Continuum damage model of low-cycle fatigue and computation of ultimate strength of locally fatigue damaged plates under uniaxial compression

Abstract

The aim of this study is to present a simple method to assess the effects of locally low-cycle fatigue (LCF) damages on the reduced ultimate strength of unstiffened ship plate structures. A LCF damage model is formulated and then it is applied to the finite element analysis (FEA) in order to identify the continuum damage mechanics (CDM) theory to be introduced in the ship structure designs. A series of non-linear FEA of simply supported plates with various locations and sizes of damages have been carried out. The large deformation theory is utilized during plastic material conditions. Based on the FEA results, an analytical formula is derived for estimating the reduced ultimate strength of ship plates with localized damages under uniaxial compression. In the assessment method, the reduced elastic modulus E^˜ is defined to calculate the material damage and the effective width b^˜ is defined to calculate the plate cross sectional area damage. A comparison between the predicting formula results and the FEA results is made for a bulk carrier's bottom plate. The presented approach is applicable for a uniaxial stress state and it is used throughout this study.