Volume 2, Issue 3 (May 1974)
Strain Measurement Techniques for Fiber Modulus Determination
Two techniques were employed to measure the tensile strain of Kevlar-49® organic fiber in an epoxy matrix. One, a direct averaging strain method, uses two linearly variable differential transformers whose hollow cores are supported by glass beads bonded to the fiber strand specimens. The other method is an indirect method using specimens of several gage lengths. The crosshead displacement for selected loads was determined for each gage length and the data were fit to a straight line by a least squares method and the unit strain calculated for each load.
The tensile modulus of the Kevlar-49® fiber strands was determined to be 20 × 106 psi (138 × 106 kPa). The variation of the averages between methods and within methods between specimens was less than five percent.