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

Crack growth paths for the STT specimens with H45, H100 and H250 cores from the static tests
are shown in the following figures. For the specimens with H45 core, the crack kinks into the
core up to 4-5 mm below the interface and then approaches the face/core interface as the crack
propagates further. However, since the fracture toughness of the H45 core is low compared to
that of the face/core interface, the crack never kinks into the interface and continues to propagate
in the core just below the resin-rich region of the core, see Figure 5.7. For the specimens with
H100 core, the crack initially kinks into the core and continues to propagate 2-3 mm below the
interface. After 45-55 mm of crack growth it eventually kinks into the face/core interface and
subsequently into the face sheet, which leads to large-scale fibre bridging, see Figures 5.8 and
5.9. For the specimens with H250 core, the crack starts to propagate in the face/core interface.
Subsequently, it kinks into the face sheet after 25-35 mm propagation and continues to propagate
in the face sheet, resulting in large-scale fibre bridging, see Figure 5.10. The static crack
initiation and propagation loads are listed in Table 5.2. It is seen that the mainly constant crack
propagation load is much lower that the crack initiation load, which can be attributed to the
initial resistance of the crack due to the accumulation of resin at the crack tip during the
manufacturing process at the predefined face/core crack.
H45 Specimen
Figure 5.7: Static crack growth path for an STT specimen with H45 core at the beginning and
end of the test.
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