Development of fatigue assessment approaches for adhesively bonded joints

The increasing global warming and pollution in our world concerns the population about the necessity to reduce the consumption of natural resources. In the last years the automobile industry has focused in reducing the consumption of their vehicles. Beside the improvement of the motors, an important aspect is the reduction of the total weight of the vehicle. The introduction of light-weight materials contributes to this aim. The use of these materials fosters novel joining technologies. Traditionally, the main joining technology in automotive industry is welding. Low cost and fast application for joining metallic components are the main benefits. The lightweight materials, such as fibre reinforced plastics, cannot be welded and alternative joining techniques are necessary. In this way, adhesive joints are becoming more important to and complement classic joining technologies such as welding, riveting or clinching. There are several advantages of its use. One advantage is the increase of the total stiffness of the body-in-white structure. Another advantage is the improvement of crash energy absorption. The most important is the possibility to join materials that cannot be welded, as for example metallic plates with glass or carbon fibre materials. The increasing use of structural adhesive opens a new investigation field. To develop an optimum design of adhesive joints it is necessary to understand the connection behaviour and derive design allowable for quasi-static dynamic and fatigue loading. The behaviour of adhesives submitted to variable amplitude loading and proper computational fatigue analysis is not yet state of art and concern of ongoing research [Sch14]. The methods applied to analyse the behaviour of adhesive are based mainly on the methods used to evaluate welded joints. They should be analysed to evaluate if they describe properly the behaviour and failure of the modern adhesive bonds. Otherwise, new methods based on the adhesive characteristics should be developed