Acoustic emission testing and acousto-ultrasonics for structural health monitoring

The global trends in the construction of modern structures require the integration of sensors together with data recording and analysis modules so that its integrity can be continuously monitored for safe-life, economic and ecological reasons. This process of measuring and analysing the data from a distributed sensor network all over a structural system in order to quantify its condition is known as structural health monitoring (SHM). The research presented in this thesis is motivated by the need to improve the inspection capabilities and reliability of SHM systems based on ultrasonic guided waves with focus on the acoustic emission and acousto-ultrasonics techniques. The use of a guided wave-based approach is driven by the fact that these waves are able to propagate over relatively long distances, interact sensitively with and/or being related to different types of defect. The main emphasis of the thesis is concentrated on the development of different methodologies based on signal analysis together with the fundamental understanding of wave propagation for the solution of problems such as damage detection, localisation and identification. The behaviour of guided waves for both techniques is predicted through modelling in order to investigate the characteristics of the modes being propagated throughout the evaluated structures and support signal analysis. The validity of the developed model is extensively investigated by contrasting numerical simulations and experiments. In this thesis special attention is paid to the development of efficient SHM methodologies. This fact requires robust signal processing techniques for the correct interpretation of the complex ultrasonic waves. Therefore, a variety of existing algorithms for signal processing and pattern recognition are evaluated and integrated into the different proposed methodologies. Additionally, effects such as temperature variability and operational conditions are experimentally studied in order to analyse their influence on the performance of developed methodologies. At the end, the efficiency of these methodologies are experimentally evaluated in diverse isotropic and anisotropic composite structures.Nach den heutigen Standards zur Konstruktion moderner Leichtbaustrukturen ist es zur Strukturüberwachung aufgrund von wirtschaftlichen, ökologischen und Sicherheitsaspekten unerlässlich, Sensoren und Module zur Datenspeicherung und –analyse in diese Strukturen zu integrieren. Den Prozess der Strukturüberwachung anhand der Messung und Analyse von Daten aus einem dezentralen Sensornetzwerk wird als „Structural Health Monitoring (SHM)“ bezeichnet. Die vorliegende Arbeit und die darin vorgestellten Untersuchungen reagieren auf den Bedarf an verbesserter Genauigkeit und höherer Zuverlässigkeit von SHM-Systemen, die auf geführten Ultraschallwellen basieren, wobei der Fokus der Untersuchung auf Schallemissions- und Acousto-Ultraschalltechniken liegt. Da geführte Wellen lange Wege zurückzulegen können und mit hoher Empfindlichkeit und Genauigkeit auf verschiedene Schadenstypen reagieren, eignen sie sich sehr gut für die Überwachung dünnwandiger Strukturen. Der Schwerpunkt der Arbeit liegt in der Entwicklung verschiedener Methoden zur Signalanalyse zur Lösung von Problemen wie Schadenserkennung, lokalisierung und identifizierung. Dies ist nicht ohne ein grundlegendes Verständnis der Wellenausbreitungsmechanismen möglich, sodass ein Modell entwickelt wird, anhand dessen die Charakteristiken der angeregten Moden sowie die Wellenausbreitung in den zu untersuchenden Strukturen analysiert werden können, um so die Signalanalyse zu unterstützen. Die Validität des entwickelten Modells wird eingehend anhand von verschiedenen numerischen Simulationen und Experimenten untersucht. Um besonders effiziente Methoden des SHMs zu entwickeln, sind robuste Signalverarbeitungstechniken zur zuverlässigen Interpretation komplexer Ultraschallwellen notwending. Aus diesem Grund erfolgt die Auswertung einer Vielzahl existierender Algorithmen zur Signalverarbeitung und Mustererkennung, die in die hier vorgestellten Methoden integriert werden. Des Weiteren wird experimentell untersucht, welchen Einfluss Effekte wie Temperaturschwankungen und Betriebsbedingungen auf diese Methoden haben. Abschließend wird experimentell die Effizienz der entwickelten Methoden bei der Überwachung diverser isotroper und anisotroper Faserverbundstrukturen nachgewiesen

La cigüeña negra, Ciconia nigra, en concentraciones postnupciales y migratorias ibéricas : fenología, actividad y estructura de edades

Las concentraciones migratorias y postnupciales de cigüeña negra han sido objeto de estudio en 22 localidades de las provincias de Ciudad Real, Cáceres y Badajoz (centro y oeste de España). Entre 2003 y 2006 se visitaron periódicamente distintos tipos de humedales con presencia habitual de la especie durante los pasos migratorios, desde el 21 de julio hasta el 10 de octubre. En 174 de las 339 visitas realizadas se detectó la presencia de cigüeña negra. El número promedio registrado de ejemplares por bando resultó de 11,3 ejemplares. Las fechas en que se contabilizaron más individuos, tanto en valores absolutos como relativos, correspondieron al período del 11 al 20 de septiembre. La mayor parte de los ejemplares datados (69,1%) resultaron adultos (plumaje de más de 3 años de edad), seguidos por jóvenes del año (20,2%) e inmaduros-subadultos (10,6%, 2-3 años de edad). A lo largo de todo el período migratorio se mantuvo constante la proporción de edades, salvo en el mes de octubre, cuando se incrementó la presencia aves juveniles. Durante las horas centrales del día se registró el mayor número relativo de aves sedimentadas en los humedales estudiados. Entre las 13:00 h y las 16:00 h (GMT + 2h) se censó el 62,7% de las cigüeñas negras presentes. Alrededor de la mitad de los individuos (52,5%) emplearon las áreas de concentración estudiadas para descansar y sestear

Damage Detection in Metallic Beams from Dynamic Strain Measurements under Different Load Cases by Using Automatic Clustering and Pattern Recognition Techniques

International audienceIn general, the change in the local strain field or global stiffness caused by damage in a structure is very small and the strain field tends to homogenize very quickly in the field close to the defect. Moreover, other environmental effects can fade the slight changes in the strain field. Only by comparing the response of the structure at several points some information about damage may be unveiled. By means of pattern recognition techniques based on the strain field, this task can be achieved. This is the basis of the strain measurements data-driven models. The main limitation of the strain field pattern recognition techniques lies in the susceptibility of the strain field to change depending on the load conditions. In the case of dynamic loads, this may reflect even a greater limitation. Robust automated techniques are required to manage these limitations. In first instance, automatic clustering techniques are needed so that data can be classified according to the load conditions and secondly, a dimensional reduction technique is needed in order to obtain patterns that often underlie from data. Within the context of this paper, a combination of Local Density-based Simultaneous Two-Level (DS2L-SOM) Clustering based on Self-Organizing Maps (SOM) and Principal Components Analysis (PCA) is proposed in order to firstly, classify load conditions and secondly, perform strain field pattern recognition. The clustering technique is the basis for an Optimal Baseline Selection. An experimental validation of the technique is discussed in this paper, comparing damages of different sizes and positions in an aluminum beam, under a set of combined loads under dynamic conditions. Strains were measured at several points by using Fiber Bragg Gratings

A Pattern Recognition Approach for Damage Detection and Temperature Compensation in Acousto-Ultrasonics

International audienceThe global trends in the construction of modern structures require the integration of sensors together with data recording and analysis modules so that their integrity can be continuously monitored for safe-life, economic and ecological reasons. This process of measuring and analysing the data from a distributed sensor network all over a structural system in order to quantify its condition is known as structural health monitoring (SHM). Guided ultrasonic wave-based techniques are increasingly being adapted and used in several SHM systems which benefit from built&#8208,in transduction, large inspection ranges, and high sensitivity to small flaws. However, for reliable health monitoring, much information regarding the innate characteristics of the sources and their propagation is essential. Moreover, any SHM system which is expected to transition to field operation must take into account the influence of environmental and operational changes which cause modifications in the stiffness and damping of the structure and consequently modify its dynamic behaviour. On that account, special attention is paid in this paper to the development of an efficient SHM methodology where robust signal processing and pattern recognition techniques are integrated for the correct interpretation of complex ultrasonic waves within the context of damage detection and identification. The methodology is based on an acousto-ultrasonics technique where the discrete wavelet transform is evaluated for feature extraction and selection, linear principal component analysis for data-driven modelling and self-organizing maps for a two-level clustering under the principle of local density. At the end, the methodology is experimentally demonstrated and results show that all the damages were detectable and i

Damage assessment in a stiffened composite panel using non-linear data-driven modelling and ultrasonic guided waves

Structural components made of composite materials are being used more often in aerospace and aeronautic structures due to their well-known properties such as high mass specific stiffness and strength. However, their application also increases the analysis complexity of such structures. Structural health monitoring (SHM) systems for these structures aim to determine the status of the system in real time such that a longer safe life and lower operational costs can be guaranteed. On that account, this paper is concerned with the experimental validation of a structural health monitoring methodology where a damage detection and classification scheme based on an acousto-ultrasonic (AU) approach is applied to a composite panel incorporating stiffening elements using a piezoelectric active sensor network in conjunction with time-frequency multiresolution analysis and non-linear feature extraction. Therefore, structural dynamic responses from the simplified aircraft composite skin panel are collected and signal features are then extracted with a signal processing and data fusion methodology in terms of the wavelet transform technique and hierarchical non-linear principal component analysis. A critical comparison with linear feature extraction methods indicates that the proposed method outperforms the traditional linear methods for the purpose of damage classification. Additionally, results show that all the damages were detectable and classifiable, and the selected features proved capable of separating all damage conditions from the undamaged state.Postprint (published version

Propiedades dieléctricas y electroquímicas de concretos sustentables

Como estrategias para contribuir en la sustentabilidad de la industria del concreto se está proyectando mejorar la durabilidad de las estructuras de concreto reforzado y el reemplazo parcial o total de sus ingredientes por materiales reciclables. En este estudio se evaluó la resistividad eléctrica y su relación con la microestructura y resistencia a la corrosión electroquímica de concretos reforzados fabricados con características de sustentabilidad, es decir, con agregados reciclados y materiales cementantes suplementarios. La resistividad eléctrica del concreto está íntimamente relacionada con la microestructura de la matriz cementante y con la estructura y distribución de poros. Por la naturaleza de sus ingredientes, es de suponerse que los concretos sustentables propuestos presentan diferente microestructura y porosidad que el concreto convencional, motivo por el cual se analizó la respuesta eléctrica y electroquímica de dichos sistemas mediante la técnica de espectroscopía de impedancia electroquímica.Peer ReviewedPostprint (published version

Autoconfianza y su relación con el rendimiento, procedencia, logros y edad en jugadoras de voleibol peruanas en categoría de formación

The objective of the present research was to determine the relation between the self-confidence and the performance, place of origin, achievements and age of Peruvian volleyball players players in training category.  This is a non-experimental, correlational, cross-sectional study. A total of 86 volleyball players, between 12 and 16 years old (age M=15.59-TD=0.74) were studied.  The sports confidence inventory was applied to these volleyball players (reproducibility of .992). The results show that there is a statistically significant positive correlation between lack of confidence and performance (r = .310; p < .01), lack of confidence and provenance (r = .280; p < .01); confidence and age (r = .244; p < .05); overconfidence and achievements (r = .235; p < .05); level of self-confidence and age (r = .236; p < .05). On the other hand, there is a negative correlation, also statistically significant, between confidence and provenance (r = -.342; p < .01); overconfidence and yield (r = -.399; p < .01); self-confidence level and provenance (r = -.387; p < .01). It is concluded that self-confidence is to a large extent associated with sports performance, the geographical region from which they come and the age of the volleyball players, except with the sports achievements obtained in training category.El objetivo de este estudio fue determinar la relación de la autoconfianza con el rendimiento, procedencia, logros y edad en voleibolistas peruanas en categoría de formación. El estudio es de naturaleza no experimental, transeccional correlacional. Se estudió a 86 voleibolistas, de edades entre 12 y 16 años (M=15.59-DT=0.74), a quienes se les aplicó el inventario de confianza deportiva (reproductividad de .992). Los resultados demuestran que existe una correlación positiva, estadísticamente significativa, entre falta de confianza y rendimiento (r = .310; p < .01), falta de confianza y procedencia (r = .280; p < .01); confianza y edad (r = .244; p < .05); exceso de confianza y logros (r = .235; p < .05); nivel de autoconfianza y edad (r = .236; p < .05). Por otro, que existe una correlación negativa, también estadísticamente significativa, entre confianza y procedencia (r = -.342; p < .01); exceso de confianza y rendimiento (r = -.399; p < .01); nivel de autoconfianza y procedencia (r = -.387; p < .01). Se concluye que la autoconfianza en gran medida se asocia con el rendimiento deportivo, región geográfica de donde provienen y edad que presentan las voleibolistas, excepto con los logros deportivos obtenidos en categoría de formación. &nbsp

Análisis de la morfología de la cabra mestiza de la subprovincia fisiográfica Volcanes de Colima, México

            The aim of this study was to characterize the morphology of the creole goat of the Volcanes de Colima physiographic sub-province, Mexico. Seventeen body measurements were taken from 371 goats older than two years and four racial indices and 17 functional indices were calculated. Data were analysed using Pearson correlation, principal component, and hierarchical cluster analysis. The rump angle, chest width and all measurements of the ears and udder showed the greatest variability. Also, the goats showed great morpho-structural harmony. Racial indices showed that goats are dolichocephalic, ellipometric, and have a convex rump, while functional indices indicated dual-purpose zootechnical aptitude. Four principal components explained 84.5% of the variation of body measurements. Rump angle, hearth girth, body length and ear length presented the highest weighting coefficients in PC1, PC2, PC3 and PC4, respectively. The hierarchical cluster analysis classified the goats into four groups: group 1 has the lower rump angle, suitable for milk production; groups 2 and 3 with a phenotype tending to dual purpose, being able to focus on the production of meat or milk; and group 4 with a phenotype predisposed to meat production.            El objetivo del presente estudio fue caracterizar la morfología de la cabra mestiza de la subprovincia fisiográfica Volcanes de Colima, México. Se tomaron 17 medidas corporales a 371 cabras mayores de dos años y se calcularon cuatro índices raciales y 17 índices funcionales. Los datos fueron analizados usando análisis de correlación de Pearson, de componentes principales y de conglomerados jerárquicos. El ángulo de caída de grupa, la anchura de pecho y todas las medidas de las orejas y la ubre fueron las que mostraron la mayor variabilidad. Asimismo, las cabras mostraron una gran armonía morfoestructural. Los índices raciales mostraron que las cabras son dolicocéfalas, elipométricas y tienen una grupa convexa, mientras que los índices funcionales indicaron una aptitud zootécnica de doble propósito. Cuatro componentes principales explicaron el 84.5% de la variación entre las medidas corporales de las cabras. El ángulo de caída de la grupa, el perímetro torácico, la longitud corporal y la longitud de oreja presentaron los mayores coeficientes para los componentes CP1, CP2, CP3 y CP4 respectivamente. El análisis de conglomerados jerárquicos clasificó a los animales en cuatro grupos: grupo 1 conformado por cabras con un menor ángulo de caída de grupa, apropiado para la producción de leche; grupos 2 y 3 con fenotipo tendiente al doble propósito, pudiendo orientarse a la producción de carne o leche; y grupo 4 con fenotipo con predisposición a la producción de carne

Risk behaviors of 15–21 year olds in Mexico lead to a high prevalence of sexually transmitted infections: results of a survey in disadvantaged urban areas

BACKGROUND: Due to the fact that adolescents are more likely to participate in high-risk behaviors, this sector of the population is particularly vulnerable to contracting sexually transmitted infections (STIs) and resultant health problems. METHODS: A survey was carried out among adolescents from poor homes in 204 small-urban areas of Mexico. Information was collected in relation to risk behaviors and socio-economic environment. A sub-group of the participants also provided blood and urine samples which were analyzed to detect sexually transmitted infections. RESULTS: The presence of Chlamydia was detected in nearly 8% of participants who had stated that they were sexually active (18%) and approximately 12% were positive for herpes type 2-specific antibodies. For both, a greater proportion of girls resulted positive compared to boys. The presence of these biological outcomes of sexual risk behavior was associated with other risk behaviors (smoking), but not with self-reported indicators of protected sex (reported use of condom during most recent sexual activity). CONCLUSION: The results presented in this study show a startlingly high prevalence of HSV-2 among sexually active Mexican adolescents in poor urban areas, suggesting that this group has participated to a great extent in risky sexual practices. The relationships between socioeconomic environment and adolescent risk behavior need to be better understood if we are to design preventive interventions that modify the determinants of risk behaviors