Damage Assessment of Structures VII

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Authors: T.R. Emery, Janice M. Dulieu-Barton
Abstract: The current paper presents a new combined technique for damage detection, localisation and establishing damage severity. The technique is based on the use of two infrared detection approaches: Pulsed Phase Thermography (PPT) and Thermoelastic Stress Analysis (TSA). A methodology is described that allows the technique to be applied to fibre reinforced composites. The usefulness of the technique is demonstrated on delaminated glass epoxy laminates. A means of developing controlled delamination damage in such specimens is developed so that real sub surface damage is evaluated in the paper.
Authors: Vincenzo Carriatore, Aldo Canova, Alberto Vallan, Bruno Vusini
Abstract: This paper deals with recent developments in non-destructive tests on operating steel wire ropes, with the aim of analyzing their conditions and residual resistance. The instruments for executing magneto-inductive tests on wire ropes - employed in cableways, chairlifts, mine elevators and, occasionally, in equipment for handling material in harbours (e.g. gantry cranes and portainers) – are commonly composed of three parts: the revealing device (detector); power supply; and a recorder, equipped with an amplification apparatus and paper rolls for printing the results. The system proposed in this work is composed of an innovative magnetic detector where the traditional paper recording system is substituted with a software interface that allows a digital recording of the signal. The performances in terms of accuracy and linearity of the proposed detector are tested through proper laboratory set up and are presented and discussed.
Authors: Paola Antonaci, Pietro G. Bocca, Davide Masera, Nicola Maria Pugno, Marco Scalerandi, Fabrizio Sellone
Abstract: The results of an experimental research on plain concrete are presented. The non-linear behavior of both virgin and damaged samples is investigated by means of ultrasonic tests: recent theoretical models, indeed, have pointed out that mono-frequency ultrasonic excitations bring to light such phenomena as harmonic generation and sidebands production, which are essentially due to the material classical or hysteretic non-linearity. The estimation of the harmonic components parameters (amplitudes and phases) is achieved through a signal processing technique based on MUltiple SIgnal Classification (MUSIC) system, which reveals to be optimal for the specific signal model here considered. The experiments described in this paper show that the material non-linear features increase with increasing level of internal micro-cracking, thus suggesting the possibility to use the ultrasonic signal analysis in the frequency domain as a valuable tool for damage assessment.
Authors: Kenneth Burnham, Gareth Pierce
Abstract: The total electrical generation capacity from wind sources in the International Energy Agency (IEA) Wind Member Countries has increased from 4 GW in 1995 to more than 51 GW in 2005 thus underlining the strategic importance of the resource. In the last year alone the UK increased its wind generation by 447 MW, an increase of 85% over that for the previous year. In 2004, wind generation formed just 0.5% of the national electric demand; this contribution is set to rise over the next few years with some predictions that wind energy will rise to 8% of the total UK demand by 2010. The rotor blades of a wind turbine system are a significant structural component of the overall system, and typically account for 30% of lifecycle costs, and contribute 34% to overall system downtime. Despite their importance, there is currently very little monitoring of the structural integrity of rotor components, and what does exist is limited. We perceive that especially with the current political and technological emphasis on offshore installations, there will be an increase in the perceived need for remote structural monitoring, and there is indeed currently great interest in this area from the wind turbine industry. This work focuses on the applications of acoustic techniques to assess the integrity of typical rotor blade structures. Preliminary results discuss the limiting aspects of acoustic based techniques based on the physics of acoustic wave propagation in typical structural components. Comparisons between acoustic emission approaches and conventional active ultrasound will be considered.
Authors: B. Peeters, Stoyan Kanev, Michel Verhaegen, H. Van der Auweraer
Abstract: One of the objectives of the EU research project InMAR (“Intelligent Materials for Active Noise Reduction”) is to reduce car engine noise by active control. An oilpan of a passenger car serves as a demonstrator. A concern in the application of active control is that the controlled system may change during service life (e.g. due to damage), and hence, may degrade the control performance. This paper presents two vibration-based methods that are able to autonomously detect damage and yield updated experimental models of the structure. A first approach is based on (operational) modal analysis. Based on vibration measurements, the modal parameters of the structure are estimated. The idea is now to automate this process so that, without human intervention, a representative dynamic model of the structure is always available. A second approach uses multiple-model estimation in the case when the state-space models have different state dimensions. To this end, an existing non-interacting multiple-model estimator has been extended to make it alert to jumps from one model to another. Both techniques (“Automatic Modal Analysis” and “Alert Autonomous Multiple Model Estimator”) will be applied to experimental vibration data from an oilpan of a passenger car subjected to damage (loosening of bolts).
Authors: Juan Pablo Casas-Rodriguez, Ian A. Ashcroft, Vadim V. Silberschmidt
Abstract: In recent decades the use of structural adhesive joints in the aerospace industry has increased considerably thanks to their high strength-to-weight ratio, low stress concentration and capacity to join different adherends. There is increasing interest in damage due to low-velocity impacts produced in adhesively bonded components and structures by vibrating loads. This type of loading is known as impact fatigue. The main aim of this paper is to investigate damage evolution in adhesive joints subjected to impact-fatigue and to compare this with damage evolution in standard fatigue (i.e. non-impacting, constant amplitude, sinusoidal fatigue). In this work, adhesively bonded lap joints were subjected to multiple tensile impacts tensile and it was seen that this type of loading was extremely damaging compared to standard fatigue. A number of methods of studying damage evolution in bonded joints subjected to fatigue and impact fatigue loading have been investigated and various parameters have been used to characterise these processes. Two modifications of the accumulated time-stress model [1-4] are proposed and it is shown that both models provide a suitable characterization of impact-fatigue in bonded joints.
Authors: Łukasz Jankowski, Marcin Wiklo, Jan Holnicki-Szulc
Authors: Nicolae Constantin, Mircea Găvan, Marin Sandu, Ştefan Sorohan, Viorel Anghel
Abstract: Low velocity impact is a frequent and inevitable in-service event, with higher occurrence in transportation structures. The damages following such an event are more diverse, extended and with more severe consequences in the case of composite materials and structures. The research work presented here concerns fibre reinforced polymeric composites in the forms of plates and pipes. It is continuing an effort meant to allow customers exploiting such structures to have a short cut in monitoring the integrity of this kind of structures. To this end, it is proposed a careful following of the impact force history recording, which can offer valuable and more direct information about the damage level produced under this insidious loading.
Authors: Luca Goglio, Marco Peroni, Massimo Rossetto
Abstract: In this paper the dynamic mechanical behaviour of two epoxy adhesives for structural bonding is investigated. The study has been focused on the influence of the strain rate on the tensile and compressive strength of specimens made of adhesive. The experimental tests have been performed with an hydraulic universal testing machine and a tension-compression Hopkinson bar. The results of the tests show that the σ−ε curve rises significantly increasing the strain rate. The Cowper-Symonds and Johnson-Cook models of strain rate dependence have been used to fit the experimental data with unsatisfactory results, thus a poly-linear fit has been adopted.
Authors: Tadeusz Uhl, Maciej Petko

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