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At which of the following internal pressures will the cylindrical vessel yield as per the Tresca criterion if the yield strength of the material in tension is 320 MPa

  • A.3.55 MPa
  • B.7.1 MPa
  • C.1.775 MPa
  • D.4.0 MPa

Answer: A

The vessel yields at an internal pressure of about 3.55 MPa.

In a thin cylinder the principal stresses are the hoop stress, the axial stress (half of it) and a negligible radial stress. Tresca says yield occurs when the largest difference of principal stresses reaches the tensile yield strength; here that is hoop minus radial:

\[ \begin{aligned} \sigma_{h} &= \frac{pr}{t} = \frac{p(1800)}{20} = 90p \\ 90p &= 320 \Rightarrow p = 3.55\ \text{MPa} \end{aligned} \]

7.1 MPa uses the hoop-minus-axial difference (45p) as if the radial stress were not the minimum. 1.775 MPa is half the correct value, and 4.0 MPa does not follow from the hoop stress.

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