Fabrication of Advanced Hybrid Composite Sandwich Panels - Testing & Simulation (FACTS)

Abstract

Research into composite materials has gained rapid popularity in many industrial applications, mentioning only a few: the marine, aerospace and automotive industries. The composite material, a specific combination of fibre reinforced resins, produces a combination and intimate relationship between the constituent materials. A superior material which is more efficient and fit for purpose is produced. The aim of this research is to extend the use of the composite by combining with a core material to produce a sandwich material combination. The fabrication of the sandwich panels, together with vacuum bagging is relatively a new concept for Malta, to produce a hybrid advanced composite sandwich panel of superior material properties and characteristics. The hybrid sandwich materials produce a weight saving, cost efficient and higher performance material, when components and structures are subjected to in service loading conditions. The resulting ‘new’ material is targeted for the marine and boat building applications.

This collaboration of research brought together the academic members of staff and a local boat builder, Buccaneer Boats Ltd. Presently, local boat builders use the traditional wet lay-up process, which is a manual procedure using low cost tools such as rollers and brushes, were the fibres which are in the form of woven, knitted, stitched or bonded fabrics are impregnated with resin and are worked into a female mould manually and the laminates are cured under atmospheric conditions. Although this present method has been used for many years and involves simple principles to teach, the laminate quality is very dependent on the skills of laminators. Structural members or hulls made of two stiff, strong skins separated by a lightweight core are referred as sandwich panels. The mechanical properties of the sandwich depend on the core, face materials and the bonding process, as well as the thickness of the core and faces. The marine core material in closed cell PVC foam which forms a highly complex 3D network which have: environmental stability (high tolerance for heat and chemical exposure); built in toughness (high ductility and damage tolerance); superior uniformity (low density variation); eliminating outgassing; compatibility (suitable for use with all polyester, vinylester and epoxy resins); no inhibition (do not inhibit resin curing mechanisms); handling (tough and easy to machine), The type of core material selected is approved by various marine classification authorities amongst which are: American Bureau of Shipping, ABS, Lloyds Register of Shipping, Det Norske Veritas, DNV and Germanisher Lloyd, GL

The face is to be made of a composite laminated, made of at least two elements to produce a material whose properties are superior to the individual elements. Most common man-made composites are polymer matrix, PMC (also known as FRP – fibre reinforced polymers (or plastics) used in marine craft fabrication), metal matrix composites, MMC and ceramic matrix composites, CMC. The use of sandwich construction in boat building requires the utilization of advance construction techniques in order to gain the maximum performance from the build materials. Vacuum bagging is one such techniques which lends itself not only to the primary structure of boats, but to all aspects of boat building. This fabrication process is an effective, cost-effective techniques utilising pressure difference to produce a superior high strength hybrid sandwich material.

Although international manufacturers of pleasure and high-speed craft (even racing and performance sailing craft) have already introduced such vacuum bagging techniques into their cored hull designs, the manufacturers keep hull specification and fabrication information as closely guarded secrets This technique is novel in Malta and this research is to take this cutting-edge manufacturing process and technology and introduce it to the local boat builder/s. The grounding and impact of hull scenarios are unfortunately quite common and although accepted as a real and identifiable problem it has not been comprehensively addressed. Presently the standards only regard material properties, thickness of panels, maximum deflection and bending moments that can be sustained under the action of hull pressures as the important controlling factors. Failure and openings of hulls may occur well below the maximum values of loading, deflection or bending moment. The new hybrid, increased strength panels can resist such failure. The sandwich construction also acts as a “double hull”, and in such scenarios, each successive layer absorbs the energy of damage, making a safer vessel and reduces the raking damage tear length Doubled hulled metal vessels were introduced after the major ecological disaster of the Exxon Valdes, proving that safety needs to be addressed. The idea of such doubled hulled high speed FRP vessels will improve the safety record and prevent “Loss of Life at Sea” as part of SOLAS since such vessels are typically high human carriage vessels. A vessel made with such a “double hull” will gain increasing popularity with the classification and certification authorities, locally and internationally.

Most boat designs are based on boat building experience rather than on full structural analysis which can be a costly endeavour. In order to reduce such costs, concept modelling is to be introduced, to validate the experimental test results.

In conclusion the focus of this research project is to achieve the optimum composite characteristics, combine the composite laminate to a core material and produce a hybrid advanced composite sandwich panel through an efficient, cost effective fabrication process achieved through rigorous experimental testing. An analytical predicative concept model has been developed to provide a simple and fast tool, which can be used to size the resulting hybrid marine hull panels.