In this paper, a new and innovative process for assembling chains of carbon nanofibers (CNFs) in epoxy, uniquely different from those generally used for chaining particles in a liquid medium, is presented. Chains of aligned CNFs are assembled in a region rich in CNFs and extended into regions where there are no CNFs. A physical explanation of the process is provided based on the conductive nature of the CNFs. By contacting the chains with the electrodes, the process of chain growth is expedited and well-ordered parallel chains with equal spacing are grown over distances of 2 cm.

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The discrepancies observed in the measured strains and those calculated on the basis of a plane-stress elasticity solution for a thick, polar–orthotropic, C-shaped ring with end loading are investigated by finite element analysis (FEA). Thick C-rings are used as test specimens for determining the tensile radial strength of composite flywheel rotors. The C-ring is modeled in three dimensions and the strains predicted on the surface of the specimen are compared with the measured strains to validate the model. The discrepancies in the strains and stresses predicted by the planestress elasticity and 3-D finite element approaches are attributed to the Poisson’s effect, which gives rise to a significant variation of stresses and strains across the axial thickness. The discrepancies depend on the geometry of the specimen. Therefore, the effects of the geometric dimensions on the variation of stresses are studied using the 3-D FEA and a guideline is proposed for selecting a C-ring specimen geometry to have approximately uniform stresses through the axial thickness.

The objective of this investigation is to evaluate a new method of testing thick, C-shaped rings for determining the radial tensile strength of thick, filament-wound composite structures such as flywheel rotors. The proposed method of loading C-rings with a hydraulic jack is simpler than previously used loading methods and is shown to be quite tolerant of eccentricity of the jack. It is shown by sectioning a C-ring that residual stresses in the specimen are negligible. Based on a detailed stress analysis and post-failure inspections of appropriately dimensioned specimens, it is concluded that failure is caused by radial tensile stress at a single critical location in the specimen. The radial tensile strengths of four candidate flywheel rotor materials measured with C-rings were generally less than strengths measured with flexure specimens. The simplicity of specimen preparation and testing by the proposed method, in conjunction with promising early results, suggests that the C-ring test method is suitable for widespread use and possible standardization.

Purpose -The presence of random noise as well as narrow band coherent noise makes the structural health monitoring a really challenging issue and to achieve efficient structural health assessment methodology, very good extraction of noise and analysis of the signals are essential. The purpose of this paper is to provide optimal noise filtering technique for Lamb waves in the diagnosis of structural singularities. Design/methodology/approach -Filtration of time-frequency information of multimode Lamb waves through the noisy signal is investigated in the present analysis using matched filtering technique and wavelet denoising methods. Using Shannon's entropy criterion, the optimal wavelet function is selected and verification is made via the analysis of root mean square error of filtered signal. Findings -The authors propose wavelet matched filter method, a combination of the wavelet transform and matched filtering method, which can significantly improve the accuracy of the filtered signal and identify relatively small damage, especially in enormously noisy data. Correlation coefficient and root mean square error are additionally computed for performance evaluation of the filters. Originality/value -The present study provides detailed information about various noise filtering methods and a first attempt to apply the combination of the different techniques in signal processing for the structural health monitoring application. A comparative study is performed using the statistical tool to know whether filtered signals obtained through three different methods are acceptable and practicable for guided wave application or not.

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