Fatigue Behaviour of Bolted Connections in Moderately Thick High Strength Steels (HSS)

High strength steels (HSS) offer a unique opportunity to reduce weight in heavy-duty machinery such as trucks, trailers and agricultural machinery. These types of applications require significant fatigue resistance. It is well known that fatigue failure typically originates at stress concentrations caused by the joining procedures. Without taking proper care of the welding process, HSS welded joints have only similar fatigue resistance as those of lower strength steel grades. Consequently, special weld improvement techniques are required to satisfy the demands with respect to increased fatigue strength. In order to further increase the fatigue resistance and avoid some of the problems associated with welding HSS, bolted connections are considered a good alternative to their welded equivalents. A main obstacle however is that the fatigue strength of HSS bolted connections and especially their fretting fatigue behaviour has been scarcely investigated in the scientific community so far. Bolted connections in general are used as an effective and versatile joining technique in a variety of engineering applications. Design rules for bolted connections are widely available in European standards including some provisions for higher strength steel grades. However, several authors have reported that current guidelines are not suited for the new generation of HSS and often lead to overly conservative design dimensions. Fretting fatigue damage - which is not addressed in current standards - is reported as one of the principal failure mechanisms in HSS bolted connections. In slip-resistant joints this is caused by small oscillatory relative movements between the contacting surfaces and leads to very high local stresses and wear, which eventually initiates cracks. The main objective of this research is to extend the existing knowledge about the failure mechanisms of HSS bolted connections under (fretting) fatigue and to produce guidelines on the optimal design for this type of connections. Consequently, we will investigate the impact of the joint parameters that have the largest influence on the fretting fatigue behaviour, such as the slip amplitude or damage at the contact interface. This evaluation will be performed both experimentally through an extensive fatigue testing program and numerically with detailed Finite Element models.

Publication year:2020

Accessibility:Closed