The increasing interest of engineering sectors, such as aerospace and automotive, in research of lighter and stronger materials has stimulated the design of new typologies of composite materials and in the development of their manufacturing processes. In this contest, composite sandwich structures represent the main solution when a high ratio of flexural stiffness to weight is required. Sandwich is a composite structure usually made of two thin and strong face sheets, usually laminated composites, bonded to a very light material core, such as lattice cores. The combination of these components makes such materials a complex structure, and their development is intrinsically linked with their manufacturing techniques. This thesis focusses on the improvements of their common weak points, providing solutions for the design, manufacturing and development of novel advanced composite sandwich structures and their components. The processes and structures studied are intended for high performance engineering applications, where sandwich materials composed of fiber reinforced polymers skins and cellular cores (such as aluminium or Nomex honeycomb) are widely used. In detail, the scope of the thesis was approached on different levels. From the manufacturing point of view, improvement of interlaminar properties of laminates was studied through analytical and experimental study of the influence of ultrasound consolidation in debulking of prepreg layers. In addition, a novel real-time non-destructive evaluation technique methodology based on an innovative undamaged baseline was developed, which is able to promptly detect defected parts in automatic composite manufacturing processes. From the design point of view, a novel high-performance carbon fibre reinforced sandwich core with thermal induced prestresses was developed. The core was analytically, numerically and experimentally characterised, proving high in-plane and out-of-plane mechanical properties and a remarkable compressive strength to density ratio. To conclude the work, a final novel 3D fibre reinforced sandwich structure, with skins and core constituted by the same material, without adhesive layers and with enhanced mechanical properties was designed, manufactured and characterised under low-velocity impact tests. Each of these approaches represents a solution for the development of novel improved sandwich structures and can be applied in engineering sectors where low number of manufacturing defects and high performance materials and structures are required.
|Date of Award||14 Sep 2022|
|Supervisor||Michele Meo (Supervisor) & Fulvio Pinto (Supervisor)|