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Everyone should read this
- Thread starter Dirk Pitt
- Start date
RichP
NAXJA Forum User
- Location
- Effort, Pa
Dirk Pitt said:
Lotta good info. My only criticism is the grade8 vs 5 and shear. If grade 8 is so much better then why did the armour plate on the bradleys and M-1's break so many grade 8's and the army replaced them with grade 5's...the side armour load is always in shear...
5-90
NAXJA Forum User
- Location
- Hammerspace
BillAVista's tech is (pretty much always) spot-on, informative, and understandable. I've been perusing his stuff for a while (I've converted most of it to .pdf for offline reference) and I've always been impressed by not only his knowledge, but his ability to put it all into simple terms. I've tried to use him as one of my models for technical writing...
Read as much of his tech as you have time for - it's worth it!
5-90
Read as much of his tech as you have time for - it's worth it!
5-90
RichP said:
A lot of the time (not sure on this instance) lesser "strength" materials are used to induce failure at an anticipated location.
For example: a Indy car is put together with lesser grade "strength" fasteners when compared to the components they are fastening. And those components are designed to break sooner than the driver cockpit. They do this so they can predict the mode of failure and absorb impact with a high degree of accuracy in directing the inertia to the desired components.
Perhaps the designers of the aforementioned tanks had something in mind than absolute strength in the plates.
Another example of this is Warn using grade 5 screws internally in it's winches. It's much safer for a screw to shear inside the winch rendering it immobile than for something outside the case of the winch to break and have a high speed projectile.
Lawn Cher'
NAXJA Forum User
- Location
- Westampton, NJ
Okay Adam, I'll admit it: you are smarter than I am. I think this job is sucking the smarts right out of me.
red91
NAXJA Forum User
- Location
- exact location unknown
Lawn Cher' said:
Thats not all its doing....Wheres the Vending machine?
Lawn Cher'
NAXJA Forum User
- Location
- Westampton, NJ
red91inWA said:
2 floors down... not worth the schlepp
Beej
NAXJA Forum User
- Location
- The Wet Coast of BC
Bolt shear strength?Dirk Pitt said:
hasta
Manufacturers use grade 5 bolts instead of grade 8 or stronger because they are cheaper. Any load strong enough to shear a grade 8 will stretch and then dramatically shear a grade 5 too. They do not act as 'fuses', this is a commonly-propagated internet myth...An example page covering shear strength in grade 5 vs grade 8 bolts
5-90
NAXJA Forum User
- Location
- Hammerspace
True, but the argument that a grade 5 will fail more slowly is also very true, and can be an important design consideration.
With steel, hard = strong. Hard also = brittle. The stronger you make the steel, the more dramatic the failure will be, and the failure will also happen in a much more immediate fashion.
Where this is a concern, and the strength of the grade 5 is adequate, it is a good idea to use the grade 5 - the extended area of plastic deformation then becomes a safety feature of the assembly.
Lower-grade bolts can also be used as "assembly fuses" - essentially creating an area of controlled failure. This is similar to the "crumple zone" idea with cars these days - make a solid cage that won't crush, and surround it with compartments that are designed to. This allows for a stronger cage (a good idea) that won't endanger anyone hitting it (?) That way, it's not like hitting a brick when you run into the car - problem is, it's a lot easier to "total" a vehicle than it was 15 years ago.
Having said all that, the SAE wasn't just making things silly when they came up with the grading system - there are valid reasons for using nearly any grade of bolts, if you look hard enough. It all depends on what you're designing. "Controlled failure" has become a damage-control option - sacrificing something you can afford to lose for something you can't. You'd be surprised what your options for safety can become once you decide to sacrifice something you don't need in a pinch...
5-90
With steel, hard = strong. Hard also = brittle. The stronger you make the steel, the more dramatic the failure will be, and the failure will also happen in a much more immediate fashion.
Where this is a concern, and the strength of the grade 5 is adequate, it is a good idea to use the grade 5 - the extended area of plastic deformation then becomes a safety feature of the assembly.
Lower-grade bolts can also be used as "assembly fuses" - essentially creating an area of controlled failure. This is similar to the "crumple zone" idea with cars these days - make a solid cage that won't crush, and surround it with compartments that are designed to. This allows for a stronger cage (a good idea) that won't endanger anyone hitting it (?) That way, it's not like hitting a brick when you run into the car - problem is, it's a lot easier to "total" a vehicle than it was 15 years ago.
Having said all that, the SAE wasn't just making things silly when they came up with the grading system - there are valid reasons for using nearly any grade of bolts, if you look hard enough. It all depends on what you're designing. "Controlled failure" has become a damage-control option - sacrificing something you can afford to lose for something you can't. You'd be surprised what your options for safety can become once you decide to sacrifice something you don't need in a pinch...
5-90
