PSI - Issue 28

S. Henschel et al. / Procedia Structural Integrity 28 (2020) 1369–1377

1372

4

S. Henschel et al. / Procedia Structural Integrity 00 (2020) 000–000

F A

F B

F C

x 2

F A = F

sin α sin α

1 2

c b

x 1

cos α +

F B = F sin α F C = F 1 2

c b

cos α −

Δ u 2 = Δ u 1 = Δ u 2 = 0

Fig. 3. Setup with the loading device and the specimen.

Fig. 4. Finite element mesh of the specimen with loads and boundary conditions.

a / W 0.5 0.7 0.6

1.1

K I / K I ( l N = 0)

a

1.0

0.45

1 −

1 +

2 −

2 +

φ

3 −

3 +

0.4

θ

0.9

8

10

12

14

l N

Notch length l N / mm

Fig. 6. Strain gauge positions. With ν = 0 . 29: ϕ = 66 . 8 ◦ , θ = 61 . 7 ◦ , r 1 = 10 mm, r 2 = 15 mm, r 3 = 20 mm.

Fig. 5. E ff ect of the notch length l N (see Figure 6) on the stress intensity factor (normalized).

The calculated stress intensity factors were compared with experimentally measured stress intensity factors. To this end, strain gauges (SG) were applied to analyze the stress field around the crack tip. Sarangi et al. (2012) suggested positions of the strain gauges. The determination of K I and K II requires six strain gauges at di ff erent positions, see Figure 6. These strain gauges form three pairs. Consequently, three sums (mode I) and three di ff erences (mode II) can be calculated. Subsequently, a system of three linear equations for each mode can be solved for each point of time. Details can be found in Sarangi et al. (2012). The strain gauges were calibrated in pure mode I loading before testing. During calibration it was assumed that K I , SG = K I (Equation (1)) and K II , SG = 0. Hence, a correction factor for each strain gauge was obtained. Consequently, small deviations from the ideal positions were corrected. Fracture surfaces were analyzed by means of scanning electron microscopy (SEM). By tilting the stage and by using the software Alicona Mex, the fracture surface topography was revealed. From the topography, the blunting of the crack tip was quantified. Details of this method were published recently by Weidner et al. (2013).