analysis effort in section - von mises

[meccanicamg]

So... I read the messages.... I think I can add something more...

I think I understand that what you did is to find a formula that allows you to determine beforehand a diameter of your rod and then then to verify it according to von mises....
for this reason you have thought about your Pythagoric method considering individual stresses and for each obtaining a diameter after that, by means of an average you have pulled out a value... .
My conclusion here is that the formula is absolutely unreliable. . (need to do tests with different loads to see that it will give values of over or underestimated diameters variable even much)... but then why use this road when using the formula of von mises in the design phase we obtain directly the result sought?? ? ?

that is why apply a formula (which you don't know how reliable it is) to get a preventive result that then must be verified when I can get the exact result directly?? ? ?

The only doubt that there can be is that one of the four points chosen to execute the design is not the most stressed point... In this case, just prepare a spreadsheet and set up a set of equations through which it will be immediately possible to determine this point.

exactly the formula is an empirical/experimental method to dimension very quickly, taking into account the various internal actions. to apply correctly von mises it is necessary to place itself in the hypothesized point of maximum effort, to correctly hypothesize the signs of the various internal actions (the maximum point is almost never that where it sees to be added both the sigma and the tau) and it is discreetly a flapping to apply it correctly especially by hand for a simple sizing. for this reason a very simple calculation of media pitagorica could speed up just the thing.

to find the maximum point would be interesting to develop in excel.. .

 

[peloritano]

Then I made a simple program with a spreadsheet... just change the stresses and in less than a second comes out the sizing of the section of the auction.. .
the conclusions that can be made are always the same.. .

what sense does it make to use a preventive sizing method (i.e. what you did that is not absolutely reliable) when properly setting equations you get the solution??

after sizing the section using the stresses according to von mises in the four canonical points I determined the maximum diameter to be assigned to the beam (32mm).. at this point (I see that for convenience' the diameter of the beam will be an even greater number than that exited from the calculations) I designed the trend of the tension of von mises along the entire outer circumference of the section and put on the same chart the admissible voltage. . as it is intuitable in all points the stress is maintained lower than the admissible voltage. . .
I have also set the equations to analytically determine the most stressed point (which I would dare to say at this point not necessary)

As soon as I have a moment of time I will try to deepen better how much discussed in the other thread

p.s. for the moment having not seen the other discussion here I used a single value of the admissible voltage

 

[meccanicamg]

My problem is to determine the correct k correction coefficient. I'm testing but I'm not able to find the law of correction.

As far as the maximum solicited point method is concerned, I understood the operation.

 

[peloritano]

I'm sorry, but I don't understand, if by correction coefficient k you mean something that you've been talking about in the other discussion, I can't say why I haven't read it carefully yet. If you mean it as a degree of security you can discuss

 

[meccanicamg]

I'm sorry, but I don't understand, if by correction coefficient k you mean something that you've been talking about in the other discussion, I can't say why I haven't read it carefully yet. If you mean it as a degree of security you can discuss

k is a correction factor that in my curves is used to translate the safety coefficient that normally takes (3 for fragile, 1.5 for ductiles etc) and has different formulations depending on the type of stresses present. I am doing some tests with the various individual actions, coupled and mixed to find the k calculation rule.

 

[meccanicamg]

Then I made a simple program with a spreadsheet... just change the stresses and in less than a second comes out the sizing of the section of the auction.. .
the conclusions that can be made are always the same.. .

what sense does it make to use a preventive sizing method (i.e. what you did that is not absolutely reliable) when properly setting equations you get the solution??

after sizing the section using the stresses according to von mises in the four canonical points I determined the maximum diameter to be assigned to the beam (32mm).. at this point (I see that for convenience' the diameter of the beam will be an even greater number than that exited from the calculations) I designed the trend of the tension of von mises along the entire outer circumference of the section and put on the same chart the admissible voltage. . as it is intuitable in all points the stress is maintained lower than the admissible voltage. . .
I have also set the equations to analytically determine the most stressed point (which I would dare to say at this point not necessary)

As soon as I have a moment of time I will try to deepen better how much discussed in the other thread

p.s. for the moment having not seen the other discussion here I used a single value of the admissible voltage

I've been thinking about the four quadrants, but there's something wrong with me:
- sigma z date i.e. that due to n is constant (ok with you)
- tau z is given by the long twist z, mz. therefore it is constantly tangent to the circumference.

Why don't I find myself with mz? Why do you have moments in your accounts?

 

[peloritano]

for the reason you said... mz from place to a tangential tension that is constantly tangent to the circumference. . I bet according to x and y axes and the result is what I wrote (including sign)

 

[meccanicamg]

incorrect corrige post #2 to solution.jpg picture 3:
max = tauz+ tauxand not with the minus sign as I wrote in the image

 

[EdS]

Sorry if I write under this old post, but it seems to me that the maximum cutting formula for a circular section (referred to the figure I attach and found above) is 4/3*t/a and not 16/3*t/a.

 

[EdS]

That's right, sorry. I didn't look at the diameter.

 

[biz]

Sorry if I write under this old post, but it seems to me that the maximum cutting formula for a circular section (referred to the figure I attach and found above) is 4/3*t/a and not 16/3*t/a.View attachment 67641

max in circular section is 4/3 t/a. comes 16 because it multiplies with the 4 of the formula of the area.