PSI - Issue 22

W. Zhang et al. / Procedia Structural Integrity 22 (2019) 251–258 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

254

4

load-displacement curve

0.05

y=0.0014x 5 -0.0107x 4 +0.0260x 3 -0.0329x 2 +0.0455x+0.0038

0.045

R=0.9956

0.04

0.035

0.03

0.025

Polynomial (Test data) Test data Test data Test data Test data Test data

0.02 load/kN

0.015

0.01

0.005

0

0

0.5

1

1.5

2

2.5

3

displacement/mm

Fig. 6. Cohesive failure process of heat-area area.

Fig. 7. Curve fitting for test results.

2.2. Accelerated degradation test From the results of the load-displacement tests, it was found that when the load increases from 5N to 20 N, the displacement approximately increases linearly, therefore this tensile process can be considered as an elastic tension stage. According to previous analysis, combined with the principle of degeneration, the applied load level of ADT can be controlled in 5~20 N under different load conditions. The loads of the ADT were selected as 5N, 10N, 15N and 20N, the durations were 20h or 40h respectively. Six sets of experiments under different conditions were carried out separately and five samples were tested for each group. In the in-situ tensile test system, the load control mode is used to monitor the displacement under static acceleration stress. At the end of the accelerated degradation time, the load-displacement test in 2.1 continued to obtain a residual cohesive curve of the specimens. 30 sets of test results were processed, the outliers that did not meet the characteristic of cracking in the adhesive overflow area were excluded. Valid results under the same test condition were averaged, as shown in Figure 8. The new load-displacement curves including accelerated process are shown in Figure 9.

adhesive strength degradation

0.7

load-displacement curve

0.05

load=5N time=20h load=10N time=20h load=20N time=20h load=15N time=20h load=5N time=40h load=10N time=40h

0.6

0.045

0.04

0.5

0.035

0.03

0.4

0.025

0.3

Tearing test constant load=5N,20h constant load=5N,40h constant load=10N,20h constant load=10N,40h constant load=15N,20h constant load=20N,20h

0.02 load/kN

displacement/mm

0.015

0.2

0.01

0.1

0.005

0

0

0.5

1

1.5

2

2.5

3

0

0

5

10

15

displacement/mm

t/s

4

x 10

Fig. 8. Displacement-time data under different load levels. Fig. 9. Load-displacement curves with ADT process Analyzing test results, there is a conclusion that even if the load is constant, the heat-seal area slowly degenerates over time, indicating that the cohesive energy has decreased. Analyzing the relationship of degradation with load level and time, there are some conclusions. As the level of applied load increases, the degradation rate increases while the loading time is the same. The test results indicate that, when the loading time is 20h and the applied load level is 5N and 10N, the corresponding maximum cohesive strength is 43N and 38N. While keeping the applied load