Lasertechnik in der zerstörungsfreien Werkstoffprüfung — ein neues holographisches Verfahren

Non-destructive Testing by Laser Measuring Techniques — A New Holographic Method . Holographic Non Destructive Testing is well suited for materials with a low elasticity modulus or bad heat conductivity, like rubber, metal-rubber-connections, adhesive connections, plastics, and fiber-reinforced plastics. The advantage of holographic testing lies in the fact that a near to true stress is possible. This stress occurs with only a fraction of the force necessary to damage the part. In many cases there is a relation between the holographic evidence and the breaking limit. By a new method the evaluation of the holograms is much more easier, because only objects with defects are showing deformation fringes.     

Zur Problematik der zerstörungsfreien Materialprüfung

Problems of Non-Destructive Testing [NDT]. It is the main aim of NDT, to look for symptoms, being qualitatively reliable, and characteristics, being quantitatively evaluable, of voluminous flaws, discontinuities and other imperfections, and to do this without any damage of the workpiece. If defects or imperfections are detected, in addition to that, a statement about their actual importance and their avoidance in future must be given. In combination with that, conclusions about kind, conditions, and, consequently, about properties of processing and practical use of the inspected material must be drawn, either from the workpiece itself or from specially required specimens, but again without any damage, i. l. the specimens remaining applicable for other investigations. The real problems of nondestructive inspection of materials and components are — besides from reliable further development of inspection methods — the combination of test result with result of stress analysis, related to properties and stress of the inspected material. A systematical survey of possibilities of destructive and nondestructive materials testing may be helpful to find a solution of these problems.     

Bruchmechanik und zerstörungsfreie Werkstoffprüfung

Requirements by Fracture Mechanics on Nondestructive Testing Methods Fracture mechanics is a tool in evaluating the magnitude of critical flaws in structures. By means of Material properties such as fracture toughness, subcritical flaw growth, and existing primary and secondary stress it becomes possible to evaluate critical values for given flaw configurations. In Section XI, Appendix A of the ASME-Nuclear Pressure Vessel Code allowable flaw dephts are usually determined as a function of flaw configuration and localisation and wall thickness. Thus one wants to enable a fracture mechanical assessment of detected defects and of the safety of a component against brittle and tough fracture. Besides, it shall be possible to get an idea about the subcritical flaw growth. Therefore Practical application of fracture mechanics is based on progress in nondestructive surveillance methods. In the presented work the guidelines for integrity assessment of flawed structures based on Appendix A are described and the problems relating with fracture mechanical approaches are outlined. Up to this day it is not possible to get quantitative statements about the configuration, localisation and magnitude of flaws in structures by means of non destructive testing. Therefore factors of safety are introduced with the goal of assuring the integrity of flawed structures.     

Über die Fehlerauffindbarkeit als Hauptforderung an die zerstörungsfreie Werkstoffprüfung

About the Detection of Imperfections as a Main Task for Nondestructive Testing The inspection uncertainty is identified which is a measure of the difference between the size of imperfection that has a high probability of being passed and the size of imperfection that has a high probability of being rejected by an inspection. Reduction of the inspection uncertainty is the only means by which one can reduce inspection errors as the acceptance of defective material units and the rejection of sound material units. The discussion is presented within a framework that allows a quantitative evaluation of the quality of the material units that pass an inspection and a determin ation of the rejection rate. Analysis of the causes of inspection uncertainty is essential to efficient strategies for improving nondestructive inspection capabilities.     

Messunsicherheit in der Werkstoffprüfung

Measurement uncertainty in testing of materials For the testing of materials the respective uncertainty has to be indicated for each measured value. From the 1995 published GUM [1] 2000 the Uncert report for different measuring methods was developed and published as Code of Practice (COP) [2–4]. These are to be represented in connection with the procedures recommended in the standards and the practical implementation.     

Die Relativierung des Spannungsbegriffes in der zerstörenden Materialprüfung

Relativity of the notion “stress” in destructive materials testing. Later developments of certain important fields in destructive testing can be correlated with the modification undergone by the notion of stress in its practical application: In connection with highly elastical and plastical deformation this notion becomes more and more relative because of its dependence on the time scale of the test; in the field of random loading the idea of a maximum tolerable stress has to be replaced by the algorythmic handling of irregular loading histories; in fracture mechanics stress can no longer be considered independently and has to be linked to influences of local distortions. Both random fatigue and fracture mechanics can by no means be regarded as entirely solved problems. Some directions are discussed in which the answers to open questions might be found. Some consequences for the conception of new testing equipment are mentioned.     

Betriebsnahe Schadenserkennung mit Hilfe der holografischen Interferometrie und eines Doppelimpulslasers

Holographic Investigation on Failure Mechanisms in Homogenous Materials There is a relation between defects occuring in the wall material of pressurized equipment and the deformation of wall surface under load. If the deformation at the surface exceeds 35 nm, it is possible to use holographic interferometry for detection. The object is illuminated by a double pulsed ruby-laser. The frequency of the flashes is very large. Therefore it is not necessary to use of a stabilized holographic equipment. In this way it is possible to detect damage progression in the material of equipment during operation with non-destructive methods. Usually the severity of a failure is characterized by the apparent perturbation of its holographic fringe pattern. The method is applicable to pressure vessels, if the holographic taken fringe pattern is related quantitatively to the size of a failure. In this report we present the experimental results which give the relation between the perturbation of the holographic fringes and the size of different kinds of failures. The size of the smallest detectable failure is smaller the critical size of a flaw in the material.     

Messung der Verformung an Elektronenstrahlschweißnähten mit Hilfe der holografischen Interferometrie

Measurement of the Deformations of EB-welded Joints by the Means of Holographic Interferometry. The field of deformations in EB-welded specimens should be measured in all directions. Therefore holographic interferometry was chosen to be the best method. Normally the deformations are so large, that the usual fringe systems cannot be solved. In order to avoid this difficulty, new diagrams were developed and based on this the holographic equipment was optimized. By means of the new diagrams and some derived diagrams it was possible, to calculate the deformations very easily. In addition a specimen-holder is described which allows the specimen to be taken out of the holographic system during the welding process.     

Der Beitrag der zerstörungsfreien Prüfung zur Zuverlässigkeit und Verfügbarkeit korrosionsgefährdeter Komponenten von Chemieanlagen

The part of Nondestructive Testing of Ensure Reliability and Availability of Components of the Chemical Process Industry under Corrosive Conditions Corrosion and wear failures very often are initialized or at a minimum influenced by faults in design, manufacturing and installation. If we reduce these faults, the result will be an increasing working life of the components. To solve this problem, we recommend the consequent use of NDT-techniques.     

Probleme der zerstörenden Prüfung von Proben mit sehr geringer Verformung

Problems of Destructive Testing of Samples with Very Low Deformation In the case of materials with very low deformation at break, for example ceramics and graphite, the stiffness of the testing machine has to fulfill requirements which must be clearly defined and capable of being checked, in order to avoid errors in the test result. Besides sensitive test factors there are also some which remain constant regardless of the spring stiffness of the testing apparatus. The effect on the commonly used loading methods (v_o = constant; \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm F}\limits^. = {\rm constant} $\end{document}) is investigated. Possibilities for corrections are discussed an appropriate algorithms are given.     

Oberflächentastschnitte als Hilfsmittel der Werkstoffprüfung

Material Testing by Means of a Stylus-Type Roughness Tracing Instrument . Our experiments and a literature of survey show the various possibilities and limits of surface roughness measurements by means of the stylus-type roughness tracing method. Through direct or, by applying an imprint technology, through indirect surface tracing on materials such as metals, plastics including coatings and lacquers (duromers, plastomers, elastomers), wood, paper, asbestos sheets, textiles and coal a connection with the properties of the materials with respect to wear, sealing and contact, roughness of fracture surfaces, material testing, surface roughness of an injection mould, process and machining, corrosion, damage analysis, optical aspect, writing pressure curves, cracking etc. has been illustrated. Two examples from the medicine (dermal and dental medicine) underline the broad range of application possibilities. In many cases the stylus-type roughness tracing method is a secondary, however, generally very informative indirect testing method. Only in some cases it is in direct connection with a certain property of material such as the surface gas tightness of asbestos sheets. The limits of the stylus-type roughness tracing method are further determined by the method of measurement (stylus pressure, radius of stylus, curvature, stylus system).     

Werkstoffprüfung mit der Schallemissionsanalyse (SEA)

Non-Destructive-Testing by Acoustic Emission . After the discussion of the physical principles and the experimental procedures of acoustic emission (a. e.) techniques, numerous examples of its applicability and capability are presented. These concern: plastic deformation of metals (ferrous- and non-ferrous-), crack-formation during heat treatment for stress-relief, crack-formation during cyclic loading, control of weld-processes, stress-corrosion cracks and finally microcrack formation in different fibre-reinforced composite materials. Advantages and disadvantages of a. e. are compared with those of other n. d. t.- methods.     

Einsatz von Heißleiter-Temperaturfühlern in der Werkstoffprüfung

Application of Semiconductor Temperature Sensors in Material Testing So called Negative Temperature Coefficient (NTC) resistors whose electrical conductivity increases rapidly with increasing temperature have arisen as a by-product of semi-conductor development. This change in electrical resistivity makes the NTC-resistor — also known as Thermistor — suitable for exact temperature measurement. Because of its high resolution and small dimensions, it can be successfully used where maximum accuracy is required and point measurement is necessary. Possible applications are in material testing etc.     

Anwendung Flüssiger Kristalle in der Materialprüfung

Application of Liquid Crystals for Materials Testing. Cholesteric liquid crystals are recently known to be suitable for temperature measurement which can be done by observation of colour variation created by the layers of the cholesteric liquid crystals. The main advantages of liquid crystals over conventional temperature measurement are their low thermal capacity and the possibility of showing large temperature maps. By the cinematographic method the variation of temperature maps as a function of time can be recorded. Until now those informations were received only by relativly costly equipment i. e. infrared cameras.     

Werkstoffprüfung von Hochleistungskeramik mit Zugproben

Mechanical testing of high-performance ceramics with tensile specimens Mechanical properties of engineering ceramics are often measured in bending. The principal limitations of these tests are discussed for linear-elastic and plastic material behaviour. From this the requirement of tensile tests is derived. For room temperature fatigue tests an optimized concept of gripping round specimens is presented. High temperature tests are performed with flat specimens allowing static and quasistatic experiments with continuous strain measurement up to ca. 1400 °C. For sintered silicon nitride tensile creep curves are reported and compared with results from bending tests.     

Probleme der Dichtebestimmung durch holographische Interferometrie bei der Anwendung in Flüssigkeiten

Zusammenfassung Die aus der Gasdynamik bekannte dreidimensionale Dichtebestimmung durch holographische Interfereometrie ist für eine Anwendung in Flüssigkeiten aufgearbeitet worden. Es konnte gezeigt werden, da? die Messungen nur mit einer sehr genau auf den zu untersuchenden Dichtegradienten abgestimmten Versuchsanordnung zum Erfolg führen k?nnen.     

Die holographische Interferometrie – ein zerstörungsfreies Untersuchungsverfahren zer Früherkennung von Bauteilschäden

Holographic Interferometry – a Nondestructive Inspection Technique for Early Detection of Construction Element Damages After a short introduction into the fundamentals of holographic of holographic interferometry, the application of this process to non-destructive material testing is explained. Practical examples of qualitative and quantitative deformation measurements carried out on building elements of different materials as well as on metallic and nonmetallic combinations show the possibilities of early recognition of manufacturing flaws and weak points due to the construction and also the determination of construction material characteristic coefficients.     

Beitrag zum Lebensdauerverhalten und zur zerstörungsfreien Bewertung geschweißter und fehlerbehafteter ultrafester Stähle

Relationship between fatigue behaviour and non-destructive assessment of weld defects of TIG-welded ultra-high strength steels With respect to the influence of welding defects on the fatigue properties of welded high strength special steels and on the dynamic load carrying capacity of joints in welded constructions, a minimum of information is available. For this reason, the preparation of an assessment standard for classifying weld defects was considered practical, whereby the character of the defects was to be determined using non-destructive testing methods. The investigations were concerned with a special method of producing specimens containing defined and reproducable defects, with the characterization of the defects using X-ray and ultrasonic techniques, and with the determination of the influence of the weld defects on the fatigue strength of TIG-welded joints. As a result of the investigations, a relationship between allowable and critical defect size with respect to an assessment standard has been sought. By introducing weighting factors for various types and sizes of defects occurring in welds the efficiency of non-destructive testing methods for the assessment of weld defects is considerably increased.