Effect of Adhesive Type on the Measurement of Modulus of Elasticity Using Electrical Resistance Strain Gauges

This study aims to point out the importance of adhesive type on strain measurement and examine the accuracy of the modulus of elasticity determination using the electrical resistance strain gauges glued on solid materials, i.e., rock and concrete. For this purpose, the effect of adhesive type on the strain gauge applications and measurements was investigated as there is no standard adhesive type for such uses in standards. Four different adhesives were used in experiments, three of which (cyanoacrylate, polyester and epoxy-based adhesive) can be widely seen in the literature. Ordinary Portland cement paste was prepared to obtain homogeneous material for sensitive measurements and comparisons. Additionally, rock core samples were tested in this study. Experimental results indicated that strain gauges used with same adhesive gave consistent deformation values for the same type of rock and paste specimens. However, remarkable deformation measurement differences up to 110 % were obtained for same paste and rock specimens when different adhesives were used. Numerical analysis via finite element method was also carried out to examine the type of adhesive and interlayer thickness. Up to 51 % strain loss obtained through the numerical models for the adhesive interlayer also pointed out that adhesive type must be taken into account in experimental studies since there is no adhesive guide for users in standards. According to the obtained results from experimental and numerical analyses, cyanoacrylate suggested the most accurate results among the adhesives owing to the thin and homogenous adhesive interlayer between the strain gauge and specimens.