Journal of Sandwich Structures & Materials

A new crack arrester was proposed, in which a different material with higher stiffness is installed on the crack propagation path. The effect of this crack arrester was experimentally evaluated for interfacial crack propagation between a carbon fiber reinforced plastic surface skin and a foam core. The experimental results indicated that the crack arrester increased the critical load of the crack growth, and approximately five times larger apparent fracture toughness was obtained near the leading edge of the arrester by considering the energy release rate. It was also confirmed that the fabrication of the crack arrester had no detrimental effect on the intrinsic properties of the sandwich panel structures.

Wide spread use of sandwich structures is still inhibited by the lack of a consistent joining technology one which is easy to work with, quantifiable and not dependent on special knowledge about manufacturing processes. A mechanical technology for joining sandwiches as developed in this article shall achieve these goals. The developing process follows the design methodology according to Pahl et al. [1]. The resulting systematic approach to the problem facilitated the generation of a complete solution field. This approach led to 18 promising concepts of 783 possible original solutions. Prototypes of those concepts showed that a reliable mechanical technology for joining sandwich elements is feasible.

Cork is a material of great value to the Portuguese economy. Unfortunately, its use is still restricted to traditional areas, with the agglomerate form in particular not being used to its full potential. The objective of this article is to analyze the viability of using cork-based material as core materials in sandwich structures in aeronautical and aerospace applications. The use of cork-based material is proposed because of its isolation properties (both thermal and acoustic) and there is no significant performance loss, when compared with the currently used materials. It presents other advantages, as well as, less wastage of energy in manufacturing and a better environmental integration, both in the transformation stage and in the end of life recycling stage. The objective of this work is to study the mechanical behavior of different sandwich specimens, with carbon/epoxy faces, and cores of different cork agglomerates and their comparison with the results obtained with similar specimens using current material cores. Experimental shear tests and three-point bending tests were carried out and the evolutions of the load— displacement curves of the different cork agglomerates/sandwiches were analyzed and discussed. The obtained results show that significant room for improvement still exists in use of cork-based core materials.

Bonded inserts are commonly used to introduce localized loads into sandwich panels. This article investigates sources of variability in the pull-out strength of metallic inserts in aramid honeycomb sandwich panels. Finite element modeling is used to investigate the sensitivity of core stresses to potting depth in partially potted inserts, which is found to be significant. Experimental specimens showed large variations in potting radii and cell wall dimensions, both critical parameters since the failure mode is predominantly core shear, adjacent to the potting. Foam core specimens were also tested and showed significantly lower variability in pull-out strength compared with honeycomb specimens.

Flexural vibration of a clamped—clamped, three-layer, one-span sandwich, unidirectional structure composed of isotropic layers is considered in the article. A new single series model of the 2D problem, obtained within the local theory of linear elastodynamics, is presented. Very realistic boundary conditions at edges of the structure, which correspond to the engineering solution with the edge stiffeners, are introduced and satisfied. Eight eigenfrequencies of the structure for two sets of input data are calculated, according to the new model, and compared with numerical and experimental results existing in the literature. A detail comparative analysis of the results is done and some conclusions are presented.