Question

What is the impact on load distribution when comparing a bolted and an adhesive connection? Explain the difference between cohesive and adhesive failures? What types of destructive tests are typically employed to characterize adhesive joints? How does the use of an adhesive joint impact fatigue performance?

Answer 1

1) As larger bolt are having larger shear area, load capacity of joint will increases with the increase in bolt dimensions.

Also load capacity of joint increases with increase in adhesive thickness which result in less shear and peel stresses. However it is also observed that due to increasing the thickness of the adhesive, peel stresses near the bolt area remain unchanged and hence the crack may occur at same load as compared to the less thickened adhesive joints.

Load capacity of joint decreases with the increasing bolt holes clearances as it allow the relative displacement between the bolt and hole which further reduce the capacity of joint.

2) Adhesive failure occurs when the adhesive pulls away from one or both of the substrates, but does not tear or split. While A Cohesive failure is a failure of adhesive film itself.

Adhesion failure Cohesion failure

3) The two main tests that is employed to characterize adhesive joints are: Ultrasonic and Sonic vibrations.

4) Using Adhesives, high fatigue resistance and longer fatigue life is possible compared to conventional joining techniques. It also has advantage of light in weight, ability to join thin components, low manufacturing cost, good sealing and vibration and good damping properties.