PSI - Issue 72

P.D.A. da Silva et al. / Procedia Structural Integrity 72 (2025) 52–60

55

Fig. 2. Geometry of the tubular adhesive joint used in the numerical analysis.

2.3. Joint fabrication and testing

The test specimens consisted of SLJ with L O of 25 and 50 mm, lengths that are frequently used in the automotive industry. To ensure that the adherends do not interfere with the expected cohesive failure mode in the adhesive, the high-strength steel described in section 2.1 was used to avoid plasticization of the adherends. The adherends were machined from a DIN 55 Si7 steel alloy plate and sandblasted along the bonding regions. This surface was then degreased before adhesive application. To prevent the adhesive from hardening, it was applied to the surface of one of the adherends and bonded to the complementary one. The specimens were then placed in a mould and left to cure at room temperature. A Rosand ® Instrumented Falling Weight Impact Tester type 5 HV was used for the impact tests. The impact test consists of dropping a weight with a defined mass which, in turn, transfers the impact E a to the specimen being tested. The upper grip is fixed to a claw using a screw. A block has been placed to guarantee proper vertical alignment, ensuring that eccentric loads act on the specimen during the test. The test weight is attached to the lower grip using a screw and a block. The transmitted impact load is registered in a load cell. The impact mass used in the machine was 26 kg, providing a reference impact E a of 40 J. 2.4. Numerical modelling An axisymmetric numerical analysis of the impact tests was performed using Abaqus ® . Axisymmetric elements were selected to model both adherends (CAX4) and adhesive (COHAX4R). For the adherends, the elements were displayed in a structured mesh, while the cohesive elements were assigned a sweep type mesh. Besides, to simulate the test’s impact E a , a solid homogeneous mass was created. Preliminary calculations showed that E a of 40 J was required to separate the adherends and, by combining this value with the impact velocity previously estimated, it was possible to define the total mass and its respective density. Elastic-plastic behavior was assumed for the adherends, and, for the adhesive, a quadratic stress criterion was employed to predict failure initiation, while damage propagation was ruled by a linear energetic criterion. A linear stress-strain behavior was assigned to the mass, and its elastic properties were defined to have no interference with the joint’s strength. The boundary conditions ( Fig. 3) were applied as follows: 1) nil longitudinal displacement at the left specimen’s edge; 2) nil radial displacement and velocity type predefined field of 1.75 m/s applied to the mass at the other edge, to assure the required E a (40 J).

Fig. 3. Set of boundary conditions for the numerical simulation.