PSI - Issue 42

Dennis Domladovac et al. / Procedia Structural Integrity 42 (2022) 382–389 Domladovac et al. / Structural Integrity Procedia 00 (2019) 000–000

388

7

4.5

external BFSM DIC processzone reaching end without gap with gap

4

3.5

3

2 J / kJ/m 2 2.5

1.5

1

0.5

0

0

1

2

3

4

5

6

7

8

COD / mm

Fig. 7. J-Integral results.

dimensions can be measured with the same position resolution, but the e ff ort preparing the specimens is comparatively higher. Moreover, the BFSM is usable to detect the gap, but, like the DIC approach, not advisable for a stand alone measuring. This is based on the fact, that the preparation of the specimen and the also the post processing is time consuming. The BFSM is useful for the investigation of the adherend’s deformation in view of the traction evaluation or the J-Integral measurement. In Fig. 7 the measurement of the J-Integral is shown. The black curves shows the evaluation by the Paris and Paris approach (Eq. 2) and the purple and orange curves the evaluation via beam theory and Eq. 3 for the measurement with BFSM and DIC. The results of the conventional and BFSM approaches agree with each other, the di ff erence by the specimen without void is ascribed to the measurement of the specimen’s end rotation. Likewise previous results for the DIC measurement, the J-Integral evaluation is also very sensitive to numerical di ff erentiation and is not advisable in case of fourfold di ff erentiation. The black circles in the diagram shows the point, were the inclinometers at the specimen’s end detect a rotation. Hence, the requirement of a unloaded end is unmet and the test cannot evaluated with conventional methods. The deflection curve approach can help to determine the traction-separation-law in this case for use e.g. in FEM simulations. Comparing the J-integral, the value for the specimen with gap is significantly smaller than for the specimen without gap. Hence, the value of the J-Integral can give a indication of the presence of the gap or other defects and seems to be more sensitive considering the material scattering. Moreover, the curves show the appearance of relaxation during the position hold, with is expressed by the rising COD and simultaneously the decreasing J-Integral. These relaxation e ff ect can be determined in the DIC and BFSM results, too. Because the curves shown in Fig. 4 and Fig. 5 chosen at the beginning and end of the five second position hold. The relaxation behaviour leads to a non-monotonic loading of the joint and, hence, the evaluation of a traction separation-law is not possible in conventional way with the J-Integral. The J-Integral evaluation shows that characterizing the material properties of the adhesive in this case of load and with a gap is not possible. Only the joint behaviour can be characterized. Further work needs to be done to better understand and describe this joint behaviour. 3.2. J-Integral evaluation

4. Conclusions

In this work, we presented a potential analysis of measurement methods to localise gaps in a soft rubber-like adhe sive joint loaded in mode I. Furthermore, the J-Integral of the DCB specimen with and without a gap was measured in two ways: The conventional method according to Paris and Paris and a approach using the adherend’s deflection curve. The following conclusions can be drawn within this study: