Experimental and numerical evaluations on the effects of adhesive fillet, overlap length and unbonded area in adhesive-bonded joints

To realize robust structural design, the effects of the adhesive fillet, overlap length and unbonded area in adhesive-bonded joints need to be fully understood and incorporated into a fatigue life estimation method. In the present work, both static and fatigue experiments are performed on six types of adhesive-bonded joints to illuminate these effects systematically. A straightforward total fatigue life evaluation method is proposed to address these effects. A statistical crack initiation model is established based on the fatigue data of bulk adhesive specimens. Growth life is calculated using the interfacial crack model and mixed mode crack growth method. Good correlation is observed between the calculated and experimental fatigue lives. Furthermore, the effects of the adhesive fillet, overlap length and unbonded area are analysed based on both calculated and experimental results. Results indicate that adhesive fillet postpones crack initiation by reducing local strain level, both overlap length and unbonded area change the growth life by length. Besides, overlap length promotes the fraction of mode II strain energy release rate in total, reducing crack growth rates and extending growth life.