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

Table 3.4: Parameters in the face/core interface fracture toughness function, Equation (3.14).
Core
GIC (J/m 2 )
Average fit
GIC (J/m 2 )
Lower bound
GIC (J/m 2 )
Upper bound
k
H130 450 280 620 0.45
H250 500 350 660 0.55
PMI 115 80 150 0.55
Figure 3.6 illustrates the typical crack path observed in the MMB specimens with PMI core. As it
is seen, the crack grows below resin-rich cells in the core for all measured mode-mixities.
Figure 3.6: Crack path for an MMB specimen with PMI core.
For specimens with H130 core and mode-mixity phase angle of 0° >> -20°, the crack path was
located below the face/core interface, see Figure 3.7. However, for the mode-mixity phase angle
of -25° >> -65°, as shown in Figure 3.8, the crack path was in the actual face/core interface. As
mentioned earlier, a toughening mechanism due to the increased negative mode-mixity is
observed in this core material as well. This trend in the fracture toughness vs. mode-mixity was
previously reported for other debonded sandwich materials tested at controlled mode-mixities,
see Berggreen et al. (2005).
Figure 3.7: Crack path for an MMB specimen with H130 core below the face/ core interface.
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