Measuring the Stress Intensity Factor for Propagating Cracks with Strain Gages

A new method for measuring the K value of a straight crack propagating in an isotropic plate is presented. A row of strain gages is placed at a constant distance above the crack line, and each gage is oriented to eliminate the second (B0) term in a three-term representation of the strains. The method of analysis then provides a solution with three-parameter accuracy. Both static and dynamic analyses were performed, and the differences between the two were found to be small for crack velocities less than 0.3cR. The method was demonstrated with an experiment on 4340 alloy steel, and results for K at a crack velocity of 656 m/s were obtained.