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Fatigue of welded high strength steels for automotive chassis and suspension applications

Shrama, Kadhum 2016. Fatigue of welded high strength steels for automotive chassis and suspension applications. PhD Thesis, Cardiff University.
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Abstract

The automotive industry is under expanding legislative pressure to decrease vehicle weight in order to enhance fuel efficiency; and to improve crash performance as well. For this purpose, hot rolled FB590 is a high strength steel (HSS) which can be used in automotive chassis and suspension applications. A major problem affecting mainly car underbodies is the effect of corrosion, often nucleating at sites where stone chipping has damaged protective coatings. Therefore, car components are frequently exposed to aggressive environments as a consequence of aqueous salts from the street coming into contact with affected and unprotected steel. This circumstance significantly decreases both the life and the appearance of the influenced parts, and may result in compromised structural strength leading to catastrophic failure. The main aim of this research is to further the understanding of the effects of simulated operational environments. Fatigue tests were initially carried out on mild steel under tensile loading and two severity-levels of corrosion as preliminary tests. Then a comprehensive programme of fatigue tests was performed on FB590 and its welds under bending and tensile loading and covering the range of environmental conditions experienced in automotive applications. There is no available data for FB590 in terms of fatigue performance in various environments and under bending and tensile loading as well. Additional techniques such as surface profilometry, scanning electron microscopy and so on were added to support the findings. The other aim was to monitor fatigue tests using a combination of Acoustic Emission (AE) and Digital Image Correlation (DIC) to identify the damage mechanisms that occur during failure although there had been limited research in this area. The combination of AE and DIC can provide much useful information to help to distinguish the different AE signals originating from various possible failure mechanisms such as plastic deformation, delamination of corrosion products or DIC paint and crack initiation and propagation. This might be utilized for an effective and powerful approach to monitoring multiple failure mechanisms; this has significant applications in automotive chassis testing. This information can provide a very valuable tool for the purpose of assessing material for automotive designers, which can then be used to decide on appropriate safety factors to avoid over-designing products and in order to ensure reliability and robustness of new products. In addition, the steel industry can also benefit from this research, as these findings can assist in enhancing the products and diminishing the effects of these environments on structural integrity.

Item Type: Thesis (PhD)
Date Type: Publication
Status: Unpublished
Schools: Engineering
Subjects: T Technology > TJ Mechanical engineering and machinery
T Technology > TL Motor vehicles. Aeronautics. Astronautics
Uncontrolled Keywords: Fatigue; Pre-Corrosion; Acoustic Emission; Digital Image Correlation.
Date of First Compliant Deposit: 18 July 2016
Last Modified: 17 Mar 2017 05:52
URI: http://orca.cf.ac.uk/id/eprint/92903

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