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This paper presents some aspects of fault-tolerant design using hardware redundancy. The voter is the key element in N-Modular Redundant Design.Hardware voters are bit voters that compute a majority of n input bits. An m-out-of-n hardware bit voter is a circuit with n bit inputs, and 1 bit -output y, such that y=l if at least m-out-of-n inputs bits have the value 1. A hardware voter can be implemented with logic gates in CMOS VLSI technology. Designers are looking for optimal designs with respect to the following criteria: circuit complexity, number of logic levels, fan-in and fan-out, power dissipation, testability, or any combinations of the previous requirements in order to obtain high reliability for the voting circuits.A detailed reliability analysis, failure modes and effects analysis of voters at the transistor level is performed using CARE tools. CARE (Computer Aided Reliability Engineering) is a powerful software tool that can be used concurrently in the phases of R&D for complex reliability analyses of electronic circuits.The main goal of these analyses is to identify the best designs of voting circuits, in terms of reliability parameters and to identify the possible technological failures that can affect them.

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-The experimental study of a highly compressible porous material, made of cellulose fibers, and imbibed with water, during stress relaxation tests on a rheometer, shows that the material relaxes when kept at constant strain as long as there are open pores. Using the relaxation curves, the behaviour under compression can be divided into two distinct zones, a poro-elastic one and a purely-elastic one, bounded by the zero-porosity limit. In the poro-elastic zone, the "non-hookean" stress-strain curve is fitted using Spriggs' expression of the elastic modulus dependence with porosity. Therefore, the elastic modulus of the porous material is expressed as an exponential function with two parameters: the elastic modulus of the fibers and the initial porosity of the material. For the purely -elastic zone the variation of stress is expressed as a sum of the residual stress obtained from the continuity equation and a Hookean stressstrain variation of a thinner material with the elastic modulus of the fibers -determined previously. The relaxation curves are fitted with a relationship between the decay stress and time, approximated with three terms of Prony series expansion of the generalized Maxwell model.

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