No abstract

There are currently one or two kinds of strain gages to measure the stress intensity factor. It might not be sometimes easy to analyze the stress intensity factor with those gages. In this paper, it is reported that our development of the new stain gage enables us to measure the stress intensity factor more easily and practically. The following features of this strain gage to evaluate the stress intensity factor are presented in this paper. (1) Strain component ε r measured around the crack tip is used to calculate the stress intensity factor. (2) To be more specifically, we employed the first and second terms of the series at the strain component ε r around the crack tip for an evaluation of the stress intensity factor. The calculation method with using our developed strain gage does not require the crack length. The newly developed strain gage was bonded to around the crack tip of the specimens, where cracks were of the opening mode or the mixed mode. We carried out tensile tests on the test pieces bonded with the gage. In conclusion, the results indicate that the developed strain gage enables us to measure stress intensity factor with an error margin within ±10% of the analytical values.

A dedicated strain gage has been developed to measure the stress intensity factor of cracks. Conventional strain gages dedicated to stress intensity factor analysis have been made by combining multiple elements into a single gage. Therefore, it took time and effort to analyze the stress intensity factor. Therefore, in this research, we have developed a dedicated strain gage that can analyze the stress intensity factor more easily than before with only one gage of one element. The developed strain gage analysis formula uses the strain component εθ formula at the crack tip. We focused on the gage angle θ that brings the second term of the crack analysis strain component εθ close to 0. By setting the second term to 0, the stress intensity factor of the first term can be analyzed accurately in consideration of the second term. The developed gage has a donut shape with radii r1 and r2 and a width of 1 mm with the crack tip as the origin, and the gage grid angle has an angle from 0 ° to 52 °. A tensile test piece with a crack opening mode load was manufactured and a tensile experiment was conducted. The experimental value of the stress intensity factor was obtained within an error of ±10% from the theoretical value.