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Abaqus has always been first choice of analysts for modeling any form of non-linearity in the model: geometric non-linearity, material non-linearity, or boundary condition non-linearity which is large sliding contact. Within material non-linearity, the most popular model is piecewise linear plasticity used to model plastic deformations in alloys or metals beyond their yield point. This blog post primarily discusses another powerful but somewhat less known non-linear material model of Abaqus used to model elastomers or rubbers.

Before getting into Abaqus’ functionalities for rubbers, let’s see what types of rubbers primarily exist, along with their mechanical characteristics:

Solid Rubbers

They exist almost everywhere: tires, weather seals, oil seals, civil engineering equipment, etc. Their main mechanical characteristics are

  • Nearly incompressible: While it is easy to stretch these materials, it is very difficult to compress them volumetrically. It’s a common observation that a rubber band can be stretched easily but a piece of pencil eraser cannot be compressed so easily. This behavior is particularly important in elastomer modeling.
  • Progressive loading and unloading cycles show hysteresis as well as damage. As cycles continue, damage progresses.

Thermoplastics

They are a physical combination of rubber materials and thermal plastics. They can be easily molded or extruded. They are not physically as strong as solid rubbers, neither resistant to heat and chemicals. They are more prone to creep and permanent set.

Elastomeric foams

Commercially, they are referred to as porous rubbers or just foams.

  • They can undergo very large strain, as large as 500% that is still recoverable. Their counterparts, crushable foams, can exhibit inelastic strains.
  • They exhibit cellular structure that may be open or closed type. Typical examples are cushions, paddings, etc.
  • The compressive stress strain curve is as follows:

Foams exhibit a linear behavior in a compressive strain range of 0% to 5%. Subsequently, there is a plateau of severe deformation at almost constant stress. In this region, the walls and plates of cells buckle under compression thereby forming a denser structure. Post buckling, the cellular walls and plates start interacting with each other, causing a gradual increase in compressive stress.

  • Due to high porosity, foams exhibit very large axial compressive strain without any lateral strain. Due to this, the Poisson’s ratio of foams is nearly zero. This behavior is critical for material modeling of foams in Abaqus.

Material models in Abaqus for rubbers

Abaqus uses the “hyperelastic materials” terminology for its material libraries that support rubbers. This is primarily because rubbers are elastic in nature even at very high strains. The basic assumptions in modeling solid rubbers are: elastic, isotropic and nearly incompressible. Foam material libraries in Abaqus are referred as “hyperfoam” and are highly incompressible. None of the rubber material models can be represented by a single coefficient such as modulus. It rather requires a strain energy density function that can have an infinite number of terms. Therefore, in Abaqus, strain energy functions have specific forms with certain numbers of parameters to be determined. Each of these function is associated with a separate material model, as shown below. […]

Today we will continue our series on the hidden intelligence of CATIA V5.  It is important to note that I am using a standard Classic HD2 license for this series In my last post, we discussed building a catalog of parts based on a single part that has a spreadsheet that drives the parameters with part numbers.  What about features?  If CATIA V5 is powerful enough to generate entire parts based on parameters, shouldn’t it also be able to be able to generate repetitive features? For instance, take a boss feature that appears on the B-Side of a plastic part. As a leader, I would not be interested in paying my designer his rates to keep repeatedly modeling a feature that may only change slightly throughout the backside! Model smarter: make once, use many times.

To do this successfully, you must address a few things – the first being how it may change. Of course you may not anticipate all changes, but a good rule of thumb is to try to model with maximum flexibility (big slabs for surfaces, overbuild everything, pay close attention to design intent) and do not use B-reps for your design. Avoid creating and building off of features CATIA builds, meaning whenever possible build your own and pick only from the tree to link to them.  The second issue to address is – what are going to be the parametric numerical inputs to drive the design? See my first post in this series on how to set these up.  i.e. Draft Angle, Wall thickness, Outer Diameter, etc.

Finally, what are going to be the geometric inputs to drive the design?  i.e. Location point, Pull Line, Slide Line, Mating Surface, etc.  A good rule of thumb here is to limit these features to as few as possible that are needed to get the job done. Sometimes it may be beneficial to sketch all this out on paper before you build it; I suggest gathering input from all the possible parties to help you in your definition.

In the example below, I have constructed a boss. Let’s review what I did. […]

Additive manufacturing is not a new technology – it was introduced in the manufacturing industry in late 80s for very niche applications. Stereolithography, a variant of additive manufacturing, was introduced in 1986 for rapid prototyping applications; however, its true potential remained hidden for a long time. Additive manufacturing primarily refers to methods of creating a part or a tool using a layered approach. As a still-evolving technology, it now covers a family of processes such as material extrusion, material jetting, direct energy deposition, power bed fusion, and more.

Additive manufacturing expands design possibilities by eliminating many manufacturing constraints. Contrary to rapid prototyping and 3D printing, there has been a shift of focus to functional requirements in additive manufacturing; however, these functional requirements may deviate from what is expected due to many factors typical of an additive manufacturing process.

  • Change in material properties: Mechanical and thermal properties of a manufactured part differ from raw material properties. This happens due to material phase change which is typical to most additive manufacturing applications.
  • Cracking and failure: The process itself generates lots of heat that produces residual stresses due to thermal expansion. These stresses can cause cracks in material during manufacturing.
  • Distortion: Thermal stresses can lead to distortion that can make the part unusable.

The additive manufacturing process is not certifiable yet, which is a major barrier in widespread adoption of these processes commercially. The ASTM F42 committee is working on defining AM standards with respect to materials, machines, and process variables.

The role of Simulation in additive manufacturing

  • Functional design: The first objective is to generate a suitable design that meets functional requirements, then subsequently improve the design through optimization methodologies that work in parallel with simulation.
  • Generate a lattice structure: Many of the parts manufactured through AM have a lattice structure instead of a full continuum. One objective of simulation in AM is to generate a lattice structure and optimize it using sizing optimization.
  • Calibrate material: As mentioned before, the material properties of a final part can differ substantially from that of the raw material. The next objective is to capture the phase transformation process through multi-scale material modeling.
  • Optimize the AM process: Unwanted residual stresses and distortions can develop in the process. It is necessary to accurately capture these physical changes to minimize the gap between the as-designed and as-manufactured part specs.
  • In service performance: Evaluate how the manufactured part will perform under real life service loads with respect to stiffness, fatigue, etc.

 

Now let’s discuss each of these objectives in more detail, with respect to SIMULIA. […]

This is Part 3 in my series on the hidden intelligence of CATIA V5. To quickly recap what we have already talked about, in my first post I discussed the importance of setting up and using parameters and formulas to capture your design intent and quickly modify things that you know are likely to change. We took those principles a bit farther in my second post and discussed the value of building a design table in those situations when you may have a design with parameters that will vary and that you want to use many times. In that case you could see that we had our rectangular tubing part and could modify its wall thickness, height, and width to make several iterations of basically any size of tubing one would ever need! You would simply keeping doing a Save as… and placing those parts in your working directory to be added into an assembly at some time (I assume).

This methodology would work fine, but today I want to focus on a very cool spin on this theory by building a catalog of your most commonly used parts which are similar enough to be captured in a single model. Using our tubing model, and picking up where we left off, we have a spreadsheet that defines the parameters that change. All we would need to do to build a catalog of each iteration of the design table is add a column to the spreadsheet named PartNumber just as I have it with no spaces in the name and then associate that to the ‘Part Number’ intrinsic parameter that is created automatically when you being a model.

Let’s get started.  I will open both the model and the spreadsheet, edit the spreadsheet with the column, and then add in some part numbers.

Part numbers added

When you save the file, the field should appear in CATIA when you click on the Associations tab. […]

This is an exciting post for me! Dassault has just come out with a couple of new bundles that blow the doors off anything I have seen previously.

CATMEE – Mechanical Engineering Excellence

The first package is named CATMEE; this would be the “Mechanical” version of the package. In Classic terms, previously for this purpose I would have recommended an MD2 trigram.  In PLM Express bundles, I would have recommended a CAC+MCE bundle to these types of users. They are typically heavy on the mechanical solid modeling portion of CATIA, and do not do very much surfacing.  CATMEE is a CAC+MCE on steroids! It includes CAT3DX (which I talked more about in my last post) AND also includes bundles for FPE (Fabricated Product), JTE (Jig and Tool Creation), PRX (Animated Product Review), FTX (3D Master), and TRE (Technical Specifications Review).

CATMEE Package Bundle

I realize that this sounds like a bunch of trigram soup. What does it really mean in CATIA V5? Well from a workbench standpoint, the CAC+MCE add-on looks like this:

CAC+MCE Workbenches

From a workbench standpoint, CATMEE looks like this:

CATMEE Bundle Workbenches

Take a closer look: you get Sheet Metal, 3D GD&T functionality (the good one, FTA!), Mold Tooling, Structure Design, and also DMU! In fact Kinematics, Space Analysis and Fitting Simulation alone can get expensive as an add-on, but here it comes with the bundle. Imagine cutting a section and it actually still being there when you click OK, and being available in the specification tree and updates when you change your part, as well as clearance checks, interference checks, etc.  MD2 and/or CAC+MCE users know exactly what I am talking about!

If you are in the market for a new seat or two this year and you are a mechanical customer, you should talk to your account manager and ask about this package; the new configurations not only help your productivity, but also help you expand your capabilities of what kinds of parts and markets you can get into.

CATMSE – Mechanical and Shape Engineering Excellence

This package is where you will really get your bang for the buck! CATMSE is a package we would have previously bundled as either an HD2 (Classic) or CAC+MCE+HDX (PLM Express). It is designed more for the mechanical and surfacing (Hybrid) type of role as a designer. Traditionally CAC+MCE+HDX overall gave you the GSD version of the Generative Shape Design workbench (better sweep functions, laws, etc) as well as a DL1 (Developed Shapes Toolbar in GSD) and a light version of Freestyle workbench (FS1). […]

Today’s topic will focus a little on the licensing side of CATIA – namely CAT3DX and the theory of what it is here for.

Several years ago, Dassault changed the way they were packaging CATIA V5 by introducing PLM Express as a way to buy it; my colleague Jason Johnson explained this in a previous post. As he had mentioned, this was referred to as CATIA TEAM PLM and was really designed to allow for connecting current CATIA V5 users of their new PLM offering, which was ENOVIA SmarTeam.  He also wrote briefly about the configurations and trigrams that make up the software.  The easiest way to think about a trigram per se is to know that a group of trigrams make up a configuration, and trigrams by themselves give you access to particular workbenches – or in some cases only add toolbars to existing workbenches.

Why does this matter? Because there is a new sheriff in town called 3DEXPERIENCE. Much more than a PLM system, the 3DEXPERIENCE platform suite of tools will assist the user in management of their daily work, projects, processes, BOMs, documents, CAD, etc.  While an old CAC (CAT) license – which was the base configuration for PLM Express – would give you access to SmarTeam by bundling in TDM and TEM trigrams, the new CAT3Dx will now give you all of that, as well as access to the ENOVIA 3DEXPERIENCE Platform, by giving you the PCS and CNV trigrams as well. These are the minimum trigrams needed to connect to the platform (the price for admission).

The Dassault idea is still the same – help CATIA v5 users move away from file-based, directory-based storage (which has always presented its own challenges) and help companies regain control of their data via the new platform. The only caveat to this is that you would install ENOVIA to manage your data, which is not as simple as throwing in a set of discs like SmarTeam was. ENOVIA requires the setting up of a database using SQL or Oracle, and then configuration of the various pieces (web server, authentication, java virtual machine, etc.).  Once this has been configured, the base PCS, CNV combination gives you the ability to vault your data and set up workspaces for where and how it will be stored, as well as do some level of change management on it. (set up Change Requests and Routes for how your data will be routed) to get it through its life cycle to release.

Creation Menu

 

The ENOVIA applications that come with the PCS, CNV combination are Classify & Reuse, Collaboration & Approvals, Collaborative Lifecycle, Design IP Classification, Exchanges Management, My Collections, My Issues, My Route Tasks, and X-CAD Design. These are plenty enough to help your team begin to get to a single source of truth – meaning, never having to guess what state the latest data is in.

ENOVIA Apps

You also have access applications for business intelligence information. This includes access to the latest technology of Dashboards.  Dashboards are ways of viewing data configured to your liking.  Not at all unlike the old igoogle portal which allowed you to customize your view of news, etc. In 2012 Dassault acquired Netvibes.

netvibes

Information Intelligence

[…]

This is a second look at the hidden intelligence of CATIA V5. Our topic today will focus on the creation and use of design tables. As I talked about in my last blog post, parameters and formulas can be used to drive your design from the specification tree based on your design intent. We will continue on using the rectangular tubing part and build several variations of that tubing that can be driven from a spreadsheet.

Design Table Icon

Most of the work has been already done, and although it is not necessary to have pre-defined parameters and formulas existing, the process is faster. We will begin by again looking at the Knowledge toolbar, this time focusing on the Design Table icon.

When the command is selected, a dialog appears asking for the name of the design table and also gives you a choice on whether or not you want to use a pre existing file or create one from the current parameter values.  The differences being whether or not you have an existing spreadsheet filled out already with all the tabulated values of what changes in each iteration of the design.

Design Table Dialog

 

In our case, to show the functionality we will choose the create with current parameter values option. Once that is decided, you choose which parameters you want to be driven by the spreadsheet.  In our case, we had some already created, so we changed the filter to User parameters, chose the values that were NOT driven by formulas (INSIDE and OUTSIDE RADII) and moved them to the inserted side by highlighting and clicking the arrow.

Parameters to Insert

At this point, we have defined that we want a spreadsheet to use columns for Height, Width, and Wall Thickness based on the current values in the model as it is at this moment. When we click OK on the dialog, it will ask us where we want to save the spreadsheet. I suggest that you do this in a place where anyone who uses the model can has at least read access to (i.e. a network drive).  Note that I can also change the type of file to a .txt if I do not have access to Excel® or any other software that can edit .xls files.

Read Access Directory

 

Once this has been defined, your design table is created, linked to your 3D model, and ready to be edited to include your alternate sizes. This is confirmed by the next dialog. To add in the other sizes, simply click on the Edit table… button and your editor (Excel or Notepad) should launch and simply fill in rows with your values.

Linked and ready to edit

Once you have edited and saved the values, you can close that software and CATIA will update based on your values.

Excel Modifications

 

CATIA Updated

Now you would just pick the value set you want and click OK for the change to appear on the screen.

File Updated

At any time, you can always go to make the changes by finding the Design Table under the Relations section of the specification tree and double-clicking on it.

Design Table under Relations

As you can see, it’s pretty easy to create a design table and drive your parametric file with multiple values. The world of CATIA V5 is all about re-use of data and capturing business intelligence we already know exists in all companies.  How can we help you? Tata Technologies has helped many companies time and again.

Stay tuned for Part 3!

 

 

 

 

 

 

I mentioned the process automation concept of ISight in a previous simulation automation blog. ISight is an open source code simulation automation and parametric optimization tool to create workflows that automate the repetitive process of model update and job submission with certain objectives associated with it. The objective could be achievement of an optimal design through any of the available techniques in ISight: Design of experiments, optimization, Monte Carlo simulation or Six Sigma. In this blog post, I will be discussing various value added algorithms in DOE technique; I will discuss other techniques in future blogs.

Why design of experiments

Real life engineering models are associated with multiple design variables and with multiple responses. There are two ways to evaluate the effect of change in design variable on response: Vary one at a time (VOAT) approach or Design of experiments (DOE) approach. The VOAT approach is not viable because:

  • This approach ignores interactions among design variables, averaged and non-linear effects.
  • In models associated with large FE entities, each iteration is very expensive. VOAT does not offer the option of creating high fidelity models with a manageable number of iterations.

With the DOE approach, user can study the design space efficiently, can manage multi dimension design space and can select design points intelligently vs. manual guessing. The objective of any DOE technique is to generate an experimental matrix using formal proven methods. The matrix explores design space and each technique creates a design matrix differently. There are multiple techniques which will be discussed shortly and they are classified into two broad configurations:

  • Configuration 1: User defines the number of levels and their values for each design variable. The chosen technique and number of variables determines number of experiments.
  • Configuration 2: User defines the number of experiments and design variables range.

Box-Behnken Technique

This is a three level factorial design consisting of orthogonal blocks that excludes extreme points. Box-Behnken designs are typically used to estimate the coefficients of a second-degree polynomial. The designs either meet, or approximately meet, the criterion of rotatability. Since Box-Behnken designs do not include any extreme (corner) point, these designs are particularly useful in cases where the corner points are either numerically unstable or infeasible. Box-Behnken designs are available only for three to twenty-one factors.untitled

Central Composite Design Technique […]

If you are in the business of designing and engineering product, then you have PLM. This is a statement of fact. The question then becomes: what is the technology underpinning the PLM process that is used to control your designs?

Because of the way that technology changes and matures, most organizations have a collection of software and processes that support their PLM processes. This can be called the Point Solution approach. Consider a hypothetical setup below:

The advantage of this approach is that point solutions can be individually optimized for a given process – so, in the example above, the change management system can be set up to exactly mirror the internal engineering change process.

However, this landscape also has numerous disadvantages:

  1. Data often has to be transferred between different solutions (e.. what is the precise CAD model tied to a specific engineering change?). These integrations are difficult to set up and maintain – sometimes to the point of being manual tasks.
  2. The organization has to deal with multiple vendors.
  3. Multiple PLM systems working together require significant internal support resource from an IT department.
  4. Training and onboarding of new staff is complicated

The alternative to this approach is a PLM Platform. Here, one technology solution includes all necessary PLM functionalities. The scenario is illustrated below:

It is clear that the PLM Platform does away with many of the disadvantages of the Point Solution; there is only one vendor to deal with, integrations are seamless, training is simplified, and support should be easier.

However, the PLM Platform may not provide the best solution for a given function when compared to the corresponding point solution. For example, a dedicated project management software may do a better job at Program Management than the functionality in the PLM Platform; this may require organizational compromise. You are also, to some extent, betting on a single technology vendor and hoping that they remain an industry leader.

Some of the major PLM solution vendors have placed such bets on the platform strategy. For example, Siemens PLM have positioned Teamcenter as a complete platform solution covering all aspects of the PLM process. (refer to my earlier blog post What is Teamcenter? or, Teamcenter Explained). All of the PLM processes that organizations need can be supported by Teamcenter.

Dassault Systèmes have pursued a similar approach with the launch of their 3DEXPERIENCE platform, which also contains all of the functions required for PLM. In addition, both are actively integrating additional functionality with every new release.

So what is your strategy – Point or Platform? This question deserves serious consideration when considering PLM processes in your organization.

For many years, finite element modeling has been the job of a specialist; the tools used to perform even simple finite element analysis have been complex enough to require a subject matter expert. This is primarily due to the complex, difficult to understand graphical user interfaces of these products. The job is made further difficult to perform due to the requirement of advanced engineering subject knowledge by the analyst.

Can a mechanical designer who uses CAD tools to create engineering drawings be trained to perform engineering simulations?

In today’s product availability scenario, the answer is “yes.”

A CAD designer using CATIA can create and execute simple finite element models within the CATIA environment by using CATIA workbenches that have been developed for simulations. This makes it intuitive and easier for designers to ensure that their parts meet their design requirements.

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How the simulation methodology gets simplified using designer level tools

  • No need of an expert level analyst tool to perform simple finite element simulation.
  • No need of manual data transfer between design and analysis departments.
  • No need of geometry clean up tools to fix data translation errors.

There are obvious benefits to adopting this simplified approach that integrates the design and analysis environments. The designer can predict design problem early in design process; subsequently the designer can check various alternatives of design in less time. This is primarily due to the tight integration of designer level tools with knowledge based engineering that allows the designer to deliver better product in less time.

Part Level Simulation

From a geometrical perspective, the simulation model can be generated at part level to begin with. The native integration within CATIA allows users to perform stress, displacement, and vibration analysis at any time in the design process, allowing more accurate sizing of parts and fewer design iterations. Individual parts consisting of solid, surface, and wireframe geometries can be analyzed under a variety of loading conditions. The analysis specifications, such as loads and restraints, are associative, with the design allowing users to perform analyses quickly and easily. These specifications are then automatically incorporated into the underlying finite element model, meaning that users do not have to work directly with the finite element model. “Virtual parts” allow items like forces, moments, and restraints to be easily modeled without having to have a detailed geometric representation.

Standard reports can be automatically generated in HTML format, providing clear and detailed information about the results of the analysis, including images associated with the computations. These reports can be used to document the analyses that have been performed and to communicate the results of the analysis to other stakeholders in the organization. CATIA V5 Analysis users benefit naturally from the overall PLM solution provided by Dassault Systèmes, including ENOVIA V5 for data and product lifecycle management. CATIA V5 Analysis users can store, manage, and version all the data associated with their product’s simulation and share the information within the extended enterprise. This unique capability allows collaboration and provides access to advanced PLM practices such as concurrent engineering and change management.

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     Assembly level simulation

 If the concept of virtual parts does not hold good anymore and the complexities of various parts interacting with each other make assembly level simulation mandatory, it is possible to create analysis models for assemblies as well. The analysis of assemblies, including an accurate representation of the way the parts interact and are connected, allows for more realistic and accurate simulation. The designer does not have to make simplifying assumptions about the loading and restraints acting on an individual part. Instead the part can be analyzed within the environment that it operates with the loading automatically determined based on the way the part is connected to and interacts with surrounding parts.

The various types of connections that can be modeled include bolted connections, welded connections, pressure fitting connections, and many more. To make the job further easier for the designer, these connections can be defined using assembly level constraints that already exist in the CAT Product model. Once the design changes, the associated assembly constraints as well as corresponding FEA connections get updated, thereby creating an updated FEA model that is ready for analysis.

         Concurrent engineering made easier 

The “assembly of analysis” capability enables concurrent engineering. For example, the various parts in an assembly can be modeled and meshed separately by different users. They can either use the CATIA V5 meshing tools or import orphan meshes (meshes that don’t have any geometry associated with them) developed outside of CATIA Analysis using a variety of different modeling tools. The user responsible for analyzing the assembly can consolidate the different meshes, connect the parts, apply the loading specifications, and run the simulation. This can significantly reduce the turnaround time when analyzing large assemblies, particularly since some of the parts may have already been analyzed and therefore, the analysis models would already be available.

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Extended solver capabilities

The basic level FEA solver present in the CATIA designer workbench is called the “Elfini” solver and can model only simpler physical problems such as linear materials, small deformations, small rotations and bonded contacts; real life problems can be much more complex and may necessitate the need of an advanced solver. To address such scenarios it is possible to include the well known non-linear solver Abaqus into the CATIA designer environment; it can model the effects of geometric nonlinearity, such as large displacements, and allows nonlinear materials to be included, such as the yielding of metals and nonlinear elastic materials like rubber. It also offers more advanced contact capabilities including the ability to model large relative sliding of surfaces in contact.

The Abaqus capability enables the effect of multiple steps to be analyzed, where the loading, restraints, contact conditions, etc., vary from one step to the next. This powerful technique allows complex loading sequences to be modeled. For example, a pressure vessel might be subjected to an initial bolt tightening step, followed by internal pressurization, and conclude with thermal loading.

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