Abstract:

In the post-buckling mode, fatal failure of a composite stiffened panel is easily induced by the separation of a skin stiffener interface,because the local buckling of the skin will cause the stringer to withstand an out-plane bending load. In this paper, four-point bending tests are performed to simulate the interface properties between the skin and the stringer after post buckling, and a progressive damage model is presented to study the interface failure mechanism and the failure process of the composite hat-stiffened panel structure which takes into consideration both the glued interface and laminate failure with a material stiffness degradation model. The numerical results are in good agreement with the experimental data, which shows that the loading span greatly affects the failure of the structure. In the 90 mm loading conditions, the adhesive layer initially failed near the inner chamfer of the web and skin, and it is mostly influenced by the Ⅱ shear mode. In the 150 mm loading conditions, the adhesive layer initially failed near the free edge of the flange, and it is mostly influenced by both the tensile mode and the Ⅰ and Ⅱ shear mode when the stringer is tensile, and influenced by the Ⅱ shear mode when the stringer is compressed. After the interface was debonded, delamination occurred on the tensile stringer chamfer between the web and the flange with increasing load, which is consistent with the ultrasonic B-scan results.

Key words: omega stringer, skin/stiffener debonding, progressive damage, visual crack closure technique, energy release rate