Savvy off-road sold? (the unofficial Savvy customer support and Savvy rant thread)

[freedom_in_4low]

Seems like the guys that enjoy doing calculations are @sab @gasiorv and @freedom_in_4low see if any of them want to do it.

I do but I much prefer (and am more qualified in) heat/energy/fluid mechanics, but yes:

Here is a neat basic article of the concept.

https://sendcutsend.com/blog/the-science-behind-bending-stiffness/

It is mostly to deal with the area moment of inertia. Think of a 2x6 laid flat vs upright for something like a floor joist.

This. The moment of inertia of a rectangle is proportional to the width and to the cube of the height. All else being the same, adding 33% to the thickness adds 33% to the moment of inertia, but adding 33% to the height would add 135%.

Since moment of inertia is based on the load axis, if you want to know how strong it is against vertical forces then the effective height in the vertical axis (and the effective width in the horizontal axis) is what goes into the moment of inertia calculation. A 45° bend would need to be 69% (hehe) wider to achieve the same height, but the effective thickness is also increased since you're measuring through the 1/4" plate at a 45° angle as well. That said, the loads aren't really vertical...the ideal bend angle of that back flange would be to make it's plane parallel to the primary load - obviously loads are variable but putting it somewhere in the middle of the expected load angles makes sense, and 45°, if that's what it is...probably isn't a horrible idea, and with extra height can easily be just as strong as the original flange or stronger in the direction that matters, but that doesn't mean the rest of the deck is just as well supported after losing 50% of its thickness through the middle. My statics and material science skills don't extend into 3 dimensions so i'll have to leave it to someone else whether 1/4" is still enough when we used to get two layers of 3/16".

 

[sab]

PNW_LJ's queries are not answered with simple calculations - it's complicated. Also, I think two different points are being discussed. First, is the stress-strain diagram and what's happening in the bend radius. Second, is the effectiveness of the flange's size and shape.

To the first point, bending the flange, by definition, occurs by plastic deformation within the plastic region shown. Plastic = permanent bending (stays bent after the load is removed) and Elastic = temporary bending (it returns when the load is removed). Bending it too far, or at too small a radius, will blow through the plastic region and into ultimate tensile failure (cracking).

To the second point, RockyTopTJ is correct. The flange increases the area moment of inertia, which is the main factor in resistance to bending. When the winch is pulling, the resultant load on the top of the bumper wants to lift the rear of the winch up, but the rear mounting bolts transfer that lifting force to the top surface of the bumper. The flange helps resist those forces. Unfortunately, there is no single formula to calculate, exactly, the stresses on the bumper. An engineer would have to use Finite Element Analysis software to calculate the effects of those forces.

However, the area moment of inertia calculations can be used to compare the rigidity of different options because the rigidity is directly related to the area moment of inertia. The problem is that a flange at an angle is a very unusual moment of inertia case. In my years as an engineer, this is the first time it's come up! Fortunately, the Internet is an amazing thing. I found a web page that actually has a calculator for this! Here it is:

https://www.engineersedge.com/calculators/section_square_case_9.htm

Using that calculator, here are the relative moments of inertia for various flange configurations:

A 1" tall flange of 3/16" thick material, at a 90° included-angle bend (the angle in the calculator is 0° for a 90° bend): .016 in^4
A 1" tall flange of 1/4" thick material, at a 90° included-angle bend: .021 in^4
A 1" tall flange of 3/16" thick material, at a 135° included-angle bend (the angle in the calculator is 45° for a 135° bend): .005 in^4
A 0.1" tall flange of 3/16" thick material, at a 90° included-angle bend (very minimal flange, essentially): .00002 in^4
A 1.414" tall flange of 3/16" thick material, at a 135° included-angle bend (same vertical height as a 1" @ 90° angle): .013 in^4

Again, these are only comparisons. In reality, the load case and stress analysis for when the winch is pulling is a lot more complicated, but these calculations do help understand the importance of a flange, and how important it is to consider the specifics of the flange's size and bend angle.

 

[mrblaine]

I do but I much prefer (and am more qualified in) heat/energy/fluid mechanics, but yes:



This. The moment of inertia of a rectangle is proportional to the width and to the cube of the height. All else being the same, adding 33% to the thickness adds 33% to the moment of inertia, but adding 33% to the height would add 135%.

Since moment of inertia is based on the load axis, if you want to know how strong it is against vertical forces then the effective height in the vertical axis is what goes into the moment of inertia calculation. A 45° bend would need to be 69% (hehe) wider to achieve the same height. But the loads aren't really vertical...the ideal bend angle of that back flange would be to make it's plane parallel to the primary load - obviously loads are variable but putting it somewhere in the middle of the expected load angles makes sense, and 45°, if that's what it is...probably isn't a horrible idea, and with extra height can easily be just as strong as the original flange, but that doesn't mean the rest of the deck is just as well supported after losing 50% of its thickness. My statics and material science skills don't extend into 3 dimensions so i'll have to leave it to someone else whether 1/4" is still enough when we used to get two layers of 3/16".

The load is actually fairly vertical. What happens when you load the winch is the front feet move or try to move downward and the rear feet try to lift. The testing we did showed that very well and even with the doubled up layers, the back of the deck still tried to bow the flange. It never reached plastic, but it did move more than I would have suspected.

 

[John Cooper]

PNW_LJ's queries are not answered with simple calculations - it's complicated. Also, I think two different points are being discussed. First, is the stress-strain diagram and what's happening in the bend radius. Second, is the effectiveness of the flange's size and shape.

To the first point, bending the flange, by definition, occurs by plastic deformation within the plastic region shown. Plastic = permanent bending (stays bent after the load is removed) and Elastic = temporary bending (it returns when the load is removed). Bending it too far, or at too small a radius, will blow through the plastic region and into ultimate tensile failure (cracking).

To the second point, RockyTopTJ is correct. The flange increases the area moment of inertia, which is the main factor in resistance to bending. When the winch is pulling, the resultant load on the top of the bumper wants to lift the rear of the winch up, but the rear mounting bolts transfer that lifting force to the top surface of the bumper. The flange helps resist those forces. Unfortunately, there is no single formula to calculate, exactly, the stresses on the bumper. An engineer would have to use Finite Element Analysis software to calculate the effects of those forces.

However, the area moment of inertia calculations can be used to compare the rigidity of different options because the rigidity is directly related to the area moment of inertia. The problem is that a flange at an angle is a very unusual moment of inertia case. In my years as an engineer, this is the first time it's come up! Fortunately, the Internet is an amazing thing. I found a web page that actually has a calculator for this! Here it is:

https://www.engineersedge.com/calculators/section_square_case_9.htm

Using that calculator, here are the relative moments of inertia for various flange configurations:

A 1" tall flange of 3/16" thick material, at a 90° included-angle bend (the angle in the calculator is 0° for a 90° bend): .016 in^4
A 1" tall flange of 1/4" thick material, at a 90° included-angle bend: .021 in^4
A 1" tall flange of 3/16" thick material, at a 135° included-angle bend (the angle in the calculator is 45° for a 135° bend): .005 in^4
A 0.1" tall flange of 3/16" thick material, at a 90° included-angle bend (very minimal flange, essentially): .00002 in^4
A 1.414" tall flange of 3/16" thick material, at a 135° included-angle bend (same vertical height as a 1" @ 90° angle): .013 in^4

Again, these are only comparisons. In reality, the load case and stress analysis for when the winch is pulling is a lot more complicated, but these calculations do help understand the importance of a flange, and how important it is to consider the specifics of the flange's size and bend angle.

Dang i had a woman tell me the same thing once....... I think!

 

[PNW_LJ]

PNW_LJ's queries are not answered with simple calculations - it's complicated. Also, I think two different points are being discussed. First, is the stress-strain diagram and what's happening in the bend radius. Second, is the effectiveness of the flange's size and shape.

To the first point, bending the flange, by definition, occurs by plastic deformation within the plastic region shown. Plastic = permanent bending (stays bent after the load is removed) and Elastic = temporary bending (it returns when the load is removed). Bending it too far, or at too small a radius, will blow through the plastic region and into ultimate tensile failure (cracking).

To the second point, RockyTopTJ is correct. The flange increases the area moment of inertia, which is the main factor in resistance to bending. When the winch is pulling, the resultant load on the top of the bumper wants to lift the rear of the winch up, but the rear mounting bolts transfer that lifting force to the top surface of the bumper. The flange helps resist those forces. Unfortunately, there is no single formula to calculate, exactly, the stresses on the bumper. An engineer would have to use Finite Element Analysis software to calculate the effects of those forces.

However, the area moment of inertia calculations can be used to compare the rigidity of different options because the rigidity is directly related to the area moment of inertia. The problem is that a flange at an angle is a very unusual moment of inertia case. In my years as an engineer, this is the first time it's come up! Fortunately, the Internet is an amazing thing. I found a web page that actually has a calculator for this! Here it is:

https://www.engineersedge.com/calculators/section_square_case_9.htm

Using that calculator, here are the relative moments of inertia for various flange configurations:

A 1" tall flange of 3/16" thick material, at a 90° included-angle bend (the angle in the calculator is 0° for a 90° bend): .016 in^4
A 1" tall flange of 1/4" thick material, at a 90° included-angle bend: .021 in^4
A 1" tall flange of 3/16" thick material, at a 135° included-angle bend (the angle in the calculator is 45° for a 135° bend): .005 in^4
A 0.1" tall flange of 3/16" thick material, at a 90° included-angle bend (very minimal flange, essentially): .00002 in^4
A 1.414" tall flange of 3/16" thick material, at a 135° included-angle bend (same vertical height as a 1" @ 90° angle): .013 in^4

Again, these are only comparisons. In reality, the load case and stress analysis for when the winch is pulling is a lot more complicated, but these calculations do help understand the importance of a flange, and how important it is to consider the specifics of the flange's size and bend angle.

Thank you Sab (and others who chimed in with an engineering perspective). These comparisons while crude, as you said they really do highlight the importance of a proper flange in our application, a lightweight bumper able to withstand strenuous winch pulls.

The load is actually fairly vertical. What happens when you load the winch is the front feet move or try to move downward and the rear feet try to lift. The testing we did showed that very well and even with the doubled up layers, the back of the deck still tried to bow the flange. It never reached plastic, but it did move more than I would have suspected.

Very interesting that the rear feet see that much vertical lift. This reinforces the importance of a proper bumper extending rearwards to reuse the factory sway bar mounting holes.

 

[PNW_LJ]

PNW_LJ's queries are not answered with simple calculations - it's complicated. Also, I think two different points are being discussed. First, is the stress-strain diagram and what's happening in the bend radius. Second, is the effectiveness of the flange's size and shape.

To the first point, bending the flange, by definition, occurs by plastic deformation within the plastic region shown. Plastic = permanent bending (stays bent after the load is removed) and Elastic = temporary bending (it returns when the load is removed). Bending it too far, or at too small a radius, will blow through the plastic region and into ultimate tensile failure (cracking).

To the second point, RockyTopTJ is correct. The flange increases the area moment of inertia, which is the main factor in resistance to bending. When the winch is pulling, the resultant load on the top of the bumper wants to lift the rear of the winch up, but the rear mounting bolts transfer that lifting force to the top surface of the bumper. The flange helps resist those forces. Unfortunately, there is no single formula to calculate, exactly, the stresses on the bumper. An engineer would have to use Finite Element Analysis software to calculate the effects of those forces.

However, the area moment of inertia calculations can be used to compare the rigidity of different options because the rigidity is directly related to the area moment of inertia. The problem is that a flange at an angle is a very unusual moment of inertia case. In my years as an engineer, this is the first time it's come up! Fortunately, the Internet is an amazing thing. I found a web page that actually has a calculator for this! Here it is:

https://www.engineersedge.com/calculators/section_square_case_9.htm

Using that calculator, here are the relative moments of inertia for various flange configurations:

A 1" tall flange of 3/16" thick material, at a 90° included-angle bend (the angle in the calculator is 0° for a 90° bend): .016 in^4
A 1" tall flange of 1/4" thick material, at a 90° included-angle bend: .021 in^4
A 1" tall flange of 3/16" thick material, at a 135° included-angle bend (the angle in the calculator is 45° for a 135° bend): .005 in^4
A 0.1" tall flange of 3/16" thick material, at a 90° included-angle bend (very minimal flange, essentially): .00002 in^4
A 1.414" tall flange of 3/16" thick material, at a 135° included-angle bend (same vertical height as a 1" @ 90° angle): .013 in^4

Again, these are only comparisons. In reality, the load case and stress analysis for when the winch is pulling is a lot more complicated, but these calculations do help understand the importance of a flange, and how important it is to consider the specifics of the flange's size and bend angle.

I have some more thoughts.

1) The front bend of the bumper (shown with arrow below), is approaching parallel to the vertical forces imposed on it. As such, it contributes to the stiffness of the winch deck.

2) As Blaine describes there is still the potential for vertical lift under heavy winching loads. If further reinforcement is desired, it may make sense to add side flanges for reinforcement, as drawn above.

An alternative could be to build the bumper out of 1/4" 6061 T6, or 3/16" 7075 T6. However, bending such 90 degree flanges is not possible in either material, which makes me question the sensibility of their use. The better solution might be to bump up the thickness of the winch plate.

 

[mrblaine]

I have some more thoughts.

1) The front bend of the bumper (shown with arrow below), is approaching parallel to the vertical forces imposed on it. As such, it contributes to the stiffness of the winch deck.

View attachment 562435


2) As Blaine describes there is still the potential for vertical lift under heavy winching loads. If further reinforcement is desired, it may make sense to add side flanges for reinforcement, as drawn above.

An alternative could be to build the bumper out of 1/4" 6061 T6, or 3/16" 7075 T6. However, bending such 90 degree flanges is not possible in either material, which makes me question the sensibility of their use. The better solution might be to bump up the thickness of the winch plate.

The flanges you drew add exactly zero to the bowing resistance of the winch deck since their constaint is outside the bolts into the frame. You could do the same with a small plate bolted down with the same bolts. That and the flange being semi connected to that same area means the rigidity wouldn't transfer.

The front bend of the bumper has a giant flange bent downward. It won't bow in that area at all. Enough force will dish the mount hole area downward but it takes a monster amount of force to do that. The winch won't survive those forces.

 

[freedom_in_4low]

The load is actually fairly vertical. What happens when you load the winch is the front feet move or try to move downward and the rear feet try to lift. The testing we did showed that very well and even with the doubled up layers, the back of the deck still tried to bow the flange. It never reached plastic, but it did move more than I would have suspected.

That makes sense.

That being the case, a little extra height in the flange can easily make up for the angle and lost thickness (of the flange itself). I'm just not sure on the "panel" in between the edges.

 

[macleanflood]

You could do the same with a small plate bolted down with the same bolts.

Isn't that effectively where we attach tow hooks and wouldn't they double as a plate?

-Mac

 

[srimes]

The load is actually fairly vertical. What happens when you load the winch is the front feet move or try to move downward and the rear feet try to lift. The testing we did showed that very well and even with the doubled up layers, the back of the deck still tried to bow the flange. It never reached plastic, but it did move more than I would have suspected.

I'll piggyback on @mrblaine's observation that the benefit of the rear flange is providing stiffness in the vertical plane because there's already a huge amount of stiffness in the horizontal plane. So even though the force from the winch is mostly horizontal, the big base plate shows no visible deflection horizontally.

 

[freedom_in_4low]

I'll piggyback on @mrblaine's observation that the benefit of the rear flange is providing stiffness in the vertical plane because there's already a huge amount of stiffness in the horizontal plane. So even though the force from the winch is mostly horizontal, the big base plate shows no visible deflection horizontally.

Yeah I was focused on the load from the rope and not thinking about the resulting moment applied to the winch.

 

[mrblaine]

Isn't that effectively where we attach tow hooks and wouldn't they double as a plate?

-Mac

My point was NOT to build a plate, my point was to explain that a plate is useless since it is just backing up what the bolts are already doing quite well so anything outside of them past the frame is as useless as a plate that isn't doing anything.

 

[mrblaine]

Yeah I was focused on the load from the rope and not thinking about the resulting moment applied to the winch.

Someday, someone really smart will be able to explain the forces that are cancelling each other out and slowing down the amount of rear lift the back feet see since the drum's rotation under load is trying to push the rear feet down, but the height of the drum above the deck is trying to rip the back bolts up and out.

 

[srimes]

Someday, someone really smart will be able to explain the forces that are cancelling each other out and slowing down the amount of rear lift the back feet see since the drum's rotation under load is trying to push the rear feet down, but the height of the drum above the deck is trying to rip the back bolts up and out.

The feet never see the forces from the motor rotating the drum as they're internal to the winch. They basically only see the force from the rope.

 

[mrblaine]

The feet never see the forces from the motor rotating the drum as they're internal to the winch. They basically only see the force from the rope.

If you turn the drum by powering on the winch and then lock it down with a large clamp, the winch body will then rotate around the drum. What am I missing?

 

[sab]

If you turn the drum by powering on the winch and then lock it down with a large clamp, the winch body will then rotate around the drum. What am I missing?

You're not missing anything. The motor develops a torque, and the torque has to be countered by two forces offset from each other. The rope can be one of those forces, but another is required to keep the body from moving.

 

[Apparition]

You're not missing anything. The motor develops a torque, and the torque has to be countered by two forces offset from each other. The rope can be one of those forces, but another is required to keep the body from moving.

Needs more free body diagram

 

[sab]

Needs more free body diagram

I'm sitting at my childhood dining room table right now, 1000 miles from home. No engineering paper to be found, and everyone knows that FBDs can't be drawn on regular paper.

 

[jjvw]

I'm sitting at my childhood dining room table right now, 1000 miles from home. No engineering paper to be found, and everyone knows that FBDs can't be drawn on regular paper.

Get the crayons out on that little table!

 

[JoseA]

The people want Free Body Diagrams