Gage Length

Of the preceding parameters, the gage length and pattern are normally the first and second selections to be made, based on the space available for gage mounting and the nature of the stress field in terms of biaxiality and expected strain gradient. A good starting point for initial consideration of gage length is 0.125 in (3 mm). This size offers the widest variety of choices from which to select remaining gage parameters such as pattern, series and resistance. The gage and its solder tabs are large enough for relatively easy handling and installation. At the same time, gages of this length provide performance capabilities comparable to those of larger gages.

The principal reason for selecting a longer gage would commonly be one of the following:

• greater grid area for better heat dissipation;
• improved strain averaging on inhomogeneous materials such as fiber-reinforced composites; or
• slightly easier handling and installation [for gage lengths up to 0.50 in (13 mm)].

On the other hand, a shorter gage length may be necessary when the object is to measure localized peak strains in the vicinity of a stress concentration, such as a hole or shoulder. The same is true, of course, when the space available for gage mounting is very limited.

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