Question

Advance (also called Constantan) has a strain sensitivity SA=2.1 for strain as large as 8%. Determine the amount of contribution due to the change in specific resistance to SA in the elastic region (Poisson's ratio v=0.30) and plastic region (Poisson's ratio v=0.30).

Answer 1

Answer:

$\frac{dP}{P} = 6.25$

Explanation:

Given data:

Sa = 2.1

$R = \frac{pl}{A}$

$\frac{dR}{R} =\frac{dP}{P} +\frac{dL}{L} (1_2V)$

$\frac{dR}{R} =\frac{dP}{P} +\epsilon (1_2V)$

$Sa = \frac{\frac{dR}{R}}{\epsilon} =\frac{\frac{dP}{P}}{\epsilon} +\frac{\epsilon (1_2V)}{\epsilon}$

$Sa = (1+2v) + \frac{\frac{dP}{P}}{\epsilon}$

change in specific resistance is given as $\frac{dP}{P}$

$\frac{dP}{P} = \frac{Sa -(1-2v)}{\epsilon}$ ........2

where v  is elastic range = 0.30

$\epsilon = 0.08$

$\frac{dP}{P} = \frac{2.1 -(1-2\times 0.30)}{0.08}$

$\frac{dP}{P} = 6.25$