A Photoelastic Technique to Predict the Direction of Edge Crack Extension using Blunt Cracks

Determination of Predominantly Mode Ii Stress Intensity Factors From Isochromatic Data

“…A comparison is also possible between the perigee angles of the experimental and theoretical fringe patterns, and the results of Bowie where the perigee angle is calculated from the ratio of stress intensity factors using the following expression [20]:…”

“…which produces K,,/K, values ranging between zero and approximately unity. Details of the different geometries analysed are shown in Table 2; further information of the specimen preparation is given in Ref, 20. The loading was uniform tension applied to each end of the plates via steel clamps fixed to a tensile testing machine.…”

“…This process continues until convergence to within a specified degree, usually in terms of the SIFs, is obtained. Now the problem with this solution methodology is that it is often difficult to obtain convergence [4,20]. In the authors' experience this is because the approximations found from a previous step do not always correlate to the solutions in the next step.…”

“…Since it is required that gi = 0 expression (18) can be re-arranged to give: From this point it is more convenient to describe the process using matrix notation. Expression (I 9) becomes: (20) where: It was found using the function g defined by Sanford and Dally (expression 15) that the solutions to A , and BN were more dependent on the data points from the fringe of the highest fringe order value which invariably is data which is closest to the crack tip. There is some advantage in using a solution routine that fits more closely to the data points nearest to the crack tip because they are more likely to be within the region that can be described by the stress field equations.…”

Experimental Determination of Stress Intensity Factors for Cracks in Turbine Discs

“…The determination of stress intensity factors using two-dimensional photoelasticity has almost been fully optimized [ 1-31. Techniques that predict the directions of crack growth have also been developed [3,4] in line with the need to assess the likely mode of failure, particularly in aircraft structures.…”