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

Figure 2.21 shows energy release rate and mode-mixity in terms of phase angle vs. load for
columns with a 50.8 mm debond and H45, H100 and H200 cores. Figure 2.21 (a) shows that G
increases significantly in a certain load regime which can be associated with the opening of the
debond. The fracture toughness values shown in Figure 2.21 (a) were determined by the TSD
tests, described in Section 4. The reduction of phase angle as the load increases, Figure 2.21 (b),
shows that the crack tip loading becomes more shear dominated at high loads.
G (J/m 2 )
1200
800
400
0
H45
H100
H200
(-24º) H45
(-29º) H100
Gc(-29), H100
G c(-24), H45
0 3 6 9 12
Load (kN)
(a)
Phase angle (deg.)
Figure 2.21: (a) Energy release rate vs. load and (b) phase angle vs. load for columns with a
50.8 mm debond and H45, H100 and H200 cores.
In order to investigate the influence of the initial imperfection on G and , columns with H100
core and 38.1 mm debond with three initial imperfection magnitudes (0.1, 0.2 and 0.5 mm) were
analysed. Figure 2.22 shows G and vs. load for these columns. From Figure 2.22 (a) it is seen
that G is not highly sensitive to the initial imperfection magnitude. The phase angle, Figure 2.22
(b), is sensitive to the initial imperfection at small loads, but appears to converge to a value about
-30 ° at higher loads, which indicates that the mode-mixity is less influenced by the initial
imperfection at higher loads.
The crack propagation load was estimated using fracture toughness data from the TSD tests.
Energy release rate and mode-mixity in terms of phase angle were determined in the interior
(centre) of the columns. Numerically predicted and experimentally determined propagation
loads, which means the maximum load in the load vs. axial displacement diagrams (Figure 2.3
(a)), for the debonded columns are listed in Table 2.5.
35
-18
-22
-26
-30
-34
-38
Load (kN)
0 3 6 9 12
(b)
H45
H100
H200