Improvements of fiber reinforced thermoplastic composite bonds: thick joint failure model, shape memory alloy reinforcements, and in-situ x-ray characterizations

Abstract

Fiber-reinforced polymer composites have continued to gain interest in the aerospace, wind, construction, and recreational industries. The ability to customize the properties of composites to fit a specific application, as well as their high strength-to-weight ratio make the material incredibly versatile and advantageous. In many cases, it is necessary to bond one composite component to another, or to a dissimilar material, such as metal or plastic. However, adhesive bonding of composite materials presents many challenges. Foremost, adhesives are generally weak when loaded in tension applications, thus rivets are used to strengthen the bond, however this greatly reduces the integrity of the composite, which is more prone to fatigue and wear. Secondly, shear strength is not well understood for gaps larger than 3 mm, which presents issues as wind turbine blades can have gaps as large as 12 mm. Understanding the mechanics of adhesive versus cohesive failure for adhesives is crucial to develop better models and manufacture stronger composite structures.Understanding adhesive failure and developing methods for stronger bonds without the use of rivets or mechanical fasteners will greatly advance the composite field, and enable more efficient, stronger, lighter structures. The present work provides alternate bonding methods to adhesives, methods for strengthening composite bonds, and void characterization and crack propagation of a single lap joint studied in 3D using an in-situ load frame inside of an x-ray computed tomography machine. A novel model for determining the cohesive-adhesive transition of methyl-methacrylate adhesives is also presented, which can aid in developing stronger bonds.