| Description |
This work is aimed towards the development of a standardized test to quantify the critical strain energy release rate, Gc, of debond growth along the facesheet/core interface under Mode I loading of sandwich composites. The single cantilever beam (SCB) configuration is used throughout this research and was seen to consistently propagate debonds along the facesheet/core interface for a wide variety of sandwich constructions, including both foam and honeycomb cores. A test fixture is described which utilizes an edgewise clamping base and lengthened loading rod to ensure Mode I dominated debond growth throughout the test. Specimen geometry and sizing (specifically specimen width, facesheet thickness, and initial debond location) are investigated in depth analytically using the Virtual Crack Closure Technique (VCCT) and experimentally using the Compliance Calibration (CC) method to ensure high (greater than 95%) Mode I dominance and accurate Gc measurements. Anticlastic bending of facesheets and plane stress conditions along the edges of the specimen were seen to cause debond curvature. For sandwich composites with cores of a continuous bond surface, a specimen width of 50.8 mm (2 in.) was seen to be sufficient to achieve fully developed, self similar debond growth. For cores of a discontinuous bond surface, a minimum specimen width of 50.8 mm (2 in.) and at least 6 cells across the specimen width was seen to be sufficient to achieve consistent Gc measurements. Facesheet thickness was not seen to alter debond growth, except when tabbing was bonded to thin facesheeted constructions in an effort to reduce deflections. The tabbed specimen saw a change in failure mode, which was also evident in Gc measurements. Initial debond location was not seen to be a factor in any of the testing. Debonds above, below, and in the interfacial bondline were all seen to propagate along the same path and debonds located at the centerline of the core were seen to "self-adjust" and shift from the centerline to the upper facesheet/core interface. |
