Band 49, Heft 6

This paper describes recent advances in automated ultrasonic techniques which have enabled fully effective and qualified inspections to be introduced for nuclear power stations. In the first example, ultrasonic phased arrays have been introduced for inspection of fillet welded structures where physical access for the operator is very awkward and the surfaces available for probe scanning are very restricted. The system has optimised the depth of field by varying the number of phased array elements fired at a given time and the inspections are substantially faster and more reliable than conventional manual inspection. In the second example, NDT Workbench significantly improves data analysis for complex geometries and defects by using 3D data displays of multiple beams and automated logging of measurements. Both examples have been formally qualified using the ENIQ (European Network for Inspection Qualification) Methodology. This was achieved more easily because of the rigorous in-house training programmes and because the Technical Justifications referred to evidence from previous related qualifications whenever appropriate.

In different NDT techniques huge developments have been achieved during the last few years with regard to crack detection and sizing. In a large range of materials, cracks are one of the most dangerous defect types. A crack is a planar reflector, which is sometimes extremely difficult to detect and to be sized. A crack can be totally open, partly closed or even totally closed because of compressive stresses. The effects of stresses cause problems, for instance, in in-service inspections of nuclear power plants in detection and sizing of closed cracks. This phenomenon causes similar effects in all kinds of plants and components. In this study some experimental inspections have been carried out as well as some FEM calculations of stress field around the crack and compared to corresponding measurements in literature. Materials used for this study are austenitic and ferritic piping steel. The dynamic load applied to the cracks was in form of different thermal cycles. The maximum temperature variations were from 20°C to 600°C depending on each dynamic loading cycle. Different types of ultrasonic methods were used in the measurements. The effect of closure on the response of normal ultrasonic practical probes was recorded. Dynamic loading during ultrasonic measurement gives clear evidence on the effect of the crack closure as well as on the amplitude variation limits in ultrasonic testing.

Kurzfassung Es werden Methoden sowie eine Vorrichtung vorgestellt, die es ermöglichen, orientierende Untersuchungen über die Eignung unterschiedlicher Werkstoffe für den Einsatz als Werkzeuge im Mikrotiefziehprozess durchzuführen. Untersucht werden unterschied- lich hergestellte Stähle, lasergenerierte Werkstoffe sowie eine DLC-Schicht. Aufgrund der sehr einfachen Probengeometrie können auch aus schwer spanbaren Werkstoffen relativ einfach Proben gefertigt werden. Zunächst werden mittels Streifenziehversuch die Reibzahlen der Paarungen Werkzeugwerkstoff — Werkstückwerkstoff ermittelt. Danach werden die Gleitweglängen, die ohne Verschleiß zurückgelegt wurden, bestimmt. Des Weiteren werden licht- und elektronenmikroskopische Untersuchungen durchgeführt zur Klärung des Verschleißmechanismus. Die vorgestellten Untersuchungen ergaben Adhäsion als hauptsächlichen Verschleißmechanismus unter den Bedingungen des Mikrotiefziehens bei den untersuchten Werkstoffkombinationen.

The emphasis of this paper is to provide an overview of the numerical computer simulation of fields and waves and its application in nondestructive testing (NDT). Several numerical methods are applied: the finite integration technique (FIT), the finite element method (FEM), the boundary element method (BEM), and the method of moments (MoM). The numerical modelling of the ultrasonic and eddy current NDT inspection technique is discussed. Similarly, the numerical computer simulation of coupled wave field problems, like the piezoelectric and the electromagnetic-ultrasonic transducer is documented. The performance of the computer simulation in nondestructive testing is presented on the basis of 3-D modelling results of the ultrasonic testing of reinforced concrete and eddy current testing of hot wire steel.

Effect of thermal oxidation on the behaviour of stainless steel (SS) in an ferrichlorid solution was investigated. Sheet specimens of austenitic AISI 316L with the observed area S = 90 cm 2 were immersed into the solution in the initial state, after heating in air isothermally at 200, 400, 600, 800 and 1000°C respectively or in temperature gradient, and after heating and subsequent cleaning of specimens in an nitric acid/hydrofluoride acid mixture. Spot potential profiles of specimens were taken up using a simple device with graphite counter-electrode i.e. by measuring local potential differences between specimen and graphite. The presence of thermal oxides enhances the non-uniformity of profile, which decreases after the removal of oxides by cleaning in the nitric acid/hydrofluoride acid mixture. However, the initial degree of uniformity is not re-established. Prolonged exposure to ferrichlorid solution provokes pitting corrosion of specimens heated isothermally at 400° C and above it or heated in temperature gradient. On such specimens pits number n p , their depths h p and orifice areas S p .

Kurzfassung Nach künstlichem Hüftgelenkersatz kann Impingement zwischen Endoprothesenhals und Pfanneneinsatz zu Luxation und Implantatschädigung führen. Mithilfe eines Finite-Elemente-Modells wur- den bei unterschiedlichen Implantatpositionen Bewegungen im künstlichen Gelenk simuliert und das Impingement- und Luxationsverhalten analysiert. Die Spannungsuntersuchungen ergaben bei Impingement und während der Subluxation Druckspannungen weit oberhalb der Fließgrenze von UHMW-Polyethylen, wodurch die Impingement-bedingte Schädigung von Pfanneneinsätzen bestätigt wurde. In der vorliegenden Arbeit wird ein neues Implantatdesign vorgestellt, welches wesentlich zur Vermeidung von Impingement-bedingtem Implantatversagen beitragen kann.

A novel, cost-effective and fast method based on electrophoretic deposition (EPD) was employed to produce nano-structured bio-active layers of hydroxyapatite (HA) on Ti-based metallic implants for orthopaedic applications. Nano-size HA powders were first synthesised using sol-gel technique and kinetically stable colloidal suspensions that contain HA powders were prepared for coating experiments using EPD. Ti6Al4V metallic alloys were coated using different processing parameters, such as deposition time and voltage to optimise coating thickness and eliminate crack formation on the surface. Different coating thickness from 10 mm to 60 mm were achievable under controlled parameters. It was showed that sintering temperature of HA layers was lowered to 500°C by using sol-gel synthesised ultra-fine (30—40 nm) HA starting powder during EPD. The thickness of the coating layers plays an important role to obtain deposits with free of cracks. EPD-formed layers up to 25 mm thickness contain no cracks on the surface but above this thickness extensive cracks are seen within the deposit. Lower sintering temperatures form stoichiometric HA with no other phases and this low temperature should contribute to minimised residual stresses within the metallic alloy which means lifetime of the metallic implant will be longer. Overall, a completely new method of making nano-bioactive-ceramic layers which results in the formation of thin and thick films with controlled microstructures and phase distribution on Ti6Al4V metallic implants was introduced.