UC Irvine

A Novel Non-Destructive Test (NDT) Methodology for Evaluating the Integrity of Adhesively-Bonded Joints

By

Sean Naraghi (Shaham Naraghijalili)

MASTER OF SCIENCE

in Engineering with concentration in

Material and Manufacturing Technology (MMT)

University of California, Irvine, 2020

Professor James Earthman, Co-Chair

Professor Ayman Mosallam, Co-Chair

The Climate Crisis is pushing engineers to use lighter materials in their designs to lower CO2 emission. This is the primary reason behind the shift from steel to lighter metallic alloys such as Aluminum Alloys, and recently to Fiber Reinforced Polymer (FRP) composites. Adhesive bonding introduces a smooth stress transfer and therefore is the most appropriate joining method when it comes to FRPs compared to mechanical fasteners such as rivets, bolts, etc. Besides, adhesive bonding has other advantages over mechanical fasteners, including reducing the final weight of the assembly, protecting the assembly against galvanic corrosion, absorbing shock and vibration, and introducing the ability to repair damaged assemblies.

The biggest hurdle against mainstream usage of adhesive bonding as the primary method of joining is the lack of reliable quality control tests to ensure a reliable bonding. This has led many engineers to avoid adhesive bonding in their designs or to take a harsh conservative approach when it comes to designing with adhesive bonding.

In this project, the possibility of using the Quantitative Percussion Diagnostics (QPD) to detect a weak bond (kiss bond) is investigated. Intentional flaws were introduced to adhesively bonded joints through multiple procedures. Samples with the ideal well bond were also fabricated. The QPD was performed on these two sets of samples, and the results were compared to see if there is a significant difference that can be used to distinguish between a well bond and a kiss bond. QPD shows some promising signs that it is capable of detecting a kiss bond.

Finite Element Analysis (FEA) is used to calculate the stress distribution in different joint conditions and configurations. The results are used to investigate the effect of joint configuration, substrate’s modulus, and bondline length. The general conclusion is that joint configurations with lower eccentricity experience lower bending, and that leads to the development of lower peel stresses. Joints that include substrates with higher modulus experience less bending and therefore develop lower peel stresses. Also, longer bondline generally enhance the performance of the joint.

A literature review was conducted in regards to surface science, surface treatment, joint design, environmental durability of joints, Non-Destructive Tests (NDTs), Fiber Reinforced polymers (FRPs), etc.