Strain gauge method is one of the essential and fundamental methods in experimental stress techniques that uses the resistance of the material to determine the stress at a point. The strain gauges can be used in a different combination called Rosette to obtain stress in various directions. This chapter intends to cover types of strain gauges, materials, and Rosette arrangements to provide the reader with an overview of the techniques. The chapter will discuss the basic physics behind the resistance measurement and take the reader into insights on how the developments were made to the application of strain gauges as experimental techniques.
TopResistance Of A Conductor
The ability of the material to resist the flow of electric current is measured as resistance (R). The unit of resistance is given in ohms (Ω), to credit the German scientist Georg Simon Ohm (1784-1854) who studied the relation between voltage, current, and resistance (Bhattacharya, 2011). The resistance of a conductor is given below:
(1) where
L is the length of the conductor, and
A is the cross-sectional area (Figure 1) and the specific resistance of the materials. The specific resistance is material-dependent and the values for general materials are available in the literature.
TopStrain Sensitivity Of The Wire
The strain sensitivity of a material refers to the change in the resistance of the material for a change in the strain. The strain sensitivity of the wire can be evaluated by differentiating Equation 1 as follows:
(2)In Equation 2, the last term dA/A can be written in terms of dL/L by considering Poisson’s ratio. For a wire of diameter D, area A is given as follows:
(3)The result of the differentiation of Equation 3 is:
(4)Further, by the Poisson’s ratio (υ) of the material:
(5)By substituting Equation 5 into Equation 4, the result is:
(6)Now, Equation 1 can be rewritten as follows:
(7)