PSI - Issue 25

F.J.C.F.B. Loureiro et al. / Procedia Structural Integrity 25 (2020) 63–70 Loureiro et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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3. Results

3.1. Experimental tests results

Fig. 2 presents the load-displacement ( P -  ) curves of the SLB joints bonded with the Araldite ® 2015. A good correlation between all specimens during elastic phase for the SLB specimens was found. The average P m for the seven specimens was 204.2 N with a standard deviation of 12.8 N. In addition, the displacement found at P m was in average 5.6 mm.

250

200

150

P [N]

100

50

0

0

2

4

6

8

10

δ [mm]

Fig. 2. Experimental P -  curves of the SLB joints bonded with Araldite ® 2015.

3.2. J I and J II estimation

The J I and J II assessment was performed through the Ji et al. (2012) approach. The procedure is demonstrated for a single specimen, more specifically the one with highest P m . Initially, the parameters  p ,  n and δ s were obtained. After fitting, the polynomial curve practically overlaps the experimental  n -  data. However, the curve’s shape is much different, and it approaches a straight line’s shape. Again, the polynomial approximation curve achieves a good representation of the experimental  S -  curve. The J I -  n curve for the same specimen was plotted, where three different stages were identified: (1) slow increase of J I with  n , (2) steady increase of J I and (3) the curve tends to a steady-state value of J I . J I is calculated by the steady state value of J I . In addition, the J II -  s curve for the same specimen was derived. At the beginning of the test, J II increases very slowly, however the rate of improvement quickly increases and ultimately a steady-state value is attained. This last stage indicates the onset of crack growth and provides the J IIC estimation. Due to small measurement errors or experimental issues, in few specimens, the initiation of the J II -  s curves began with slight positive or negative slope, which then reflects on small variations to the ideal zero-stress initiation of the cohesive laws.

0.5

0.4

0.3

0.2 J I or J II [N/mm]

0.1

0

80

90

100

110

a [mm] JI

JII

Fig. 3. Representative experimental R-curves from the SLB joints bonded with the Araldite® 2015.