Influenza del trattamento laser di CFRP sulla resistenza meccanica di giunti incollati

Nowadays composite materials play a fundamental role in structural design, particularly in the aeronautical and automotive fields. In fact, in these sectors it is essential to reduce the weight of the components as much as possible, without compromising performances. This aspect has led to the growing use of structural adhesives as a solution to the problem of coupling between the various parts of a structure. These, in fact, allow to obtain, with respect to the traditional fixing techniques, a greater uniformity in the distribution of the stress and to avoid any type of processing on the adherends to form the joint. In the case of composite bonded joints, the cause of failure that occurs in most applications is to be attributed to the presence of defects, responsible for fractures, delaminations and detachments between the adhesive and the adherend. This last type of problem, commonly identified as an adhesive failure, is, among all the possible failure methods of a bonded joint, very common. The quality of the bonding, in fact, can be easily compromised due to inadequate pre-treatment, contamination of the surfaces to be glued and a strong sensitivity of the adhesive to particular environmental conditions (temperature values, humidity concentrations, presence of aggressive solvents), for example. The use of a laser source for pre-treating the surface to bond can increase the reliability of the bonded joint. The constant increase in the applications of bonded joints has also led to the development of mathematical models for analysing their behaviour. For example, the ability to predict the bonding strength depending on the intensity with which the laser treatment is performed can be very useful in the joint design phase. However, this presupposes the need to model correctly the behaviour of the interface in the construction phase of the numerical model. This thesis illustrates the effectiveness of a laser texturing and a possible approach methodology for modelling and determining numerical parameters capable of simulating the real behaviour of an interface in order to predict its mechanical strength. In particular, the first part consisted in the production of laminates and joints, in the execution of laser treatment and, finally, in the implementation of flexural tests. In the second phase of the work activities a 2D numerical model based on cohesive elements was developed, therefore the numerical parameters relating to the interfaces of the tested joints were therefore derived through direct and inverse method.