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donniemateno
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ladies and gents
I have been set a question for homework which is one where if you get one part wrong then the rest of your answers are in correct. It is a 3 questions in one question and i have answered 1 and 2 but can't seem to do part 3
the question is
A torque T = 75Nm is applied to a thin-walled steel tube having a rectengular cross-section of 12mm by 72mm . the tube has a constant wall thickness of 4mm . calculate shear stress at the wall and the factor of safety using tresca theory assuming the yield strength is 180 MPa. using the table below ( I've attached as a jpeg) work out the maximal stress and calculate its value.
i have got :
used the formula t(shear)=T/(2tAm)
so 75/2*(0.04)*(12*72) = 10.9 MPa or rounded up to nearest whole 11 Mpa
Tresca theory
first work out hoop stress which is 11mpa * (0.72*0.012/0.004) = 2376 n/m^2 ( seems really high) divide my 180 mpa by this i get a fos = 0.76 so a fail?
part 3 of the question
the formula to use is tmax = T/(k1bt^2)
where b is the longer side of the strip
t is the shorter side thickness of tube
k1 is the empircal constant depending on the ratio of b/t and is obtained using the table ( attached as jpeg)
so bt on mine is ( this is a guess) by multiplying the 72mm by the 4mm and using the number on the table closest to mine? i got 288 so i have used 4 = b/t and k1 = 0.282
putting the numbers into the equation 75/(0.282*4^2) = 16.62Mpa
I have been set a question for homework which is one where if you get one part wrong then the rest of your answers are in correct. It is a 3 questions in one question and i have answered 1 and 2 but can't seem to do part 3
the question is
A torque T = 75Nm is applied to a thin-walled steel tube having a rectengular cross-section of 12mm by 72mm . the tube has a constant wall thickness of 4mm . calculate shear stress at the wall and the factor of safety using tresca theory assuming the yield strength is 180 MPa. using the table below ( I've attached as a jpeg) work out the maximal stress and calculate its value.
i have got :
used the formula t(shear)=T/(2tAm)
so 75/2*(0.04)*(12*72) = 10.9 MPa or rounded up to nearest whole 11 Mpa
Tresca theory
first work out hoop stress which is 11mpa * (0.72*0.012/0.004) = 2376 n/m^2 ( seems really high) divide my 180 mpa by this i get a fos = 0.76 so a fail?
part 3 of the question
the formula to use is tmax = T/(k1bt^2)
where b is the longer side of the strip
t is the shorter side thickness of tube
k1 is the empircal constant depending on the ratio of b/t and is obtained using the table ( attached as jpeg)
so bt on mine is ( this is a guess) by multiplying the 72mm by the 4mm and using the number on the table closest to mine? i got 288 so i have used 4 = b/t and k1 = 0.282
putting the numbers into the equation 75/(0.282*4^2) = 16.62Mpa