Two-Element Tee (90-degree) Rosettes

Consider first the two-gage 90-degree rosette, with the gage axes aligned with two orthogonal axes, x and y, on the test surface. When using this type of rosette, the x and y axes would ordinarily be the principal axes, but this need not necessarily be so. The correct strains along any two perpendicular axes can always be calculated from the following equations in terms of the indicated strains along those axes:

  Eq. (509.6)

  Eq. (509.7)

where:

  = the indicated (uncorrected) strain from gage no. 1.
  = the indicated (uncorrected) strain from gage no. 2.
  = corrected strains along the x and y axes respectively.

( Note : Generalized correction equations for any combination of transverse sensitivities are given in the Appendix .)

The term in the denominators of Equations (509.6) and (509.7) is generally in excess of 0.995, and can be taken as unity:

  Eq.(6a)
  Eq.(7a)

Data reduction can be further simplified by setting the gage factor control on the strain-indicating instrumentation at instead of , the manufacturer's gage factor. Since,

Equations (6a) and (7a) can be rewritten:

  Eq. (6b)
  Eq. (7b)

where:

  = strains as indicated by instrumentation with gage factor control set at  

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