Looking to create a better frame for my e-motorcycle

[Synco]

TL;DR Summary

Well people i want to go from my steel/aluminum frame to the best material in the market. I have seen that exist a relation between Mpa(Yield strengh-elastic limit)/density but i get a very weird relation in a strange unit K*(m^2)/(s^2) which(K= any real number) is the expansion of an area in the time, but, what is it doing here if I'm searching the strongest material to reduce weight?

Well people i want to go from my steel/aluminum frame to the best material in the market. I have seen that exist a relation between Mpa(Yield strenght-elastic limit)/density but i get a very weird relation in a strange unit (m^2)/(s^2) which is the expansion of a growing area in the time, but, what is it doing here if I'm searching the strongest material to reduce weight?

Ok
1Mpa= 1000000 N/m^2
N=Kg*(m/s^2)
Density= Kg/m^3

so

Yield Strength/Density is:
((Kg*(m/s^2))/m^2)/(Kg/m^3)= m^2/s^2
according to this link
https://www.symbolab.com/solver/ste...}\right)/\left(K\cdot g/m^{3}\right)?or=input

Why Yield Strength(elastic limit)/Density?
If we think in total resistance( I'm not a mechanical engineer) we can imagine the following case:

Imagine that you have a hollow bar of X material with an L length with a volume V, using it as lever. If you fill the bar with the same material you can apply more force without breaking it or curve it and if the density tends to 0, for say something, you are filling the hollow bar without changing the weight so much, so we can think that's a benefit fill the bar without compromise the weight. In contrary case if the density tends to infinite(we have a black hole XD) you are adding so much weight without getting a benefit, so the correct "sense" of the density it is to go to 0.
Occurs exactly the contrary case with yield strength, if it goes to 0 it is useless if it goes to infinite it is awesome as a lever. Hence, the "correct" "sense" it is to grow. So the bigger number the better for this application.

But, if we are talking about volumes, resistance to pressure and weight, In what moment the acceleration of the expansion of the area it is representative to define what material it's better than the other to resist the same pressure by less weight?

 

[Lnewqban]

Welcome, @Synco !

Could you show us a link to that misterious k?

Take a look at what materials have been used for modern high performance bicycles and motorcycles.
Consider the price and difficulties to work with those materials.

Regarding your example of filling a tube:
Resistance to bending forces is gained slower than weight.
For that reason you don't see bicycle's frames made of solid material.

Not only strength of the material is important, a bicycle needs also a rigid frame.
For that reason, the material is placed as far apart as possible; therefore, the tubular shapes that you see in modern light bicycles.

 

[jack action]

If I understood you correctly, you want to know the meaning of $m^2/s^2$?

There is none.

The unit you are interested in is $Pa/(kg/m^3)$ or more likely $Mpa/(kg/m^3)$, which may be rewritten as $MPa.m^3/kg$ . It is defined as a strength per density, that's it.

You already know that pressure is defined as a force over an area, which has the unit $Pa = N/m^2$. It can be reduced to $kg/m/s^2$. Trying to make sense of this basic unit is pointless.

 

[Frabjous]

Another way to look at it. m²/s² is energy per unit mass. Since the energy is from yield strength, this is an approximation of how much energy is needed per unit mass for deformation to occur. In theory, the bigger it is, the better.
This is a approximation for “ductile” materials. If cracking is an issue, it will probably not be of much use.

 

[jrmichler]

i want to go from my steel/aluminum frame to the best material in the market.

You are looking at the wrong material criterion. The criteria relevant to motorcycle frames are both:

1) Strength to weight ratio, and
2) Stiffness to weight ratio.

Steel, titanium, and aluminum all have similar strength to weight ratios, and stiffness to weight ratios. Optimally designed frames from each material will have similar weight, strength, and stiffness. Certain dimensions will be different. For example, aluminum will have larger diameter tubes. Carbon fiber has advantages, but has a large learning curve.

Motorcycle handling requires a stiff frame, especially in torsion. Proper frame design and triangulation are more important than the material. Other factors include weldability, fatigue resistance, corrosion resistance, appearance, machinability, material availability, and material cost. An appreciable portion of the weight of the finished frame is attachments for the headset, stand, rear wheel, motor mounts, battery mounts, wiring, brakes, seat, luggage rack, etc.

All of which is why the best frame material for most individual builders is good old 4130 Condition N aircraft tubing. It's readily available in many sizes and wall thicknesses, easily weldable, affordable, and has good fatigue resistance. That's because it was specifically designed for aircraft use, where the material requirements are virtually identical to the material requirements for motorcycle frames.

And that's why I built this CLWB bicycle frame from 4130 tubing. It survived a stress test that include riding down a flight of stairs, and over 3000 miles of riding. The frame was still good when I saw it about ten years after selling it.

 

[berkeman]

It survived a stress test that include riding down a flight of stairs

Well that must be a pretty good story!

 

[Baluncore]

The lowest weight will come from a space frame or truss structure, built out of thin walled tube. That represents the majority of bicycle structures today.

It is most convenient to fabricate the frame from stock tube with a round section, but an elliptical section is also possible and may provide a strength/weight advantage.

Given the choice of material and processes available today, it would also be possible to vary the diameter of the truss members over the length of each tube. That would make the tube fusiform, like the wooden spokes used in old wagon wheels. That shape allows longer tubes that can better resist buckling while handling axial compression, with some side forces.
https://en.wikipedia.org/wiki/Fusiform

Fusiform struts can also have more flexibility at the end joints where the diameter is less. Torque is resisted by the large diameter, but can safely twist the ends where the members are joined. That can reduce stress at the lugs or welds, while providing the weight advantages of plastic design.

Lastly, you can drill or punch holes at neutral points in the material to reduce the weight. That high-tech weight reduction of bicycles has been called "drillium".

 

[jrmichler]

Well that must be a pretty good story!

Not really. I needed to stress test it before trusting it on bumpy city streets. The frame flexed enough to bounce the generator off the rear tire going down the steps. The generator is barely visible behind the seat back and above the rear tire. A little frame flex plus the 2.125" rear tire really helped the ride quality.

I liked the handling. If I entered a curve too fast, the rear tire would slide out, the bike would go down, and I (several times) ended up sitting on the side of the seat without a scratch or bruise.

 

[Synco]

Welcome, @Synco !

Could you show us a link to that misterious k?

Take a look at what materials have been used for modern high performance bicycles and motorcycles.
Consider the price and difficulties to work with those materials.

Regarding your example of filling a tube:
Resistance to bending forces is gained slower than weight.
For that reason you don't see bicycle's frames made of solid material.

Not only strength of the material is important, a bicycle needs also a rigid frame.
For that reason, the material is placed as far apart as possible; therefore, the tubular shapes that you see in modern light bicycles.

I committed a mistake, yeah i used the K as a constant and for Kilos, They are different. I just tried to say if you transform from Mpa to N/m^2 you are going to get a K*(N/m^2) with K as real number.
I didn't know that, a hollow tube resists more pressure than one solid of the same weight, thank you. With your last advice, can i guess that the best material for this it's graphene?

If I understood you correctly, you want to know the meaning of $m^2/s^2$?

There is none.

The unit you are interested in is $Pa/(kg/m^3)$ or more likely $Mpa/(kg/m^3)$, which may be rewritten as $MPa.m^3/kg$ . It is defined as a strength per density, that's it.

You already know that pressure is defined as a force over an area, which has the unit $Pa = N/m^2$. It can be reduced to $kg/m/s^2$. Trying to make sense of this basic unit is pointless.

Yes you understood well in the first point.
If you want to do a prediction or think how it works something, you need to know what are saying the units, that's why they are there. To say in some way, the units are an "abbreviation" of the equation that comes the value, it's like a reminder, like post it "hey this number comes from there and it's this".
If you replace all the values that you took, you are going to get m^2/s^2.

Another way to look at it. m²/s² is energy per unit mass. Since the energy is from yield strength, this is an approximation of how much energy is needed per unit mass for deformation to occur. In theory, the bigger it is, the better.
This is a approximation for “ductile” materials. If cracking is an issue, it will probably not be of much use.

Yes i thought that, J/Kg, but that is something in thermodynamics. It's like be solving a problem in Kinematics and suddenly appears an A or ampere, so you are going to say, "What is it doing the current in a Kinematic problem?" just to express how i feel.
Well an interpretation in Nm/Kg which should be the Torque/Weight, how much torque you need to deform a bar in a irreversible way for a given amount of mass of that material.

You are looking at the wrong material criterion. The criteria relevant to motorcycle frames are both:

1) Strength to weight ratio, and
2) Stiffness to weight ratio.

Steel, titanium, and aluminum all have similar strength to weight ratios, and stiffness to weight ratios. Optimally designed frames from each material will have similar weight, strength, and stiffness. Certain dimensions will be different. For example, aluminum will have larger diameter tubes. Carbon fiber has advantages, but has a large learning curve.

Motorcycle handling requires a stiff frame, especially in torsion. Proper frame design and triangulation are more important than the material. Other factors include weldability, fatigue resistance, corrosion resistance, appearance, machinability, material availability, and material cost. An appreciable portion of the weight of the finished frame is attachments for the headset, stand, rear wheel, motor mounts, battery mounts, wiring, brakes, seat, luggage rack, etc.

All of which is why the best frame material for most individual builders is good old 4130 Condition N aircraft tubing. It's readily available in many sizes and wall thicknesses, easily weldable, affordable, and has good fatigue resistance. That's because it was specifically designed for aircraft use, where the material requirements are virtually identical to the material requirements for motorcycle frames.

And that's why I built this CLWB bicycle frame from 4130 tubing. It survived a stress test that include riding down a flight of stairs, and over 3000 miles of riding. The frame was still good when I saw it about ten years after selling it.
View attachment 319339

So in that way graphene it's best material for this?

The lowest weight will come from a space frame or truss structure, built out of thin walled tube. That represents the majority of bicycle structures today.

It is most convenient to fabricate the frame from stock tube with a round section, but an elliptical section is also possible and may provide a strength/weight advantage.

Given the choice of material and processes available today, it would also be possible to vary the diameter of the truss members over the length of each tube. That would make the tube fusiform, like the wooden spokes used in old wagon wheels. That shape allows longer tubes that can better resist buckling while handling axial compression, with some side forces.
https://en.wikipedia.org/wiki/Fusiform

Fusiform struts can also have more flexibility at the end joints where the diameter is less. Torque is resisted by the large diameter, but can safely twist the ends where the members are joined. That can reduce stress at the lugs or welds, while providing the weight advantages of plastic design.

Lastly, you can drill or punch holes at neutral points in the material to reduce the weight. That high-tech weight reduction of bicycles has been called "drillium".

I was thinking like you but, I don't know if the frame should be an elliptical bar or a rectangle bar. How i demonstrate which is better than the other? i suspect that's better a retangular frame.

Thanks for your advise people. Let's discuss more about this

 

[Synco]

What do you say about carbyne? or it's better graphene?

 

[jrmichler]

That would be a short lived motorcycle frame because, according to this quote from the Wikipedia article about carbyne: A carbyne can occur as a short-lived reactive intermediate.

Since you have fallen in love with the tensile strength of graphene, you could start by making a simple part from it. I suggest making a simple tensile test specimen. Then measure the tensile strength and compare to the strength of commercially available materials. After that, investigate the compressive and torsional strength. Then figure out how to build real parts.