PSI - Issue 41

T.F.C. Pereira et al. / Procedia Structural Integrity 41 (2022) 14–23 Pereira et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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the centers of the lower and upper faces of the structural element, whose meshes between the two parts to be connected must coincide. These meshes can be constructed by shell elements, solid elements, or a combination of both. It was possible to conclude that, in addition to reducing computation time, this cohesive element leads to a structural response very close to the real one. The developed element, thanks to the simplicity of calibration compared to the existing cohesive elements, the simplicity of implementation, and the reduced computation time becomes more interesting and suitable for industrial usage. By using the Cowper-Symonds method, Liao et al. (2011) carried out a three-dimensional (3D) numerical study to evaluate the effect of the adherends’ Young's modulus ( E ), initial impact velocity, L O , and adhesive thickness ( t A ), on stress propagation waves and stress distribution of a SLJ subjected to impact loads. These characteristics were compared with similar joints under static loads. Additionally, experimental strain responses and strength under impact loads of a SLJ build with steel (S45C) adherends and SW1838 epoxy resin were measured. By comparing the numerical results with the experimental data, a reasonable agreement was found, thus validating the 3D analysis. Results showed that the maximum principal stress under impact increases as E of the adherends increases, L O decreases, t A decreases, and impact velocity increases. Finally, as the initial velocity converges to zero, the stress distribution presents a similar pattern in the static tests, although with higher values. This work studies the different CZM conditions used to model an adhesive layer in a SLJ subjected to impact loading. The numerical results were validated using experimental data. In this study, four L O were considered. The evaluated modelling conditions were the decoupling of loading modes with triangular law, cohesive law shape, damage initiation criteria and damage propagation criterion. 2. Materials and methods 2.1. Geometry and materials Fig. 1 presents the evaluated SLJ design, whose relevant dimensions are the total length ( L T ) of 180 mm, adherend thickness ( t P ) of 3 mm, joint width ( b ) of 25 mm, t A =0.2 mm and L O =25 mm.

Fig. 1 – Joint design dimensions and boundary conditions.

Different adherend materials were equated between the CZM validation and numerical studies. For the validation analysis, DIN 55 Si7 steel adherends were used, consisting of a silico-manganese alloy, typically treated in the quenched and tempered condition. The mechanical properties of this alloy are detailed in a previous work (Valente et al. 2020): E =210 GPa, tensile yield stress (  y )=1078 MPa, tensile strength (  f )=1600 MPa, tensile failure strain (  f )=6%, Poisson’s ratio (  )=0.3 and density(  )=7.8. On the other hand, a CFRP (SEAL ® Texipreg HS 160 RM; Legnano, Italy) was used as adherend for the numerical analysis. This composite material (whose orthotropic elastic properties are presented in Table 1) is widely used in the automotive industry due to its excellent properties such as low density, high tensile strength, low coefficient of thermal expansion and high resistance to abrasion and corrosion. Moreover, this type of materials is increasingly present in engineering areas that require lightness and strength. However, its limitations are the relatively high cost and low impact strength. The plastic deformation of the adherends was not considered in the numerical simulations due to the absence of this occurrence. The chosen adhesive was the Araldite ® AV138 (Table 2). Mechanical and fracture characterization of this brittle adhesive was carried out in a previous work by Campilho et al. (2011). The tensile mechanical properties were determined by tensile tests in bulk specimens. Additionally, the shear mechanical properties were assessed with Thick Adherend Shear Tests. The fracture properties of the adhesive, namely tensile fracture energy ( G IC ) and shear fracture energy ( G IIC ), were obtained from Double-Cantilever Beam and End-Notched Flexure tests, respectively.