Advantages and drawback of bonded joints
The main advantages that have the bonded joints are that they add little weight to the part and that the stress distribution is better as it is not necessary to have a hole.
However, it is impossible to unassembled the components once they are bonded. These joints are sensible to the temperature and humidity. It is necessary to do an excellent surface preparation for assuring the joint. It is difficult to know how it is the joint with an inspection.
Types of stress
- Peel stress: it is known as the transverse normal stress through the thickness direction caused by the adherend bending.
- Shear stress: stress state that is parallel to the surface of the material. The shear stress is constant over the overlap length. It is maximum at the ends of the overlap and it is reduced at the middle. However, as an example, in a single lap joint, if the overlap length is increased by two times, it will not resist a force two times higher. The joint could carry more load, but not the double.
Types of bonded joints
Depending on the loads that has to resist the joint, as well as the complexity of it, exists the following type of bonded joints for composite materials:
- Butt joint
- Strap joint
- Simple lap joint
- Tapered lap joint
- Double strap joint
- Double lap joint
- Stepped lap joint
- Tapered double strap joint
- Scarf joint
Bonded joints failure modes
The following are type of failure modes in bonded joints in composite laminates under plane loading:
- Tensile failure: the reinforcement has failed
- Shear-out failure: the matrix has failed
Good practices
- Surface preparation: a bad surface preparation would mean that the adhesive would have a premature failure.
- Use quasi-isotropic laminates.
- In case of using a simple lap joint or similar, the external lamina of each laminate must be at 0º so the load can be transferred from one part to another.
