Local buckling of cracked and pin-loaded plates: Fid-Bau Portal

Local buckling of cracked and pin-loaded plates

Zhuang, W.Z.L. / Baird, J.P. / Williamson, H.M.

The interaction between buckling and fracture may affect crack growth in thin riveted aircraft fuselage structures. Buckling may also complicate and induce the phenomenon of multisite damage in aircraft fuselages. This phenomenon in thin-walled structures is studied through an idealized model, a cracked and pin-loaded hole in a plate. Despite this simplification, a better understanding of the mechanisms of fatigue and fracture in thin-walled structures is obtained by a finite element model and an experiment, using holospeckle interferometry. The experimental studies show the presence of a combination of tearing mode III as well as opening mode I fracture mechanisms at the cracks in the pin-loaded plates after local buckling. The numerical analyses show that holospeckle interferometry and Mindlin element method are powerful tools for investigating fracture buckling of cracked and pin-loaded plates. In the stress analysis of cracked and pin-loaded plates, it has been shown that a high compressive stress concentration is developed near the region at the top of pin-loaded hole and a high tensile stress concentration near the crack tip. The extent and the magnitude of the region of compressive stresses near the top of the pin-loaded hole decrease as the crack length is reduced. When the crack length was reduced to less than 1.0 mm, the extent and magnitude of the region of compressive stress at the top of the pin-loaded hole decrease rapidly. That is, the contact stress field was highly sensitive to crack length for small cracks. Local buckling loads and modes were predicted and measured using holospeckle interferometry and the Mindlin plate FEM. A parametric study has shown that when crack length increases, the value of the critical buckling loads decreases, and the critical buckling loads for the pin-loaded hole of smaller diameter are more sensitive to the crack lengths than those for larger holes. This shows that there is a strong interaction between buckling and fracture under the circumstances investigated. Using holospeckle interferometry, the fringe images have shown, that before local buckling, the fracture mode may be considered as opening mode 1; after local buckling, the fracture mode changes into a combined mode, opening mode 1 plus tearing mode 3.