Volume 18, Issue 1 (January 1990)
The Linearity of Clip Gages Used in Fracture Mechanics Tests
The measurement of displacement in fracture toughness tests is generally accomplished using clip gages. This paper describes an experimental study to examine the performance of a number of clip gages. It is shown that double cantilever clip gages exhibit a non-linear response. The degree of non-linearity is shown to vary with temperature. In relation to fracture mechanics test methods it is demonstrated that in some instances relaxation of the test standards is required to-encompass the gage performance. Where data can be stored digitally, the non-linear response can be accounted for using a third-order polynomial calibration. An analytical study shows that the non-linearity is inherent for the large displacements often incurred in fracture mechanics tests.