Issue 52

M. Fouzia et alii, Frattura ed Integrità Strutturale, 52 (2020) 281-298; DOI: 10.3221/IGF-ESIS.52.22 282 I NTRODUCTION he bonding assembly methods are more and more used in aeronautics due to the important use of composite materials. The bonded joints have the advantage of being rigid and lighter. Moreover, the drilling of holes for bolts in composite structures is costly and may locally compromise the resistance of the structure by delamination. Thus, when it is possible to use bonded joints it is more feasible than the use of bolted joints [3]. However, the certification standards do not always allow only bonded joints. In some circumstances bolts and rivets may be added or coupled to the bonded joints for the purpose of increasing rigidity allowing then the certification of the product. These additional mechanical fasteners are often placed in a way to assure the certification but do not always allow an improvement in mechanical performance of the joint since the two assembly processes do not work in synergy. First of all, it is important to know the works done in the domain of hybrid joints. For this aim a literature review is made in this subject in the following sections. B EHAVIOR OF A SINGLE LAP HYBRID JOINT UNDER TENSILE LOAD Secondary deflection ig.1 illustrates the way a single lap hybrid joint is deformed under tensile load. In this type of joint the load is eccentric with respect to the neutral axes of the substrates. This causes a secondary deflection in the joint which leads to peeling stresses in the adhesive as shown in Fig.2. For composite material joints, it is possible to reduce the secondary deflection by positioning the oriented plies in the direction of the load near the joint plane. This allows reducing the eccentricity between the load transfer lines of the two substrates [1]. The increase of the thickness of the substrates also allows the reduction of the secondary deflection by increasing the rigidity [2]. Figure 1: Deflection of a single lap hybrid joint under tensile load Figure 2: Principal stresses in an hybrid joint: 1) peeling in the adhesive, 2) shear of the adhesive 3), matting in the substrates, 4) normal force in the substrates. T