dimensioning

[viper]

Hello everyone, I find myself having to size a forged car rim.

I designed it with pro/e software and fem it with pro/mechanica.

I have woheler curves of my material with relative substance curves of 10% and 90% with confidence in the data of 95%.

once I know the number of cycles for which it must resist the rim, within my curve and determine the sigma value of the admissible voltage.
Supposing that it takes as a voltage value that relative to the curve to 90% of chances of substance, how much longer do I have to lower my voltage value to be safe?

in my machine construction book tells me to divide the admissible voltage for the worsening coefficients kd, kl, kf, kv, where respectively are:
kd coefficient taking into account the size
kl coefficient that takes into account the surface finish
kf coefficient taking into account the shape effect
kd coefficient taking into account the applied stress

My considerations are as follows:
kd = 1.5 because rim is size > 300mm
kl = 1.15 because rim obtained from mechanical labor
I have no idea!
kv = 1 because rotary bending

Now I ask you whether my considerations are correct and whether it still has to add a security factor or not.

thanks for the help

 

[MacGG]

Hello Viper,

Do you know the rims break for side and front impact?

do you know that there is a law in this regard which defines such conditions that the cechyon must overcome?

If a situation of this type happens, and a clique occurs, the model can be optimized in order to avoid propagation.

Therefore, a fatigue analysis of this type, on car wheels, does not need.

Hi.

♪

 

[viper]

Hello, macgg,

the rims do not break exclusively for side or front bump.
automobile manufacturers require to check the rim for rotating bending and rolling as a minimum more tests such as impact and lbf tests.

the demands are that the rim resists rotary bending to x cycles for a certain f load. That's why my question.

I don't know anything about the rules you're talking about, if you're telling me a huge favor (unless you're not talking about the tuv prescriptions)

I hope I've explained and I'm sorry for the answer you gave me.

Hi.

viper

 

[MacGG]

Hello Viper,

I haven't read your last one.

Anyway, I'm telling you,
if you refer simplemnete to the wohler curves and calculate the tension through a fe software, you do not have to take into account all the parameters that are defined by the construction manual, in which you already have a relae model and not idealized as an ideal beam. therefore the only parameter that you have to take into account, is that related to the type of processing, although personally, I already use the wohler curves characterized as well as from the material, also from how the object is produced (for fution) and what kind of mechanical processing has done (fresh, turning, lapping, ...). so in your case, use only kl=1.15, all others put them to 1. now for the safety factor (or stupidity, as it would be better to say), since noe exists a normative parameter in this sense, I would consider it as a generic organ in motion and therefore k=1.5.

As regards legislation, I mean that for certification, so for example that of the tuv; you will see that in order to satisfy it, it will not be important to satisfy the aspects of fatigue, as to the aspects I mentioned to you.

Hi.

♪