYS’s Sara Louie launched into a discussion on some of the new Antenna Systems modeling capabilities, simulating multiple physics and large domains with ANSYS products.  The ability to model the entire interaction of an antenna including large environments was fascinating.

Lunchtime discussions focused on the presentations in the morning as well as people sharing what they were working on.

img_1632The afternoon started with a review by Hoang Vinh of ANSYS of the ANSYS AIM product. This was followed by customer presentations. Both Galtronics and ON Semiconductor shared how they drive the design of their RF systems with ANSYS HFSS and related tools.  Then Nammo Talley shared how they incorporated simulation into their design process and then showed an example of a projectile redesign from a shoulder launched rocket that was driven by simulation in ANSYS CFX.  They had the added advantage of being able to show something that blows up, always a crowd pleaser.

ping-ansysAnother break was followed by a great look at how Ping used CFD to improve the design of one of their drivers.  They used simulation to understand the drag on the head through an entire swing and then add aerodynamic features that improved the performance of the club significantly. Much of the work is actually featured in an ANSYS Advantage article.

We wrapped things up with an in depth technical look at Shock and Vibration Analysis using ANSYS Mechanical and Multiphysics PCB Analysis with the full ANSYS product suite.

The best part of the event was seeing how all the different physics in ANSYS products were being used and applied in different industries.  WE hope to have similar events int he future so make sure you sign up for our mailings, the “ANSYS – Software Information & Seminars” list will keep you in the loop.

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ANSYS Breakthrough Energy Innovation Campaign is live!

As the worldwide demand for energy continues to grow every year, energy systems simulation is becoming an indispensable tool for improving the way energy is produced and consumed. At the same time, concerns about climate change are leading to stricter emissions regulations and calls for sustainable design in all future energy systems. Clearly, breakthroughs in energy innovation are needed to meet these formidable challenges.

Join PADT in exploring the impact of breakthrough energy innovation as well as how ANSYS simulation solutions can be used to help combat the challenges that this area presents.

This campaign covers five main topics:

  1. Advanced Electrification
  2. Machine & Fuel Efficiency
  3. Effective Lightweighting
  4. Thermal Optimization
  5. Aerodynamic Design
Information on each topic will be released over the course of the next few months as the webinars take place.
The campaign will consist of a series of webinars explaining the applications of ANSYS simulations software with regards to each topic, along with additional downloadable content.

Sign Up Now to receive updates regarding the campaign, including additional information on each subject, registration forms to each webinar and more.

More information regarding the campaign in general can be found Here.

artwork-for-bei-campaign

Video Tips: Node and Element IDs in ANSYS Mechanical

This is a common question that we get, particularly those coming from APDL – how to get nodal and element IDs exposed in ANSYS Mechanical. Whether that’s for troubleshooting or information gathering, it was not available before. This video shows how an ANSYS developed extension accomplishes that pretty easily.

The extension can be found by downloading “FE Info XX” for the version XX of ANSYS you are using at  https://support.ansys.com/AnsysCustom…

Classification of Cellular Solids (and why it matters)

Updated (8/30/2016): Two corrections made following suggestions by Gilbert Peters: the first corrects the use of honeycomb structures in radiator grille applications as being for flow conditioning, the second corrects the use of the Maxwell stability criterion, replacing the space frame example with an octet truss.

~

This is my first detailed post in a series on cellular structures for additive manufacturing, following an introductory post I wrote where I classified the research landscape in this area into four elements: design, analysis, manufacturing and implementation.

Within the design element, the first step in implementing cellular structures in Additive Manufacturing (AM) is selecting the appropriate unit cell(s). The unit cell is selected based on the performance desired of it as well as the manufacturability of the cells. In this post, I wish to delve deeper into the different types of cellular structures and why the classification is important. This will set the stage for defining criteria for why certain unit cell designs are preferable over others, which I will attempt in future posts. This post will also explain in greater detail what a “lattice” structure, a term that is often erroneously used to describe all cellular solids, truly is.

1. Honeycomb

1.1 Definition
Honeycombs are prismatic, 2-dimensional cellular designs extruded in the 3rd dimension, like the well-known hexagonal honeycomb shown in Figure 1. All cross-sections through the 3rd dimension are thus identical, making honeycombs somewhat easy to model. Though the hexagonal honeycomb is most well known, the term applies to all designs that have this prismatic property, including square and triangular honeycombs. Honeycombs have a strong anisotropy in the 3rd dimension – in fact, the modulus of regular hexagonal and triangular honeycombs is transversely isotropic – equal in all directions in the plane but very different out-of-plane.

Figure 1. Honeycomb structure showing two-dimensional, prismatic nature (Attr: modified from work done by George William Herbert, Wikipedia)
honeycomb_bmwi3
Figure 2. Honeycomb design in use as part of a BMW i3 crash structure (Attr: adapted from youkeys, Wikipedia)

1.2 Design Implications
The 2D nature of honeycomb structures means that their use is beneficial when the environmental conditions are predictable and the honeycomb design can be oriented in such a way to extract maximum benefit. One such example is the crash structure in Figure 2 as well as a range of sandwich panels. Several automotive radiator grilles are also of a honeycomb design to condition the flow of air. In both cases, the direction of the environmental stimulus is known – in the former, the impact load, in the latter, airflow.

2. Open-Cell Foam

openfoam
Figure 3. Open cell foam unit cell, following Gibson & Ashby (1997)

2.1 Definition
Freeing up the prismatic requirement on the honeycomb brings us to a fully 3-dimensional open-cell foam design as shown in one representation of a unit cell in Figure 3. Typically, open-cell foams are bending-dominated, distinguishing them from stretch-dominated lattices, which are discussed in more detail in a following section on lattices.

2.2 Design Implications
Unlike the honeycomb, open cell foam designs are more useful when the environmental stimulus (stress, flow, heat) is not as predictable and unidirectional. The bending dominated mechanism of deformation make open-cell foams ideal for energy absorption – stretch dominated structures tend to be stiffer. As a result of this, applications that require energy absorption such as mattresses and crumple zones in complex structures. The interconnectivity of open-cell foams also makes them a candidate for applications requiring fluid flow through the structure.

Metal_Foam
Figure 4. SEM image of a metallic open-cell foam (Attr: SecretDisc, Wikipedia)
openfoam-deform
Figure 5. FEA simulation of open cell foam unit cell under compression, showing predominant mode of deformation is on account of bending

3. Closed-Cell Foam

closedfoam
Figure 6. Open cell foam unit cell representation [following Gibson and Ashby, 1997]
3.1 Definition
As the name suggests, closed cell foams are open-cell foams with enclosed cells, such as the representation shown in Figure 6. This typically involves a membrane like structure that may be of varying thickness from the strut-like structures, though this is not necessary. Closed-cell foams arise from a lot of natural processes and are commonly found in nature. In man-made entities, they are commonly found in the food industry (bread, chocolate) and in engineering applications where the enclosed cell is filled with some fluid (like air in bubble wrap, foam for bicycle helmets and fragile packaging).

3.2 Design Implications
The primary benefit of closed cell foams is the ability to encapsulate a fluid of different properties for compressive resilience. From a structural standpoint, while the membrane is a load-bearing part of the structure under certain loads, the additional material and manufacturing burden can be hard to justify. Within the AM context, this is a key area of interest for those exploring 3D printing food products in particular but may also have value for biomimetic applications.

Closed_cell_metal_foam_with_large_cell_size
Figure 8. Closed cell Aluminum foam with very large cells [Shinko Wire Company, Attr: Curran2, Wikimedia Commons]

 4. Lattice

4.1 Definition
Lattices are in appearance very similar to open cell foams but differ in that lattice member deformation is stretch-dominated, as opposed to bending*. This is important since for the same material allocation, structures tend to be stiffer in tension and/or compression compared to bending – by contrast, bending dominated structures typically absorb more energy and are more compliant.

So the question is – when does an open cell foam become stretch dominated and therefore, a lattice? Fortunately, there is an app equation for that.

Maxwell’s Stability Criterion
Maxwell’s stability criterion involves the computation of a metric M for a lattice-like structure with b struts and j joints as follows:

In 2D structures: M = b – 2j + 3
In 3D structures:
M = b – 3j + 6

Per Maxwell’s criterion, for our purposes here where the joints are locked (and not pinned), if M < 0, we get a structure that is bending dominated. If M >= 0, the structure is stretch dominated. The former constitutes an open-cell foam, the latter a lattice.

There are several approaches to establishing the appropriateness of a lattice design for a structural applications (connectivity, static and kinematic determinism etc.) and how they are applied to periodic structures and space frames. It is easy for one (including for this author) to confuse these ideas and their applicability. For the purposes of AM, Maxwell’s Stability Criterion for 3D structures is a sufficient condition for static determinancy. Further, for a periodic structure to be truly space-filling (as we need for AM applications), there is no simple rigid polyhedron that fits the bill – we need a combination of polyhedra (such as an octahedron and tetrahedron in the octet truss shown in the video below) to generate true space filling, and rigid structures. The 2001 papers by Deshpande, Ashby and Fleck illustrate these ideas in greater detail and are referenced at the end of this post.

Video: The octet truss is a classic stretch-dominated structure, with b = 36 struts, j = 14 joints and M = 0 [Attr. Lawrence Livermore National Labs]

4.2 Design Implications
Lattices are the most common cellular solid studied in AM – this is primarily on account of their strong structural performance in applications where high stiffness-to-weight ratio is desired (such as aerospace), or where stiffness modulation is important (such as in medical implants). However, it is important to realize that there are other cellular representations that have a range of other benefits that lattice designs cannot provide.

Conclusion: Why this matters

It is a fair question to ask why this matters – is this all just semantics? I would like to argue that the above classification is vital since it represents the first stage of selecting a unit cell for a particular function. Generally speaking, the following guidelines apply:

  • Honeycomb structures for predictable, unidirectional loading or flow
  • Open cell foams where energy absorption and compliance is important
  • Closed cell foams for fluid-filled and hydrostatic applications
  • Lattice structures where stiffness and resistance to bending is critical

Finally, another reason it is important to retain the bigger picture on all cellular solids is it ensures that the discussion of what we can do with AM and cellular solids includes all the possibilities and is not limited to only stiffness driven lattice designs.

Note: This blog post is part of a series on “Additive Manufacturing of Cellular Solids” that I am writing over the coming year, diving deep into the fundamentals of this exciting and fast evolving topic. To ensure you get each post (~2 a month) or to give me feedback for improvement, please connect with me on LinkedIn.

References

[1] Ashby, “Materials Selection in Mechanical Design,” Fourth Edition, 2011
[2] Gibson & Ashby, “Cellular Solids: Structure & Properties,” Second Edition, 1997
[3] Gibson, Ashby & Harley, “Cellular Materials in Nature & Medicine,” First Edition, 2010
[4] Ashby, Evans, Fleck, Gibson, Hutchinson, Wadley, “Metal Foams: A Design Guide,” First Edition, 2000
[5] Deshpande, Ashby, Fleck, “Foam Topology Bending versus Stretching Dominated Architectures,” Acta Materialia 49, 2001
[6] Deshpande, Fleck, Ashby, “Effective properties of the octet-truss lattice material,”  Journal of the Mechanics and Physics of Solids, 49, 2001

Notes

* We defer to reference [1] in distinguishing lattice structures as separate from foams – this is NOT the approach used in [2] and [3] where lattices are treated implicitly as a subset of open-cell foams. The distinction is useful from a structural perspective and as such is retained here.

New Second Edition in Paperback and Kindle: Introduction to the ANSYS Parametric Design Language (APDL)

APDL-Guide-Square-Advert-1After three years on the market and signs that sales were increasing year over year, we decided it was time to go through our popular training book “Introduction to the ANSYS Parametric

Introduction_to_APDL_V2-Kindle-Ipad-1
I’ll be honest, it was cool to see the book in print the first time, but seeing it on my iPad was just as cool.

Design Language (APDL)” and make some updates and reformat it so that it can be published as a Kindle e-book.   The new Second Edition includes two additonal chapters: APDL Math and Using APDL with ANSYS Mechanical.  The fact that we continue to sell more of these useful books is a sign that APDL is still a vibrant and well used language, and that others out there find power in its simplicity and depth.

This book started life as a class that PADT taught for many years. Then over time people asked if they could buy the notes. And then they asked for a real book. The bulk of the content came from Jeff Strain with input from most of our technical staff. Much of the editing and new content was done by Susanna Young and Eric Miller.

Here is the Description from Amazon.com:

The definitive guide to the ANSYS Parametric Design Language (APDL), the command language for the ANSYS Mechanical APDL product from ANSYS, Inc. PADT has converted their popular “Introduction to APDL” class into a guide so that users can teach themselves the APDL language at their own pace. Its 14 chapters include reference information, examples, tips and hints, and eight workshops. Topics covered include:

– Parameters
– User Interfacing
– Program Flow
– Retrieving Database Information
– Arrays, Tables, and Strings
– Importing Data
– Writing Output to Files
– Menu Customization
– APDL Math
– Using APDL in ANSYS Mechanical

At only $75.00 it is an investment that will pay for itself quickly. Even if you are an ANSYS Mechanical user, you can still benefit from knowing APDL, allowing you to add code snippets to your models. We have put some images below and you can also learn more here or go straight to Amazon.com to purchase the paperback or Kindle versions.

Introduction_to_APDL_V2-1_Cover

PADT-Intro-APDL-pg184-185 PADT-Intro-APDL-pg144-145 PADT-Intro-APDL-pg112-113 PADT-Intro-APDL-pg100-101 PADT-Intro-APDL-pg-020-021