Testing of shear pins
Testing of shear pins
(OP)
Hi,
The design i am working on uses a shear pin to avoid damging the equipment (in fault scenario). In order to commission the equipment we are testing a singe hsear pin to see what the failure load is. However, we are unsure if a single test is sufficient for testing shear pins. Can anyone provide some guidance on the testing of shear pins (i.e. what is best practice?). I have had a look and it seems we should expect variations of upto 15%, but for our shear pin do we nee to test a certain number of times over a full range of tolerances?
Thanks
Andrew
The design i am working on uses a shear pin to avoid damging the equipment (in fault scenario). In order to commission the equipment we are testing a singe hsear pin to see what the failure load is. However, we are unsure if a single test is sufficient for testing shear pins. Can anyone provide some guidance on the testing of shear pins (i.e. what is best practice?). I have had a look and it seems we should expect variations of upto 15%, but for our shear pin do we nee to test a certain number of times over a full range of tolerances?
Thanks
Andrew





RE: Testing of shear pins
You need to test a population sufficient to capture the variation in both dimensions and material properties.
RE: Testing of shear pins
Thanks
RE: Testing of shear pins
RE: Testing of shear pins
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RE: Testing of shear pins
First since it is a shear pin safety problem, you have to decide the range of failure with an associated probabity that any shear pin would fail within that range .
Then you go to the mfr and ask for his capability of meeting that requirement
If it can be done your testing is rather staightforward using the techniques of sampling suggested above.
For instance, let's say that you want the shear pin to fail between 80000psi and 100,000 psi with a probability of 0.95. Assuming a normal distribution, you would like the mean to be about 90000 and since p=0.95, you need 2 sigma to be 10000 or less.
Now when the lot comes in for checking, you use the sampling methods to get sigma and the mean , verifying that
mean-2sigma > 80000
mean+2sigma < 100000
RE: Testing of shear pins
RE: Testing of shear pins
First up you need a testable requirement, something like "99% of pins must fail at X kN or less, but none must fail before Y kN".
I'd create a model that predicts the load for the relevant factors. Then I'd verify the model against real tests for the outliers and the centre. Then I'd use the model, and the known tolerances and distribution for each parameter to predict the entire population of loads.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Testing of shear pins
You make your shear pins from rod representative of the piece you will use. Use a random number table and use the Student T curve to get a sample size representing 95% confidence level. Those are tested under a control setting in the laboratory. You're looking for the material properties and loading as a result of failure by shear.
For example, I apply a fluid hydraulic pressure to the pump out plug for which the shear pin properties are desired. The test is preformed with good repeatability, therefore you get a confident and tightly grouped bunch of numbers for load and shear strength of the material in question.
Done. Good luck with it.
Regards,
Cockroach
RE: Testing of shear pins
Plot your results on normal distribution paper or a weibull chart to make sure that you are getting a normal distribution.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Testing of shear pins
RE: Testing of shear pins
RE: Testing of shear pins