PADT Events – January 2017

Welcome to 2017. We are all very excited about what we have planned for events this year. As we travel around the country, and the world, we hope to have to chance to meet many of you who follow PADT. 2017 will look a lot like 2016 except that, based on your feedback, we will be trying more on-line webinars and events.  As always, contact us if you have any questions.


Launch of ASU Manufacturing Research and Innovation Hub

01/18/17
ASU Polytenic Campus
Mesa, AZ

PADT will be on-hand at ASU Polytechnic school for the launch of ASU’s new Manufacturing Research and Innovation Hub. Stop by to see their new facilities and meet the students and staff along with partners like PADT that helped make it happen.
Learn more

ANSYS Startup Program Webinar: The Significance of Simulation

01/25/17
Online

This seminar will discuss how ANSYS simulation software can be used by startups to shorten their time to market and reduce their manufacturing costs. We will discuss what simulation is and how to use it effectively, as well as go over the ANSYS Startup Program and how it gives early stage companies access to world class simulation.
Learn more

Invited Speaker at the 2017 Arizona Science Bowl (High School Event)

01/28/17
ASU West Campus
Glendale, AZ

PADT’s Dhruv Bhate, PhD will speak to students at the High School Science Bowl. This is a great event, and if you have never been, you should go. The level of technology and scientific rigour fo these Middle School and High School kids is amazing.
Learn more

Tesla Test Drive at PADT

01/30/16
PADT Tempe
Tempe, AZ

Yes, you read that right. We will be inviting customers to come to PADT and see how the simulation and 3D Printing technologin we sell, support, and use is applied to advanced automotive systems – Cool Cars! Tesla Motors has been kind enough to partner with us to allow a select few the oportunity to test drive a Tesla. Look for your invite via email and register quickly, space is limited.
Learn more

The next webinar of the ANSYS Breakthrough Energy Innovation Campaign is now available!

 Register here to watch

Thermal Optimization for Energy Efficiency 

Nearly everything has an optimal operating temperature and thermal condition. Millions of dollars each year are spent generating and transporting thermal energy to achieve thermal goals. Thermal optimization not only improves the economy of transporting energy, maintaining building temperatures, manufacturing processes and products, it improves their efficiency as well. Engineers use simulation to reveal detailed pictures of thermal processes, providing a deep understanding of all aspects of thermal management.

Join our experts for this Webinar to learn how you can capture thermal processes in powerful simulations, seamlessly identify multiphysics interactions that impact performance, and quickly achieve thermal optimization using integrated design optimization tools.
Register Here – or Click Here for more information on Thermal Optimization

This webinar is presented by Richard Mitchell and Xiao Hu

Richard Mitchell is the Lead Product Marketing Manager for Structures. He joined ANSYS in 2006 working in pre-sales and support roles. Before this Richard was an ANSYS user working for a high tech company in the UK. He worked as an analyst on space and vacuum tube technologies.

 

Xiao is a principal engineer at ANSYS Inc. Xiao has spent a combined 12 years of his career at ANSYS and Fluent corporation working with customers in the modeling and simulation of powertrain related applications. Xiao spent his earlier years with Fluent working on engine CFD applications.

Keep checking back to the Energy Innovation Homepage for more updates on upcoming segments, webinars, and other additional content.

Metal 3D Printing a Shift Knob

I have always had an issue with leaving well enough alone since the day I bought my Subaru. I have altered everything from the crank pulley to the exhaust, the wheels and tires to the steering wheel. I’ve even 3D printed parts for my roof rack to increase its functionality. One of the things that I have altered multiple times has been the shift knob. It’s something that I use every time and all the time when I am driving my car, as it is equipped with a good ol’ manual transmission, a feature that is unfortunately lost on most cars in this day and age.

prevknobs

I have had plastic shift knobs, a solid steel spherical shift knob, a black shift knob, a white shift knob, and of course some weird factory equipment shift knob that came with the car. What I have yet to have is a 3D printed shift knob. For this project, not any old plastic will do, so with the help of Concept Laser, I’m going straight for some glorious Remanium Star CL!

One of the great things about metal 3D printing is that during the design process, I was not bound by the traditional need for a staple of design engineering, Design For Manufacturing (DFM). The metal 3D printer uses a powder bed which is drawn over the build plate and then locally melted using high-energy fiber lasers. The build plate is then lowered, another layer of powder is drawn across the plate, and melted again. This process continues until the part is complete.

The design for the knob was based off my previously owned shift knobs, mainly the 50.8 mm diameter solid steel spherical knob. I then needed to decide how best to include features that would render traditional manufacturing techniques, especially for a one-off part, cost prohibitive, if not impossible.   I used ANSYS Spaceclaim Direct Modeler as my design software, as I have become very familiar with it using it daily for simulation geometry preparation and cleanup, but I digress, my initial concept can be seen below:2016-10-18_16-19-33

I was quickly informed that, while this design was possible, the amount of small features and overhangs would require support structure that would make post-processing the part very tedious. Armed with some additional pointers on creating self supporting parts that are better suited for metal 3D printing, I came up with a new concept.

2016-10-18_16-24-24

This design is much less complex, while still containing features that would be difficult to machine. However, with a material density of 0.0086 g/mm^3, I would be falling just short of total weight of 1 lb, my magic number. But what about really running away from DFM like it was the plague?

2016-10-18_16-23-31

There we go!!! Much better, this design iteration is spec’d to come out at 1.04 lbs, and with that, it was time to let the sparks fly!

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Here it is emerging as the metal powder that has not been melted during the process is brushed away.

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The competed knob then underwent a bit of post processing and the final result is amazing! I haven’t been able to stop sharing images of it with friends and running it around the office to show my co-workers. However, one thing remains to make the knob functional… it must be tapped.

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In order to do this, we need a good way to hold the knob in a vise. Lucky for us here at PADT, we have the ability to quickly design and print these parts. I came up with a design that we made using our PolyJet machine so we could have multiple material durometers in a single part. The part you need below utilizes softer material around the knob to cradle it and distribute the load of the vise onto the spherical lattice surface of the knob.

img_7765img_7764

We quickly found out that the Remanium material was not able to be simply tapped. We attempted to bore the hole out in order to be able to press in an insert, and also found out the High Speed Steel (HSS) was not capable of machining the hole. Carbide however does the trick, and we bored the hole out in order to press in a brass insert, which was then tapped.

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Finally, the shift knob is completed and installed!

Want to learn more, check out the article in “Additive Manufacturing Media.”

 

ANSYS Breakthrough Energy Innovation Campaign – Thermal Optimization

Information regarding the next topic in the Breakthrough Energy Innovation Campaign has been released, covering Thermal Optimization and how ANSYS simulation software can be used to help solve a variety of issues related to this topic, as well as capture all thermal processes.

Additional content regarding thermal optimization can be viewed and downloaded here.

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

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

The next webinar of the ANSYS Breakthrough Energy Innovation Campaign is now available!

Turbocharge Rotating Machinery Efficiency with Simulation
 
Rotating machinery users demand increased efficiency, reliability and durability while expecting compliance with regulatory mandates to reduce emissions and noise. Simulation pinpoints solutions and guides trade-offs early in the design process before significant investments have been made. By reducing the need for expensive prototypes and test rigs, simulation delivers better performance at lower cost.
By watching this webinar you will:

● Understand the concept of a virtual prototype and how it reduces development costs while optimizing product performance.

● Identify seven essential features that must be included in a simulation in order to maximize the performance and efficiency.

● Learn how ZECO Hydropower used ANSYS simulation tools coupled with high performance computing to develop a new and optimal intake for a Kaplan turbine in half of the usual time. They were able to reduce civil engineering infrastructure costs to ensure they would be competitive in emerging markets.

● Walk through ZECO’s simulation process and results including CFD turbomachinery simulation, parallel computing, parametric modeling, and optimization tools.

Register here to watch – or Click Here for more information on Machine & Fuel Efficiency
This webinar is presented by Brad Hutchinson and Alessandro Arcidiacono.
Keep checking back to the Energy Innovation Homepage for more updates on upcoming segments, webinars, and other additional content.

SFF Symposium 2016 Paper: Predicting the Mechanical Behavior of ULTEM-9085 Honeycomb Structures

Our work on  3D printed honeycomb modeling that started as a Capstone project with students from ASU in September 2015 (described in a previous blog post), was published in a peer-reviewed paper released last week in the proceedings of the SFF Symposium 2016. The full title of the paper is “A Validated Methodology for Predicting the Mechanical Behavior of ULTEM-9085 Honeycomb Structures Manufactured by Fused Deposition Modeling“. This was the precursor work that led to a us winning an 18-month award to pursue this work further with America Makes.

Download the whole paper at the link below:
http://sffsymposium.engr.utexas.edu/sites/default/files/2016/168-Bhate.pdf

Abstract
ULTEM-9085 has established itself as the Additive Manufacturing (AM) polymer of choice for end-use applications such as ducts, housings, brackets and shrouds. The design freedom enabled by AM processes has allowed us to build structures with complex internal lattice structures to enhance part performance. While solutions exist for designing and manufacturing cellular structures, there are no reliable ways to predict their behavior that account for both the geometric and process complexity of these structures. In this work, we first show how the use of published values of elastic modulus for ULTEM-9085 honeycomb structures in FE simulation results in 40- 60% error in the predicted elastic response. We then develop a methodology that combines experimental, analytical and numerical techniques to predict elastic response within a 5% error. We believe our methodology is extendable to other processes, materials and geometries and discuss future work in this regard.

Figure
Fig 1. Honeycomb tensile test behavior varying as a function of manufacturing parameters
The ASU Capstone team (left to right): Drew Gibson, Jacob Gerbasi, John Reeher, Matthew Finfrock, Deep Patel and Joseph Van Soest.
Fig 2. The ASU Capstone team (left to right): Drew Gibson, Jacob Gerbasi, John Reeher, Matthew Finfrock, Deep Patel and Joseph Van Soest.

ANSYS R17 Topological Optimization Application Example – Saxophone Brace

topo-opt-sax-a2What is Topological Optimization? If you’re not familiar with the concept, in finite element terms it means performing a shape optimization utilizing mesh information to achieve a goal such as minimizing volume subject to certain loads and constraints. Unlike parameter optimization such as with ANSYS DesignXplorer, we are not varying geometry parameters. Rather, we’re letting the program decide on an optimal shape based on the removal of material, accomplished by deactivating mesh elements. If the mesh is fine enough, we are left with an ‘organic’ sculpted shape elements. Ideally we can then create CAD geometry from this organic looking mesh shape. ANSYS SpaceClaim has tools available to facilitate doing this.

topo-opt-sax-a1Topological optimization has seen a return to prominence in the last couple of years due to advances in additive manufacturing. With additive manufacturing, it has become much easier to make parts with the organic shapes resulting from topological optimization. ANSYS has had topological optimization capability both in Mechanical APDL and Workbench in the past, but the capabilities as well as the applications at the time were limited, so those tools eventually died off. New to the fold are ANSYS ACT Extensions for Topological Optimization in ANSYS Mechanical for versions 17.0, 17.1, and 17.2. These are free to customers with current maintenance and are available on the ANSYS Customer Portal.

In deciding to write this piece, I decided an interesting example would be the brace that is part of all curved saxophones. This brace connects the bell to the rest of the saxophone body, and provides stiffness and strength to the instrument. Various designs of this brace have been used by different manufacturers over the years. Since saxophone manufacturers like those in other industries are often looking for product differentiation, the use of an optimized organic shape in this structural component could be a nice marketing advantage.

This article is not intended to be a technical discourse on the principles behind topological optimization, nor is it intended to show expertise in saxophone design. Rather, the intent is to show an example of the kind of work that can be done using topological optimization and will hopefully get the creative juices flowing for lots of ANSYS users who now have access to this capability.

That being said, here are some images of example bell to body braces in vintage and modern saxophones. Like anything collectible, saxophones have fans of various manufacturers over the years, and horns going back to production as early as the 1920’s are still being used by some players. The older designs tend to have a simple thin brace connecting two pads soldered to the bell and body on each end. Newer designs can include rings with pivot connections between the brace and soldered pads.

topo-opt-sax-01
Half Ring Brace

 

Solid connection to bell, screw joint to body
Solid connection to bell, screw joint to body
Older thin but solid brace rigidly connected to soldered pads
Older thin but solid brace rigidly connected to soldered pads
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Modern ring design
Modern Dual Degree of Freedom with Revolute Joint Type Connections
Modern Dual Degree of Freedom with Revolute Joint Type Connections

Hopefully those examples show there can be variation in the design of this brace, while not largely tampering with the musical performance of the saxophone in general. The intent was to pick a saxophone part that could undergo topological optimization which would not significantly alter the musical characteristics of the instrument.

The first step was to obtain a CAD model of a saxophone body. Since I was not able to easily find one freely available on the internet that looked accurate enough to be useful, I created my own in ANSYS SpaceClaim using some basic measurements of an example instrument. I then modeled a ‘blob’ of material at the brace location. The idea is that the topological optimization process will remove non-needed material from this blob, leaving an optimized shape after a certain level of volume reduction.

Representative Solid Model Geometry Created in ANSYS SpaceClaim. Note ‘Blob’ of Material at Brace Location.
Representative Solid Model Geometry Created in ANSYS SpaceClaim. Note ‘Blob’ of Material at Brace Location.

In ANSYS Mechanical, the applied boundary conditions consisted of frictionless support constraints at the thumb rest locations and a vertical displacement constraint at the attachment point for the neck strap. Acceleration due to gravity was applied as well. Other loads, such as sideways inertial acceleration, could have been considered as well but were ignored for the sake of simplicity for this article. The material property used was brass, with values taken from Shigley and Mitchell’s Mechanical Engineering Design text, 1983 edition.

topo-opt-sax-07
Applied Boundary Conditions Were Various Constraints at A, B, and C, as well as Acceleration Due to Gravity.

This plot shows the resulting displacement distribution due to the gravity load:

topo-opt-sax-08

Now that things are looking as I expect, the next step is performing the topological optimization.

Once the topological optimization ACT Extension has been downloaded from the ANSYS Customer Portal and installed, ANSYS Mechanical will automatically include a Topological Optimization menu:

topo-opt-sax-09

I set the Design Region to be the blog of material that I want to end up as the optimized brace. I did a few trials with varying mesh refinement. Obviously, the finer the mesh, the smoother the surface of the optimized shape as elements that are determined to be unnecessary are removed from consideration. The optimization Objective was set to minimize compliance (maximize stiffness). The optimization Constraint was set to volume at 30%, meaning reduce the volume to 30% of the current value of the ‘blob’.
After running the solution and plotting Averaged Node Values, we can see the ANSYS-determined optimized shape:

topo-opt-sax-10
Two views of the optimized shape.

What is apparent when looking at these shapes is that the ‘solder patch’ where the brace attaches to the bell on one end and the body on the other end was allowed to be reduced. For example, in the left image we can see that a hole has been ‘drilled’ through the patch that would connect the brace to the body. On the other end, the patch has been split through the middle, making it look something like an alligator clip.

 

Another optimization run was performed in which the solder pads were held as surfaces that were not to be changed by the optimization. The resulting optimized shape is shown here:

topo-opt-sax-11

Noticing that my optimized shape seemed on the thick side when compared to production braces, I then changed the ‘blob’ in ANSYS SpaceClaim so that it was thinner to start with. With ANSYS it’s very easy to propagate geometry changes as all of the simulation and topological optimizations settings stay tied to the geometry as long as the topology of those items stays the same.

Here is the thinner chunk after making a simple change in ANSYS SpacClaim:

topo-opt-sax-12

And here is the result of the topological optimization using the thinner blob as the starting point:

topo-opt-sax-13

Using the ANSYS SpaceClaim Direct Modeler, the faceted STL file that results from the ANSYS topological optimization can be converted into a geometry file. This can be done in a variety of ways, including a ‘shrink wrap’ onto the faceted geometry as well as surfaces fit onto the facets. Another option is to fit geometry in a more general way in an around the faceted result. These methods can also be combined. SpaceClaim is really a great tool for this. Using SpaceClaim and the topological optimization (faceted) result, I came up with three different ‘looks’ of the optimized part.

Using ANSYS Workbench, it’s very easy to plug the new geometry component into the simulation model that I already had setup and run in ANSYS Mechanical using the ‘blob’ as the brace in the original model. I then checked the displacement and stress results to see how they compared.

First, we have an organic looking shape that is mostly faithful to the results from the topological optimization run. This image is from ANSYS SpaceClaim, after a few minutes of ‘digital filing and sanding’ work on the STL faceted geometry output from ANSYS Mechanical.

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This shows the resulting deflection from this first, ‘organic’ candidate:

topo-opt-sax-15

The next candidate is one where more traditional looking solid geometry was created in SpaceClaim, using the topological optimization result as a guide. This is what it looks like:

topo-opt-sax-16

This is the same configuration, but showing it in place within the saxophone bell and body model in ANSYS SpaceClaim:

topo-opt-sax-17

Next, here is the deformation result for our simple loading condition using this second geometry configuration:

topo-opt-sax-18

The third and final design candidate uses the second set of geometry as a starting point, and then adds a bit of style while still maintaining the topological optimization shape as an overall guide. Here is this third candidate in ANSYS SpaceClaim:

topo-opt-sax-19

Here are is the resulting displacement distribution using this design:

topo-opt-sax-20

This shows the maximum principal stress distribution within the brace for this candidate:

topo-opt-sax-21

Again, I want to emphasize that this was a simple example and there are other considerations that could have been included, such as loading conditions other than acceleration due to gravity. Also, while it’s simple to include modal analysis results, in the interest of brevity I have not included them here. The main point is that topological optimization is a tool available within ANSYS Mechanical using the ACT extension that’s available for download on the customer portal. This is yet another tool available to us within our ANSYS simulation suite. It is my hope that you will also explore what can be done with this tool.

Regarding this effort, clearly a next step would be to 3D print one or more of these designs and test it out for real. Time permitting, we’ll give that a try at some point in the future.

ANSYS Startup Roadshow – November 18th, Phoenix AZ

Phoenix!

The Co-Owner of PADT, Inc. Eric Miller will be at The Gateway Center for Entrepreneurial Innovation (CEI) this Friday, November 18th, from 12-1pm to discuss how ANSYS software is helping new entrepreneurs drive success through simulation.

This is a free event, and while registration is not required it is preferred.

The presentation will include a discussion on:

  • What simulation is and how it can be applied to product development

  • How partnering with PADT and ANSYS can be crucial to the success of a startup
  • How using ANSYS software will help deliver ideas to market more rapidly and cost effectively. Thus saving money, time, and increasing the probability of success.

Click Here for directions and additional registration information.

Eric will also be presenting information on the ANSYS Startup Program, which provides entrepreneurs with access to various ANSYS multiphysics simulation products bundled and priced specifically for early stage startup companies.

Acceptance to this program is limited to companies who are not current ANSYS customers and meet a variety of qualifications.

Those who are eligible will also receive access to the ANSYS Customer Portal for marketing opportunities and customer support.

Visit Padtinc.com/ANSYS_Startup to see if you qualify for this program, or Click Here to register to attend the startup presentation on November 18th.

We look forward to seeing you there

ANSYS 17.2 Executable Paths on Linux


ansys-linux-penguin-1When running on a machine with a Linux operating system, it is not uncommon for users to want to run from the command line or with a shell script. To do this you need to know where the actual executable files are located. Based on a request from a customer, we have tried to coalesce the major ANSYS product executables that can be run via command line on Linux into a single list:

ANSYS Workbench (Includes ANSYS Mechanical, Fluent, CFX, Polyflow, Icepak, Autodyn, Composite PrepPost, DesignXplorer, DesignModeler, etc.):

/ansys_inc/v172/Framework/bin/Linux64/runwb2

ANSYS Mechanical APDL, a.k.a. ANSYS ‘classic’:

/ansys_inc/v172/ansys/bin/launcher172 (brings up the MAPDL launcher menu)
/ansys_inc/v172/ansys/bin/mapdl (launches ANSYS MAPDL)

CFX Standalone:

/ansys_inc/v172/CFX/bin/cfx5

Autodyn Standalone:

/ansys_inc/v172/autodyn/bin/autodyn172

Note: A required argument for Autodyn is –I {ident-name}

Fluent Standalone (Fluent Launcher):

/ansys_inc/v172/fluent/bin/fluent

Icepak Standalone:

/ansys_inc/v172/Icepak/bin/icepak

Polyflow Standalone:

/ansys_inc/v172/polyflow/bin/polyflow/polyflow < my.dat

Chemkin:

/ansys_inc/v172/reaction/chemkinpro.linuxx8664/bin/chemkinpro_setup.ksh

Forte:

/ansys_inc/v172/reaction/forte.linuxx8664/bin/forte.sh

TGRID:

/ansys_inc/v172/tgrid/bin/tgrid

ANSYS Electronics Desktop (for Ansoft tools, e.g. Maxwell, HFSS)

/ansys_inc/v172/AnsysEM/AnsysEM17.2/Linux64/ansysedt

SIWave:

/ansys_inc/v172/AnsysEM/AnsysEM17.2/Linux64/siwave

The first webinar of the ANSYS Breakthrough Energy Innovation Campaign is now available

download-6

Register here to watch

Simulation of Planar Magnetic Components – Possible or Impossible?

Planar magnetic components consisting of a ferrite magnetic core and numerous conductor/insulation layers have been in use for many years. Historically, determining temperature dependent winding and core losses has only been possible using iterative testing of physical models due to the difficulty in determining 3-D frequency and thermal dependency. The only way to accomplish this now is to use frequency and thermally dependent material properties in a 2-way spatially coupled simulation.

Additionally, you can only construct a frequency dependent system model that accurately represents the real device after the steady-state temperature condition has been reached throughout the device.

Recent breakthrough developments in simulation technology and high-performance computing from ANSYS make it possible to design, simulate and optimize planar magnetic components without building physical models or compromising simulation fidelity.

This webinar demonstrates how you can use ANSYS software tools, featuring a customized interface complete with manufacturer libraries, to automatically set up and then solve a frequency dependent, 2-way coupled magnetic-thermal model.

Register here to watch

This webinar is presented by Mark Christini, the lead ElectromagneticsMark Christini Application Engineer at ANSYS.

He has been working in design, development, application and manufacturing of electrical devices and systems for the past 30 years. Mark has a strong interest in transformers of all kinds ranging, from small electronic transformers to large oil-filled EHV power transformers.

Keep checking back to the Energy Innovation Homepage for more updates on upcoming segments, webinars, and other additional content.

ANSYS Startup Roadshow Kickoff – CEI Phoenix

Click Here to Register

Click Here to Register

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.