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Mandrel Testing Strain Distribution

10/22/2012 10:43 PM

Mandrel Testing Strain Distribution - Summary of Problem

Background

I have received a scholarship to investigate the effect of mechanical stresses on energy pipeline exterior protective coatings. I will conduct mandrel testing with 10 different diameters to pipe samples with and without protective coatings on the exterior (Tensile) side of the specimen. From these tests I am required to find the non-uniform strain distribution on the exterior side of the specimen, with a particular interest in the points with the highest stress concentrations. These points are of particular interest as they will also be the points of highest stress concentration in the protective coatings and therefore be the most likely points of fracture in the protective coatings.

Initial Key Questions

1. How can I calculate/determine the strain applied to the tensile side of the test specimens from the mandrel test?

2. How can I calculate/determine the non-uniform strain distribution over the tensile side of the test specimen and therefore find the points of highest and lowest strain?

Secondary Questions

1. Can the non-uniform strain distribution be predicted theoretically? using FEA? and how?

Possible Solutions

Apply multiple strain gauges to the tensile side of the test specimen during mandrel testing?How to interpret this data and get a useful strain distribution from it?

Any help would be greatly appreciated

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#1

Re: Mandrel Testing Strain Distribution

10/22/2012 10:55 PM

What are the, "energy pipeline exterior protective coatings"? Or does that matter?

Have you done any independent research?

How do you propose to proceed?

Do you have a mentor, or is that our function?

Good luck, have you solicited help from other forums?

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#3
In reply to #1

Re: Mandrel Testing Strain Distribution

10/23/2012 12:48 AM

At this stage the protective coatings are irrelevant and my supervisor has told me not worry worry about them yet.

I have done some research and have determined that it could be possible to use a range of small strain gauges on the bottom of the test sample. But i am unclear on how i will actually set up the experiment and interpret the output usefully. I am also unclear on if this is the best way to go about the testing.

My supervisor is a chemist and has presented this problem to me but he is unsure of how to proceed and has left it up to me to figure out as he doesn't have a mechanical background.

I am in the initial stages of research and trying to figure out a plan of attack for the project.

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#4
In reply to #1

Re: Mandrel Testing Strain Distribution

10/23/2012 12:49 AM

Also what other forums do you recomend? this is the only one i have used thus far.

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#7
In reply to #4

Re: Mandrel Testing Strain Distribution

10/23/2012 9:02 AM

And if you had read the FAQs you would know that we don't do homework here.

I'd research ASTM test methods.

  1. ASTM A884 / A884M - 12 Standard Specification for Epoxy Coated ...
  2. Paint Standards and Related Coating Standards - ASTM International
  3. ASTM A934 / A934M - 07 Standard Specification for Epoxy Coated ...
  4. ASTM Paint Color Specifications.
  5. ASTM - Paint Collection | IHS
    I don't believe any more will be forthcoming from me. You should do your own work.
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#8
In reply to #7

Re: Mandrel Testing Strain Distribution

10/23/2012 6:31 PM

Ok sorry Lyn. I am doing my own research its just that i am struggling to find direction at this current time. I am a second year mechanical engineering student and this is the first research i have ever done. Its the hardest project i have attempted in my course thus far. cheers

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#2

Re: Mandrel Testing Strain Distribution

10/22/2012 10:58 PM

Please elaborate on the Mandrel Testing. Will this test simulate bending the pipe as is done in the field on underground pipelines, or something else?

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#9
In reply to #2

Re: Mandrel Testing Strain Distribution

10/23/2012 7:22 PM

Figure 1 - Mandrel with previously bent test specimen

Figure 2 - Mandrel with previously bent test specimen in test machine

Figure 3 - Test Machine

Here are some pictures of the mandrel testing i am going to conduct. Ten more mandrels have been ordered, all of varying diameter. This does not simulate pipe bending in the field, but it is meant to simulate stresses on existing pipes that have already been installed and are in use.

I plan to stick small strain gauges on the bottom (tensile) side of the specimen as i bend them. The real problem i have right now is if this is the best way to find the experimental strain distribution on the tensile side of the test specimens or if there is a better way. Also how i am going to interpret the output of the strain gauges and whether there is a program that can interpret this data. From my research thus far i have not found this information.

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#10
In reply to #9

Re: Mandrel Testing Strain Distribution

10/23/2012 9:23 PM

OK. That answers some questions. You'll be bending flat specimens. From your original post, I was envisioning bending an actual pipe, which would be a lot more difficult. You said you're a second year student - just starting second year? What you are really doing is bending a simple beam. The basic theory of beam deflection should cover the strain condition you are imposing. Are you taking (or have you taken) a Solid Mechanics or Strength of Material course? If so, maybe you can study ahead and see what's happening. If not, maybe you can get an upper classmate or prof. to assist you. You could then use strain gages to confirm or adjust your actual results to theory. If you have specific sticking points, I'm sure someone will try to assist. But be warned, this site has a 'no homework' policy and if you come back without showing honest effort on your part, you will get some rude comments (you might anyway). Good luck.

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#11
In reply to #10

Re: Mandrel Testing Strain Distribution

10/23/2012 10:48 PM

I have just finished second year and have completed "statics and dynamics" and "mechanics of materials" and did quite well in both. I understand that i am bending a simple beam and probably didn't explain myself very well initially. I understand point and distributive loads but in this case the mandrel will start off applying a point load and then a gradually increasing distributive load as the beam is bent. This scenario has not been covered in any of the material i have studied. I thought i would simulate the process using FEA and find the theoretical strain that way. My professor wants me to also find the experimental strain distribution using the mandrels and doing the actual test. So i can compare the theoretical and experimental results. It's the Experimental results i am having trouble figuring out how to find, but i am sure there will be a very simple solution i just haven't found it yet. Thank You for all your help

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#13
In reply to #10

Re: Mandrel Testing Strain Distribution

10/24/2012 6:56 PM

Hey guys thought i might update you with my progress, I have come up with two solutions for the experimental testing and two solutions for the theoretical testing. Have a look a let me know your thoughts if your interested.

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#14
In reply to #13

Re: Mandrel Testing Strain Distribution

10/24/2012 7:31 PM

Yeah, the loading condition is not conventional, i.e. it's not a point and not an evenly distributed load and the deflection is constrained. I think that strap in the middle is actually exerting an upward force most of the time. I think the mandrel imposes the shape (strain) of a constant moment condition, doesn't it?

Sure, fill us in. Got a link to post or more info?

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#15
In reply to #14

Re: Mandrel Testing Strain Distribution

10/24/2012 8:15 PM

That's interesting you say that the strap might impose an upwards force, i had not thought of that. It might alter the results.

Here are my possible solutions

Experiment Questions

1. What is the best method to calculate/determine the strain applied to the tensile side of the test specimens from the mandrel test?

2. What is the best method to calculate/determine the non-uniform strain distribution over the tensile side of the test specimen and therefore find the points of highest and lowest strain?

Possible Solutions

1. Apply multiple strain gauges to the tensile side of the test specimen during mandrel testing. How to interpret this data and get a useful strain distribution from it? Is there a program I can use to interpret the strain gauge data?

2. Draw grid lines on the tensile side of the specimen using etching and position a camera looking at them. This may not be appropriate as the %strain will be so low that it may be too hard to pick up the strain.

Theoretical Analysis Questions

1. What is the best way to predict the non-uniform strain distribution theoretically? Using FEA? And how?

Possible Solutions

3. Use solid Works to model the specimen and use a 3-D scanner to get the dimensions of the mandrels and therefore find their diameter

4. OR Use solid Works to model the specimen and use the CAD drawings from the mandrel manufacturer to get the dimensions and diameter of each mandrel. This method may not be as accurate as the 3-D scanner depending on the manufacturer's accuracy and tolerances.

I was thinking that I would model all 10 mandrels and find their theoretical strain distributions and then use the strain gauges on only a few of the actual test specimens. If the strain output is the same as the theoretical model then I could just use the theoretical model for the rest of the experiments and not worry about putting strain gauges on the rest of them.

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#5

Re: Mandrel Testing Strain Distribution

10/23/2012 2:06 AM

First search HERE

Then HERE

Finally come back with feedback. Good hunting!

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#6

Re: Mandrel Testing Strain Distribution

10/23/2012 2:19 AM

I have work in the coating industry for a few years and have tested many applied materials adhesion properties to various substrates. Are you wishing to see the results of the metal moving under stress and strain which occurs in the normal operations of installation and use. If so I would 1st find out what coatings you are looking at. 2 nd get with the coating suppliers and ask their lab personal for some help. I have found that my reinventing the wheel sometimes was not needed as it had been done already. But, if that is not the case. A good supplier will work with you to come up with an approved method of testing. ASTM may also have guide lines in place covering your request as well.

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#12

Re: Mandrel Testing Strain Distribution

10/23/2012 11:00 PM

"simulate the process using FEA and find the theoretical strain" HERE

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