Strain Gage Methods for Determining Stress Intensity Factor of the Edge Cracks in the Strip Subjected to Transverse Bending. 1st Report. Analysis of Single Edge Crack and Double Edge Crack.

Abstract

This paper describes the strain gage method for determining the stress intensity factor of a edge crack in a strip subjected to transverse bending. The kinds of edge crack are single edge crack and double edge cracks. This paper proposes two methods of stress intensity factor analysis. One of them is the method using only one datum of the nearest gage at the crack tip (1 point gage method), and the other is the method using 5-gage data in the extrapolation (5 point gage method) . The strain gages used in this paper are super-small-sized strain gages consisted of 5 grids, gage length 0.15 mm and pitch of gages 0.5 mm. The 4-point bending tests of a strip were carried out using the universal testing machine. For the single edge crack, the accuracy of the stress intensity factors determined by the experiments are within ±10 percent, except for the data of crack length a/W=0.1 by the 5 point gage method, compared to the analytical values. For the double edge cracks, the accuracy is within ±16 percent.