Analysis of the effect of face sheet debonding in the bending of composite sandwich beam

• Main Author: Peh, Jin Zhuang
• Other Authors: Chai Gin Boay
• Format: Final Year Project
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Aeronautical engineering
• Online Access: http://hdl.handle.net/10356/64839
• Institution: Nanyang Technological University

With the increase acceptance of sandwich structures in weight critical applications, such as in the marine and aviation industry, it is essential to understand the structural behavior and failure mechanism of these structures. Sandwich structures are susceptible to unconventional failures such as face-core debonding. Therefore, the aim of this project is to analyse the effect of face-core debonding on the structural behavior of composite sandwich beams. Composite sandwich beams with varying extent of face-core debond at the top interface were fabricated. 16 layers of carbon laminating prepreg were used to fabricate the face sheets. The core was Nomex honeycomb of cell size 13mm and core height 25mm.The failure modes of these composite sandwich beams under 3-point bending loads were determined. Indentation tests were conducted on 0% & 20% face-core debond sandwich beams to further understand the structural response. At least two specimens of each face-core debond configuration were tested and the results were consistent. Results were analysed and possible explanation of observations were presented. Core shear, core crushing, face-core debonding, face sheet fracture and face sheet delamination were failure modes observed. The results revealed that the adhesive film was crucial in enabling effective transfer of stresses from the face sheet to the core. A new parameter, stiffness recovery ratio, was introduced to quantify the change in stiffness observed during the bending process. In order to characterise the indentation behaviour of the sandwich beams, the face affected region and core buckling region of the indented sandwich beams were measured during experiment as well as through video footage. With the use of graphs, the relationships between the face affected region, core buckling region and indentation displacement were established. The load vs indentation displacement graph was also examined to further develop an understanding of the indentation behaviour. In the conclusion, the significant findings and experimental limitations were highlighted. Thereafter, recommendations were presented for future work to improve the reliability and usefulness of the experimental data gathered.