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7075 aluminum thread pull-out force question Question
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Posted by: N74DV ®

03/03/2004, 02:08:29

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Basically what I'd like to know it if I have a 1/2-13 steel bolt threaded into a 7075 aluminum block about 1", what force would it take to fail the threads in the aluminum and pull out the bolt?

Not looking for an exact number here just an estimate.

 


 




DJ V. Mesa, AZ


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Thread Stress, Pull-Out, Engagment Calculation and Formula Smile
Re: 7075 aluminum thread pull-out force question -- N74DV Post Reply Top of thread Forum
Posted by: Administrator ®

03/03/2004, 10:53:49

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Just so everybody knows, after I publish a few hydraulic - flow formula and calculators, I will be publishing a series on this topic "Thread Stress, Pull-Out, Engagment Calculation and Formula".

Here is my work in progress, the calculators are still being worked on:

/thread_strength/thread_bolt_stress.htm

 

BTW, nice posts everybody!






Modified by Administrator at Wed, Mar 03, 2004, 15:28:18

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Re: 7075 aluminum thread pull-out force question
Re: 7075 aluminum thread pull-out force question -- N74DV Post Reply Top of thread Forum
Posted by: BJH ®

03/03/2004, 10:30:17

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Attached is some helpful info regarding thread-stripout...hope it proves helpful...

Thread Engagement To Prevent Stripping
Reference:Electro-Mechanical Design Handbook by Ronald A. Walsh
Page 10.31:

Same Materials: Material the same for both internal and external threaded parts

E = 2 (Ats) / [π * Dm { ½ + (n (Pd – Dm) / sq root of 3))}] where…

E = length of engagement (inches)
Dm = maximum minor diameter of internal thread (inches)
N = number of threads per inch
Ats = tensile stress area of screw or bolt (inches squared)
Pd = minimum pitch diameter of external thread (inches)
------------------------------------------------------------
Different Materials:(i.e. internal thread of lower strength than externally threaded part); Page 10.44

Relative Strength: R = Ase * (Se) / Asi * (Si) where…

R = relative strength factor (no units)
Ase = shear area of external thread (inches squared)
Asi = shear area of internal thread (inches squared)
Se = tensile strength of external thread material (psi)
Si = tensile strength of internal thread material (psi)

If R <= 1, then length of engagement is adequate. If R > 1, then the length of engagement (G) to prevent strip-out is given as… G = E R

Note:
Ase = π * n * E * Dm [ ( 1/2n) + {(Pd - Dm) / sq root 3}]

Asi = π * n * E * Dm [ ( 1/2n) + {(Dm - Dp) / sq root 3}] where…

Dp = maximum pitch diameter of internal thread
Dm = minimum major diameter of external thread







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Re: 7075 aluminum thread pull-out force question
Re: 7075 aluminum thread pull-out force question -- N74DV Post Reply Top of thread Forum
Posted by: Cragyon ®
Bart
03/03/2004, 09:45:19

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You can do the following (this is onlt an estimate),

stress = load/area

The area is the thread stress area, you can look in  a chart or, use the following calculator /thread_stress_area_a.htm .

(Use major diameter for an external thread anbd minor diameter for an internal thread your calculations)

Determine the yield strength of you weakest part (the aluminum).

Then,   yield stress = [load maximum]/(thread stress area * number of threads of engagement)

or,

load maximum = [yield stress] * [thread stress area * number of threads of engagement)

 

 






Modified by Cragyon at Wed, Mar 03, 2004, 10:46:03

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