PSI - Issue 54

Johannes Kaiser et al. / Procedia Structural Integrity 54 (2024) 26–33 Johannes Kaiser et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Both PC grades also show an influence on the Young's modulus and the Poisson's ratio. However, since the maximum test temperature is significantly below the glass transition temperature, the influence here is to be classified as lower. 4.3. Crack tip heating Several test specimen shapes are available for the determination of the crack tip heating and the evaluation of the J-integral. The different shapes also have an influence on the crack tip heating that occurs. The SENT shape (see Fig. 1, left) has proved to be the ideal specimen shape. Due to the stress-free installation of the specimens over the pinning and the ideal force application without tilting of the specimens, results with a significantly lower standard deviation can be determined. By combining a thermography camera and a digital image correlation system, it is now possible to link the temperature rise to every single time step during the failure process (see Fig. 4). Therefore, it is possible to assign the temperature increase in the fracture process zone and the crack tip measured by means of the combined setup of thermography and digital image correlation temporally and spatially to the analog force and displacement information of the universal testing machine and to the local deformations of the test specimen.

1000

strain field

Test force

Crack tip temperature

80

II

III

I

800

III

I

II

Temperature in ° C

60

600

40

400

temperature field

Force in N

20

III

II

200

I

0

0

0

1

2

3

4

Displacement in mm

Figure 4 Exemplary force-displacement curve with one-sided DIC and IR evaluation for PC h at 5 mm/min

Figure 5 shows the influence of the test speed on the crack tip temperature for the materials investigated. All three materials investigated show a dependence of the temperature increase on the test speed.

0 20 40 60 80 100 Crack tip temperature in ° C PCn_CT PCh_CT PS_CT

PCn_SENT PCh_SENT PS_SENT

1

10

100

1.000

Test speed in mm/min

Fig. 5. Occurring crack peak temperature as a function of test speed, test specimen geometry and material