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Project

Effect of forming process on fatigue fracture behaviour of high strength steel.

In modern society, the application of High Strength Steels (HSS) has been proven to be highly versatile. Small as well as large scale constructions benefit from the enhanced mechanical properties of these metals. Through a high strength-to-weight ratio, substantial weight reductions can be achieved, whilst maintaining overall performance and safety. Additionally, a higher strength contributes to an increased maximum payload and structural integrity. For this reason, HSS are preferred for various transportation applications, heavy-duty machinery and large civil constructions. The components used, mostly require a specific outline or cross-section for structural purposes. This is achieved by secondary forming processes that deform the material to a desired shape. However, these processes induce localised residual stresses and strains, that can act as structural hotspots when service loads are applied. In addition, a higher strength is generally paired with a decreased formability and this can have a significant influence on the damage accumulation during forming and resulting mechanical performance after forming. Since transportation and civil applications are often subjected to a variety of complex, repeating service loads, fatigue fracture is one of the main concerns in mechanical design. In that sense, it becomes imperative that the characterization of the fatigue fracture behaviour should consider pre-deformation. This project will investigate the effect of a forming process followed by fatigue loading for several frequently used HSS grades. Experimental and numerical techniques are developed, where benchmark specimens are designed, modelled and tested. Advanced numerical modelling is applied to integrate the forming simulation in fatigue analysis and improve predictive accuracy. The feasibility of Digital Image Correlation (DIC) for material model calibration, FEM validation and strain monitoring during fatigue is clearly demonstrated. The main goal is to derive a validated work flow for identifying the fatigue behaviour of cold-formed HSS. 

Date:14 Aug 2017 →  11 Mar 2022
Keywords:Fatigue, High Strength Steel, Forming process, Digital Image Correlation, Finite Element Analysis, Air bending
Disciplines:Materials science and engineering
Project type:PhD project