Low cycle fatigue life prediction of thin stiffened plates under repetitive stresses

Repetitive stresses can have a significant influence on the fatigue lives of stiffened structures. A method for the assessment of fatigue lives of a series of rectangular perfectly flat stiffened plates is described which is based on a fracture mechanics approach. Stiffened plates are selected from the deck structure of real sea going ships and inland waterway vessels. The main portion of ship’s structure is usually composed of stiffened plates. Between girder and floors, stiffeners are furnished to plates usually in the longitudinal direction. Under various loads applied to a ship, such as those due to cargo, buoyancy and waves, these stiffened plates are subjected to fluctuation in combined in plane and lateral loads. In present work a series of detailed numerical analysis of stiffened plates subjected to fluctuating lateral loads are performed for different stiffener arrangements by finite element approach using general purpose software (ANSYS). The results are plotted on a unique curves of number of life cycles, N, versus number of stiffeners of varying depth for thin plates. The results of this analysis are used to influence improvements in the design. Finally an optimized stiffener arrangement for the design fatigue life is expressed in explicit form based on the results of numerical investigations of the non-linear behaviour of stiffened plates by means of the fracture mechanics approach