A Fracture Mechanics Based Methodology to Address Face Sheet/Core Disbonding in Composite Sandwich Structures
Krueger, R., Adams, D., Berggreen, C., Hoyt, D. M., Saseendran, V.
2024 American Society for Composites (ASC) 39th Annual Technical Conference, San Diego, CA, November 2024.
Face sheet /core disbonding poses a threat to the structural integrity of a sandwich component. In this study a methodology is proposed to predict the onset and growth of face sheet/core disbonding in sandwich structures. The methodology is similar to the one used for delaminations in monolithic composite laminates where an assessment is typically made by measuring a critical strain energy release rate. Two general steps are required to address the phenomenon associated with face sheet/core disbonding. First, a reliable means of characterizing face sheet/core disbonding has to be established. The Single Cantilever Beam (SCB) test has been identified as the most appropriate configuration to develop an ASTM standardized test method for determining the Mode I dominant fracture toughness of sandwich constructions. Additionally, the development of a guide for Mode I fatigue based on the static SCB test is proposed. Further, a Sandwich Mixed-Mode Bending (S-MMB) test for mixed-mode I/II fracture toughness of sandwich constructions based on the ASTM MMB test for laminates is suggested. Second, analysis methods are required to help assess the likelihood of a structure exhibiting critical disbonding. As an example, the Crack Surface Displacement Extrapolation (CSDE) method was used to assess disbond growth in a sandwich panel containing an artificial disbond and predicted growth was compared to test results. A rapid engineering analysis tool based on an energy-based Rayleigh-Ritz approach is also discussed.