Editorial: Special Issue on Sensors Systems for Structural Health Monitoring

Editorial for invited special edition on SH

Analysis techniques for eddy current imaging of carbon fiber materials

Carbon fiber materials become more and more important for many applications. Unlike metal the technological parameters and certified quality control mechanisms for Raw Carbon Fiber Materials (RCF) have not yet been developed. There is no efficient and reliable testing system for in-line inspections and consecutive manual inspections of RCF and post laminated Carbon Fiber Reinforced Plastics (CFRP). Based upon the multi-frequency Eddy Current system developed at Fraunhofer IZFP, structural and hidden defects such as missing carbon fiber bundles, lanes, suspensions, fringes, missing sewing threads and angle errors can be detected. Using an optimized sensor array and intelligent image pre-processing algorithms, the complex impedance signal can be allocated to different carbon fiber layers. This technique enables the detection of defects in depths of up to 5 layers, including the option of free scale measuring resolution and testing frequency. Appropriate parameter lists for optimal error classifications are available. The dimensions of the smallest detectable flaws are in the range of a few millimeters. Algorithms and basic Eddy Current C-Scan processing techniques for carbon fiber material testing are described in this paper

Thermographic Characterization of the Material Microstructure Using Dissipative Effects

The cyclic mechanical loading of a test specimen leads to a periodic variation of the surface temperature due to the thermoelastic effect. Additionally, the temperature of the specimen increases due to dissipative effects. Since this dissipation depends upon the microstructure of the material in a characteristic manner, thermographic measurements performed during mechanical cyclic loading allow determination of the materials state, wich depend upon already endured fatigue load of the material. If the material is loaded with high power ultrasound then a nondestructive characterization of fatigue state and an estimation of the remaining lifetime are possible. The paper presents results of thermographic characterization of fatigue in titanium alloys that are typical aerospace materials

Simulation instationärer Wärmeleitungsprozesse bei der Impuls-Video-Thermographie

Um die Grundlage für eine Schichtdickenbestimmung beschichteter Materialien sowie für eine quantitative Fehleranalyse mit Hilfe des Impuls-Video-Thermographieverfahrens zu schaffen, wurden im Rahmen einer Diplomarbeit Modellrechnungen auf der BAsis der instationären Wärmeleitungstheorie durchgeführt. Zur Lösung der entsprechenden Differentialgleichungen für den ein- und zweidimensionalen Fall wurde die Finite-Elemente-Methode verwendet, wobei die speziellen Randbedingungen der Impuls-Video-Thermographieprüftechnik, einschließlich der Lichtabsorption in einer Oberflächenschicht berücksichtigt wurde

Algorithmen für die automatische Fehlererkennung in der radioskopischen Schweißnahtprüfung

In den letzten Jahren ist die moderne Radioskopietechnik mehr und mehr eine echte Alternative zur herkömmlichen Radiographie geworden. Dazu trugen vor allem die geringeren Kosten, die Möglichkeiten einer sehr schnellen Erzeugung eines Abbildes des Prüfobjektes sowie die gestiegene Bildqualität bei. Aufgrund des großen personellen Aufwandes für die Prüfung und der großen Belastungen, die bei einer automatischen Fertigung an das Prüfpersonal gestellt werden, gibt es seit Jahren verstärkte Bemühungen, für die Auswertung der Radioskopien eine automatische Alternative zu schaffen. Damit könnte gleichzeitig eine Objektivierung der Prüfung erreicht werden. Zur automatischen Auswertung der Radioskopien werden Methoden und Verfahren der Bildverarbeitung herangezogen

Nano evaluation in electronics packaging

The challenge of nano packaging requires new nondestructive evaluation (NDE) techniques to detect and characterize very small defects like transportation phenomenon, Kirkendall voids or micro cracks. Imaging technologies with resolutions in the submicron range are the desire. Possible evaluation methods are for example x-ray microscopy, x-ray tomography, ultrasonic microscopy and thermal microscopy. However, techniques with this resolution can not be found on the market. The "Center for Non-Destructive Nano Evaluation of Electronic Packaging" (nanoeva®) is taken up to develop this equipment in cooperation with the electronics industry and to transfer the knowledge to colleagues in industries and research institutions. The new center is a common organization of Fraunhofer IZFP-D and the Electronics Packaging Lab with its Centre of Microtechnical Manufacturing (ZP) of the Technische Universität Dresden

Development of GMR eddy current sensors for high temperature applications and imaging of corrosion in thick multi-layer structures

Detection and quantification of corrosion damage in aircraft structures is essential for condition based maintenance strategies and for the extension of the life of the aircraft. The eddy current technique was found to be one of the most favorable methods for the determination of thickness loss due to corrosion because this technique is capable of detecting corrosion in several layers of a multi-layer structure. A limitation for the eddy current technique is the eddy current penetration depth. Decreasing the analyzing frequency can increase the eddy current penetration depth. Giant Magneto Resistive sensors are highly sensitive magnetic field sensors, they have better signal to noise ratio for very low frequencies than conventional coils systems. Moreover these sensors are very efficient over a broad frequency range. Hence they allow the use of the multifrequency concept for multi-layer structures of higher thickness. Images of corrosion damage can be generated separately for different layers of a multi-layer structure by using deep penetrating GMR based eddy current probes and data acquired from the multi-frequency eddy current testing. This paper describes the design of deep penetrating GMR based eddy current probes and their application for generating images of corrosion in different layers with the help of a MAUS scanner

Application of the Positron Lifetime Spectroscopy as Method of Non-Destructive Testing

In order to show the suitability of the Positron Lifetime Spectroscopy (POLIS) as a method of Non-Destructive Testing (NDT) several iron alloys / steels were mechanically damaged (tensile stress, fatigue, creeping). The positron annihilation parameters show clear changes during all applied kinds of damage. After tensile stress as well as after creeping a homogeneous distribution of damage in the sample was detected. During the very first elastic cycle of a fatigue experiment, a change in the defect structure occurs in well annealed materials. A modified spectrometer for in the field mapping is presented

Development of components for an industry approved hollow-axle testing system

High speed railway train systems are a growing transportation solution in the beginning of the twenty-first century. Special attention has to be paid to their structural security and reliability. The hollow-axles of trains are subjected to massive stress at speeds up to 500km/h. This constant stress damages the axles over time. Therefore, the axles must be inspected periodically to prevent failure. One of the most common testing techniques is ultrasonic inspection to detect cracking inside the hollow-axle. An automated hollow-axle testing system built by an industrial partner needed completely new software and ultrasonic electronics. The testing system should be able to test hollow-axles of high speed trains such as ICE, Shinkansen, TGV and CRH in just a few minutes per axle. All testing data has to be stored for further analysis. The complete system has to operate in harsh environments and still provide reliable testing results. Based on the proven mechanical system for hollow-axle testing, a new electronics and software system was developed. The electronic system was derived from recently developed PCUS® pro ultrasonic electronics. This system is energy efficient, small and delivers clear images with highest signal-to-noise ratio (SNR). In this configuration, the PCUS® pro can handle up to eight ultrasonic channels and is connected to the host PC via USB. The new software was developed using modern tools and techniques such as Scrum, Domain Driven Design and Test-Driven Development. All B-Scan, C-Scan and TD images are calculated in real time and are stored together with the raw measurement data. All demands were met, and many additional features Such as interaction in the inspection phase and post-processing were added to the software suite. In this paper we will show the testing system benefits, the developing challenges and the results of the worldwide use of our testing system