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

Figure 5.34: Drawing of debonded sandwich panels with an image of a manufactured panel.
Table 5.4: Face and core material properties.
Material E (MPa) G (MPa)
Face sheet 19400 7400 0.31
Core: H45 50 15 0.33
All specimens were reinforced with wooden inserts at the edges to avoid crushing of the core.
The debond was introduced before the resin infusion by inserting a piece of 0.025 mm thick
Airtech release film on the core in the centre of the panels and sealing the edges with resin. The
test rig consists of welded steel square profiles with a wall thickness of 3 mm. A 4 Mpix Digital
Image Correlation (DIC) measurement system (ARAMIS 4M) was placed above the panels to
monitor 2D surface strains and displacements in order to estimate the crack growth continuously
during the experiments. The test rig was inserted in an MTS 810 servo-hydraulic testing machine
with a maximum capacity of 100kN and an integrated T-slot table upon which the test rig was
positioned and fixed. However, a smaller 25 kN load cell was used in the experiments to increase
the accuracy of the load measurements, see Figure 5.35. To load the centre of the debond using
the actuator of the testing machine a hole of a diameter of 6 mm was drilled at the centre through
the entire thickness of the panels, and the centre of the debond was bolted to a long steel rod
connected to the actuator piston, see Figure 5.37 and 5.38. The panels were fixed to the test rig
by twelve steel clamps and four 6 mm thick steel plates as shown in Figure 5.37. To avoid
harmful side forces on the testing machine actuator, which may be generated by an uneven
debond growth during the fatigue loading, the setup in Figure 5.36 was used. The setup includes
a lubricated bronze cylinder in which the actuator piston of the testing machine can move freely.
The cylinder is connected to the four columns of the testing machine by adjustable steel arms. In
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Wood inserts
Debond