Triple correlation for detection of damage-related nonlinearities in composite structures

Nonlinear effects in vibration responses are investigated for the undamaged composite plate and the composite plate with a delamination. The analysis is focused on higher harmonic generation in vibration responses for various excitation amplitude levels. This effect is investigated using the triple correlation technique. The dynamics of composite plate was modelled using two-dimensional finite elements and the classical lamination theory. The doubled-node approach was used to model delamination area. Mode shapes and natural frequencies were estimated based on numerical models. Next, the delamination divergence analysis was used to obtain relative displacements for delaminated plies. Experimental modal analysis test was carried out to verify the numerical models. The two strongest vibration modes as well as two vibration modes with the smallest and largest motion level of delaminated plies were selected for nonlinear vibration test. The Fisher criterion was employed to verify the effectiveness and confidence level of the proposed technique. The results show that the method can be used not only to reveal nonlinearities, but also to reliably detect impact damage in composites. These results are confirmed using the statistical analysis

Damage detection by using FBGs and strain field pattern recognition techniques

A novel methodology for damage detection and location in structures is proposed. The methodology is based on strain measurements and consists in the development of strain field pattern recognition techniques. The aforementioned are based on PCA (principal component analysis) and damage indices (T 2 and Q). We propose the use of fiber Bragg gratings (FBGs) as strain sensor

Analysis of elastic nonlinearity for impact damage detection in composite laminates

This paper concerns the experimental analysis of nonlinear response features of a composite laminate plate for impact damage detection. The measurement procedure is based on the Scaling Subtraction Method (SSM) and consists in exciting the damaged specimen with two sinusoidal signals at different amplitude. The linearly rescaled response signal at low amplitude excitation is subtracted from the response at large amplitude excitation to extract the nonlinear signatures. The latter are analysed in the time domain to infer the presence of damage. Results are compared with frequency domain analyses using the nonlinear vibro-acoustic modulation technique (NWMS). Changes in amplitude and phase as well as modulation effects of the acquired responses are also monitored. Surface-bonded, low profile piezoceramic transducers are used for excitation and sensing. Both measurements techniques are applied to detect barely visible impact damage in laminate composite plate. Non-destructive penetrant-enhanced X-ray inspections are carried out to characterize the extent of internal damage. The behavior of the nonlinear features and the sensitivity of each technique are also investigated in the paper

VIBROTHERMOGRAPHY FOR IMPACT DAMAGE DETECTION IN COMPOSITES STRUCTURES

The paper investigates modelling aspects related to application of vibrothermography for detection of barely visible impact damage in composite structures. Low-velocity impact tests were performed to introduce multiple delaminations into carbon/epoxy composite plate. Damage severity was revealed using well-established non-destructive evaluation techniques. Vibrothermography was used subsequently to show good agreement with classical damage detection techniques. Following these experimental investigations, numerical simulations were performed to assess feasibility and sensitivity of vibrothermography for impact damage detection. Numerical results were validated using experimental data showing very good qualitative and encouraging quantitative agreement. The study demonstrates that virtual impact damage detection using vibrothermography can be performed as part of structural design to assess sensitivity of the method in real engineering applications. Copyright © 2012 John Wiley & Sons, Ltd

Extended PCA visualisation of system damage features under environmental and operational variations

Copyright 2009 Proceedings of SPIE, the International Society for Optical Engineering. One print or electronic copy may be made for personal use only. Systematic electronic or print reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.This paper explores the use of Principal Component Analysis (PCA), an extended form of PCA and, the T2- statistic and Q-statistic; distances that detect and distinguish damages in structures under varying operational and environmental conditions. The work involves an experiment in which two piezoelectric transducers are bonded on an aluminium plate. The plate is subjected to several damages and exposed to different levels of temperature. A series of tests have been performed for each condition. The approach is able to determine whether the structure has damage or not, and besides, gives qualitative information about its size, isolating effects of the temperature.Peer ReviewedPostprint (author's final draft

Generation of higher harmonics in longitudinal vibration of beams with breathing cracks

Classical nonlinear vibration methods used for structural damage detection are often based on higher- and sub-harmonic generation. However, nonlinearities arising from sources other than damage – e.g. boundary conditions or a measurement chain – are a primary concern in these methods. This paper focuses on localisation of damage-related nonlinearities based on higher harmonic generation. Numerical and experimental investigations in longitudinal vibration of beams with breathing cracks are presented. Numerical modelling is performed using a two-dimensional finite element approach. Different crack depths, locations and boundary conditions are investigated. The results demonstrate that nonlinearities in cracked beams are particularly strong in the vicinity of damage, allowing not only for damage localisation but also for separation of crack induced nonlinearity from other sources of nonlinearities

Mutations in the C-terminal region of the HIV-1 reverse transcriptase and their correlation with drug resistance associated mutations and antiviral treatment

<p>Abstract</p> <p>Objective</p> <p>Replication of HIV-1 after cell entry is essentially dependent on the reverse transcriptase (RT). Antiretroviral drugs impairing the function of the RT currently aim at the polymerase subunit. One reason for failure of antiretroviral treatment is the evolvement of resistance-associated mutations in the viral genome. For RT inhibitors, almost all identified mutations are located within the polymerase; therefore, general genotyping confines to investigate this subunit. Recently several studies have shown that substitutions within the RNase H and the connection domain increase antiviral drug-resistance in vitro, and some of them are present in patient isolates.</p> <p>Aim</p> <p>The aim of the present study was to investigate the prevalence of these substitutions and their association with mutations in the polymerase domain arising during antiretroviral treatment.</p> <p>Materials and methods</p> <p>We performed genotypic analyzes on seventy-four virus isolates derived from treated and untreated patients, followed at the HIV Centre of the Johann Wolfgang Goethe University Hospital (Frankfurt/Main, Germany). We subsequently analysed the different substitutions in the c-terminal region to evaluate whether there were associations with each other, n-terminal substitutions or with antiretroviral treatment.</p> <p>Results</p> <p>We identified several primer grip substitutions, but almost all of them were located in the connection domain. This is consistent with other in-vivo studies, in which especially the primer grip residues located in the RNase H were unvaried. Furthermore, we identified other substitutions in the connection domain and in the RNase H. Especially E399D seemed to be associated with an antiretroviral treatment and N-terminal resistance-delivering mutations.</p> <p>Conclusion</p> <p>Some of the identified substitutions were associated with antiviral treatment and drug resistance-associated mutations. Due to the low prevalence of C-terminal mutations and as only a few of them could be associated with antiviral treatment and N-terminal resistance-delivering mutations, we would not recommend routinely testing of the C-terminal RT region.</p

Rescaled Local Interaction Simulation Approach for Shear Wave Propagation Modelling in Magnetic Resonance Elastography

Properties of soft biological tissues are increasingly used in medical diagnosis to detect various abnormalities, for example, in liver fibrosis or breast tumors. It is well known that mechanical stiffness of human organs can be obtained from organ responses to shear stress waves through Magnetic Resonance Elastography. The Local Interaction Simulation Approach is proposed for effective modelling of shear wave propagation in soft tissues. The results are validated using experimental data from Magnetic Resonance Elastography. These results show the potential of the method for shear wave propagation modelling in soft tissues. The major advantage of the proposed approach is a significant reduction of computational effort