Investigation of Fatigue Crack Propagation in Adhesively Bonded Joints used in Aluminium Vehicle Structures

摘要

Adhesive Bonding is an attractive alternative to conventional joining methods,such as welding and mechanical fastening. In applications such as primaryaircraft structures or automobiles elements adhesive bonding competes withtraditional bolting, riveting or welding. The advantages of adhesive bondingincludes high strength/weight ratio, possibility to join any combination ofmaterials, high corrosion resistance and improved fatigue performance. Although,adhesives can be used alone, most of the volume manufacturers can't afford thelevel of quality control required and have opted to employ hybrid joining methodscontaining adhesives with spot welds or self piercing rivets because they do nothave a reliable software method to analyze and predict the lifetime of bonded orriveted joints. In analysing adhesively bonded joints for design purposes,important properties to consider are strength, stiffness, weight and nature ofstress distributions.In this research, a new mathematical method based on stiffness drop ofadhesively bonded joints has been investigated and presented to determine thefatigue crack propagation rates and obtain the crack growth curves for thesejoints. This method makes use of the raw laboratory fatigue test data and finiteelement based stiffness data of bonded joints. This concept has been tested andvalidated for T-peel and single lap shear bonded joint configurations. The bondedjoint configurations were prepared using aluminium alloy AA5754 and theadhesive used was Betamate Epoxy adhesive 4601, which is high performance,heat curing, epoxy adhesive. The entire tests were conducted under constantamplitude loading using an R ratio of 0.1 and frequency of 10Hz. The damagemodels for this work were developed using computational fracture mechanicstools in abaqus.Various curve fitting models were reviewed and employed in this method tocombine the stiffness data obtained from FE damage models and fatigue testdata of T peel and single lap shear bonded joints to calculate the fatigue crackpropagation rates. The methodology investigated in this work provides a way toobtain the fatigue crack growth curves for adhesively bonded joints by combiningthe finite element modeling data with fatigue test data of bonded joints.