Failure modes of sandwich structures with composites faces
Aleksander Muc, Rafał Nogowczyk Politechnika Krakowska, Wydział Mechaniczny, Instytut Konstrukcji Maszyn, Zakład Konstrukcji Kompozytowych, al. Jana Pawła II 37, 31-864 Kraków
Quarterly No. 4, 2005 pages 31-35
DOI:
keywords:
abstract Sandwich construction consists of two faces (made of materials with high mechanical properties), separated by a core (made of lightweight materials). Comparing a monocoque structure with sandwich structure having the same weight one can observe that both structures have similar extensional stiffness but the latter has much higher flexural stiffness. Stresses caused by inplane loads are the same in both types but bending stresses are much lower in sandwich construction. Thanks to its excellent flexural stiffness sandwich structures with composite faces are commonly used in engineering constructions. However, they are vulnerable to more failure modes than monocoque structures. In the article we present four failure modes: 1) face wrinkling (Fig. 6), 2) core shear instability (Fig. 7), 3) overall buckling, 4) face dimpling or monocell dumpling (only in sandwiches with honeycomb core). The failure modes depend on many conditions. Among them are the material properties of which faces and core are made. Because of their extraordinary mechanical properties, composite materials are often used as faces. As a core, various materials are used. They can be divided into three groups: 1) homogeneous structure (Fig. 2) - i.e. balsa, 2) honeycomb structure (Fig. 3), 3) heterogeneous structure (Fig. 4) - i.e. foam. In the paper we present properties of some composite materials (Table 1) and foam core materials (Fig. 5). In sandwich structure with honeycomb core fourth mode of failure (face dimpling or monocell buckling) can be observed. However, in many constructions it may be neglected. This paper is an introduction in order to consider whether sandwich constructions may be modeled using 2D or 3D theories. Results of further analysis’ will be presented in subsequent papers. Key words: sandwich construction, sandwich core, failure mode, composite, delamination, core shear instability