I am going to use the following example to illustrate the effects of different average element size

Average Element Size is not the size of the mesh element. It is best explained as following

This is illustrated below

Below are examples of using different average element sizes

An average element size of 0.05 will create an element size of 5mm, in our example, hence will create 2 element across the thickness of the plate. It is normally good practice  to create at least 2 more elements across the thickness to get a better distribution of stress.

Note: A smaller average element will take a longer time to analyze………..

Hope you found this post useful I will be discussing more on Meshing in the next couple of weeks.

This information is extracted from my book Up and Running with Autodesk Inventor professional 2012 Part 1 – Stress Analysis, which offers a wealth of information including tips and guidance.

If the answer is YES then you can join the only FREE dedicated support forum on Linked In.

To joint the forum click on the following link   http://www.linkedin.com/groups?gid=2061026&trk=hb_side_g

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Another key difference between remote force and force is that remote force also induces moment/torque as soon as remote point is defined other than (0,0,0)

A good example of this is when tightening a bolt using a wrench which is fully illustrated by our friends @ Being Inventive and the full article can be read at

http://beinginventive.typepad.com/being-inventive/2011/06/meaning-of-remote-force-in-stress-analysis.html

The above bracket has a localized high stress around the force applied on a point. This Stress can be considerably higher than the operational stress and by applying a more dense mesh around this simply lead to a much higher stress. This phenomenon is known as stress singularity where the stress become infinite as illustrated by the following formula

 STRESS (infinite) = FORCE / AREA OF POINT (almost = 0)

Therefore to avoid Stress Singularities when applying loads it is recommended not to apply loads at points and small edges. 

Stress Singularities can also occur by applying constraints on points and small edges–even faces with sharp corners as illustrated below.

In the above example stress singularities resulted from using automatic convergence whereas the image on next page of the same model is showing the same stress in the area of interest by using the default mesh and no automatic convergence. So interpret results with care

Finally another cause of stress singularity is over simplification of components. Let’s look at the following example.

In this example the fillets were removed to simply the analysis, however when using the automatic convergence the maximum stress value would not converge as all the stress is concentrated around the edge as shown. In this scenario it would advisable to un suppress the fillets (or in cases when fillets are not modeled –is to use fillets to distribute loads).

So in summary to avoid stress singularities within models is to:

1. Avoid applying loads on edges and small edges
2. Avoid restraining faces with sharp corners, including points and small edges.
3. Apply fillets and chamfers to evenly distribute loads

 I hope this will help you gain more confidence in your stress results…..

Here I will use a simple I-Beam to outline the Pro’s and Con’s of using either Frame and Stress Analysis. The I-Beam will be fixed at one end and a load of  1000 Newton applied at the other (Like a cantilever).

Stress Analysis - Below are the Stress and Displacement results obtained from Stress Analysis

Pro’s -

1. Can use non-content centre components
2. Beams do not have to be modelled using Frame-Generator

Con’s -

1. Number of Elements required can be very excessive to get reasonable results
2. Stress Singularities in the component
3. Longer Analysis times – related to point 1 (Con’s)
4. Impractical (or impossible) to analyze assemblies with large number of beams – unless you have access to Super computers.

Frame Analysis - Below are the Stress and Displacement results obtained from Frame Analysis for the same beam

Pro’s -

1. No Stress Singularities in the component
2. A lot quicker to analyze than using solid elements
3. Now possible to analyze large structures, consisting of uniform cross-section structures/frames

Con’s -

1. Frames/Structures have to be modelled using content centre components or
2. Frames/Structures have to be generated using Frame-Generator
3. Cannot analyze localized connections (Bolts/Welds etc but can be achieved using both Frame & Stress Analysis)

RESULTS:

The displacement results from both analyzes are almost identical within 2% margin – well below th 10% default setting. Again the stress results in this case are within 8% although acceptable for comparison purposes-the main difference here is due to stress singularities, in the stress analysis, resulting from applying boundary conditions.

Hope you found this useful. There are more tips and guidance on Stress and Frame Analysis-including solving actual design problems in my new Inventor 2011 Simulation book.

When Frame Analysis is activated from within Assembly environment the frame structure of the assembly are automatically  converted into beam elements with all the associated properties collected from the content centre.

Any gaps between the beams are automatically joined using rigid links

Once the Boundary Conditions including loads and Restraints have been applied you can run the analysis to determine results

The results post-processing includes enhancements to the report generator including the ability to create a report in rtf.format making it easier to customise reports.

Other key features includes assigning material to multiple components and the  Simulation Guide which can guide the novice user through the simulation process.

Up and Running with Autodesk Inventor Simulation 2011 is dedicated to the requirements of Inventor users who need to quickly learn or refresh their skills and apply the dynamic simulation, stress analysis, frame analysis, and optimization capabilities of Inventor Simulation 2011. Providing clear guidance and all-important real-world tutorials, the step-by-step, heavily-illustrated approach of this book will help designers, engineers, and manufacturers of all skill levels become Simulation experts.

Read the full press release by clicking the link below

PRESS RELEASE