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The present Technical Report was written with the intention of fulfilling for needs: (i) for an introduction of research workers in the Technical Working Areas (TWAs) of VAMAS to modern statistical methods and techniques appropriate to improve the effectiveness of experimental research in the scope of the VAMAS co-operative projects in materials science and engineering; (ii) for illustrating the power of such approaches by giving an outline of more recent applications in science and technology; (iii) for developing a feeling on the role and importance of statistical consulting under these circumstances; and (iv) for presenting objectives and a programme to provide and promote statistical consulting within VAMAS by developing the TWA / Advisory Group “Statistical Techniques for Interlaboratory Studies and Relates Projects”.
The aim of this thesis was the development of switchable information carriers based on shape memory polymers (SMPs) and the investigation of their durability. Deployed as a new kind of security label, such technology may be an effective tool to prevent counterfeiting and product piracy.
Thermoplastic as well as thermoset SMPs turned out to be applicable as a specific substrate for the fabrication of switchable information carriers. In particular, a physically cross-linked and semi-crystalline poly(ester urethane) (PEU), and a chemically cross-linked epoxy-based polymer were investigated. Both SMPs were able to undergo distinct changes in shape upon triggering, which is commonly known as the shape memory effect (SME).
A key step for the fabrication of switchable information carriers was the development of a suitable technique for a surface-specific coloring of the polymeric base material. In particular, it was necessary to have a thin coat of paint in order to assure sufficient surface contrasts within the subsequently laser-engraved barcodes (e.g. quick response (QR) codes). In detail, coloring was conducted by diffusion of staining solutions, based on organic dyes, into the polymeric matrix. As a result of properly selected exposure times, homogenous layers of paint having thicknesses of about 100 μm, could be produced.
In order to obtain room temperature stable, temporary shapes with non-decipherable code information, various programming procedures were applied to the information carriers. These were either based on tensile or on compressive deformation. For instance, when using plane steel plates in the course of compressive deformation, code areas were randomly distorted. By contrast, selective distortions could be achieved using a steel ball type indenter. However, the triggering of the SME resulted in almost complete shape recoveries. As a result, the information carriers could reliably be switched back to readable states.
Before the developed information carriers can be brought onto the market, it is important to evaluate their durability against various environmental impacts. Artificial weathering was conducted exemplarily on blue and black colored QR code carriers based on PEU. Various scenarios were selected: exposure to UVA irradiation and aging in aqueous solution. In both cases, the durability was investigated at temperatures below and above the switching temperature of the employed SMP. It turned out, that the limiting factor for the usage of switchable information carriers was a lack of contrast and thus was dye-related. In the case of UV irradiation, the color of the dyes started fading, culminating in unreadable QR codes. For hydrolytic degradation, the non-colored code regions were stained in the course of aging. This originates from the fact that the organic dyes used for coloring were soluble in water. As a consequence, they were able to diffuse easily in and out of the swollen polymeric matrix. For both scenarios, aging at elevated temperature caused acceleration of the observed effects. However, the shape memory properties of the PEU were only slightly influenced by the applied aging scenarios.
Next, an additional thermo-responsive security feature was added to the information carriers. Therefore, thermochromic pigments (T-PIGs) were embedded into a PEU matrix. However, in contrast to the organic dyes, the size of the thermochromics microcapsules was too large to diffuse into the polymeric matrix. Thus, another procedure for a surface-specific coloring of the PEU was developed. This mainly included the preparation of a PEU-paste doped with T-PIG by solution mixing. The thermochromic paste was deposited by means of a solvent casting technique as thin layer atop the PEU plaque. After solvent evaporation, tightly connected PEU/PEU-T-PIG laminates were obtained. Beyond that, the layer thickness was adjustable by using a doctor blade for the paste deposition. Subsequent laser ablation finalized the QR code carriers. These were readable at room temperature, but unreadable above the color switching temperature of the employed T-PIGs due to a lack of contrast. Hence, the obtained multifunctional information carriers were characterized by distinct shape memory properties and tunable color switching performances. Furthermore, the combination of several T-PIGs having different colors and switching temperatures resulted in surfaces with multiple and unique temperature-dependent changes in color. Besides that, information carriers with temporarily concealed information could be obtained by covering the QR code with an additional layer doped with T-PIG.
Two introductory reports on a Systems approach to tribology, refs (1) and (2), have been discussed at the previous meeting of IRG-OECD (London, 1973). The new concepts derived from General Systems Theory, and Mathematical Systems Analysis are combined in the present report and applications in tribology are worked out in greater detail.
In introducing the subject it is pointed out once more:
(i) all tribo-mechanisms are by definition complex Systems;
(ii) friction and wear are operators of tribo-systems (in terms of either a verbal or a mathematical theory of sets);
(ii) therefore friction coefficients and wear rates cannot be instrinsic material properties.
The nature of complexity in the verbal description of tribo-mechanisms is analyzed, and logical ruies, needed in the analytical procedure, are given;the mathematics are summarized in the Appendix.
A general classification of tribo-mechanisms is developed by step-wise analysis, and mathematical expressions for friction and wear processes in steady state Systems are given.
The recent experimental advances made by IRG-OECD (refs (15) and (16)) on failure criteria in thin film lubrication are presented in the terminology of Systems analysis, but merely äs an example for the formalization of non-linear tribo-processes.
It is concluded that neither the verbal nor the mathematical Systems analysis have, at present, more predictive power than a conventional Interpretation of experimental results. However, dangerous logical errors in the concepts of friction and wear can now be eliminated and, by doing so, a new outlook on tribometry is gained. The practical engineering consequences for the future, functional control of tribo-machinery have already been predicted by Schlösser (ref. 18).
In der vorliegenden Arbeit wird die Ultraschallausbreitung in akustisch anisotropen, homogenen Werkstoffen mit stengelkristalliner Textur wie austenitischen Plattierungen und Schweißverbindungen, austenitischem Guss oder geschweißten Komponenten aus austenitischem Gus modelliert. Die Ergebnisse dieser Arbeit dienen als Vorgabe für Prüfanweisungen und Regelwerke, die besser als bisher an den Prüfgegenstand angepasst sind.
Annual Report 2002/2003
(2003)