Impact test - 100ft.lbs

[gareth71]

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?

 

[KENAT]

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.

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[gareth71]

Thanks and yes, I can manage to multiply 3 numbers together 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.

 

[rb1957]

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 ?

 

[marty007]

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).

 

[BUGGAR]

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

 

[KENAT]

m kg - for energy what a horrible abortion of a unit.

I'd used 1 lb force = 4.45 Newtons and work from there.

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[gareth71]

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

 

[KENAT]

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?

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[IRstuff]

or a 13.8 kg mass dropped 1 m ;-)

TTFN
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[gareth71]

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.

 

[1gibson]

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?

 

[Strong]

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

 

[hydtools]

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

 

[SWComposites]

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?

 

[gareth71]

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.

 

[Tmoose]

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

 

[KENAT]

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

Until some guy with a JCB catches the edge of it, or Alan Titchmarsh slams a mattock into it while gardening or something.

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[BUGGAR]

"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.

 

[gareth71]

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".