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- Hydrogen assisted cracking (2)
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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.