PSI - Issue 33

R.F.P. Resende et al. / Procedia Structural Integrity 33 (2021) 126–137 Resende et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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adhesives, from brittle to ductile. The comparison between the use of NNRPIM and FEM showed similar distributions of stresses and strains, which allowed to validate the use of NNRPIM in these analyses. It should be added that the use of CLS in conjunction with the NNRPIM provided accurate results in all tested adhesives. This work aims to implement the von Mises (vM) and Exponent Drucker-Prager (EDP) criteria into a user-built meshless method software based on the Radial Point Interpolation Method (RPIM), for the strength prediction of adhesively-bonded single-lap joints (SLJ). Validation with experiments is undertaken for a medium-ductile adhesive (Araldite ® 2015) with varying overlap lengths ( L O ). Stress and strain distributions were plotted in the adhesive layer, and the failure load ( P m ) was assessed by continuum mechanics failure criteria. 2. Experimental work 2.1. Materials The adherend material used for the experimental work was the aluminum alloy Al6082-T651. This adherend material was chosen because of the wide field of structural applications and for his acceptable strength and ductility. The tensile mechanical properties of this material were characterized in previous works (Campilho et al. 2011, Campilho et al. 2011) by performing tensile bulk tests, resulting in the P -  curve of sample. The obtained properties after data analysis are presented in Table 1 ( E is the Young’s modulus,  the Poisson’s coefficient,  y the tensile yield stress,  f the tensile strength and  f the tensile failure strain).

Table 1. Mechanical properties of the aluminum adherends (Campilho et al. 2011, Campilho et al. 2011).

Property

Value

70 . 1±0 . 83

(GPa)

0.30

y (MPa) f (MPa)

261 . 67±7 . 65 324 . 00±0 . 16 21 . 70±4 . 24

 f (%)

The adhesive material chosen for the experimental work was the Araldite ® 2015. This adhesive is a structural epoxy and bi-component with moderate ductility. The Araldite ® 2015 present a  y and  f that many adhesives, but its ductility and  f enables levelling the stress at the overlap ends by plasticity before failure, resulting in an improved behavior. This adhesive was tested and the respective properties detailed in de Sousa et al. (2017). The tensile mechanical properties ( E ,  y ,  f and  f ) was resulted from bulk tests to dogbone specimens. The fabrication process for these specimens followed the indications stipulated in the NF T 76-142 French standard. The shear mechanical properties (shear modulus - G , shear yield stress -  y , shear strength -  f and shear failure strain -  f ) were estimated by Thick Adherend Shear tests (TAST). In this special case, the 11003-2:1999 ISO standard was considered for fabrication and testing protocols. The TAST specimens was made with DIN C45E steel adherends, and was undertaken curing in a rigid mold to be able that the cured specimens was aligned. Table 2 summarizes the collected data and relevant parameters for the yield criteria, defined later.

Table 2. Mechanical properties of the adhesive (de Sousa et al. 2017).

y (MPa) f (MPa)

E (GPa)

1 . 85±0 . 21

14 . 6±1 . 3 17 . 90±1 . 8 43 . 90±3 . 4

0.35 1 12 . 63±0 . 61 f (%) 21 . 63±1 . 61 DP 4 . 77±0 . 15

y (MPa) f (MPa)

DP

1.46

2

0.057

f (%)

3

G (GPa) 0 . 56±0 . 21 1 Data from the manufacturer; 2 Calculated from tensile and shear experimental data; 3 Calculated from Equation 6.