Out-of-plane bending stress intensity factor analysis of cracks in a strip using single-element strain gage

Abstract

In recent years, the authors have developed a dedicated strain gage (hereafter referred to as a K-value gage) and an analysis method that can analyze the stress intensity factor of a crack with a single element. The developed single-element K value gage can obtain the opening mode stress intensity factor of the simulated crack within ±5% of the theoretical value. In this study, using this single-element K-value gage, a simulated crack was inserted into one side edge of the strip and an attempt was made to analyze the stress intensity factor when an out-of-plane bending load was applied. M.L.Williams introduced the stress equation for the out-of-plane bending load acting on a strip crack. In this study, the stress equation was converted into the strain εθ equation, and the K-value gage equation was derived. The K-value gage formula defined a K-value gage grid angle of 104 degrees for a Poisson's ratio of 0.3. In order to examine the validity of the derived strain gage equation, out-of-plane bending experiments were carried out on strips with simulated cracks inserted. When a/W=0.2 and 0.3, the crack length a with respect to the strip width W was obtained within ±10% of the theoretical value. When a/W=0.1, the error was 10-15%.

Keywords

• experimental stress analysis
• strain gage
• stress intensity factor
• fracture mechanics
• crack
• experimental mechanics
• stress concentration
• nondestructive inspection
• stress-strain measurement