written 7.9 years ago by | • modified 4.6 years ago |
1000 kg/$cm^2$. The modulus of elasticity of the metal is 2 × ${10}^6$ kg/c$m^3$. Calculate the percentage change in the resistance of the strain gauge. What is the value of Poisson’s ratio?
written 7.9 years ago by | • modified 4.6 years ago |
1000 kg/$cm^2$. The modulus of elasticity of the metal is 2 × ${10}^6$ kg/c$m^3$. Calculate the percentage change in the resistance of the strain gauge. What is the value of Poisson’s ratio?
written 7.9 years ago by |
Gauge Factor $G_f$=2
Stress =1000 kg/$(cm)^2 $
Modulus of elasticity=ε=2×$(10)^6$ kg/$(cm)^3$
Formulae –
Modulus of elasticity=ε=$\frac{Stress}{Strain}$
Change in Resistance=$∆R=G_f$×Strain
Poisson's ratio=$μ=(G_f-1)/2$
Solution –
Before we calculate the change in resistance, we have to deduce the value of strain. Strain is given by the ratio of stress and modulus of elasticity,
Strain=$\frac{Stress}ε$
=$\frac{1000}{(2×10^6 )}$
=500×$10^{(-6)}$
Strain=500 μm⁄m
Now, change in resistance is given by,
∆R=$G_f$×Strain
=2×500 μ
∆R=1 ×$(10)^{(-3)}$
Change in resistance in percentage,
Therefore, change in resistance is 0.1%.
Further, Poisson’s ratio is given by,
$μ=\frac{(G_f-1)}2$
$μ=\frac{(2-1)}2$
μ=0.5
With this value, it is evident that the metal has a Poisson’s ratio in the upper limit which is 0.5. Generally, Poisson’s ratio always falls between 0 and 0.5. For gold, it is between 0.42 and 0.44; for copper, it is 0.33; and for steel, it is between 0.27 and 0.30.
For the given figures, the change in resistance is 0.1% and the Poisson’s ratio is 0.5 or $\frac{1}2$.