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8–6. Determine the maximum force P that can be exerted on each of the two pistons so that the circumferential stress in the cylinder does not exceed 3 MPa. Each piston has a radius of 45 mm and the cylinder has a wall thickness of 2 mm.

Respuesta :

Answer:

[tex]P=2.66\ N[/tex] is the maximum safe load.

Explanation:

Given:

  • diameter of the cylinder, [tex]d= 90\ mm[/tex]
  • thickness of the cylinder wall, [tex]t=2\ mm[/tex]
  • maximum bearable stress, [tex]\sigma=3\ MPa[/tex]

Firstly we find that:

[tex]\frac{t}{d} =\frac{1}{45} <\frac{1}{20}[/tex]

⇒ This is a thin cylinder.

We know axial stress and hoop stress is given by

[tex]\sigma_a=\frac{P.d}{4t}[/tex]

[tex]\sigma_h=\frac{P.d}{2t}[/tex]

⇒ Axial load will always be larger than the circumferential load under while other parameters are same.

So we find the load in case of axial stress:

[tex]30=\frac{P\times 90}{4\times 2}[/tex]

[tex]P=2.66\ N[/tex] is the maximum safe load.

Answer:

The maximum force is 846.11 N.

Explanation:

Given that,

Stress = 3 MPa

Radius = 45 mm

Thickness = 2 mm

We need to calculate the internal pressure

Using formula of internal pressure

[tex]\sigma=\dfrac{p\times r}{t}[/tex]

[tex]p=\dfrac{\sigma t}{r}[/tex]

Put the value into the formula

[tex]p=\dfrac{3\times10^{6}\times2\times10^{-3}}{45\times10^{-3}}[/tex]

[tex]p=0.133\times10^{6}\ Pa[/tex]

We need to calculate the maximum force

Using formula of maximum force

[tex]p=\dfrac{P}{A}[/tex]

[tex]P=p\times A[/tex]

Here, P = force

p = internal pressure

Put the value into the formula

[tex]F=0.133\times10^{6}\times\pi\times(45\times10^{-3})^2[/tex]

[tex]F=846.11\ N[/tex]

Hence, The maximum force is 846.11 N.