Omicrom

Power=Force(vector) * (dot product) Velocity (Vector) Velocity is easy , it is the velocity in m/s Force is not so easy , There are 2 main contributors: Drag force = 0.5 * density * Velocity^2 * Frontal area * Drag coefficient Which is more or less equal to Drag force = 0.24*Velocity^2 (mountainbiker) and 0.186*Velocity^2 (road bike on drops) Rolling resistance= mass(rider+bike) * gravitational acceleration * Rolling resistance coefficient Which is equals : mass*9.8*0.014 (mountainbike) and mass*9.8*0.003 (road bike) So you sum the forces and multiply it by velocity (in m/s) and that will give you power. To answer your question about why it differs , the user inputs for bike type and mass are probably set incorrectly. O and in a slipstream the drag force is decreased by 30% (if I recall correctly)

Unlike metals carbon fibre is not subject to metal fatigue, so theoretically it should last you a very very long time. I would suggest taking it for a ultra sound check just to see if all is still fine and there is no delaminations caused by knocks.

I you are going to chuck the frame I will take it!

Here is a photo of the bike so far. As mentioned previously it will be a commuter bike and I've rebuilt it with some used components. Including a cracked fox fork and gummed up Slx brakes. I will attempt to repair both of them as well. I am going to redo the drive-train with a Rapide single-speed kit. The picture posted here is as the bike was tested.

I rode the frame for the first time tonight for about 10minutes with the accelerator on. I did a few bunny-hops peaking at 2.5g's. Tyres and shock were at operating pressures. everything held up good for now. I will post photo's of the build so far tomorrow.

Hi wiledog , being a long term experiment I cannot tell you if it will hold up as of yet. Although the stresses in the frame are much less at that particular spot than in mine it should theoretically hold up longer than the weld on the bike I did. A few things that count in your favor would be the fact that the initial crack was not due to fatigue but rather a brittle fracture and that it is easier to weld in that spot. I will ride my frame until January and If everything seems fine I will contact you regarding repairing your frame.

Unfortunately I think I will get hurt if it fails or not. I am by no means a professional enduro rider

Hi Hubbers so today was the big repair day. After cleaning all the weld areas again, back purging the frame with argon and doing a few “warm-up welds” I felt ready. On initial arc I shook so much I had to stop take a few breaths and go at it again. The rest of the welding didn't go any better; between struggling to reach spots with the torch and filling up the holes I drilled I had my hands full. I am by no means pleased or proud of the welds, and I have done much better welds before on thinner material. I wanted to have as little possible torch time on the frame and keep the heat affected zone as small as possible. Unfortunately due to the struggle that was not possible and I ended up with big fillets that I just smooved out with the torch. The results are not as hoped but I feel the hope in the repair is not lost since I managed to salvage it. Being aluminium it will eventually fail again, it is not like steel that has a fatigue limit, no matter how small the applied load it will eventually fail due to fatigue. The frame held approx 3-4 years out of the factory so if these repairs last half of that time I will be pleased, and I will probably weld it again since the frame will stay naked. Lessons learnt today, Use a gas lens, you can have much longer tungsten stick out and reach tighter fillets that way. Use a stubby kit so the torch can have a better angle inside the frame. If it doesn't work stop and have a go at it again.

Attached is 2 screenshots of the simulation done , It is a track frame I designed .I just tweaked the tube profiles for the simulation and added two tabs at the BB to apply additional vertical forces. I used a safety factor of 2.

No I did't incorporate all the tube bends and profiles, I just used the appropriate diameters and wall thicknesses making sure my cross sectional area is correct. Will do

Download an accelerometer app on cellphone, strap it to the bike securely so no movement takes place. Ride around for a set time , say 2 minutes. Have a look at the peaks and try to sort them in 3 categories, low med and high at even intervals. manually count the peaks of each interval. ect. 0-2G 90 times 2-4G 40 times 4-6G 10 times Set up a static simulation in your favorite CAD or simulation program with a model of your bike. calculating the applied force from F=ma =(weight of you and bike)[(top interval in G)*9.81] decide where you want to apply the total force, amount at top of seat post and amount at BB (doesn't have a big influence because each member in a bike frame is essentially a two force member and the both act in 'almost' linearly to seat tube) apply horizontal forces at BB Use the results and a probe to measure stress at given points. Repeat for each of the G force intervals you chose. calculating fatigue Get the SN formula for the given material and use the relations in which they occur and calculate the fatigue as a %. use 100% for point of failure. and solve x which is the amount of fatigue cycles.

It's as fair question, Stripping that part of the frame only will require a colour match and I am no paint expert, so I feel it would have left me with a silly looking patch if I've done that myself. If I strip the whole frame I can just go ahead and paint it one colour and it will look alright. I suspected there might be another crack due to the amount of time he rode the bike like that. Stripping the whole frame mean I could try another avenue of repair. I hope it makes sense

I am going to heat that part of the frame ,wrapped in aluminium foil ,with a blowtorch to about 200'C. This is only to relieve the stresses caused by the welding. I have done my calculations and a simulation has shown that the max stress in that region will be around 40MPa with the riding I intend to do. Which will give me a fatigue live of around 5*10E6 stress cycles considered that the alloy will not be aged again as it's supposed to. Regarding filler rod I intend on using 4043 in 3.2mm thickness.

I am going to heat that part of the frame ,wrapped in aluminium foil ,with a blowtorch to about 200'C. This is only to relieve the stresses caused by the welding. I have done my calculations and a simulation has shown that the max stress in that region will be around 40MPa with the riding I intend to do. Which will give me a fatigue live of around 5*10E7 stress cycles considered that the alloy will not be aged again as it's supposed to. Regarding filler rod I intend on using 4043 in 3.2mm thickness.

Step 1 Cleaning the frame with a mild detergent and removing any grease from the paint to have a clean surface for the paint stripper to work on. Step 2 Apply the paint stripper and let it do it's thing. I used Built it branded paint stripper and 500ml proved to be more than enough for 3 coats. Step 3 Wash the frame again with a mild detergent, to remove excess paint stripper and lose bits of paint. The clean frame actually looked quite nice and I am thinking of keeping it that way for a brushed aluminium look. Upon closer inspection 3 cracks was found on the frame , as well as 3 lose bottle cage nuts. The welding on the frame did look good accept for 2 or 3 spots and I suspect that more than one person welded on the frame (it was probably a production line setup). Step 4 Clean all the cracks with acetone, and drill the tips of the cracks to stop the crack from spreading. Step 5 File down the crack to form a "v" all along the crack. This helps to stay on course during the weld because it is quite difficult to see such a small crack next to the arc and it will give the weld bead a slightly flatter appearance. Step 6 Clean all the cracks again with acetone, On the inside as well as the outside, to remove any possible weld contaminants. The frame is now ready for welding and tomorrow is the big day.