PSI - Issue 18

2

Ibrahim Al Zamzami et al. / Procedia Structural Integrity 18 (2019) 255–261 Author name / Structural Integrity Procedia 00 (2019) 000–000

256

Nomenclature K

negative inverse slope

N A

reference number of cycles to failure

R

load ratio (R=σ min /σ max ) probability of survival

P S T σ

scatter ratio of the endurance limit range for P S =90% and P S =10%

Δσ A

endurance limit range at N A cycles to failure

With the reduction in the total weight of a vehicle leading to a reduction in fuel consumption (Schuber et al. 2001), current developments in the transportation industry seek to replace the ferrous metal components with lightweight structural metals such as aluminium alloys. As a result, in recent years, special attention has been given to the development of welding technologies capable of metallurgically assembling aluminium to steel to achieve not only robust hybrid joints but also higher productivity (Okamura & Aota 2004, Katayama 2004, Kato & Tokisue 2004, Lu et al 2009). Because aluminium alloys and steel have incompatible thermal and physical properties, as well as different metallurgical characteristics, fusion welding becomes problematic. During welding, the formation of intermetallic phases (Fe-Al) deteriorates the strength of the joints by introducing brittle layers at the interface between the two materials (Qin et al. 2004, Kimapong & Watanabe 2005, Taban et al. 2010, Węglowski 2013). To solve this problem, different welding techniques have been developed and optimized in recent years. ColdArc® welding technology, marketed by EWM (www.ewm-group.com), offers excellent arc stability and highly controlled heat input and was selected for use in this study (Goecke 2005, Cao et al. 2014). The importance of fatigue failure associated with different welding processes is well recognised and a considerable amount of literature has been published on the effect of the welding process on the durability of welds subjected to fatigue loading. When comparing the strength of the welded and non-welded components made of the same material, there is a significant reduction in the fatigue strength of the welded components (Fricke 2003, Haryadi & Kim 2005, Susmel & Tovo 2006, Susmel et al. 2009, Borrego et al. 2014). This reduction in strength is caused by the formation of residual stresses, imperfections and distortions during the welding process. In addition, localized stress concentrations are common and result in high stress/strain gradients in the toes/roots of the weld, which causes fatigue cracks near these critical regions (Schijve 2009, Susmel et al. 2011, Susmel, 2010). The understanding of the fatigue behaviour of weldments made of different materials (in particular, aluminium alloys and steel) is very limited. Before examining the fatigue behaviour of welded aluminium to steel joints, it is important to understand the static behaviour of these assemblies. A recent experimental study (Al Zamzami et al. 2018) investigated the static behaviour of thin aluminium-to-steel welded joints with different geometrical configurations including butt, lap, and cruciform welded joints and butt-welded joints with different inclination angles varying from 0º to 60º. The study has shown that regardless of the configuration of the joints or the angle of inclination, breakage of these hybrid joints always occurred in the heat affected zone on the aluminium side. The investigation also confirmed that EC9 (Eurocode9 1998) could be used to design this type of joint against static loading with a high level of accuracy. The present work reports the findings of an experimental study on the fatigue behaviour of aluminium-to-steel thin welded joints subjected to uniaxial cyclic loading (Al Zamzami et al. 2019). The purpose of this study is to recommend an appropriate design strategy suitable for accurately estimating the fatigue strength of aluminium-to-steel welded connections. 2. Experimental procedure The experimental work presented here provides a detailed investigation into the behaviour of aluminium-to-steel thin welded joints subjected to fatigue loading. The aim of this investigation is to check the accuracy and reliability of the nominal stress approach for estimating the fatigue strength of the aluminium-to-steel thin welded joints. The materials used in this investigation were aluminium alloys, AA1050 and cold-rolled low-carbon steel EN 1013:1991.