College

A cylindrical orthopedic pin is fixed at one end and placed under a 1D axial load at the other with force \((f)\). Assume the pin is a LEHI material with a diameter of 2 mm, a length of 2 cm, and a Young's modulus of 2 GPa. How much axial force \((f)\) in Newtons is required to extend the pin by 0.1 mm?

Answer :

Approximately 31.4159 Newtons of axial force would be required to extend the pin by 0.1 mm.


To calculate the axial force required to extend the pin by a certain amount, we can use Hooke's law, which states that the stress (σ) in a material is proportional to the strain (ε) it undergoes. In mathematical terms, this relationship is expressed as:

σ = E * ε

where σ is the stress, E is the Young's modulus, and ε is the strain.

In this case, we want to find the force (f) required to produce a specific strain of 0.1 mm (or 0.0001 m) in the pin. We know the diameter (d) of the pin is 2 mm (or 0.002 m), and its length (L) is 2 cm (or 0.02 m).

The strain can be calculated using the following formula:

ε = ΔL / L

where ΔL is the change in length and L is the original length.

Given that ΔL = 0.1 mm (or 0.0001 m) and L = 0.02 m, we can calculate the strain:

ε = 0.0001 m / 0.02 m

= 0.005

Now, we can substitute this strain value into Hooke's law equation to find the stress:

σ = E * ε

= 2 GPa * 0.005

= 10 MPa

Finally, we need to convert the stress into force. The stress is defined as force (f) divided by the cross-sectional area (A) of the pin:

σ = f / A

Rearranging the equation, we have:

f = σ * A

The cross-sectional area of a cylindrical pin can be calculated using the formula:

A = π * (d/2)^2

Substituting the given values:

A = π * (0.002 m / 2)^2

= π * (0.001 m)^2

= 3.14159 * 0.000001 m^2

= 3.14159e-6 m^2

Now, we can calculate the force:

f = σ * A

= 10 MPa * 3.14159e-6 m^2

≈ 31.4159 N

Therefore, approximately 31.4159 Newtons of axial force would be required to extend the pin by 0.1 mm.

Learn more about Newtons here:

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