PSI - Issue 14

Mohd Tauheed et al. / Procedia Structural Integrity 14 (2019) 354–361 Mohd Tauheed/ Structural Integrity Procedia 00 (2018) 000–000

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6

0 10 20 30 40 50 60 70 80 90 100

y = 1.13E+09δ 6 - 2.33E+08δ 5 + 1.80E+07δ 4 - 6.63E+05δ 3 + 1.13E+04δ 2 - 1.89E+00δ + 1.99E-03

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2,5

Experimental

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1 G II , N/mm

Shear traction, MPa

0,5

0

0

0,02

0,04

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0,02

0,04

Shear separation (δ), mm

Shear separation (δ), mm

Fig. 6 (a) Evolution of G II as a function of separation δ during fracture test of ENF (b) Experimentally obtained mode II traction separation law and its bilinear approximation

3.1. Determination of Mode II Traction-separation Law The procedure is identical to the one followed to extract mode I TSL. Evolution of mode II energy release rate ( G II ) was plotted against separation across the adhesive thickness using the direct method as shown in Fig. 6 (a). DIC technique was used to determine the shear separation ( δ ). Here, the specimen undergoes bending during a test and the adhesive layer no longer remains horizontal at the crack tip location. Therefore, pure horizontal displacements given by DIC cannot be considered as shear separation. Similar to DCB specimens, a 6 th degree polynomial was fit to the evolution of G II with separation, which was later differentiated to obtain the mode II TSL and bilinear approximations to the experimentally determined mode II TSL is shown in Fig. 6 (b). 4. Strength prediction of single lap shear joints An SLS specimen is used for determining failure strength under mixed-mode loading conditions. The ASTM D3163 standard test method was followed in specimen preparation as shown in Fig. 7. Figure 8 (a) shows the test setup used to test SLS speicmens under displacement control at a constant rate of 0.5 mm/min. The failure criteria for a mixed mode cohesive zone model is given by, � � � �� � � �� � ��� � � (5) A 2D finite element cohesive zone model of single lap joint was create in ANSYS APDL. The cohesive parameters extracted from the mode I and mode II fracture tests were used for the cohesive elements. Two different FE models were developed. In one model, the adhesive layer was not modelled, instead zero thickness cohesive elements were used to define the fracture path. In another model, a finite adhesive thickness of 0.3 mm was modelled and fracture path was defined within the adhesive layer by using zero thickness cohesive elements. Figure 8 (b) shows that both FE models closely predict the experimentally measured load vs. displacement response, thereby validating the ability of the FE models to predict failure loads. Moreover, since the differences between both FE models are negligible, the effect of the compliant adhesive layer on the failure response are insignificant. A B