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Solid Edge ST6 First Looks: Simulation and Linear Static Stress

By John Evans, September 24, 2013

The products we design have to perform well; they must operate safely and behave in a manner expected by their users. Having an accurate understanding of how products will perform under a variety of conditions is critical to our success, and so possession of that understanding during the design process is a sound investment.

Solid Edge ST6 from Siemens PLM Software offers a simulation environment that complements its unique modeling capabilities, allowing us to validate products before they are built. Not only can we validate the designs we made in Solid Edge, but through a blend of Synchronous Technology and Smart Dimensions, we can use Solid Edge to simplify, validate, and optimize designs imported from other MCAD packages.

In this First Look article, I describe Solid Edge Simulation and the linear static stress analysis of a part, in this case a barrel chamber (see figure 1). I used Solid Edge ST6 to design a new rifle, and then applied linear static stress analysis tools to evaluate and improve the design.

Figure 1: The design project I created in Solid Edge ST6

The needs for the rifle are: to be as simple as possible, to be rugged, and to be portable in the smallest possible package. Here are the highlights of my experiences in using Solid Edge ST6 to validate and improve the design.

Solid Edge Simulation

Solid Edge ST6 provides a good foundational analysis environment, because it is backed by the robust Nastran NX solver. NASTRAN is short for "NASA Structural Analysis," and is the name of the very first finite element analysis program, developed in the 1960s for NASA. Being in the public domain, its core code has since gone on to power many solvers; Nastran NX is Siemens PLM's version.

Solid Edge allows us to design and then validate the design within the same set of part and assembly files; there is no need to export model data to an external program. Being integrated, Solid Edge shows us a consistent user interface and workflow, only changing the ribbon set for each function. In this way, users new to simulation will probably pick up the process faster, as they navigate the system using common, already-understood tools.

Moreover, the software now includes a wonderful optimization tool to help us identify the best design based on criteria we specify. During the analysis process, Solid Edge takes the model data and our environmental setup, and hands the information to Nastran, which analyzes it and then post processes the results. The results are displayed graphically and numerically in a variety of ways.

Solid Edge makes a number of studies available to us:

In this First Look, I examine the first study, linear static stress analysis.

Linear Static Stress on Parts

The cartridge of my design is spec'd as "7.62x51mm NATO." The rifle cartridge was developed by NATO (North Atlantic Treaty Organization) in the 1950s to be the standard for small guns.

I wanted to ensure that my chamber design would meet current standards and handle high pressure loads of the cartridge. To help me validate the design before I moved too far in the design process, I used Solid Edge's linear static stress analysis. The ribbon for simulation work is shown in figure 2.

Figure 2: Linear static stress commands in the Simulation ribbon

The setup process used by Solid Edge is common to the industry, and so users of other MCAD systems should have little difficulty following along:

  1. Defining the simulation model
  2. Applying loads
  3. Applying constraints
  4. Meshing
  5. Solving
  6. Reporting

Siemens PLM hit the mark by making the environment easy to understand and to establish the simulation model rapidly. I successfully completed my initial analysis in just one hour, including running an optimization. That's kicking when you're fairly new to the environment!

Here are some of the highlights I picked up while studying the rifle's barrel chamber.

Create New Study

To begin, I chose New Study and used its default settings (see figure 3), which employs the iterative solver with a tetrahedral mesh.

Figure 3: The Create Study dialog box's default settings

To keep solution times down to a minimum, I turned on the Generate Only Surface Results and Do Not Process All Results After Solve options, and kept them on until I was ready for a more specific validation.

The options under Mesh Types are as follows:

And then these are three additional controls:

Figure 4: The Materials Table after adding AISI 4150 Steel. (It took a while to realize that to get the Add to Library option to turn on I had to edit the name)

Geometry Panel

Solid Edge allows us to select which bodies to include in the analysis. This is a nice option, but took a while for me to get used to. My barrel design is composed of two bodies - a main barrel section and the helical engagement body. Using separate bodies allows me to tune and manipulate the helical delay, without wrecking the chamber that is cut precisely according SAAMI (Sporting Arms and Ammunition Manufacturers' Institute) specifications.

I found, however, that the Define Geometry option rejected the multiple bodies in the part file until they were joined through a union. This is not a problem (in both the simplified and unsimplified versions of the component) but I found this requirement odd, because I like to retain those key solids in the part file as construction bodies - an approach incredibly handy, especially when unforeseen edits occur after the analysis.

Applying Structural Loads and Constraints

I applied a simple radial pressure to the inner walls of the chamber at the SAAMI proof load of 83,000PSI (pounds per square inch). The Solid Edge interface uses the standard method of us picking a surface, it prompting for a value and then accurately interpreting unit string suffixes.

I did not want anything constraining the expansion of the elements in the study, and so I utilized the cylindrical constraint. To my surprise, there were sufficient options to relax the constraint (see figure 5).

Figure 5: Applying constraints using the options panel to tune in and out DOF as desired

I also employed the Sliding Along Surface constraint along the planar face of the barrel nut to limit unnecessary DOF (degrees of freedom) in the model. The combination worked out perfect for what I needed.

Meshing and Simplification

Meshing turned out to be more time-consuming, but I expected that for small diameter changes and helical features. This surface mesh took only three seconds, a nominal time (see figure 6).

Figure 6: The dialog box for overall mesh sizing. I received an error message when I tried to set element-size-to-overall-length ratio too small; I'd rather make the determination myself

I used the built-in Simplification environment to remove portions of the barrel and engagement helices that were not critical to this phase of the study (see figure 7). Simplification makes short work of plugging holes and removing simple faces. I did experience, however, some unresolved problems with model simplification, due to complex face relationships in my design's receiver component. After some frustration I realized I could introduce necessary features to another part, and then delete the offending receiver altogether.

Figure 7: The simplified barrel and chamber (at right); the option bar (above) allows me to accept and reject bodies, trading out the complex analysis model for a simplified version. (The almighty Remove Geometry function is the red X on the options panel, and permits me to introduce new bodies

Once simplification was completed, Simulation allowed me to adopt the simplified version of the part without having to use alternate part files or jump through (too many) hoops - one of Solid Edge's great benefits.

Results

Unlike other Solid Edge's modeling and analysis workflows, Simulation Results have their own environment. The model tree is removed, and a menu and ribbon interface specific to reviewing solutions are displayed (see figure 8). The ribbon interface is organized into four menu tabs: general tools, display options, color bar controls, and viewing options.

Figure 8: Simulation Results ribbon places all the viewing and tuning options at our fingertips, without needing to fumble through other modeling tools

The Simulation panel shifts to the left side and is populated with the results of the study, which are retained after we exit the results environment (see figure 9).

Figure 9: Chamber static pressure analysis' Max Principal Stress results shown with deformation exaggerated by 3%. (I've always been a fan of Siemens' color schemes for results)

Let me quickly list a summary of the tools I found notable:

  • Result Contour Styles - specifies smoothed, banded, elemental, or ISO contour
  • Probe - with improved probe data table
  • Dynamic ISO Contour - specifies target contours to identify the shape of the stress migration of the 3D meshed model
  • Deformation Display panel - changes the overdone, 10%-deformation scaling to actual
  • Settings panel - offers a pull-down list of configuration settings that can be saved as desired, to avoid the need for repeated changes
  • Basic animation controls
  • Display panel - contains translucency settings and control of the face and edge coloring
  • Color Bar panel - includes the standard max and min results probes, results scaling, contour color schemes, and display positions for color bar and header
  • View tab - a collection of view angles and styles common throughout the Solid Edge design interface. I particularly liked the section plane tools and used them often during the review process
Reporting

Reports are simple and wonderful, with options that allow us to export to Web pages and two versions of Word (see figures 10 and 11).

Figure 10: Preformatted report's linked table of contents

Solid Edge's report formatting is possibly the cleanest and most easily used one that I have ever seen exported from any simulation software. Everything behaves as we expect. For instance, tables expand as we add data, allowing us to easily build on to the report.

Figure 11: Word-formatted report exported from Solid Edge

The initial results indicate that the barrel design is on the right track; however, some alterations will be necessary to reach the target pressure loads.

In part 2 of this article I'll discuss how the optimization process helped me investigate the feature relationships and dial in the best balance of mass and positioning for this design.

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About the Author

John Evans has 30 years experience in the aerospace design, engineering and fabrication, as well as 18 years with MEP and civil engineering. He is certified with AutoCAD Civil 3D and Inventor. More...

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