(Note: LANDRACING.COM donations are not tax deductible)


This is a public forum. The opinions expressed here don't
necessarily reflect the feelings of The Folks That Run The Site (that's us)
unless we explicitly say so, ok?


Author Topic: Team Go Dog, Go! Modified Partial Streamliners  (Read 1014425 times)

0 Members and 1 Guest are viewing this topic.

Offline wobblywalrus

  • Hero Member
  • *****
  • Posts: 5307
  • Age: 67
  • Location: backwoods Oregon
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3540 on: March 03, 2020, 02:01:29 PM »
This link is to a reference for the following series of posts.  https://mechanicalc.com/reference/bolted-joint-analysis#internal-thread-dimensions

The short bolts attach the brake disk to the adapter ring.  The materials and use are the same as before the ring was installed.  The factory recommended torque can be used for them.  The long bolts are custom made from titanium to fit the adapter.  The installation torque needs to be calculated.  The bolts will be tightened down to provide the maximum clamping force the threads can withstand.

There are three ways the fastener can fail.  One is to strip the internal threads in the wheel.  Another is to strip the external threads on the bolt.  The last is to break the bolt from tensile stress.  This usually occurs across the bolt where the threads meet the unthreaded shank.  All three failure types will be calculated.  The first will be stripping the internal threads in the wheel.

These are M8 x 1.25 threads and the bolt has an 8 millimeter nominal diameter.

The engagement length will be determined.  This is the length of the portion of the threaded hole that is expected to carry the load.  According to the reference for a bolt going into a blind hole, the ENGAGEMENT LENGTH = BOLT NOMINAL DIAMETER = 8mm

The thread height, is what it says.  The thread pitch is the distance between the threads along the bolt axis.  It is 1.25mm

THREAD HEIGHT  = [(SQUARE ROOT OF 3)/2] x THREAD PITCH = 1.73 / 2 x 1.25 = 1.08mm

The internal thread pitch diameter needs to be figgered.  INTERNAL THREAD PITCH DIAMETER = BOLT NOMINAL DIAMETER - (0.75 x THREAD HEIGHT) = 8 - (0.75 x 1.08) = 7.19mm

It will be assumed the internal threads will tear out at their roots by shear from the bolt.  The area of this shear needs to be calculated.  INTERNAL THREAD SHEAR AREA = 3/4 x pi x INTERNAL THREAD PITCH DIAMETER x ENGAGEMENT LENGTH = 3/4 x 3.14 x 7.19 x 8 = 135 square mm or 0.210 square inches

The wheel is assumed to be cast from T6 AlSi7Mg0.3 alloy with a minimum tensile yield stress of 200 MPa or 29,000 psi.  This yield stress is also applicable to similar alloys used to make wheels.  The failure will be in shear and the tensile yield stress will not be appropriate.  The tensile yield stress will be multiplied by 0.577 to get the shear yield stress.  See reference.  SHEAR YIELD STRESS = 0.577 x TENSILE YIELD STRESS = 0.577 x 29,000 = 16,700 psi.

The preload force is the tension applied to the bolt during installation.  The maximum allowable preload stress will be 0.64 percent of the shear yield stress on these wheel threads as per the reference.  MAXIMUM ALLOWABLE PRELOAD FORCE = 0.64 x SHEAR YIELD STRESS x INTERNAL SHEAR AREA = 0.64 x 16,700 x 0.210 = 2,240 lbs

This is not much.  Some thread inserts might be needed in the wheel if there are any indications the threads are stripping.  The inserts increase the internal shear area dramatically with a resultant tolerance for increased bolt preload.  The next post will be about external thread shear failure.       

 

Offline wobblywalrus

  • Hero Member
  • *****
  • Posts: 5307
  • Age: 67
  • Location: backwoods Oregon
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3541 on: March 04, 2020, 10:47:53 AM »
Coarse threads are most commonly used in soft materials like aluminum.  They are a little bit stronger than fine threads.  The M8 x 1.25 is a coarse thread.

The last post addressed stripping in the internal threads in the aluminum wheel.  This post covers stripping of the external threads on the bolt.  The external thread pitch diameter is 7.19 mm as calculated in the previous post.  The engagement length is 8 mm as mentioned in the earlier post, too.

The external thread shear area is smaller than the corresponding internal area.  This is 'cause the shear is assumed to occur at the base, often called root, of the thread.  The external thread root diameter is considerably smaller than the internal root diameter, hence the difference in shear areas.

The external thread shear area is calculated as follows:  EXTERNAL THREAD SHEAR AREA = 5/8 x pi x EXTERNAL THREAD PITCH DIAMETER X ENGAGEMENT LENGTH = 5/8 x 3.14 x 7.19 x 8 = 113 square mm or 0.175 square inches

The titanium is 6Al4V alloy which is often called structural titanium.  Its tensile yield stress is 128,000 psi.  The shear yield stress, calculated using the factor in the previous post, is SHEAR YIELD STRESS = 0.577 x 128,000 = 66,200 psi.  An ultimate shear stress of 79,800 psi is listed in a reputable publication.  This is 83 percent higher than the calculated yield stress.  It is typical for the yield stress to be this much lower than the ultimate stress so the 0.577 factor, although an approximation, is likely to be a good one.  The calculations will use SHEAR YIELD STRESS = 66,200 psi 

Using the preload factor and formula in the previous post, MAXIMUM ALLOWABLE PRELOAD FORCE = 0.64 x 66,200 x 0.175 = 7,410 pounds.  This is more than the 2,240 pounds the internal threads will withstand.  The wheel threads will strip before the bolt threads if too much force is applied.  The next post will be about tensile failure in the bolt.

Offline Lemming Motors

  • Sr. Member
  • ****
  • Posts: 434
  • Location: United Kingdom
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3542 on: March 04, 2020, 11:00:33 AM »
This mechanical analysis makes me feel inadequate. Seriously impressed with the knowledge and application of same on this forum.

I liked it when the dog was helping  :laugh:
A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.

Offline wobblywalrus

  • Hero Member
  • *****
  • Posts: 5307
  • Age: 67
  • Location: backwoods Oregon
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3543 on: March 05, 2020, 12:07:25 PM »
The yard looks like the surface of the moon.  The dogs are busy.

This fastener business is obscure stuff.  It is totally normal for a person to not understand the details.  Hopefully these attachments and posts will make it easier to comprehend.

The bolt is inserted through the adapter ring and into the threaded hole until the end hits the threads.  Some prussian blue has been spread onto the bolt and the corner of the scale is used to make a mark on the dye at the surface of the adapter. 

 

Offline wobblywalrus

  • Hero Member
  • *****
  • Posts: 5307
  • Age: 67
  • Location: backwoods Oregon
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3544 on: March 05, 2020, 12:23:24 PM »
The distance between the mark and the bolt head is measured with calipers.  The calipers are moved down to the pointy end of the bolt.  The span within the calipers are the embedded threads.  The length of this embedded thread distance should always be at least the width of the bolt.  My preference is that or a minimum of ten threads, whichever is longer.

Here is a reference attachment. https://www.fastenal.com/en/78/screw-thread-design

The attachment shows how forces are distributed along the embedded length.  Note the number of threads it takes to transfer the load.  Often when we thread a plate and put a bolt through it we do not have the full embedment length depth that is needed and this concentrates the stresses onto a smaller area.  Sometimes the threads are overloaded when we do this.  There are plenty of threads in the wheel to carry the loads in this project.

The punch in the last picture shows the most heavily loaded thread.  The bolt will break here is there is a tensile or fatigue failure.  The tensile force capacity of the bolt will be calculated here.

Offline wobblywalrus

  • Hero Member
  • *****
  • Posts: 5307
  • Age: 67
  • Location: backwoods Oregon
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3545 on: March 05, 2020, 12:56:39 PM »
The external thread tensile stress area is used for the load calculations and it is discussed in the Bolted Joint Analysis reference cited a few posts previous. It is calculated like this:  EXTERNAL THREAD TENSILE STRESS AREA = (pi/4) x {[BOLT NOMINAL DIAMETER - (0.982 x THREAD PITCH)] SQUARED]} = (pi/4 x {[8 - (0.9382 x 1.25)] SQUARED} = 36.6 square mm = 0.0567 square inches

Considering tensile force, the maximum allowable preload is based on the 128,000 psi tensile yield stress for the titanium alloy.  A 0.64 multiplier is used as per the previous calculations.  MAXIMUM ALLOWABLE PRELOAD FORCE = 0.64 x TENSILE YIELD STRESS x EXTERNAL THREAD TENSILE AREA = 0.64 x 128,000 x 0.0567 = 4,640 pounds

Now we have the three forces:  internal stripping, wheel = 2240 lbs, external stripping, bolt = 7,410 lbs, and tensile yield = 4,640 lbs.  The wheel threads are the weak link in this connection system and they will govern the bolt tension.

Offline salt27

  • Hero Member
  • *****
  • Posts: 1501
  • Age: 63
  • Location: S.W. Orygun
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3546 on: March 05, 2020, 02:07:02 PM »
Coarse threads are most commonly used in soft materials like aluminum.  They are a little bit stronger than fine threads.


Bo, is this specific to a bolt in soft material?

I was under the impression that fine thread bolts were stronger in both tension and shear.

  Don

Offline manta22

  • Hero Member
  • *****
  • Posts: 3607
  • Age: 81
  • Location: Tucson, AZ
  • What, me worry?
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3547 on: March 06, 2020, 09:32:03 AM »
Bo is right, Don.
Regards, Neil  Tucson, AZ

Offline Stainless1

  • Administrator
  • Hero Member
  • ***
  • Posts: 7718
  • Age: 69
  • Location: Near Furley and Kechi KS
  • Robert W. P. "Stainless" Steele
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3548 on: March 06, 2020, 09:44:35 AM »
I think both of them are right.... at least from what I have learned....
When threading into soft material use course threads, they are deeper... harder to strip
When threading into hard material use fine threads...
Stainless
Red Hat 228.039, 2001, 65ci, MSA Bockscar Lakester with a little N20 
MSA Bockscar Lakester #1000 my fastest mile 245 and change, 84 ci turbobusa motor... but Corey's 233 MPH H/BFL record is still 3MPH faster than mine.

Offline Rex Schimmer

  • Hero Member
  • *****
  • Posts: 2439
  • Age: 77
  • Location: Fulton, CA
  • Only time and money prevent completion!
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3549 on: March 06, 2020, 11:52:10 AM »
The ROT (Rule of Thumb) that Stainless use is correct, soft material (aluminum, mag) use coarse threads hard material (steel) use fine threads. Any threaded bolt joint in a soft material that will be dis-assembled should be coarse threads or you will regret it.
If you decide to use a thread insert in a soft material, which I highly recommend for any highly stressed bolt applications, only use the keyed insert style, not the Helicoil style. The keyed insert will allow you to use a fine thread fastener in a soft material  and do not require a special tap for installation as the Helicoil system does.  Helicoils are good for replacing spark plug threads but I would use the keyed insert for everything else.

Rex
Rex

Not much matters and the rest doesn't matter at all.

Offline wobblywalrus

  • Hero Member
  • *****
  • Posts: 5307
  • Age: 67
  • Location: backwoods Oregon
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3550 on: March 06, 2020, 02:14:31 PM »
Hooke's Law is credited to a guy named Hooke.  See page 572 of the attached reference. https://books.google.com/books?id=NaZwZK2xm-QC&pg=PA572&lpg=PA572&dq=developed+length+hookes+law+stretched+bolts&source=bl&ots=1EddqZVK-J&sig=ACfU3U2YvTJLcIiOoVal8kCF-uaA8GtfOg&hl=en&sa=X&ved=2ahUKEwi6-pzy3oToAhXzGzQIHffbAsUQ6AEwCnoECAgQAQ#v=onepage&q=developed%20length%20hookes%20law%20stretched%20bolts&f=false

This titanium flanged shoulder bolt has a clamping force vs bolt stretch relationship that is not on any reference chart I can find.  This needs to be calculated before the torque vs clamping force curve can be derived.

For this calculation, Hooke's Law will be used as follows.  Bolt Stretch = Force x (A + B + C + D)

"A" is the portion of the force multiplier that considers stretch within the bolt head.  Input are:  BOLT SHANK DIAMETER = 0.386 inches, BOLT SHANK AREA = (pi / 4) x 0.386 = 0.117 square inches, and for structural ti MODULUS OF ELASTICITY = 16,500 ksi

HEAD STRETCH PORTION OF MULTIPLIER = (0.4 x BOLT SHANK DIAMETER) / (MODULUS OF ELASTICITY x BOLT SHANK AREA) = (0.4 x 0.386) / (16,500 x 0.117) = 0.000080 inches per kip

"B" is the part of the force multiplier for the stretch in the bolt shank.  Input are SHANK LENGTH = 0.838 inches.  Modulus of elasticity and shank diameter are same as before.

SHANK STRETCH PORTION OF MULTIPLIER = SHANK LENGTH / (MODULUS OF ELASTICITY x SHANK DIAMETER) = 0.838 / (16,500 x 0.117) = 0.000434 inches per kip

"C" is the part of the force multiplier for the exposed threaded portion between the shank and the spacer ring.  Input are EXPOSED THREAD LENGTH = 0.209 inches.  EXTERNAL THREAD TENSILE STRESS AREA was calculated for the previous stripping analysis.  It is (pi / 4) x {[8 - (0.9382 x THREAD PITCH)] squared} = (pi / 4) x {[8 - (0.9382 x 1.25) squared =  36.6 square millimeters = 0.0567 square inches.  Modulus of elasticity is unchanged.

EXPOSED THREAD PORTION OF MULTIPLIER = EXPOSED THREAD LENGTH / (MODULUS OF ELASTICITY x EXTERNAL THREAD TENSILE STRESS AREA) = 0.209 / (16,500 x 0.0567) = 0.000223 inches per kip

"D" is the portion of the force multiplier for the embedded threads and the material that surrounds them.  Input is NOMINAL BOLT DIAMETER = 8 mm = 0.315 inches, NOMINAL BOLT AREA = (pi / 4) x 8 squared = 50.3 square mm = 0.0779 square inches, and MODULUS OF ELASTICITY = 10,000 ksi for the wheel.

EMBEDDED THREAD AND SURROUNDINGS PORTION OF FORCE MULTIPLIER = (0.4 x NOMINAL BOLT DIAMETER) / (MODULUS OF ELASTICITY x NOMINAL BOLT AREA) = (0.4 x 0.315) / (10,000 x 0.0779) = 0.000162 inches per kip

Added together, the force multiplier = 0.000080 + 0.000434 + 0.000223 + 0.000162 = 0.000899 inches per kip

BOLT STRETCH = FORCE x 0.0899 inches per kip  A kip is 1000 pounds force.  The bolt will be stretched in the next post and the torque vs stretch relationship will be figgered.       

Offline Rex Schimmer

  • Hero Member
  • *****
  • Posts: 2439
  • Age: 77
  • Location: Fulton, CA
  • Only time and money prevent completion!
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3551 on: March 06, 2020, 05:38:48 PM »
I did this experiment with a couple of young Boeing engineers at Van Dyne Engineering, in Huntington Beach. Stu Van Dyne wanted to show the difference between the most accurate way to preload a bolt, measuring the stretch, compared to using a torque wrench. One of the most important things you need to be accurate with a torque wrench is a hardened washer and good lube under the bolt head. Done correctly it was almost as accurate as measuring the stretch. There are lots of situations that you cannot measure stretch so you have to depend on a torque wrench, done properly it can be pretty reliable and accurate.

Rex
Rex

Not much matters and the rest doesn't matter at all.

Offline Interested Observer

  • Sr. Member
  • ****
  • Posts: 399
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3552 on: March 06, 2020, 07:11:47 PM »
Wobbly, not that it makes any significant difference, but I believe in part D you have gone astray by using the aluminum modulus instead of the bolt modulus.  You may want to check on that.  That part D calc is just an approximation of stretch in the bolt at that section, and as you pointed out, the load distribution into the bolt via the threads is varied--ergo, the calc is an approximation.  Besides, what would the modulus of the surrounding material have to do with the amount of load applied to the bolt?

Offline wobblywalrus

  • Hero Member
  • *****
  • Posts: 5307
  • Age: 67
  • Location: backwoods Oregon
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3553 on: March 06, 2020, 10:59:11 PM »
You are correct.  I fixed the calculations.

Offline Speed Limit 1000

  • Hero Member
  • *****
  • Posts: 1180
  • Age: 70
  • Location: Denver, Colorado
Re: Team Go Dog, Go! Modified Partial Streamliners
« Reply #3554 on: March 07, 2020, 12:11:29 PM »

If you decide to use a thread insert in a soft material, which I highly recommend for any highly stressed bolt applications, only use the keyed insert style, not the Helicoil style. The keyed insert will allow you to use a fine thread fastener in a soft material  and do not require a special tap for installation as the Helicoil system does.

Rex

You do use a standard tap but with slightly larger drill. For a 1/2-13 tap you use the drill size for the 1/2-20 tap
John Gowetski, red hat @ 221.183 MPH MSA Lakester, Bockscar #1000 60 ci normally aspirated w/N20