Process monitoring and quality assurance with a microwave radar sensor

By means of microwaves it is possible to perform nondestructive and online capable testing in the domain of material properties, geomaetric dimensions (e.g. thickness) and detection of defects like flaws, delaminating or voids. Often the examination can be performed without contact. Preferred materials to be tested are dielectrics since they are partly transparent with respect to microwaves. A measurement and testing system based on a Frequency Modulated Continuous Wave (FMCW) radar sensor at ca. 94 GHz has been built up and applied on different processes and objects like injection molding with gas bubble injection, contact less imaging of inner defects and measurement of plastic coat thickness on steel pipelines. Furthermore thin metallic layers on dielectric substrates could be characterized with low priced monofrequent microwave sensors at 9.4 GHz

The situation of acoustic emission in Germany

This presentation summarizes the situation of acoustic emission (AE) testing in Germany in research, development and industrial application. First a short overview on AE history in Germany is given. The AE activities in the field of testing of pressurized nuclear power components in the seventies and eighties are descibed. These activites dealt with creation of reliable base knowledge on AE, development of an optimized measuring technique and determiation of the physical limitations of the method. It has been shown that the probability of detecting macroscopic nongrowing flaws cannot be quantified during hydrotest. The may be one of the reasons that there was no breakthrough in industrial application. The other main reasons are the lack of reproducibility of flaw detection and the lack of defect size determination. Growing flaws can be surveilled with local instrumentation with high sensitivity even under in-service conditions. However, this potential of AE testing is presently not use d in the field of nuclear power technique. AE testing has gained some acceptance in the domain of chemical industry for requalification tests of out-dated tanks, vessels and pipes. Recently there are some efforts to apply AE testing during gas pressure tests of vessels mainly as an additional measure to protect the personnel. Some potential and promising future applications can be found in the field of monitoring of tool wear and breakage

Die elektrische Emission beim Versagen von Faserverbundwerkstoffen und ihren Komponenten

Deformation and failure of fiber-reinforced materials (FRM) can cause electric charge displacements. This, consequently, leads to variations in the external electric field. These can be observed and recorded during the loading process without any contact to the sample. Analyzing, these signals named electric emission (EE) can be done individually and also statistically when an acoustic emission equipment is used. Fracture of carbon and glass fibers yields EE signals of large amplitudes, whereas the polycarbonate matrix material exhibits smaller ones. The signals obtained in a tensile test with the composite materials exceed the ones of the matrix material but do not attain those of the fiber material. From the shape of the EE signals conclusions can be made on the elementary fracture process. From these experiments it can be concluded that the EE method is a valuable tool with respect to the detection of failure occurence of composite materials as is the acousti emission technique. The EE Technique is a field method and does, therefore, not require any sample preparation. This makes it a low cost technique which can be possibly applied in the field as well as in the laboratory

Überwachung des Spritzgießens mit einem Radarsensor

Im Rahmen von experimentellen Untersuchungen sowie mit Simulationsrechnungen konnte gezeigt werden, dass es möglich ist, die Position einer Gasblase beim Spritzgießen von Kunststoffformteilen mit der Gas- und Wasserinjektionstechnik (GIT, WIT) mit Hilfe von Mikrowellen im Millimeterwellenbereich zerstörungsfrei und online zu ermitteln. Die Methode eignet sich somit zur Prozessüberwachung

Observation of stable crack growth in AL203-ceramics by acoustic microscopy and acoustic emission

In certain ceramics one observes an increase in crack resistance with increasing crack length (R-curve behaviour). This phenomenon is explained by two controverse models: 1) the crack resistance grows by an increase of microcrack density at the crack tip; 2) the crack resistance grows by the interaction of the serrated crack surfaces behind the crack tip. The crack grawth in Al2o3-ceramics has been studied by Scanning Acoustic Microscopy (SAM) and Acoustic Emission (AE). The results of both methods show that both increase of microcrack density and interaction of crack surfaces occur and should play a role in increasing the crack resistance

Charakterisierung von Streuern und Defekten mittels Mikrowellen im Freifeld und Vergleich mit theoretischen elektromagnetischen Modellen und mit den Gesetzmäßigkeiten bei der Ultraschallprüfung

Mit Hilfe breitbandiger Mikrowellenmeßsysteme ist es möglich, Streukörper, die in eine Matrix anderer Zusammensetzung eingebettet sind, zu charakterisieren. diese Methoden wurden bislang in der Radartechnik im Frequenzbereich bis zu einigen GHz angewendet und können, wie diese Untersuchung zeigt, auch im Bereich der Millimeterwellen (ca. 30-300 GHz) im Freifeld eingesetzt werden. Die gefundenen abhängigkeiten der Zeitsignalamplituden von der Streuergröße und dem Abstand zwischen Streuer und Antenne stimmen sowohl mit denen der Radartechnik im Fernfeld als auch mit den gesetztmäßigkeiten in der Ultraschallprüfung überrein. Die Analyse der Streuewinkelabhängigkeit sowie die detalierte Signalanalyse im Zeit- und Frequenzbereich erweitern die Möglichkeiten der Streuercharakterisierung