Study On Fatigue Crack Propagation And Stress Intensity Factor Of Surface Cracks

Fatigue is the main reason to failures of engineering structures and components. It is agreed that the life of a bridge relates to fatigue crack life which initiate as surface crack. Therefore, it is very important to study the propagation of surface crack.Stress intensity factor (SIF) of surface crack is discussed firstly. The empirical equation (Newman-Raju, e.g.) is not available for the SIF solution here, for the surface crack shape is out of the scope of application, or the crack locates where the stress field is irregular. Finite element analysis(FEA) is applied to calculate SIFs. Three numerical examples are calculated and the results are coincident with test data, which means that the FEA method is efficient for SIF solution of surface crack in plates under tensile and bending loads.The SIFs of surface crack located in the box structure are also computed in this thesis. The FEA results are applied to design fatigue test of the box structure. The location of the crack initiation predicted by FEM agrees with the experimental results.The modification to Newman-Raju empirical equations for SIFs calculation of surface crack in plates is brought forward according to FEA results, and the modified equations are useful for the cases that the surface crack extends to large size in either depth or width direction. The crack shapes are predicted based on the modified equation. The results show that the modified equations proposed are efficient, and can be used in other cases.