FAILURE MODE MAPS FOR NATURAL FIBER REINFORCED COMPOSITE SANDWICH PANELS

JUAN PABLO VITALE; GASTON FRANCUCCI; ARIEL STOCCHI

Munich

Conferencia; 17th European Conference on Composite Materials; 2016

The increasing requirement for bigger, faster and lighter vehicles has increased the importance of efficient structural arrangements, making sandwich constructions a well-established technique in lightweight component design.Sandwich panels are widely used as a means to build high-performance lightweight structures, and their weight reduction can be used to increase the payload, to increase the speed or just to reduce the energy consumption with maintained loading capability and top speed. Sandwich panels are used not only because of their advantages in terms of weight saving and structural performance, but also as an effective means to reduce costs. Thus, there is always an interest in the development of new materials and designs for low-cost high-performance cores. At the same time, there is also an increasing interest to substitute glass and carbon fibers by natural ones, as well as replacing the traditional cores such as pvc foams, Nomex and aluminum honeycombs. Natural fibers present some advantages when compared to their synthetic counterparts: they are cheaper, they have lower mass per unit area, they are eco-friendly, recyclable and biodegradable by nature, they do not produce skin irritation, and they provide good acoustic-insulating properties. Fiber reinforced honeycomb cores were obtained by Vacuum Assisted Resin Transfer Molding (VARTM). The clearance between the inserts, and thus the honeycomb wall thickness, was t= 1 ±0.10 mm. The cell size was 12 mm. To prepare the fiber-reinforced honeycombs, jute fabrics were placed between the inserts following a zigzag pattern in the ribbon direction In order to facilitate the placement of the reinforcement and its uniform distribution along the walls, the fiber fabrics were put in place at the same time the inserts were fixed to the bottom plate. The walls and the nserts with the shape of the cells were kept in place by screwing them to the bottom plate. Afterwards, the resin was injected into the mold. Skins of bidirectional glass fiber and jute fabrics were obtained by VARTM. The resin used was a general purpose polyester. The cores and the skins were bonded using the same resin. Three point bending tests were carried out to study the mechanical behaviors of the sandwich beams. Based on theoretical approaches a map predicting the failure mechanism for a given material combination and beam geometry in three point bending can be constructed. In this work failure maps for commercial foam cores, and manufactured fiber reinforced honeycombs cores are presented for different face sheet / core combinations. Core and skin failure mechanisms as core shear, indentation, skin yield and skin wrinkling were included into the models. The aim of this work is not only to develop alternatives to traditional cores. The investigation of the mechanical properties, manufacturing process and prediction of failure modes for flexuralsolicitations were also discussed.