Mechanics of Solids 2011 Part 8

Tham khảo tài liệu 'mechanics of solids 2011 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 1-98 Section 1 Gage Sensitivities and Gage Factor The electrical-resistance strain gage has a sensitivity to both axial and transverse strain. The magnitude of the transverse strain transmitted to the grid depends on a number of factors including the thickness and elastic modulus of the adhesive the carrier material the grid material and the width-to-thickness ratio of the axial segments of the grid. Sometimes it is necessary to calculate the true value of strain that includes all contributions from c_ _ R R 1 - vK a Sg 1 Kte K where a is the normal strain along the axial direction of the gage t is the normal strain along the transverse direction of the gage V0 is Poisson s ratio for the calibration beam and Kt is the transverse-sensitivity factor of the gage. The strain gage sensitivity factor Sg is a calibration constant provided by the manufacturer. By using Equations and the percent error involved in neglecting the transverse sensitivity can be calculated. These errors can be significant for large values of both Kt and t a so it may be necessary to correct for the transverse sensitivity of the gage Figure . FIGURE Error as a function of transverse-sensitivity factor with the biaxial strain ratio as a parameter. Strain Analysis Methods Electrical-resistance strain gages are normally employed on the free surface of a specimen to establish the stress at a particular point on this surface. In general it is necessary to measure three strains at a point to completely define either the stress or the strain field. For this general case where nothing is known about the stress field or its directions before experimental analysis three-element rosettes are required to establish the stress field. This is accomplished by using the three-element gage with orientations at arbitrary angles as shown in Figure . Using this setup the strains x e and gxy can be determined. These values can be used to determine the principal strains .

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