The use of high-strength steel in structural components is becoming more and more attractive. For weight-saving reasons, typical applications include telescopic cranes, tippers, trucks and trailers. However, in spite of the advantages of high yield strength, the use of these steels faces some important challenges.
These steel components are often subjected to bending and fatigue loading conditions. It is well known that, under critical loading conditions, cyclic stress can occur at critical locations on such bent components. The combination of these two aspects − i.e. bending and fatigue − can cause micro-cracks to develop at the inner surface of the bent area. If the cracks propagate, rupture can result.
Furthermore, not all of the cracks observed could be properly explained using available standard fatigue approaches from literature. So, OCAS launched a detailed study in which low cycle fatigue was studied on several high-strength grades using advanced techniques to separate crack initiation and propagation lifetimes. After bending and fatigue testing, the fracture surface of the broken specimen was analysed. The study also included the effect of surface treatment on fatigue performance as well as the influence of different bending ratios.
Modelling stress
Finite element modelling was used to simulate the bending process and fatigue loading. Thanks to the numerical results, extra information could be obtained on stress gradients inside the bending area, which cannot be monitored using the experimental set-up. The good correlation with observed experimental data confirms finite element modelling as a convenient method for studying the behaviour of structures subjected to metal processing (such as bending) with regard to their fatigue performance.
An article on analysing fatigue in high strength steel for crane applications was published in the January 2018 issue of “International cranes and specialized transport”, p.20-21.
“The developed methodology will help us better understand the effect of micro-structural features on the low cycle fatigue performance of high-strength steel”
