Felipe Wolff-Fabris

An investigation on the flexural properties of balsa and polymer foam core sandwich structures: Influence of core type and contour finishing options:

Polymer foams are frequently used as core materials in sandwich structures for applications such as aerospace, naval, and wind industry. It is known that the core material contributes to the overall mechanical properties of these sandwich structures up to a remarkable extent. In addition, due to the curvature and geometrical complexities of several applications, these cores are available with special cuts/grooves (finishing options) to provide bendability and better resin infusion during processing. The goal of this study is to investigate the mechanical performance of synthetic polymer foams as core materials for sandwich structures. Balsa wood, which is the most common traditional structural core, was used as reference material. Glass fiber reinforced epoxy was employed as face sheets. End-grain Balsa wood, commercially available polyvinyl chloride and polyethylene terephthalate, and experimental grades of polyurethane foams were chosen as alternative core materials. Quasi-static flexural tests were carried out using a four-point bending setup according to ASTM C 393. Sandwich properties such as stiffness, core shear strength, and energy absorption were determined and compared. The contour cuts filled with resin show a reinforcing effect against transverse shear stresses leading to higher shear strengths. Digital image correlation was used to study the yielding and permanent strain of the foam core sandwich beams.

Toughened high performance epoxy resin system for aerospace applications

Abstract The present study describes the results of a detailed investigation of the fracture toughness and fatigue crack growth behaviour of epoxy resins used for aeronautic applications. More specifically, the influence of incorporating thermoplastic or triblock copolymers to neat resin in order to increase the toughness is evaluated. The experimental results deduced from static as well as dynamic loading conditions highlight the varying degree of effectiveness of the chosen toughening approaches. In combination with electron microscopic analysis of the fracture surfaces, the basic structure-property relationships and deformation mechanisms are presented and the different strategies to improve the fatigue behaviour are discussed.