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Eingeladener Vortrag
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Today’s light weight design trends lead to a growing application of high-strength structural steels (yield strength ≥ 690 MPa). The mechanical properties of the weld and the component safety have to meet the increased requirements of these steel grades. However, high residual stresses in welded components are detrimental to their safety and integrity. Analyses concerning weld stresses in high-strength steels welded under component related restraint conditions revealed that heat control significantly affects global and local stresses. This occurs especially in highly restrained joints due to superimposing local and global stresses and may cause crack-critical stress-levels. In this study weld tests were performed with plates of high-strength steel in a special test facility. The experimental setup allowed transferring defined restraint conditions to the test welds similarly to real components. Temperature and reaction forces due to restraint were observed online while welding and cooling of multilayer-component MAG-welds. Mobile X-ray diffraction was used for local stress determination in the weld seam areas of the restrained specimens. It was found that interpass temperature has a major influence on the local and global welding forces and stresses. Thus, among the analysed results especially transverse residual stresses of the heat affected zone were strongly affected.
The writing materials of the Silk Road book cultures in Turfan – Analysis of inks and pigments
(2014)
Manuscript fragments discovered in the oasis of Turfan and in other sites of present-day China in the beginning of the 20th century by A. Grünwedel and A. von Le Coq, represent one of the most fascinating cultural testimonies of people who both lived there and travelled along the trade routes between East and West. To determine the different materials used for writing and painting the Chinese, Sanskrit, Manichaean, Syrian, Sogdian, Tocharian and Uighur fragments of the Berlin collection, analysis of inks and pigments were conducted using non-destructive methods. The research was funded by the German Research Foundation DFG for a period of three years. The identification of specific techniques of preparation allows manuscript groups and sub-groups to be specified, aiding their cultural assignment. This is important for further cultural studies, for the development of conservation strategies and the identification of forgeries.
In the majority of cases, the red color of cinnabar on objects of cultural heritage is well preserved, though turning black is often claimed and has been the subject of investigations. To evaluate conditions for the stability of the pigment and understand the reactions, in this paper the problem is approached from various viewpoints. First of all the natural form cinnabarite is compared with the artificially prepared pigment vermilion. This establishes a differentiation of types in terms of quality, depending on structural impurities. With regard to the pigment’s reactions influencing the discoloration, the most commonly mentioned environmental factors, such as radiation or halogens, are evaluated. In relation to various usages, the pigment’s structural stability is then viewed in connection with adjacent pigments, glues, and the substrate, which may lead to a brown or black coloration or even the release of mercury, whereas the color is preserved in most cases when used on lime or in ink and lacquer. Due to the materials’ properties, attention is drawn to the fact that discoloration to a brownish-black is not necessarily a sign of damage and harmful reaction products, but may indicate good preservation of the painted material, provided that the mercury can be bound in the substrate.
The paintings and manuscripts discovered in the sealed ‘library cave’ in Dunhuang, Western China, contain the earliest surviving examples of Tibetan artistic and scribal practice (9the10th centuries AD). Despite their importance, their material characteristics have not previously been studied. The present paper discusses the results of the analysis of paper and pigments in a selection of items across a variety of forms and functions: (i) Buddhist manuscripts, (ii) official letters, (iii) hung paintings, (iv) ritual items, (v) banners, and (vi) stencils and preliminary sketches. The material analysis of these items is presented in historical context, to address three research questions. First, whether there is a correspondence between the materials used in the creation of these objects and their geographical origin. Second, in terms of the choices made in the available materials and techniques, whether there is a detectable correlation between materials chosen and the intended function of the objects. Third, whether the characteristics of the objects analysed here be considered to be part of a broader Central Asian artistic and scribal culture. The authors conclude that a local culture of paper and pigment production can be detected in these results, though further research is needed especially on the geographical origin of raw materials for pigments. The results show that artists and scribes made technological choices in paper and pigments depending on the function of the objects they were creating. Finally, understanding of the broader Central Asian context of these results will depend on future analysis of material from other archaeological sites, and comparison with the results of this study.
Electrochemical half-cell potential measurements for the detection of reinforcement corrosion
(2014)
This specification describes the application of electrochemical half‐cell potential measurements (frequently also called potential mapping) for the detection of reinforcement corrosion in reinforced concrete structures. Areas of corroding reinforcement steel can be located in a nondestructive manner by means of this procedure. Half‐cell potential measurements are used in order to detect chloride‐induced corrosion. However, it is not recommended in order to assess the risk of carbonation‐induced corrosion. For this purpose the determination of the carbonation depth and the concrete cover appear to be more appropriate.
The content of this specification exclusively refers to the application of mobile, local variable reference electrodes, which are only placed on the concrete surface while measuring. The technique distinguishes itself thereby from the range of corrosion monitoring systems with stationary installed reference electrodes and sensor systems, respectively, whereby it is possible to continuously track measurements within the area of the installed electrodes. However, these methods are not dealt with in this specification.
Emergency response units increasingly use pressure cylinders made from fibre composites for breathing air as elements of personal protective equipment (PPE). Such applications expose the composite cylinders to harsh temperature and handling conditions. At least in Europe, standards have been used for certifying PPE, which are designed and mandatory for the approval of pressure receptacles for the transport of dangerous goods. Therefore, service conditions specific to PPEs are not accounted for in these standards. In this paper, BAM (Federal Institute for Materials Research and Testing) investigates the residual safety of a composite cylinder design at the end of their designated service life of 15 years. The cylinders (test pressure PH 450 bars; 6.8 Litres) are of one design type with aluminium liner and fully wrapped with carbon fibres, which is commonly considered a “Type III” cylinder. All cylinders were used as PPE by the Berlin fire department and randomly picked in three samples of 25 cylinders each before tested.
At BAM, the cylinder samples underwent hydraulic load cycle tests (LCT), conventional burst tests (BT) and so called slow burst tests (SBT). A concept for quantification of strength degradation already introduced by BAM was applied. This concept is based on a probabilistic assessment of the average strength and scatter of each sample of cylinders. The strength distributions of the used PPEcylinders is shown and analysed. Some unexpected effects are shown and a refinement of the statistical assessment is introduced.
Design of a cementitious coating system for corrosion protection: Phase 1 binder materials selection
(2014)
This paper presents the first results of an ongoing research project on the development of a cementitious thin layer coating system with high resistance against chloride penetration and carbonation. It is intended to display the decision process used for selecting raw materials as well as the conclusions based on test results and theoretical deliberations. In this phase, only the influence of the binder materials was analyzed concerning mechanical properties. The system should enhance the durability of new and old concrete structures exposed to aggressive environments, be based on market available materials and fulfill the requirements of the German guideline for concrete repair (Rili-SIB).
Design of a cementitious coating system for corrosion protection: Phase 1 binder materials selection
(2014)
This paper presents the first results of an ongoing research project on the development of a cementitious thin layer coating system with high resistance against chloride penetration and carbonation. It is intended to display the decision process used for selecting raw materials as well as the conclusions based on test results and theoretical deliberations. In this phase, only the influence of the binder materials was analyzed concerning mechanical properties. The system should enhance the durability of new and old concrete structures exposed to aggressive environments, be based on market available materials and fulfill the requirements of the German guideline for concrete repair (Rili-SIB).