Stress Analysis Results?

[NeedHelp]

Hi, I have started using the stress analysis application in 2008 Pro Inventor. Having never attempted to use this much before, i'm not sure about the results that i'm getting. Basically without trying to sound dim!! What do the results actually mean. Can someone recommend some literature on this or a good tutorial that explains how to accuratley make sense of the results??

[JD Mather]

What do the results actually mean.

 

http://www.amazon.com/Building-Products-Element-Analysis-Software/dp/156690160X/ref=sr_1_6?ie=UTF8&s=books&qid=1242310813&sr=1-6

 

and of course you will need to sign up for a class.

[shift1313]

Without understanding the context of what you are doing, the results will not be useful. Having an understanding of constraints and loads is cruicial before attempting any sort of FEA.

 

When you perform FEA(finite element analysis) the software(ansys in this case) is actually looking how the load is distributed throughout the part. This is based on the geometry obviously and also the material( atomic structure and all its physical properties). The accuracey of the distribution also is dependant on mesh size. A mesh is applied to your part and the resolution of this mesh will determine how accurate the distribution is.

 

Inventor should have a help file that will walk you through the basic procedure, but like i said without an understanding of the physical relations you are attempting to simulate the results are junk. If the part isnt correctly restrained or loaded the data will tell you nothing. Also these results are only to help "focus" your design and should not actually replace hand calculations and common sense. The software will help optimize your design by pointing out theoretical weak spots.

 

Here are a few screen shots of a big brake upgrade i designed and i used inventor to help narrow down how i wanted to restrain the plate and also material and thickness.

 

 

that was 3/8" steel only using the small hole where MAX is and the original caliper bracket holes on the left to hold the plate

 

 

same material leaving out the small hole as a bolt location.

 

You can see that changing the constraints makes a huge difference in stress distribution of the model. Understanding why this is so and what the effects are is cruicial. Not only for the part you are designing but the hardware you use, what its connected to etc. For instance in this case, the more rigid the plate was, the higher the stress concentration at fillets was. The more the plate was allowed to flex(max deformation) the lower the stress concentration was but in this case designing the bracket to handle the stresses rather than allow deflection was key.

 

With the help of the software my final model ended up being 3/8 steel plate and i used 4 locating holes.

 

 

[NeedHelp]

Matt,

Thanks for taking the time with such a detailed reply!! I do have a reasonable understanding of the physical loads and constraints on a part. But I think the part i am really struggling with, is the colored graph up the side of the results. For instance on your second example the figure at the bottom of the graph is 0.019 and at the top is 1.834. Now if you had to explain to someone what these mean(simply)?? How would you do it?? Also i have noticed that yor results are in psi!! mine are in MPa!! is there some way i can change this??

[shift1313]

Sure thing. Once you have run the simulation you will have several result drawings to choose from. Both of the ones I had listed are equivalent stress. The color bar relates to the drawing. You can see Min and Max listed, those correlate to the min(.019) and max(1.834) values(both x 1e4psi or 18340psi). The colors on the bar give the values of each color region on the part. In the picture attached i drew some lines to the part. The distribution is based on the mesh created during analysis. The finer the mesh, the more accurate the distribution will be.

 

As for the units. Your drawing is probably metric so your units will be as such(MPa = 1 N/m^2). My drawing was in inches so my units were PSI(lbs/inch^2)

 

As for the other drawings, there is a deformation drawing(numbers and color bar correlate to a distance displaced), Max stress etc.

 

Let me know if this does/doesnt make sense and ill try to elaborate.

[NeedHelp]

Hi, That does make sense, there is a paticular part that i have created(unable to show, as it is sensitive). The part has been stress tested by our customer. I noticed that they used ANSYS for the exercise, so i have been trying to re-create there results or at least get close to them. I have noticed that on their equivalent stress result the type is listed as Equivalent(von-mises) Stress, with the units being Pa. I am assuming that thhis is only available in the full version of ANSYS and not the version that comes with Inventor? Also is there anyway of testing a component to failiure. If so, how is this done. Thanks again for your help.

 

Mike

[shift1313]

Well the Factor of Safety is what will tell you failure. If you have a factor of safety of 2 and you are applying 500lbs of force the part can withstand 2x that or 1000lbs of force. Remember to keep in mind these results are not to be used as a replacement for hand calculations, just as guidelines to help narrow a design. If the FoS is below 1 it signifys a failure.

 

Von-mises is a type of yield analysis that applies to plastic deformation(mainly in ductile parts like metals). The units are based off your model and the significant digits. If your units are metric for the model, your equivalent stress will be in Pascals. If the resulting stress is large the units will be MPa.

 

Ill add a bit more later, i have a meeting to head to.

[shift1313]

Here is a link that may have the answers to your question about versions, i dont have the time right now to look through it unfortunately.

 

http://www.ansys.com/autodesk/

 

I dont know if there are different levels of the ansys solver but there are certainly different types. It is possible to export to a full external version of ansys but unfortunately I just dont use Inventor for analysis.