PSI - Issue 51

Mohammad Reza Khosravani et al. / Procedia Structural Integrity 51 (2023) 81–87

85

Mohammad Reza Khosravani et al. / Procedia Structural Integrity 00 (2022) 000–000

5

80

2000

70

1600

60

50

1200

40

Force [N] 800

30

20

400

10

0

0

0

0.01 0.02 0.03 0.04 0.05 0.06 0.07

0

0.5

1

1.5

2

2.5

3

3.5

Displacement [mm]

Fig. 3. Load-displacement and stress-strain curves of examined dumbbell-shaped specimens.

A series of three-point bending test was carried out by applying a single point force at mid-span on the top surface of a simply supported SENB specimen which has a pre-crack on the bottom surface, also at mid-span. The bottom is under tension under this setup and enables an easy method for mode I fracture testing without requiring specimen grips. It is noteworthy that the tests were repeated six times to confirm that the obtained results are reliable. Fig. 4 shows a SENB specimen under test conditions and the obtained force-displacement curve.

800

700

600

500

400

Force [N]

300

200

100

0

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Displacement [mm]

Fig. 4. The SENB specimen under test conditions and obtained load-displacement curve.

The nominal bending strengths σ N for all specimens can be calculated from the peak load P and measured specimen dimensions using:

P bD

3 PS 2 BD 2

σ N = c n

(1)

=

where P denotes the peak load, P / bD is the general equation for nominal strength, and c n is a constant dependent on the geometry. For SENB geometry, the constant c n is commonly chosen to be equal to 3 S / 2 D , so that σ N equals the maximum elastic stress in the beam. For all specimens it can be seen that the load increased linearly, then reached a peak and then decreased in a stable fashion. The load decrease corresponds to propagation of the crack. In this study, in order to provide better insight into the fracture behavior of the specimens, the fracture region of the SENB specimens were examined using a 3D laser microscope and also by a free-angle observation system. This visual investigation reveals that the fracture trajectory in the SENB specimen is straight and along the initial crack. In fact, for all SENB