PSI - Issue 50

Danila D. Vlasov et al. / Procedia Structural Integrity 50 (2023) 299–306 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

300

2

Strictly speaking, polymer composites themselves are a filler glued with epoxy resin (glue), so the use of adhesives to connect the finished parts looks quite natural. However, certain difficulties arise here. The glued surfaces have to be very carefully processed and prepared; all the fine details of the process - temperature, time and gluing force - have to be respected in the adhesive process. Moreover, stress concentrations appear at the ends of the joint, which significantly reduces the strength and, consequently, the effectiveness of the adhesive joint. Various types of adhesives are used to increase the strength of adhesive joints: soft and hard. The stiffer the adhesive (the higher its modulus of elasticity), the stronger the connection, which has been experimentally shown. 2. Theoretical foundation Although the joint with overlap is the easiest to make, it is not easy to operate. In the simplest case of uniaxial tension, the overlapping joint is subject to bending due to eccentric tension (Fig. 1).

Fig. 1. Adhesive joint with overlap: (a) – after the load is applied; (b) – after the load is applied.

However, the use of double overlapping or additional tabs on the parts allows the problem to be reduced to a form in which only the normal tensile stresses σ in the joint elements and only the shear stresses τ xz in the adhesive layer are considered (Fig. 2).

Fig. 2. Modified adhesive joint with overlap: (a) - with additional tabs; (b) - double overlapping.

This problem was solved in 1938 by Volkersen. Let's consider the performance of an overlapping adhesive joint with tabs, i.e. without taking into account bending (Fig. 3, a). The elements of the joint are made of the same material E1=E2=E with the same thickness h1=h2=h . The length of the adhesive joint is equal to l , and the shear modulus and thickness of the adhesive layer are equal to G and δ , respectively. The joint is loaded with tensile axial force N .