Comparative fractographic analysis of co-bonded and secondary bonded carbon fiber reinforced composites subjected to Mode I delamination

Adhesive bonding technologies for thermosetting polymer composites have been applied in several industrial sectors, such as marine, automobile, construction, and aeronautical industries due to their excellent mechanical behavior over conventional joining methods. One of the main drawbacks of this joining technology is that they are prone to delamination whilst in service. The overall composite joint structural performance depends upon several factors related to the joint manufacturing process such as surfaces preparation procedure, loading condition, adhesive type, aging effects, and inspection procedures. For this reason, there is clear need to better understand how the joint behavior is affected by these factors and the failure causes in order to improve the design and the joint performance. Within this context, this work presents a comparative fractographic analysis for two different joints types named co-bonded and secondary bonded tested under Mode I delamination at room temperature. One sample of each was observed through fractographic analysis, to identify similarities and differences between the fracture aspects, which may explain differences in toughness values and fracture behaviors. The main contribution of this article is a new failure analysis methodology focused on a better understanding on failure characteristics of adhesive joints providing a deep and critical insight into main failure mechanisms and damage sequence in composite bonded joints, which may aid analytical validation and numerical models for this type of joints developed elsewhere. Although fracture toughness (GIc) values of each joint are quite similar, some failure aspects and adhesion mechanisms differentiate these two bonding technologies