Experimental and numerical investigation on ultimate strength of double-stiffened plates with pre-existing cracks under extreme axial cyclic loads

Objective Fatigue crack defects readily occur in ship stiffened-plate components during service. Crack evolution under extreme axial cyclic loads considerably changes the ultimate load-bearing capacity of structures. Few existing investigations focus on ultimate-strength evolution of double-stiffened plates with pre-existing cracks subjected to cyclic axial loading. This paper carries out axial cyclic-loading model tests and numerical simulations for cracked double-stiffened plates, to reveal how initial cracks and cyclic-load forms influence failure modes and ultimate strength.

Method Three groups of double-stiffened plate specimens with different pre-existing through-thickness cracks are designed. Axial cyclic-loading mechanical tests are implemented to record deformation history. Parametric analyses are performed to study the effects of crack distribution, accumulative plastic deformation and loading mode on ultimate compressive strength and failure modes.

Results Test results indicate that the ultimate strength of the stiffened plate with symmetrically distributed cracks across the stiffeners is the largest. The ultimate strength of the stiffened plate decreased by about 40% after three cycles of loading when considering the residual deformation under the load conditions set in this experiment. While without considering the residual deformation, the decrease in ultimate strength after three cycles is only within 10%. The reduction is also around 10% when tensile load is included in the cycles.

Conclusion Pre-existing crack defects and high-amplitude cyclic loads synergistically degrade the ultimate bearing performance of double-stiffened plates. The main load-bearing area of the stiffened plate is near the stiffeners, and residual deformation under extreme axial cyclic loading has a significant impact on the ultimate strength of the stiffened plate. The tensile load in the cyclic loading has an enhancing effect on the ultimate strength of the stiffened panel. The established finite-element model satisfactorily reproduces mechanical responses of cracked stiffened plates under cyclic loading. It provides experimental data and simulation tools for residual-ultimate-strength evaluation of ship grillage structures.