TWI Industrial Member Report Summary 369/1988
By S W K Chan and P J Tubby
The application of fracture mechanics assessment methods for assessing the significance of defects in welded construction requires accurate determination of stress intensity solutions for typical joint configurations. At present, numerical methods such as finite element analysis are most widely used. 'Thermoelastic technique (SPATE) is a new expenmental stress analysis technique based on the measurement of infrared radiant flux emitting from the surface of a body under cyclic stress. It has been shown elsewhere that accurate stress intensity solutions can be derived from SPATE results obtained by scanning a cracked body with simple geometry under mode I and mode II loading. Hence, the SPATE method offers an alternative to numerical analysis, or a means of validating the numerical methods. In addition, it is anticipated that the new technique could be used for analysing a cracked body with complex geometries not easily analysed by numerical methods, for example semi-elliptical surface cracks in plates and cylinders, or tubular connections with weld toe cracks.
In the present study, the SPATE technique has been applied to the case of a weld toe crack in a transversely stressed fillet weld geometry. A method of analysing the stress pattern to obtain both mode I - and II stress intensities was developed. The results are comnared with those obtained using The Welding Institute's finite element program, and the practical application of the SPATE technique in the determination of stress intensity factors is critically reviewed.