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Impact test - 100ft.lbs

Impact test - 100ft.lbs

Impact test - 100ft.lbs

(OP)
Hi, I've got a test standard which states the component must withstand an impact of 100 ft.lbs, I dread to ask this question but I just have to... is this test dropping a weight of 1lb from 100 ft? Therefore a 10lb weight from 10ft?

In metric measurements I've worked it as 13.7m kg

The reason for my question is that it seems like an incredibly difficult test and some competitors claim to have met it with their products. It says the test should be done with a steel weight with 2 inch spherical radius, a shame I can't do it with a foam weight with a 2 inch spherical radius.

Is my assumption of 1lb from 100ft correct, or is there the difference between mass and weight so I can divide the whole thing by gravity?

RE: Impact test - 100ft.lbs

A force times a distance can be a unit of torque or a unit of energy. https://en.wikipedia.org/wiki/Joule

I'd assume in your case probably the latter.

Given that gravitational potential energy = mgh I suggest you back calculate the required drop height.

Is it the Imperial/American units throwing you off with 'lb' being used both as a mass and the equivalent force under normal earth gravity?

I ask because this is an A-level or maybe just GCSE physics or applied math problem.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Impact test - 100ft.lbs

(OP)
Thanks and yes, I can manage to multiply 3 numbers together wink although it was o-levels when I did it.

As the impact is probably an energy then I think you're right - I can divide my 13.7mkg by 9.81m/s to drop the 1kg weight from a mere 1.4m which sounds more plausible.

RE: Impact test - 100ft.lbs

as kenat says, potential energy means you can swap weight for height (100 lbs at 1ft = 10 lbs at 10ft).

another day in paradise, or is paradise one day closer ?

RE: Impact test - 100ft.lbs

Is this a Charpy Impact Test (low-temperature fracture toughness), or something else?

If it is a Charpy Impact Test, then there are very standard methods for testing. I speak from an ASME VIII-1 pressure vessel code perspective, where you are referenced to SA-370 or ISO 148 (Parts 1, 2, and 3).

RE: Impact test - 100ft.lbs

I've also seen a similar test for safety glazing and racing helmets. Please tell us your test standard.

RE: Impact test - 100ft.lbs

(OP)
Agreed, I'm expecting my university to revoke my degree any minute now. I was just converting through from ft.lbs

RE: Impact test - 100ft.lbs

Oops, I think I'd missed a step when I was looking at your post and made my smart ass comment but I still get another out come when I went through it again.

l lbf = 4.45 N (courtesy of Google)
1 ft = .305 m (courtesy of Google and my 12" ruler)
accn from gravity = g = 9.81 m/s^2 (courtesy of it being drummed into me through my secondary education and beyond)
mass = M (cause I don't want to confuse with m for meters)
height = h (because, well it's obvious really)

4.45*.305*100 = 135.7 Nm = 135.7 Joules = Mgh = M*9.81*h

135.7/9.81= 13.8 mkg

So 1 kg mass dropped 13.8 meters?

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Impact test - 100ft.lbs

(OP)
That's very bad, it's the same as I got in my first post.

As an old manager used to say "don't tell me that answer, tell me the answer I want to hear"

To give a little background this test is for an enclosure for fibre optics, they're almost all moulded from polypropylene which despite being around 10mm thick due to the height of its ribs would never survive a 1kg mass from 13.8 metres, or 10kg (22lb) from 1.4m (over 4½ feet)

I was really hoping the lb-force would help me out! But I appreciate the help, unfortunately there's nobody else at work I can talk this over with.

RE: Impact test - 100ft.lbs

How much does the component weight? Can you drop it from a calculated height, does that stay within the letter of the test requirement? Get the impact but without squashing the component between the floor and a weight?

RE: Impact test - 100ft.lbs

Google: Charpy impact test
Charpy test does use impact energy units of lb.-ft.
If it is not this the test type, then possibly the test standard or specification you have has a typo. Can you present at least a portion of the document for context of the terminology?

Walt

RE: Impact test - 100ft.lbs

Drop a 16 lb bowling ball from 6.25 ft.
Or a 4 in diameter steel ball from 10.54 ft.
Ted

RE: Impact test - 100ft.lbs

This sounds like an aircraft damage tolerance requirement. Or is it something else?

Yes, it means drop something like 10 lbs from 10 ft.

What is the component that has to meet this?

RE: Impact test - 100ft.lbs

(OP)
BUGGAR (Structural)
24 Feb 16 18:38
I've also seen a similar test for safety glazing and racing helmets. Please tell us your test standard.


I think you're right, this kind of test would trouble a racing helmet, it's that kind of impact. It just seems a bit excessive for fibre optic enclosures that are underground.

1gibson (Mechanical)
24 Feb 16 21:22
How much does the component weight? Can you drop it from a calculated height, does that stay within the letter of the test requirement? Get the impact but without squashing the component between the floor and a weight?


Sneaky, but I like it. I've just re-read the test spec and I don't think that's allowed, unfortunately.


Strong (Mechanical)
24 Feb 16 21:30
Google: Charpy impact test
Charpy test does use impact energy units of lb.-ft.
If it is not this the test type, then possibly the test standard or specification you have has a typo. Can you present at least a portion of the document for context of the terminology?


Good suggestion for the Charpy test, I pulled out a test example and it said 75 ft.lbs was around 102J and 160 ft.lbs is 217J. That confirms my fear that approx 137J is what I need. No typo in the test document, there are other enclosures which require 50 ft.lbs for lesser tests.

Thanks, everyone.

RE: Impact test - 100ft.lbs

It Might be helpful to copy and paste a few paragraphs out of the standard you are bound to.

RE: Impact test - 100ft.lbs

"It just seems a bit excessive for fibre optic enclosures that are underground."

Yes and no. I just watched a backhoe excavate near a sewer. Of course, they obliterated the sewer line they were supposed to avoid.

RE: Impact test - 100ft.lbs

(OP)
I don't think anything is JCB-proof so perhaps it really is for spades that come zooming through the topsoil.

I think the copyright lawyers would hunt me down if I copy too much of the standard, but here's part of it. You guys will bail me out, won't you?


All closures shall be tested in their installed position using mounting hardware provided by the manufacturer. In all cases, the
impact device shall have a 50-mm (2-inch) spherical radius at the point of contact.

A closure shall not exhibit any mechanical damage after being subjected to mechanical impact at the cold and hot installation temperatures specified in Section 5.1.4, “Test Conditions/Temperatures.” The impact energies in Table 5-5 shall apply.

Table 5-5 Impact Criteria Levels
Environment________________Impact (ft-lbs)_____________Test Procedure
Buried, Underground______________100_________________Drop Tube
Wall Mount_____________________50_______________Pendulum & drop tube
Aerial_________________________50____________________Pendulum
Thin-walled closure_______________10_______________Pendulum or drop tube

NOTE: Damage to field-replaceable components that is not service affecting is permitted including damage to the manufacturer-supplied
closure mounting base.

It is desirable that a closure shall not exhibit any mechanical damage after
being subjected to mechanical impact at the cold and hot operating temperatures


I'm reading through the rest of the standard to see if I can get it classified as a thin-walled closure and what the problems of that would be in terms of the product in the market. The note after the table of "...damage is permitted..." looks like a get-out clause at first glance, but I would rather not pass the test and have to add the caveat of "it smashed to a million pieces".

RE: Impact test - 100ft.lbs

The more I think about it, my mattock example may not be far off in the amount of energy involved. Where it would be off is that the blade or even worse pick side will concentrate the impact force.

Sledge hammer would be closer but that's harder to imagine as an accident!winky smile

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Impact test - 100ft.lbs

Another underground scenario may be during hydro-excavation and someone using a digging bar to knock soil and rocks loose. Oops, hit that box.

Ted

RE: Impact test - 100ft.lbs

Is a closure just the door portion of an enclosure?

"A closure shall not exhibit any mechanical damage after being subjected to mechanical impact."

A complete lack of "ANY physical damage" in my mind demands no chipped paint, or scratches, or even small dents, and is way beyond closing and latching and sealing properly.

I'm probably just naive, but a direct nudge or tap from a gently pawing earth moving device seems like more than 100 lb ft of energy.

RE: Impact test - 100ft.lbs

(OP)
A closure is a box, something that goes around stuff. Some people call it an enclosure, but a pedant would say an enclosure is what's enclosed in a closure, for example a letter is enclosed in an envelope. The envelope is the closure.

Anyway, back on track, it's a good point about any physical damage. I read that as it would still seal correctly but it's open to interpretation!

RE: Impact test - 100ft.lbs

there's a long way between "loss of function" (OP) and "no damage" (Tmoose). the adjective "mechanical" could mean damage that prevents the mechanism from functioning correctly, or it could mean a dent (in that the dent was mechanically introduced) ... "paint clips" might be excluded.

another day in paradise, or is paradise one day closer ?

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