Fatigue Assessment Of Components Research Articles

Comparison of the continuum damage and fracture mechanics in fatigue assessment of components containing residual stresses

In the present study, the fatigue crack growth life of standard and smooth notched specimens containing residual stresses are evaluated based on the continuum damage and fracture mechanics approaches. It is indicated that fatigue crack growth lives assessed by the continuum damage model are closer to the experimental results, with a difference of <10% in the specimens containing residual stresses. The total stress intensity factor range is used to consider the effects of residual stresses in the estimation of fatigue crack growth life based on the fracture mechanics. It is found that in existing residual stresses, the stress intensity factor is not a proper parameter to evaluate crack tip zone. Fatigue crack initiation life is experimentally obtained based on assessing variations of the slope of unloading curve in the force-displacement diagram of fatigue experiments. The cycle including a change in the slope is considered as fatigue crack initiation event. Isotropic and kinematic hardening parameters of ASTM A516 pressure vessel steel are considered in finite element analyses. Tensile residual stresses are introduced into the notched specimens by employing four-point-bending with a magnitude of around 90% of the yield stress of the material. The results indicate that at least 65% of the fatigue life of the specimens is decreased due to the presence of tensile residual stresses. Tensile residual stresses are measured using the hole-drilling technique.

01.16: Fatigue behaviour analysis of bolts in tee‐stub steel connections

ABSTRACTHigh strength bolted joints are efficient systems commonly used in a large set of industries as railway industry, steel construction, offshore structures or wind power structures. In recent years the lightening of steel structures has become of major concern and generates the need for higher material properties. Therefore the fatigue assessment of components is essential in order to ensure the reliability and the safety of structures using bolted connections.Tee stubs are elementary components used in the actual standard EN‐1993‐1‐8 to predict the mechanical behaviour of steel bolted connections under static loading. The Tee stub model is used to consider the evolution of the prying forces in addition to the direct applied load. Thus the axial stresses in the bolts are influenced by the prying forces in addition to the applied axial load and bending moment. However, the common method does not take into account the influence of the bolt bending moment which may have relevant influence upon its fatigue life. Thus, a 3D finite element model, able to take into account elastic‐plastic behaviour of the materials, large displacements and unilateral contact between the connected parts, has been developed in order to accurately predict the stress distribution in the bolt. A parametric study has been performed to evaluate the influence of the bolt bending moment on the mean value and the amplitude of axial stresses in the bolt versus the flange thickness, the bolt eccentric position and the pretension force. Then an analytical method has been used to assess the bolt fatigue life, according to the design standard for steel structures (EN 1993‐1‐9) and has been compared to the VDI 2230 standard traditionally used for the design of mechanical connections.The study highlights the influence of the preload force in the bolt that reduces the bending moment and thus the axial alternating stress in the bolt which is the main damaging parameter influencing the design under high cycle fatigue.