Inserts are used to transfer localized loads to structures made of sandwich composites. Stress concentrations near inserts are known to cause failures in sandwich panels. Experimental insert pull-out tests show that the load to failure can vary by 20% between batches of sandwich panels. Clearly, uncertainties in the mechanical properties of core and adhesive potting materials have to be accounted for in the optimal design of inserts in sandwich composites. In this paper, we use an one-dimensional computational model of an insert in a homogenized honeycomb sandwich panel to explore the utility of reliability methods in design. We show that the first-order reliability method (FORM) produces accurate estimates of loads that lead to low failure probabilities. We also observe that FORM is sensitive to the failure criteria and may not converge if the failure surface is not smooth and convex.

An one-dimensional finite element model of a sandwich panel with insert is derived using the approach used in the Thomsen model. The one-dimensional model produces results that are close to those of a two-dimensional axisysmmetric model. Both models assume that the core is homogeneous. Our results indicate that the one-dimensional model may be well suited for small deformations of sandwich specimens with foam cores.

This paper describes a novel class of meta-materials that exhibit significantly greater transmission loss than conventional sound insulation systems of similar size and weight over selected frequency bands. This is achieved by the action of small resonator elements distributed throughout the wall at spacings much smaller than the wavelength of structural vibrations in the base wall material. The research reported here is at an early stage. Experiments are described which demonstrate enhanced transmission loss in small proof-of-concept samples and a simple theoretical model is presented.

Elastic meta-materials or meta-composites can be designed to have a negative effective mass density at certain vibration frequencies, thus blocking wave propagation through the material within that frequency band. The negative mass behaviour is generated by resonant structures within the material that oscillate 180 degrees out of phase with the acoustic pressure waves applied to the surface. As this research is in its initial stages this paper describes work in progress in both the experimental and numerical domains, and some early results from solids containing geometrically, simple spring-mass resonant structures. Behaviour is characterized experimentally by dynamic tests of individual resonators as well as impedance tube measurements of panel-like structures containing multiple resonant elements. The experimental results exhibit clear evidence of the expected resonances, and partial band gap behaviour. Finite element models of both single resonant elements and impedance tube specimens are being developed, and the current status of these models is described. Their results to date show good agreement with the mass law and qualitative agreement with the experimental results.(C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim