Residual Strength and Fatigue Lifetime of ... - Solid Mechanics

Crack length [mm]
Crack length [mm]
150
120
90
60
30
0
0 20000 40000 60000 80000 100000
Cycles, N
Figure 5.17: Fatigue crack growth from the visual measurements and measurements using
DIC vs. cycles for the STT specimens with (a) H45 (b) H100 and (c) H250 core.
250
200
150
100
50
0
(c)
Crack length [mm]
200
150
100
Figure 5.18: Fatigue crack growth vs. cycles for the STT specimens with (a) H45 (b) H100
and (c) H250 core.
5.2.2 Fatigue Characterisation of the Face/Core Interface
Mixed Mode Bending (MMB) tests were conducted on pre-cracked MMB sandwich specimens,
as introduced in Chapter 3, to characterise the fatigue behaviour of the face/core interface of the
STT specimens, as shown in Figure 5.19. The MMB test rig allows a range of mode-mixities to
be achieved at the crack tip for different lever arm distances, denoted as c in Figure 5.19. A
servo-hydraulic MTS 858 testing machine with a maximum capacity of 100kN was used to load
the MMB specimens. However, a smaller 25 kN load cell was mounted on the actuator to
increase the accuracy of the load measurements.
102
Visual
50
STT H45-1
STT H45-2
50
0
STT H100-1
STT H100-2
0
STT H250-1
STT H250-2
0 50000 100000 0 50000 100000 0 50000 100000
Cycles, N
Cycles, N
Cycles, N
(a) (b) (c)
DIC
Crack length [mm]
150
100