PSI - Issue 13

Ralf Lach et al. / Procedia Structural Integrity 13 (2018) 34–38

37

Author name / Structural Integrity Procedia 00 (2018) 000 – 000

4

a

b

3

2

2

1

1

d

c

3

3

2

1

1

Fig. 3. SEM images of the fracture surface of rolling rings broken at (a) 8 % deformation, (b) 13 % deformation and (c) 17 % deformation, and (d) broken after static loading; 1 – notch, 2 – stable fatigue growth, 3 – unstable crack growth/brittle fracture.

3. Results and discussion

It has been found that the frequency does not influence N B of laser sintered rolling rings made of PA12 (Grießbach (2012)), whereas N B is decreasing logarithmically with increasing deformation (eccentricity) and can be approximated by Equation (1), see Figure 2:

  

  

 

 E E N N E E 0 x 0 B ln    

(1)

with the material-dependent parameter N 0 = 8510  2700, the low cycle deformation E 0 = 15.84  0.58 (in %) und the fatigue deformation limit E  = 6.91  0.84 (in %). The frequency-independent N B values indicate that only negligible heating occurs inside the specimens within the frequency range investigated (100 – 250 cm – 1 ). The decreasing N B in Figure 2 is due to the transition from fully stable crack propagation to mixed stable – unstable crack propagation with increasing deformation. This transition has been shown by analyzing the fracture surfaces of the broken specimens after test using optical microscopy and scanning electron microscopy (SEM). Figure 3 shows SEM images of the fracture surfaces of the broken rolling rings for different deformations where the flakiness of the