Development and analysis method of single element strain gage for stress intensity factor analysis in crack opening mode (Verification of analysis accuracy by simulated crack)

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.