PSI - Issue 42

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

384

3

rotary encoder

specimen

optical fi bre inclinometer

350

F

12

38

x

50

50

load cell

optical fi bre position

ѳ 1

10

t=15

DIC sensor

10

shearography

3

ѳ 2

gap

points of COD measurement

points of rotation measurement

lighting

axis of load introduction

y z

x

F

Fig. 1. Sketch of the specimen (all dimensions in millimetres).

Fig. 2. Picture of the test setup.

5, Baumer AG, Frauenfeld, Switzerland) with a resolution of 320000 steps per full turn were used to measure the rotational angles of the load introduction points. Two inclinometers (NA2-05, SEIKA Mikrosystemtechnik GmbH, Wiggensbach, Germany) with resolution of ± 0 . 02 ◦ were placed at the end of the specimen to measure the end rotation of each adherend, allowing for a determination of the instant at which the process zone reaches the end of the speci men. The data were recorded with an external measuring software (DASYLab 13, National Instruments, Texas, USA) and measuring card (Goldammer G0A-1024-3, Goldammer GmbH, Wolfsburg, Germany). For the DIC evaluation, two 12 MP cameras (acA4112-20um, Basler AG, Ahrensburg, Germany) were used to capture the deformation of the adherends and the Crack Opening Displacement (COD) during the test. The whole specimen was recorded with a measuring window about 390 mm by 290 mm, corresponding to a resolution of 0 . 1 mm per pixel. The pictures were then analysed with VIC-3D software (Correlated Solutions Inc., Irmo, USA). The BFSM were performed with optical fibres bonded to the adherend’s lower and upper surface (cf. Fig. 1). The distributed fibre optics measurement system (ODiSI-B 5500, Luna Innovations Inc., Roanoke, USA) acquired the backface strain of the specimen with a positional resolution of 0 . 65 mm. The shearography measurements were carried out with an SE2 sensor (isi-sys GmbH, Kassel, Germany) in order to be able to measure the first derivative of the surface deformation. For the measurement, a shear amount y = 2 mm and a shear angle of 0 ◦ were set. The tests were performed in cross head displacement control with the electro-mechanical testing machine. The procedure started with a constant displacement rate of 0 . 2 mm / s for ten seconds, then the position is hold for five seconds, and so on, as shown in Fig. 3. Holding the position for five seconds was caused by the recording rate of the shearography system (9 fps) and the need for eight images to calculate the interferogram. The first four images are needed for the reference condition and the second four images for the deformed condition. Within the acquisition of each of the four images, there may not be a large displacement of the component. The long position hold between 75 s and 120 s was also caused by the shearography system, which needed time for saving the data before taking new pictures.

20

15

hold position: wait to save shearography

10

hold position for shearogra phymeasurement point

5

displacement rate 0.2 mm/s for 10 s

cross head displacement / mm

0 20 40 60 80 100 120 140 160 180 200 time t / s 0

Fig. 3. Test procedure.