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- Hydrogen assisted cracking (2)
- Maintenance (2)
- Ultrasound (2)
- Antenna (1)
- Band shape analysis (1)
- Bridge management (1)
- Böden (1)
- Chloride Induced Corrosion (1)
- Component testing (1)
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Thermal shock cycle experiments between room and cryogenic temperatures on polymer composites
(2002)
A reference material for calibration and testing of instruments with nanometric lateral resolution
(2002)
Unusual relaxation behavior of water inside the sodalite cages of faujasite-type molecular sieves
(2002)
Molecular dynamics of 4n-octylcyanobiphenyl confined to nanoporous molecular sieves of SBA-type
(2002)
Rapid and accurate non-destructive evaluation (NDE) techniques are needed to assess the in-place condition of concrete structures. However the time and effort required to perform NDE tests using conventional surface-mounted contact sensors hinder rapid evaluation of full-scale structures. The authors are cooperating in research to develop rapid and robust methods that collect mechanical wave signals from concrete structures and to characterize defects in concrete
using that signal data. The suitability of surface waves and laser-based, non-contact wave detection techniques for this purpose are examined here. After a brief introduction to non-contact sensing, an experimental set-up is described and results from experimental tests are presented. Mechanical surface waves in a concrete slab specimen are generated with several different conventional sources. The ability of a laser vibrometer to detect wave propagation from concrete that does not have any reflective treatment (normal concrete surface) is demonstrated, allowing the generation of ultrasonic images. Test results from a concrete specimen containing a subsurface defect are then presented. The obtained ultrasonic images illustrate some limitations of using surface waves to detect subsurface defects in concrete, although approaches to improve the results are proposed.
Reliability of Routine Radiographic Film Evaluation - an Extended ROC Study of the Human Factor
(2002)
Many radiographic exposures and film evaluations are made daily in a typical industrial NDT laboratory. But questions remain regarding the precise probability of detecting discontinuities, including the reliability of each individual inspector or laboratory. Although most experienced inspectors of the laboratories evaluate each radiograph, the actual quantitative reliability of each of these inspectors remains unknown.
In order to estimate the performance of representative inspectors and laboratories involved in NDE, volunteer laboratories from Croatia and Hungary conducted a series of round-robin inspections using X-ray films of welds. While the RRT is still in progress, the authors try to summarize the results of the second round and discuss the evaluation method. The results of the first round had been reported already. The focus is here to present the new results in terms of additional inspectors and a new more field oriented evaluation scheme.
So far the results of a total of 35 inspectors of the different laboratories were evaluated. Those inspectors were selected who have done usually the work of radiographic film interpretation. They have from a half up to 35 years professional experience. For better overview we created four groups: maximum 4 year-experience, from 5 to 12 year-experience, from 15 to 25 year- experience and from 26 to 35 year-experience.
Discussing the circumstances of the RRT with the participants, many of them expressed, they could not exactly follow the prescription of the test. According to their professional experience the small discontinuities can be omitted because of the strictest acceptance level accept them. So the most experienced evaluators did not write the small gases and slags into the list, which yield a wrong reliability of detection. As a consequence we should accomplish two types of evaluation: taking into consideration of all discontinuity and only the bigger once they are over the acceptance level.
In addition we analyzed the true values in a critical review. These developments were made and the new results of the evaluation of the testers were more precise and reliable.
The corresponding results are evaluated and presented in a ROC diagram where the p(TP) is plotted against the p(FP). The p(TP) means the probability of a true positive indication (correct defect finding) and p(FP) means the probability of a false positive (false alarm) indication. From the mean value of all inspectors maximum operation points we can estimate a representative overall reliability in terms of a correct indication rate of about 68 % (64 % new) and a false call rate of about 17 % (8 % new). This is a reasonable result within the strict 1 cm score.
The reliability investigations are dedicated to throw light on the performance of the NDE system with respect to the required aim. This is especially of interest when it is looked for life damaging objects in the case of mine seeking and when it is even more difficult to distinguish between the different suppliers of methods concerning their actual capability.
In accordance with the conception of EFNDT WG5 and CEN BT 126 CW 07 the authors have the aim to transfer the knowledge in reliability measurement of NDE systems to the reliability measurement of mine detection systems. For this the three basic ways to investigate the reliability of NDE signals will be described. The first way of investigation, the performance demonstration, is preferred e.g. in the US American nuclear power industry. This is an integral consideration of the non destructive test as a system where the whole NDE system is packed in a black box and only the input in terms of the real existing flaws in the component is considered and compared to the output in terms of the indications of the human inspector or of the automated system. The second - the European tradition relies on a standardized description of physical/technical parameters of the NDE system which are preconditions for successful system performance. The third approach - the modular conception - is a marriage of both: The signal chain is cut into main modules.
Each module is assessed in a most appropriate individual way e.g. via modeling calculations. The single results are joint together according to the reliability theory of systems where the reliability of the total system is composed of the reliability of the subsystems. Separating criteria for the system were proposed through a reliability formula developed during a series of European-American workshops on NDE reliability. A further essential parameter especially for demining systems are the repeatability and reproducibility. Their affect on the reliability and its scatter will be investigated. Examples for the ROC/POD approach in terms of the investigation of the reliability of ultrasonic manual testing and for first attempts for the reliability investigation of demining data will be presented.
It will be strongly recommended to apply the ROC/POD and Modular Conceptions to the assessment and optimization of mine seeking systems.
During the second European-American Workshop on NDE Reliability, September 99 in Boulder, the term NDE reliability was defined as the degree that an NDT system is capable of achieving its purpose regarding detection, characterization and false calls. The most common but also most expensive - way to determine this degree of capability in e.g. defect detection is to make just a performance demonstration using realistic test samples and to count the correct detections and false calls. For a more efficient way of reliability evaluation we propose to decompose the system into main modules e.g. according to the reliability formula set up on the first workshop: into f(IC) a function of IC the intrinsic capability, determined by the physics and the technique of the NDE method representing an ideal upper bound of the reliability and g(AP) a function of AP the industrial application factor like surface state or limited access to a component in general diminishing the ideal capability and finally h(HF) the function of the human factor which is in general also diminishing the ideal capability. The workshop proposed a rather plain mathematical shape for the formula R = f(IC) g(AP) h(HF) which should be considered merely as a philosophical expression but not as exact mathematical formula to be applied for evaluation of e.g. POD data. We propose to decompose the NDE system into modules in terms of functions of IC, AP and HF if appropriate or additional ones if necessary and then to analyze the mutual relationships of the terms via fault tree analysis. Finally the total reliability of the system is composed of the reliability of the subsystems via the rules of statistical systems theory.
First trials for this approach of data analysis will be presented via examples from NDE systems in the aerospace industry.
Radiography is a helpful method to identify the inherent structure of unexploded ordnances (UXOs). Portable Computed Radiography (CR) systems on the basis of phosphor imaging plates , have attracted attention for NDT-applications during the last few years. A portable IP system ACR 2000 has been tested for X-ray inspection of UXO's in the field. Digitised radiographs are presented to explain the needs and demands for a reliable characterisation of UXO's. Computed radiographs of UXOs are compared with film radiographs exposed in the same way, to evaluate the reliability and to identify advantages and disadvantages of the CR system for UXO inspection. Film based and CR systems provide sufficient information for identification of chemical warfare agents in UXO's, which is an essential problem for explosive ordnance disposal. The advantages and the potential of the portable CR system is discussed on the basis of experiences gathered during different field trails.
The existence of some 100 million active mines threatens human life and curtails substantially the economic base in over 70 countries. Humanitarian demining is tedious and it currently only employs metal detectors, prodders, dogs and armoured mechanical vehicles.
Achieving a world free of mines within a period of 10 years as stipulated in international treaties requires safer and more efficient technologies. In response to this challenge the Working Group 5 of the European Federation for Non-Destructive Testing (EFNDT WG5) was founded in Berlin in March 1999. The subject of this working group now consisting of 50 members from 17 countries is the detection of antipersonnel mines (APMD). The basic idea was to investigate existing NDT methods into their ability to aid mine detection. The scope of activities ranged from collecting available information, setting up links to related organisation, defining terminology and standards to selecting dedicated research projects. Since some of these tasks are already conducted by other organisations on an European and international level the attention of the working group has been focused mainly on two R&D areas and on reliability assessment studies. Otherwise, EFNDT WG5 APMD nevertheless remains open to novel approaches in mine detection. Aim of all activities is to provide deminers with safer and more efficient tools than merely with prodders and metal detectors currently used for their dangerous task.
Improved Detection of Tendon Ducts and Defects in Concrete Structures Using Ultrasonic Imaging
(2002)
At the beginning of the 90s the general opinion was, that ultrasonic inspection methods using pulse-echo technique were not suitable for the inspection of concrete because of the inhomogeneity and the strong scattering behavior of the embedded aggregates. In the meantime the progress in the development of new equipment and inspection strategies in connection with ultrasonic imaging techniques turns the pulse-echo technique into a powerful tool to solve problems related to concrete materials. These imaging techniques - developed for the inspection of homogenous materials like steel of aluminum - could be adopted to the very low frequencies needed for concrete inspections.
The functional expression of human bone derived cells grown on resorbable bioactive glass ceramics
(2002)
Investigation of interphases between thermoplastic and thermosetting polymers - an AFM approach
(2002)
Micro damage structures of fiber reinforced polymers (FRP) can be characterized nondestructively by X-ray refraction topography, which images inner surfaces. The damage accumulation after fatigue treatment of short glass fiber reinforced polybutylene terephthalate (PBT-GF) is correlated to the applied load and the number of cycles. Micro cracks and fiber/matrix debonding during fatigue can be detected separately due to their different direction of X-ray small angle scattering. The residual strength over the crack surface decreases by a linear decay as 30 %, 60 % and 90 % of the materials lifetime is passed.
Fire Tests with LPG Vessels
(2002)
The results and execution of many full scale fire engulfment tests on 3.6 and 4.85 m³ LPG tanks, protected with thin sublimation and intumescent coatings, mineral wool with steel jackets, vermiculite coatings and water spray systems, are presented.
Additional furnace tests with coated steel plates have been carried out to optimize the necessary coating thickness.
Similarly, an overview of the test conditions for the recognition based on technical rules and BAM requirements for fire protection systems of LPG tanks will be shown and explained.
When the internal pressure reaches the vessel bursting pressure a violent tank rupture, fragmenting of the shell and spontaneous release of the content are the consequences. In case of LPG this event is called "boiling liquid expanding vapour explosion (BLEVE)" with expanding fireball as an additional severe consequence.
For this reason the sufficient fire protection of LPG vessels is an important item.
The tests demonstrated sufficient vessel safety during 90 minutes of a full fire engulfment.
It will also be shown that the examinations and results are transferable to bigger tanks.
The transferability of the test results is illustrated by diagrams which show the dependence of the coating thickness against the shell thickness of the tank.
All tested tanks were equipped with pressure relief valves (PRVs) and partially filled with propane.
The gelcasting process was used for manufacturing porous ceramic bodies from nano sized powders. 3 different powders with specific surface areas between 12 and 30 m²/g were used. Solid content of the corresponding slurries was dependent on the milling procedure and the use of a suitable dispersant. For bimodal GradeA powder solid content was as high as 58 vol%. For sintering temperatures between 1250 and 1600°C the porosity varied between 45 and 20%, whereas the pore radii varied between 50 and 91nm. The grain size of crystallites in the sintered microstructures was about 1um. The reflection ratio for visible light increased in comparison to a reference sample made from conventional powder from 0.8 to 0.95 in the wavelenght range around 400nm.
The effectiveness of pressure relief devices on cylinders and tanks from a German point of view
(2002)
Fire accidents during road and rail transport are not occurring very often. In particular fire accidents with total fire engulfment of tanks seem to be rather rare. Up to now authorities in Europe officially are of the opinion that in densely populated regions like Europe in the space of time between the beginning of a fire and the rupture of a tank measures could be taken like cooling of the heated tank surface and evacuation of the area probably affected by an explosion. Therefore, no requirements with regard to fire protection measures concerning transport tanks for land mode like the application of safety relief devices have to be met. Due to some catastrophic accidents being discussed in public even European authorities are considering the pros and cons of fire protection measures.
Nevertheless in sparsely populated regions and during transport at sea fire accidents have been looked at since ever as seriously dangerous events. Therefore, multi modal tanks for the transport of dangerous goods have to be fitted with safety relief devices. The delivery capacity of these devices has to be such that, in the event of total fire engulfment, the pressure inside the tank does not exceed certain limits.
With regard to accident records and results of fire tests it has to be stated that portable tanks may rupture violently, even if the tanks are fitted with pressure-relief devices adequately designed for the heat flux of full fire engulfment.
Therefore, the lecture will be dealing with the results of fire testing of tanks and conclusions to be drawn and considerations on:
the advantages of different fire protection measures for transport tanks,
the pros and cons of safety relief devices for cylinders and transport tanks,
improvement of regulations and recommendations.
The interaction of nanosecond laser pulses in the ultraviolet wavelength range and femtosecond laser pulses in the near-infrared region with the direct semiconductor SiC and the composite compound SiC-TiC-TiB2 was investigated in respect to resulting physicochemical processes. Surface analytical techniques, such as XPS, µ-Raman, and EDX were used to identify the chemical changes between untreated and laser-treated areas. Single-pulse irradiation led to material
modifications in the condensed state in most instances. Multi-pulse results differed depending on the pulse duration. In the nanosecond case, melting of the surface and redeposited material (debris) were observed. With femtosecond pulses instead, only negligible melting and few debris could be detected. Additionally, periodic structures (ripples) appeared, with parallel orientation and in most cases two different periodicities for a particular material. Laser ablation of all the studied compound materials exhibited preferential ablation of the lighter component elements. Crystal structure changes of the irradiated surface were observed as a consequence of laser-induced melting and resolidification. An oxidation process interfered with all this processes so that unstoichiometric oxides were formed.
The removal and accelerated corrosion monitoring of metal coating systems is of general interest in materials science
and engineering technology. The femtosecond and nanosecond laser ablation and delamination at 800 nm and 532 nm,
respectively, of anodic oxide layers on aluminium alloys in electrolyte contact were investigated. Laser-induced
modifications of the oxide layer resulted in an ionic contact between electrolyte and metal, which produced a current
transient and thus allowed the in-situ electrochemical monitoring of the modification. Oxide coatings with different
optical properties, almost transparent and opaque, were examined. The transparent anodic oxides showed contrasting
ablation mechanisms in the nanosecond and femtosecond pulse duration regime: nanosecond pulses caused spallation,
whereas femtosecond treatment led to ablation. Current signals measured in the transparent film were consistent with
light absorption below the metal-oxide interface and with film spallation. Irradiation of the opaque coating yielded ionic
current transients within the so-called shock-affected-zone of the oxide layer. This investigation provided insight into the
role of the penetration depth of light and the heat-affected zone, the extent of the shock-affected zone, and the defect
formation in the coating and at the solid-solid interface between metal and oxide.
Optical filters and fabrics are important parts of laser safety equipment such as goggles and curtains. A choice of these materials with varying absorption spectra is investigated with respect to their resistance to Ti:sapphire femtosecond laser radiation (800 nm wavelength, 1 kHz repetition rate). Pulse durations down to 30 fs and multiple-pulse irradiation conditions are employed to evaluate technically relevant damage thresholds. The ablation threshold fluences of the absorbing filters are comparable to those observed for transparent materials with 30-fs-pulses. These investigations together with scanning electron microscopy of the surface morphology after laser treatment provide insight into the interaction mechanism of the short pulses with the materials.
Long-term experiences with cathodic corrosion protection of steel reinforced concrete structures
(2002)
Feste Referenzmaterialien für die Spurenanalytik umweltrelevanter organischer Schadstoffe erfordern aufgrund der geringen thermischen Belastbarkeit der Analyten besondere Aufarbeitungsstrategien für die Herstellung repräsentativer Teilproben. Das in der Fachgruppe I.2 seit 1994 für diesen Zweck systematisch aufgebaute technologische Instrumentarium wird vorgestellt, und das im Laufe der Jahre angesammelte Know How wird anhand von Beispielen vermittelt. Das im Laboratorium I.21 entwickelte Qualitätssystem für eine optimale Logistik der Arbeitsabläufe der Probenherstellung und -verwaltung sowie für eine bedarfsgerechte Charakterisierung der Materialien wird ausführlich erläutert.
Bezüglich der Verwendung der Referenzmaterialien wird herausgestellt, daß es zwei gleichberechtigte Anwendungsrichtungen gibt: die interne Qualitätskontrolle mit zertifizierten Referenzmaterialien (ZRM, z.B. für die Methodenvalidierung) und die externe Qualitätskontrolle (Proficiency Testing = Kompetenzbewertung von Prüflaboratorien). Referenzmaterialien für das Proficiency Testing, die im Umweltbereich in viel größeren Stückzahlen umgesetzt werden können als ZRM, weisen bezüglich Homogenität und Charakterisierung die gleichen Qualitätskriterien wie ZRM auf. Diese Materialien haben - auch im internationalen Maßstab - stark an Bedeutung gewonnen.
Ein englisches Abstract gibt es nicht, aber eine Grobgliederung zur Vortragsankündigung:
This lecture includes:
· the technological and logistical aspects of reference material preparation and sub-sampling and subsequent sample management,
· appropriate measurement strategies for homogeneity and stability studies,
· the use of relevant statistical tests to evaluate those measurement data,
· the organisation of interlaboratory studies based on traceable measurements
A detailed diagnostic study of the interaction of nanosecond laser pulses from the near-ultraviolet into the near-infrared
wavelength range with various types of contemporary and ancient parchments is presented. The advantages of laser
cleaning due to the absence of chemical agents, spectroscopic selectivity, micro-precision, computer-aided handling can
only be verified when physico-chemical diagnostics guarantee destructionless processing. Scanning Electron Microscopy
(SEM) data are correlated with morphological changes in dependence on the laser fluence and wavelength. The
question, to what extent the chemical degradation of collagen is affected by various laser treatment parameters, could be
resolved by Transmission Electron Microscopy (TEM) of collagen fibres collected from the outermost laser-exposed
surface layer. It is also shown how Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT), and
Pyrolysis Capillary Gaschromatography (PY-CGC) can be employed in the chemical diagnostics of laser cleaning of
parchment. This study suggests that the ageing status of parchment artefacts plays a major role in assessing the laser
cleaning limits.
Commercially available absorption filters (Schott BG18 and BG36) were investigated with respect to their single- and
multi-pulse ablation threshold using laser pulses from a Ti:Sapphire laser in the range between 30 and 340 fs. It could be
observed, that the threshold fluence decreases for shorter pulse durations. The similarity of the measured multi-pulse
threshold fluences with those of undoped glass material (around 1 J/cm^2 for a pulse duration of 30 fs) suggests that, for
very short pulses, the threshold is independent on the doping level and therefore, linear absorption does not significantly
contribute to laser-induced damage. For >100 pulses per spot and all pulse durations applied, the threshold fluences
saturate. This independence on the number of applied pulses leads to technically relevant damage threshold values.