FRACTURE INITIATION IN FOAM-CORE SANDWICH STRUCTURES DUE TO SINGULAR STRESSES AT CORNERS OF FLAWED BUTT JOINTS

Defective butt joints in sandwich structures create the presence of 90 degrees corners from which fracture is very likely to be initiated du e to the stress intensification caused by the geometric and material d iscontinuity at the corner. In this article the singular stress field, both the singularity and the stress intensity factors, at the bimater ial corner are computed, and the field amplitudes obtained are then us ed to predict the onset of damage growth ill sandwich beams with bimat erial corners of different material combinations. A parametric study i s used to develop an empirical relation between stress intensify facto rs and geometric and material parameters. Static strength predictions are compared with tests of sandwich beams with simulated defective but t joints, and the correlation is satisfactory. It is concluded that gr eat care must taken in manufacturing to avoid flawed butt joints, whic h have a large influence on the load-bearing capacity.