half shaft design

[hoba]

Hey guys about the half shaft design i choose 4340 alloy steel and the diameter of the shaft will be 19.3 mm and it will be solid shaft the torque of the engine is 55 N.m and the reductions ratio will be 20.3 i want to know if my design is true or not?????

t=16T/pi*D^3
t=shear stress
T=total torque on the shaft
D=diameter of the shaft
i make the calculation and the t=776 Mpa
and the 4340 has a tensile strength of 861 MPa in the normalaized condition so its allowable shear strength will be 861*.66=568.26 MPa
so the design will not be safe
Can I heat treat the shaft to rise its tensile strength to 1800 and divided by 1.5(safety factor) and multiply it with .66(to convert it to shear strength ) the number will be 594 Mpa and it will be safe
plz help meeeee I think I do it the wrong way

[hoba]

Hey guys about the half shaft design i choose 4340 alloy steel and the diameter of the shaft will be 19.3 mm and it will be solid shaft the torque of the engine is 55 N.m and the reductions ratio will be 20.3 i want to know if my design is true or not?????

t=16T/pi*D^3
t=shear stress
T=total torque on the shaft
D=diameter of the shaft
i make the calculation and the t=776 Mpa
and the 4340 has a tensile strength of 861 MPa in the normalaized condition so its allowable shear strength will be 861*.66=568.26 MPa
so the design will not be safe
Can I heat treat the shaft to rise its tensile strength to 1800 and divided by 1.5(safety factor) and multiply it with .66(to convert it to shear strength ) the number will be 594 Mpa and it will be safe
plz help meeeee I think I do it the wrong way

[kcapitano]

Hi hoba

Try using the 'find' function on these forums. There are a number of good threads on half shaft design, heat treatment and whatever other questions you might have. (They certainly helped me)

Regarding your calculations:

1) Half-shafts are a problem of fatigue strength, not tensile strength, so the allowable torque will be much less than you think.

2) If you are asking whether or not 4340 can be heat treated, it can and there are books that can explain it better than me. Engineer to Win would be a good start.

3) Why did you choose a FOS of 1.5? If you just pulled it out of your behind then it's mostly useless.

4) 1800/1.5X0.66 does not equal 594, so where did that number come from?

Good luck