What is a structural adhesive? https://www.intertronics.co.uk/2018/04/what-is-a-structural-adhesive/

A structural adhesive is an adhesive which “hardens” or cures into a material capable of holding two or more substrates together, bearing the forces involved for the lifetime of the product. It is often termed a “load-bearing” adhesive. The product may undergo shock, vibration, chemical exposure, temperature excursions or many other types of potentially weakening or destructive agents, and still be bonded. The substrates may be the same, or quite different, ranging from metals, plastics, glass, rubbers, ceramics or composites. The parts may be under constant load, or intermittent loads and shocks.

What are epoxy adhesives? https://www.hotmelt.com/blogs/blog/adhesive-academy-epoxy-explained

Withstands heat, water and harsh chemicals.
Has highest adhesion and flexible enough to be molded into different shapes
Durable; withstand heavy loads – excellent structural adhesives
Comes in one-component or two-component systems (difference is in curing temperatures)
One-Component Epoxy Adhesives are cured between 250 – 300 degrees Fahrenheit
- Formulated without a catalyst and cures faster than two-component epoxy systems
- Excellent adhesive properties
- Resistant to harsh external environments
- Excellent alternative to welding and rivets
Two-Component Epoxy Adhesives
- Cured at lower temperatures compared to one-component systems
- Curing done with catalyst and process can be accelerated by heat
- Cross-linking in the polymers increases during this heat acceleration process to give the epoxy superior properties
Choosing the Right Epoxy Adhesive
- Work life – how long it takes for the epoxy adhesive to harden and dry
  - How long you have to manipulate the adhesive; you don’t want the epoxy adhesive to harden and dry before your job is done. You also don’t want your materials to shift and slide after your job is complete because your epoxy adhesive has not dried and hardened in time.
- Cure time – length of time it takes for internal chemical reactions to complete and the epoxy to reach its full strength
- Type of substrates
  - Some special epoxy adhesives have been developed
- Colour
  - Highly visible jobs should have epoxy adhesives blend in with the substrate

Advantages of Adhesives Over Mechanical Assembly https://www.masterbond.com/techtips/advantages-adhesives-over-mechanical-assembly

Structural adhesives now offer a new solution to replace traditional mechanical assembly. These kinds of adhesives are user-friendly and allow for the permanent assembly of similar and dissimilar substrates. Some of the benefits of using adhesives in your assembly application include:
Bonding a wide variety of substrates
Even distribution of stress on the load
Protection from corrosion
Ability to resist flex and vibration
Minimal increase in weight of assembly
Easy automation
Minimal shrinkage upon cure
Excellent cohesive strength
Superior chemical and heat resistance

https://sciencecentre.3mcanada.ca/latest/can-you-use-adhesive-as-an-alternative-to-rivets-and-welds

Greater design potential
- Mechanical fasteners can’t accommodate tolerance of light, thin and dissimilar materials
- Structural adhesives can bond a larger variety of materials together
- Smooth, seamless finish
Increased productivity
- Mechanical fastening can require equipment and extra processing time
- Saves time and space on the floor
More durable
- Rivets and welds could leave behind heat distortion and stress points that can be vulnerable to stress and breakage
- Structural adhesives create continuous bonds that disperse force, and don’t damage the substrates

Additional Resources on Structural Adhesives

Calculating Adhesive Strength Required

What are the modes of failure for adhesive joints:

Fracture mechanics: https://en.wikipedia.org/wiki/Fracture_mechanics

Mode I: Opening mode - A tensile stress normal to the plane of the crack
Mode II: Sliding mode - A shear stress acting parallel to the plane of the crack and perpendicular to the crack front.
- Adhesives exhibits the highest resistance to fracture
Mode III: Tearing mode - a shear stress acting parallel to the plane of the crack and parallel to the crack front

Joint resistance is increased by designing geometry that: