Force and sound data fusion for enhanced tap testing scanning of composites

Coin or hammer tap testing is one of the oldest methods of NDT inspection. Inspection techniques originated with human operators observing the tonal change of the audible sound produced by striking were later automated with use of mechanical instruments that measured surface stiffness from the contact time of the striker. Numerous applications have evolved from this technique, from predicting rock falls to defect detection and identification in composite structures. Since operator applied tap testing requires extensive training and knowledge of the part’s structure to accurately locate defects, it is widely regarded as a subjective method and does not allow for digitised recording of results or validation against reference standards. In addition, this type of tap testing is generally confined to simple structural materials such as thin skin composites with foam or honeycomb cores, where defects can easily be identified. More complex structures with varying thicknesses present a much greater challenge for this method, as defects may have a similar response signal to thinner, non-defective regions, so neither force nor sonic data can differentiate between the two. This article seeks to introduce a novel analysis technique, applying the principle of resonant membranes to global and local frequency perspectives to generate two functions. The first sharpens tap testing images from the sonic and force responses returning greater clarity when observing the underlying structure, the second creating a local ranking of defect positions allowing an automatic highlighting of regions of high depth flux. The outcome is a process that enables operators to identify disbonds within an unknown composite structure with greater precision than either force or sound approaches on their own in lieu of prior information of defect, surface, or global resonance modes. The developed technique is suitable for application with a robotic platform to unknown curved composites surfaces since future developments will aim to achieve robotised TT deployment. The algorithm is validated within a laboratory environment on a physical reference sample, representative of an RNLI Severn class lifeboat hull, imitating a dry-dock inspection scenario

Impact-acoustics inspection of tile-wall bonding integrity via wavelet transform and hidden Markov models

The impact-acoustics method utilizes different information contained in the acoustic signals generated by tapping a structure with a small metal object. It offers a convenient and cost-efficient way to inspect the tile-wall bonding integrity. However, the existence of the surface irregularities will cause abnormal multiple bounces in the practical inspection implementations. The spectral characteristics from those bounces can easily be confused with the signals obtained from different bonding qualities. As a result, it will deteriorate the classic feature-based classification methods based on frequency domain. Another crucial difficulty posed by the implementation is the additive noise existing in the practical environments that may also cause feature mismatch and false judgment. In order to solve this problem, the work described in this paper aims to develop a robust inspection method that applies model-based strategy, and utilizes the wavelet domain features with hidden Markov modeling. It derives a bonding integrity recognition approach with enhanced immunity to surface roughness as well as the environmental noise. With the help of the specially designed artificial sample slabs, experiments have been carried out with impact acoustic signals contaminated by real environmental noises acquired under practical inspection background. The results are compared with those using classic method to demonstrate the effectiveness of the proposed method. (C) 2009 Elsevier Ltd. All rights reserved.City University of Hong Kong [9610024-630: ITRG006-06

Nondestructive Evaluation and Structural Health Monitoring Based on Highly Nonlinear Solitary Waves

Recent decades have witnessed the rapid growth and acceptance of nondestructive evaluation (NDE) techniques in assessment of infrastructures' conditions. Assessing the conditions of infrastructures is important to determine their safety and reliability which have a great impact on today's society. The existing NDE techniques include acoustics, ultrasound, radiology, thermography, electromagnetic method, optical method, and so on. Properly employed NDE techniques can reduce the maintenance and repair cost and improve the reliability of the infrastructures. In the last two decades, the study of the highly nonlinear solitary waves (HNSWs) has received much attention. Most of these studies focused on the propagation of HNSWs in granular systems, but little work on applications of HNSW-based NDE method has been done. HNSWs are mechanical waves that can form and travel in highly nonlinear systems, one-dimensional chain of identical spheres is one of the most common systems that can support the generation and propagation of HNSWs. In the study presented in this dissertation, a new NDE technique based on the generation and propagation of HNSWs was investigated and applied to different structural materials. First, fundamental research on the generation of HNSWs in a chain of stainless steel beads by laser pulses was conducted. The results showed that the laser-based generation of HNSWs produces results that are equivalent to those obtained by means of a mechanical striker. Then, the feasibility of tuning HNSWs by electromagnetically induced precompression was demonstrated experimentally. By changing the precompression on the chain of particles, the properties of the HNSWs could be tuned in a wide range. Then a HNSW-based transducer was designed and built. The transducer was remotely and automatically controlled by National Instruments PXI running Labview. The ability of the new transducer to generate repeatable HNSWs was assessed. Finally, the HNSW transducer was used to monitor cement setting, concrete curing and epoxy curing, to evaluate the bond condition of an aluminum lap-joint, and to detect the impact damages in a composite plate. The results showed that the HNSW-based technique is promising for structural NDE. A pilot numerical study on acoustic lens which is a device can focus the acoustic waves at a focal point was also conducted

Aeronautical engineering: A continuing bibliography with indexes (supplement 210)

This bibliography lists 409 reports, articles and other documents introduced into the NASA scientific and technical information system in January 1987

Untersuchungen zur zerstörungsfreien Prüfung von CFK-Bauteilen für die fertigungsbegleitende Qualitätssicherung im Automobilbau

Ein großer Vorteil von Kunststoffbauteilen ist neben funktionellen Vorzügen die Kosten- und Gewichtsreduzierung durch integrale Gestaltungsmöglichkeiten. Es können Geometrien umgesetzt werden, die mit metallischen Werkstoffen nur unter hohem Aufwand realisierbar sind. Insbesondere im Bereich der Faser-Kunststoff-Verbunde (FKV) gibt es hohen Forschungsbedarf hinsichtlich Reduzierung von Herstellungskosten, Erhöhung der Langlebigkeit aber auch der Reparaturfähigkeit. Die Erkennung von Defekten ist dabei eine grundlegende Voraussetzung. Für einen FKV-Serieneinsatz im Automobilbau gibt es jedoch kein bekanntes und ausreichendes Prüfkonzept der Schadenserkennung für die geforderten Stückzahlen. Die aus der Luft- und Raumfahrt bekannten Methoden lassen sich aufgrund ihres hohen apparativen Aufwandes und der eingeschränkten Tauglichkeit bezüglich geometrisch komplexer Bauteile nicht unmittelbar übernehmen. Es bestehen andere Anforderungen an ein Prüfkonzept für FKV-Bauteile im Automobilbau. Im Rahmen dieser Arbeit wurden zerstörungsfreie Prüfmethoden hinsichtlich ihrer Eignung zur Detektion nicht sichtbarer Schäden systematisch untersucht und bewertet. Der Fokus lag dabei auf Bauteilen aus kohlenstofffaserverstärkten Kunststoffen des Automobils, die sowohl eine flächige als auch eine mehrfach gekrümmte Bauteilstruktur mit nicht-homogenen Wanddicken aufweisen können. In Abhängigkeit von der Art der Schädigung, etwa Einschlüsse, Zwischenfaserrisse oder Delaminationen wurden die unterschiedlichen Verfahren vergleichend in Hinblick auf Detektionssicherheit, -grenzen und Einschränkungen durch gegebene geometrische sowie werkstoffliche Bauteilausführungen bewertet und ein Konzept für eine fertigungsbegleitende Qualitätssicherung entwickelt