Experimental Investigations of Static and Fatigue Crack Growth in Sandwich Structures with Foam Core and Fiber-Metal Laminates Face Sheets

Debonding of face-core interface is the most important damage mechanisms which make loss of structural integrity in sandwich structures. In this paper, mode-I and mode-II fracture of facecore interface in sandwich structures have been investigated under both static and fatigue loadings. The considered sandwich structures contain of different face sheet fiber-metal laminates and the core material is polyvinyl chloride foam. Several specimens are fabricated and the experiments are carried out to find the effects of initial debonding location and various fiber-metal laminate face sheets on the fracture toughness under static and fatigue loadings. Double cantilever beam specimens are used for mode-I and end notch flexure specimens for mode-II loading conditions. The resistance strength curves are plotted for mode-I and mode-II under static loading to find the instability point which is the border of stable and unstable crack growth and determine the critical crack length too. The strain energy release rates of mode-I and mode-II are also obtained for fatigue loading to investigate the resistance against damage evolution. Also, the global damage parameter is defined for both static and fatigue loading which is the combination of all damage mechanisms occurred in sandwich structures. Finally, the more efficient layup configurations under static and fatigue loadings among the investigated layups are introduced in mode-I and mode-II fracture conditions separately.