Filtern
Erscheinungsjahr
- 2011 (194) (entfernen)
Dokumenttyp
- Beitrag zu einem Tagungsband (194) (entfernen)
Sprache
- Englisch (194) (entfernen)
Schlagworte
- CCS (7)
- Corrosion (7)
- Steel (7)
- Concrete (6)
- Strain sensor (6)
- Computed tomography (5)
- Structural health monitoring (5)
- CO2-storage (4)
- Emission (4)
- Fibre optic sensors (4)
Influence of the main laser welding parameters on process stability and resulting weld quality were investigated. Effects of weld edge preparation on the weld appearance and quality were considered. The obtained welded joints were subjected to radiographic tests for detection of internal imperfections. Metallurgical characterisation of the samples regarding the resulting phase composition and hardness was conducted. Tensile and potentiodynamic tests were performed to evaluate the mechanical and corrosion properties. The results provide an insight into the advantages and limitations of the laser welding process for joining high-manganese alloyed stainless steels. Conditions for the production of defect-free and corrosion-resistant welds having good mechanical properties could be determined.
Determining scatter ratios at high energies (> ~ 1MeV) presents challenges not immediately obvious from measurements at conventional X-ray energies. This includes reduced attenuation even in heavy elements as well as a stronger forward bias of scattering. In order to check the reliability of different measurement setups with regard to material thicknesses, distances, and collimation, attenuation and scattering were separately simulated using a Monte Carlo model. The simulation results help in understanding the sources of radiation scattered into the detection area, thereby aiding in eliminating undesired contributions.
The present contribution highlights recent trends in investigating hydrogen diffusion and cracking in steel welds. For such studies, supermartensitic stainless steels (SMSS) have exemplarily been selected. These materials have been used for offshore and marine constructions for about two decades now. They present a versatility of improved properties such as high strength to thickness ratio, good weldability and good corrosion resistance. However, as shown by respective failure cases, SMSS welds might become prone to hydrogen assisted cracking and the degradation phenomena are more easily to investigate due to the nearly homogeneous martensitic microstructure than in other materials. Generally, it has to be distinguished between cracking that occurs during or shortly after fabrication welding, or during subsequent operation of SMSS components. In order to achieve crack avoidance during fabrication and service, conclusive test sequences have to be applied, ranging from field tests at real components and full scale tests investigating the materials behavior under real service conditions to basic and small scale tests, such as tensile and corrosion tests, oriented more towards a materials ranking. Considerable testing of SMSS welds has been carried out and the present paper particularly summarizes spotlights on 1:1 scale component testing of welded tubulars, slow strain rate testing and basic tests oriented to elucidate the hydrogen behavior and degradation in SMSS weld microstructures. Also, permeation tests, hydrogen dependent degradation of mechanical properties and thermal desorption spectroscopy are adressed. As a specific item, first results of lately conducted investigations for tracking hydrogen movement in such weld microstructures by using high energy synchrotron radiation are elucidated.
The extremely low acoustic impedance of polypropylene ferroelectret combined with its piezoelectric properties makes this material suitable for construction of aircoupled ultrasonic transducers for non-destructive testing. For the fabrication of transducers with a stable quality, the reproducibility of their key parameters is of interest.
The reproducibility was evaluated by means of (i) impedance spectroscopy and (ii) pulse-echo measurements. (i) Impedance spectroscopy was applied to identify the resonance frequency, the coupling factor and the acoustic impedance of several nominally identical transducers. (ii) Pulse-echo measurements yielded the signal form of these transducers.
The variation of the signal amplitude measured with pulseecho technique was about 10 dB. A part of this variation Comes from the deposition of transducer electrodes and another part from local variations of ferroelectret properties. The variation of the signal amplitude was caused by the observed variation of the coupling factor, which was also about 10 dB. The variation of the acoustic impedance was only about 1 dB, thus having no effect on the variation of the signal amplitude.
These results indicate that the variability can be reduced by improving the control of electrode deposition and by optimizing the production technology affecting the reproducibility of material properties.
The failure of laminates usually is initiated by the failure of the plies with the maximum transverse stresses. The failure of those plies generally reduces the load carrying capability of the laminate, even though they carry only a small part of the external load. The analysis of failure under off-axis stresses accordingly is essential for the prediction of the strength of laminates. This is taken into account in the "mechanisms based failure criteria" e.g. by Puck. Most of these inter fiber failure criteria are not based on the micromechanics of the failure process but on prescribed stress interaction functions. The failure of plies under transverse loading obviously is governed by the bond strength between fiber and matrix fiber. The interfacial debonding was studied e.g. by Paris et al. and Corea et al.. The bond strength between fiber and matrix usually is measured by using micromechanical tests e.g. pull-out, push-out or fragmentation tests. Stress analyses as well as fracture mechanical analyses show that the interfacial failure over a large range is dominated by shear stresses (Kim and Mai, Pisanova et al, Marotzke and Qiao). The stress distribution arising in those experiments however differs from the stresses acting in a lamina under transverse loading. In transverse failure of a lamina, radial stresses as well as shear stresses are dominating the failure process of the interface. In addition longitudinal shear stresses are present. Experimental work concerning off-axis loading of single fibers was done e.g. by Tandon and Kim and by Ogihara and Koyanagi. They studied the influence of the fiber alignment by using a specimen in form of a cruciform with skew wings.
Different types of lasers are used nowadays for a number of technological Solutions, Modem high power solid-state lasers with high brightness of Radiation like Fiber or disc lasers find ever more applications in welding technology. Apart from the replacement of the CC>2-iasers traditionaHy used fcr these purposes, they provide new technological possibilities of metal treatment, such as using industrial robots and remote welding with high power laser radiation. The possibility of flexible optical fiber delivery of the radiation to any point gives a great technological advantage and permits welding processes to be realized with complicated weld seam geomelries and different positions using a minimum of additional fixtures. The short wavelength of the high power solid state lasers (1.07 ’m) causes another advantage. The coefflcient of inverse 170
Bremsstrahlung absorption from free electrons in plasma for such radiation is about 100 times lower than for the COi-iaser radiation. Owing to this fact, using the solid state lasers allows it to avoid a negative influence of the welding plume.
However, a short wavelength can lead to another kind of laser Radiation attenuation, which is connected with the formation of a cloud consisting of small metal particles that absorb and scatter laser radiation. This cloud arises due to the condensation of hot metal vapor by flying out from the deep Penetration channel and broadening in relatively cold atmosphere over the metal Surface.
Some theoretical and experimental approaches were made in advance in Order to estimate the influence of the Condensed particles on laser radiation and welding quality.
In this paper a systematic study including the determination of the Cloud size and its dynamical characteristics is presented. The results were obtained within the scope of the first stage of the metal vapor condensation process Investigation during welding with high power fiber lasers.
Wear tests are often used in engine development in order to characterize the functional profile of surfaces interacting with lubricants. This paper proposes a new test procedure to determine Stribeck-type curves for the tribosystem piston ring/cylinder liner involving test pieces prepared from engine components. The Variation of the friction coefficient with sliding speed depends on the structure and Constitution of the base oil, the viscosity index, the surface topography of the liner and ring, and the friction modifiers used. Novel organic friction modifiers of low molecular mass not only reduce the friction coefficients under mixed / boundary lubrication, but also in the fluid film regime. In addition, the influence of surface roughness on the wettability of surfaces can be significant for both static and dynamic wetting. For this reason, the interaction of the lubricant with the surfaces was also investigated to enable a correlation between the surface properties of the liquid and solid phases and the tribological behavior.
The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of semiconductors and dielectrics by linearly polarized high-intensity Ti:sapphire fs-laser pulses (τ ~100 fs, λ ~800 nm) is studied experimentally and theoretically. In the experiments, two different types of LIPSS exhibiting very different spatial periods are observed (socalled LSFL low spatial frequency LIPSS, and HSFL - high spatial frequency LIPSS), both having a different dependence on the incident laser fluence and pulse number per spot. The experimental results are analyzed by means of a new theoretical approach, which combines the generally accepted LIPSS theory of J. E. Sipe and co-workers [Phys. Rev. B 27, 1141-1154 (1983)] with a Drude model, in order to account for transient changes of the optical properties of the irradiated materials. The joint Sipe-Drude model is capable of explaining numerous aspects of fs-LIPSS formation, i.e., the orientation of the LIPSS, their fluence dependence as well as their spatial periods. The latter aspect is specifically demonstrated for silicon crystals, which show experimental LSFL periods Λ somewhat smaller than λ. This behaviour is caused by the excitation of surface plasmon polaritons, SPP, (once the initially semiconducting material turns to a metallic state upon formation of a dense free-electron-plasma in the material) and the subsequent interference between its electrical fields with that of the incident laser beam, resulting in a spatially modulated energy deposition at the surface.
Upon multi-pulse irradiation, a feedback mechanism, caused by the redshift of the resonance in a grating-assisted SPP excitation, is further reducing the LSFL spatial periods. The SPP-based mechanism of LSFL successfully explains the remarkably large range of LSFL periods between ~0.6 λ and λ.
Nondestructive testing (NDT) methods are applicable in many ways for defect detection as well as optimization of packaging production processes. The visual inspection method is the technique which is mostly used, although neither the customer nor a skilled inspector may be aware of this.
Techniques like ultrasound for wall thickness measurement, the application of x-ray techniques or the use of dye penetrant techniques for crack detection are rather well known to the NDT family. However, acoustic emission techniques can also be helpful for the characterization of packaging materials. In this paper the employment of x-ray computer tomography (CT) for measurement of wall thickness in plastic jerrycans, especially on the edges, and its possible optimization of production processes will be discussed.
A comparison of the CT and ultrasonic examinations of wall thickness and the reliability of this measured data are also important points for the discussion, especially if some safety factors can be derived from the results.
The leakage test is also good for jerrycans, IBCs or other kinds of drums for the transportation and storage of dangerous goods. The disadvantage of this kind of test is that a lack of quality, e.g. wall thickness deterioration, cannot be detected if the wall thickness withstands the internal pressure. Therefore, especially for Quality assurance, the other, previously mentioned techniques are better for a statistical assessment of a batch. This paper is focused on the comparison of different NDT results with special emphasis on the large range of material mechanical properties.
Fires on waste dumps, surface landfills, Underground stowing or storage facilities of Recycling factories may have multiple harmful effects on individuals on site and on environment.
Possibly several tens of thousands of tons flare up plunging vast areas in smoke and releasing large amounts of flue gases. Experience shows that fire fighting takes days or even weeks and moreover, as long as hidden glowing nests exist fires may break out repeatedly weeks or months later. In the light of this, fire prevention is much easier to manage than extinction. It is of internst to identify the geometrical and physical conditions under which the mid-term or long-term storage of recycling materials can be performed avoiding self-ignition. Our Guideline presents a novel method developed at BAM which combines experimental tests on lab-scale with numerical simulations in Order to obtain permissible geometries of deposits and storage times at which self-ignition can be certainly avoided (Berger 2010).
A time domain spectrometer in the range of 0.5–2 THz was used for time of flight (ToF) measurements of THz pulses for imperfection detection in non metallic materials. The measurements were performed in comparison to the established ultra sound pulse echo (PE) and time of flight diffraction (ToFD) technique. No coupling agent and no contact to the surface is required for THz ToFD measurements. Plastic test specimen with notches, voids and drilled side holes were used to study reflected and diffracted response signals. No major differences were observed between the UT and THz ToFD records for the first surface of the notches, voids and holes. Additionally to the UT records also signals were obtained from its back side and a second raw of holes. The THz measurement is fast and has the potential to substitute UT applications in some industrial areas. Within the German project 'Handheld' the potential for miniaturization of the time domain equipment is explored for efficient application.
Use of higher-alloyed metallic materials and duplex steels for transport tanks of dangerous goods
(2011)
Compatibility evaluations of selected metallic materials under the influence of dangerous goods are published in the BAM-List - Requirements for Tanks for the Transport of Dangerous Goods” as basis for substance-related prototype approvals for tank Containers designed for the carriage of dangerous goods.
There is a request of the tank manufacturing industry and transportation Companies to incorporate additional materials into the BAM-List, especially corrosionresistant materials because of the large number of corrosive dangerous goods.
One solution to solve corrosion Problems is to line the tank with a polymeric material, an alternative solution is the application of high-alloyed stainless steels and nickel-based alloys as there are alloy 926 (1.4529), alloy 31 (1.4562) and alloy 59 (2.4605).
But there is an interest to use cost-efficient steels with high strength values and concomitant adequate corrosion resistance such as duplex Steel 1.4362 too. This Steel grade was originally developed as a substitute for the austenitic grades 1.4404 and 1.4571. Due to the lower content of the alloy elements nickel and molybdenum this duplex steel is a cost-efficient alternative to molybdenum containing austenite.
Due to the limited number of corrosion test results with welded test samples of these high-alloyed materials and the duplex steel under the influence of corrosive dangerous goods a comprehensive test Programme was performed with these materials in Cooperation with ThyssenKrupp VDM and Deutsche Edelstahlwerke GmbH.
It can be concluded from the test results that the "superaustenitic steels” 1.4529 and 1.4562 as well as the nickel-based alloy 2.4605 are a really good alternative as tank materials for the transport of dangerous goods in comparison to the lining of the tanks. Due to the reduced alloying content, in particular Nickel (3.7 %) and Molybdenum (0.15 %), a lower resistance of the duplex steel 1.4362 compared to the austenitic CrNiMo-steels was observed in acidic media. The duplex Steel is an alternative to the austenitic steels, especially in alkaline media. The test results are included in the current 10th edition of the BAM-List and therefore available for the costumer.
Correlation of aldehyde emissions and fatty acids content in pine wood and oriented strand boards
(2011)
Indoor air quality is important for human health and comfort. To ensure good indoor air quality contamination by volatile organic compounds (VOC) should be minimised. The aim of the project is the reduction of unsaturated aldehydes which can emit from oriented Strand boards (OSB): These aldehydes have an impact on the health based evaluation of emissions from products for indoor use according to the AgBB (Ausschuss zur gesundheitlichen Bewertung von Bauprodukten, Committee for Health Evaluation of Building Products) scheine (AgBB 2010). The model OSB were produced in a pilot plant using well known raw materials (Pinus sylvestris at different trunk heights) under using various processing parameters (Wilke et al. 2011).
OSB emit predominantly monoterpenes and aldehydes. Aldehydes are oxidation products of fatty acids in wood. The conditions which affect the oxidation process are the fatty acid concentration and composition, the oxygen content, the sample surface and the presence of compounds which indicate, inhibit or stop the oxidation respectively. The oxidation rate rises with an increasing number of double bounds in the fatty acid, e.g. the oxidation rate between oleic, linoleic and linolenic acid correspond to 1:12:24. One of the most important products of fatty acid oxidation is hexanal. It is generated during the oxidation of linoleic acid. This study shows a direct correlation between aldehyde emission and oxidation, hexanal can be used as an indicator for oxidation.
With the implementation of glass casting in France in the second half of the 17th century, larger mirrors could be produced. So-called tin-mercury mirrors were made by coating glass with tin amalgam. Today, many historical mirrors are partly damaged, the image quality is compromised, and the material integrity of the mirror is threatened. The transformation from tin into an oxide starts at the surface of the amalgam and proceeds down to the glass surface. The mercury dissolves as a liquid or gaseous phase. The amalgam layer is destroyed, so that conservation is necessary. Conservators must follow strict safety precautions while handling amalgam mirrors because of possible mercury emissions and corrosion of the amalgam, during which elemental mercury accumulates near the mirror frame in droplets and is emitted into the air.
In a research project, the quantity of the mercury emissions from historical mirrors was examined and a technique to decrease these emissions was developed.
Indoor air pollutants influence the health and comfort of building occupants and consequently the energy consumption of the building. The pollutants are emitted by various sources.
Among these sources, building products are of particular importance. To control the emission of pollutants from building materials, a few different voluntary labelling Systems have been introduced in Europe. In Germany also mandatory “Principles for the health assessment of construction products used in interiors” have been applied for the technical approval of floor coverings since 2004. This procedure is based on the assessment scheine of the Committee for Health-related
Evaluation of Building Products (AgBBScheme). The sensory-limit settings for building-material label Blue Angel offer consumer to differ not only low-emission but also low-odour Building materials from another building materials.
Product emissions chamber testing involves a complex protocol with several sources of measurement uncertainty (ASTM, 2010; ISO, 2006). Despite the potential for significant variability in measurement results within and among laboratories, there is no Standard method available to assess the accuracy of emissions chamber test results. Recently, Germany’s Federal Institute for Materials Research and Testing (BAM) started a program to evaluate the performance of laboratories testing for the AgBB (German Committee for Health-related Evaluation of Building Products) labelling scheme (Wilke et al., 2009). Test method validation was conducted through interlaboratory studies (ILS) with over 30 participants. Simultaneously, the National Institute of Standards and Technology (NIST) and Virginia Tech (VT) started a program to develop a series of reference materials that mimic real building products, can be tested in typical emissions chambers, and have independently known emission rates (Cox et al., 2010). BAM, NIST and VT subsequently joined forces to conduct a series of inter-laboratory studies using the prototype reference material. A pilot ILS was conducted with BAM and NIST followed by an expanded ILS with several participating countries. Results from these interlaboratory studies have the potential to define an internationally-accepted Standard approach to validate results from product emissions tests.
Fusion welding is widely used in the automotive industry to join metal structures. It is well-known that distortions and residual stresses occur during and after the welding process. Many procedures exist to decrease these negative heat effects of welding, but are often coupled with highly cost intensive experiments. The implementation of a welding Simulation tool to reduce this very expensive experimental procedures is therefore of high interest. Despite the fact that the automotive industry is a key sector for Simulation procedures, welding Simulation Software is nevertheless not yet widely implemented. This is mainly due to the complexity of the Simulation tools requiring expert users and the resulting high time to Solution.
In this study, a new fast thermo-mechanical Simulation of a complex and large laser beam welded automotive sheet metal assembly with several non linear welds is simulated. Assumptions and simplifications of the complex physical welding phenomenon, which are made to keep the computational cost and the complexity of the Simulation in an industrial frame, are discussed. The calibration time of the phenomenological heat source model has been optimized with a very fast analytical thermal model and the resulting simulated temperature fields match perfectly with the measured ones. Additionally, the user experience and the time-to-solution are kept within a reasonable time frame for arr industrial environment. All Simulation results are validated with experimental results.
The application of fluorescent materials improves the visibility for of warning symbols. BAM has used a measurement device to characterize fluorescent materials, which is based on the two-monochromator method. The result of this measurement method is an illuminant independent characteristic of the fluorescent material, called the Donaldson matrix, In view of its age and speed, the measurement device had to be re-designed and re-built. The new measurement facility is explained in greater detail in the paper. First measurement results and a comparison to the older device are also described.
In comparison with traditional measuring Systems (pressure cells, piezometers and inclinometers which produce only point measurements) fibre optic sensors are well suited for spatiallydistributed monitoring purposes. The very tiny optical fibres of a diameter of less then 1 mm can operate as sensors in strong electromagnetic fields, under “harsh” explosive and Chemical environments and under ionizing radiation.
This article studies the three dimensional transient weld pool dynamics and the influence of joint preparation angle on welding of low carbon structural steel plates using the ForceArc® process. ForceArc is a new gas metal arc welding technology which allows adequate fusion and penetration with a smaller V groove angle. This enhances welding efficiency significantly because of reduction of layers and low material consumption.
The deformation of the weld bead is calculated with an accurate coupling of the heat transfer with fluid flow through continuity, momentum and the energy equations combined with the effect of droplet impingement, gravity, electromagnetic force, buoyancy, drag forces and surface tension force (Marangoni effect). Four different angles of V groove are employed with the same welding parameters and their influence on the weld pool behavior and weld bead geometry is calculated and analyzed, to allow subsequent calculations of residual stress and distortion of the workpiece.
Such a simulation is an effective way to study welding processes because the influence of all the welding parameters can be analyzed separately with respect to thermal cycle, weld bead formation, and the microstructure of the weld. Good agreement is shown between the predicted and experimentally determined weld bead dimensions. It was found that with a larger groove angle, the penetration depth increases. Furthermore, a higher wire feeding rate is needed to fill the larger groove. The model presented can be used for further analyses of GMAW processes as well as input data for the numerical calculation of welding induced residual stresses and distortions using Computational Weld Mechanics CWM.
Despite the numerous possibilities to influence the properties of repair mortars by modifications of the mixture proportioning, it is almost impossible to change an individual property without influencing other mortar properties. When optimising a mixture, it has to be decided for each individual case, which of the mortar properties needs to be treated with the highest priority. Most properties can be altered by several different measures, which may vary in effectiveness, side effects and cost efficiency. As the prevention of shrinkage induced constraining cracks is crucial for the durability and Service life of a concrete repair task, in the presented paper special attention is paid to the influences on the mortar’s shrinkage behaviour. On the basis of parameter studies it is shown, how it may be beneficial in certain cases to accept the worsening of some general properties if by this measure another property, which is essential for the individual application task, can be enhanced significantly. In general a tailor-made approach for the mixture proportioning seems beneficial but due to the complexity of the constituents’ interactions in repair mortars, it bears a high risk of unexpected malfunctions.
This paper presents volume heat sources and the corresponding functional analytical Solutions for the transient temperature field. The considered energy distributions are normal, exponential and parabolic. The method follows the common approach in Computational Welding Mechanics (CWM) to account for the physics of the welding process and the resulting temperature field by phenomenological models for heat conduction. Therefore, the used heat source models are apparent heat sources that incorporate the real heat input as well as the fluid flow in the weld pool and the latent heat connected with phase transformations. The heat source models provide welding characteristics like thermal cycle and Fusion line in the cross section within short computational time. Consequently, inverse techniques on basis of optimisation algorithms enable the adaptation of the models to the experimental data efficiently. Furthermore, the direct evaluation of the energy distribution for the experimental fusion line in the cross section is demonstrated which enhances the numerical optimisation by reducing the number of unknown model Parameters and providing a reasonable initial guess within the model parameter space. The proposed temperature field models are validated with real laser beam welding experiments.
In the present work, the titanium alloy Ti-6.8Mo-4.5Fe-1.5Al (Timetal LCB) was investigated with respect to the microstructural evolution during strain controlled fatigue loading. The alloy was developed to reduce the generally high material costs of β-alloys by substituting expensive beta stabilizers by using a standard Fe-Mo master alloy. One possible application seen in the automotive industry is the substitution os suspension structural parts currently made of steel, suc as suspension springs. These components require a high strength and fatigue resistance.
Prevention of the explosion of acetylene cylinders involved in fire: experiments and simulations
(2011)
In order to assess the effectiveness of water cooling of acetylene cylinders involved in fire, a total of 13 bonfire tests with 8.9-, 10
and 50-l-cylinders were performed. During the experiments the pressure
in the cylinder and the temperature at different locations within the porous material and on the Shell surface as well as the flame temperature were measured. Overall 8 burst tests were performed, in order to determine the times to explosion for the cylinders. Cylinders failed not later than 15 minutes from the ignition of the bonfire, often with generation of a fireball. During the other 5 tests, the fire was extinguished before the expected burst and the cylinder was cooled with water. In 2 of the 5 extinction experiments, the explosion of the cylinder could be prevented. Noticeably, in one case the on-set of the decomposition of acetylene had already been observed, before the cooling was started. In spite of that, the cooling was still effective. The interpretation of the current results and of the data from previous tests with 40-l-cylinder suggests that single acetylene cylinders involved in fire might be saved by cooling, if their pressure does not exceed a value of about 45 bara. The recorded values of pressure and temperature were used to develop and validate a mathematical model for the prediction of the heat transfer in acetylene cylinders during the exposure to fire and the afterward cooling. The predictions agreed well with the experimental results.
The inhalation of 222Rn (radon) is one of the most important reasons for lung cancer, after smoking. Usually, the geological subsoil and the building ground are the dominant sources for enhanced indoor radon levels. Additionally, building materials can increase indoor radon concentrations when these materials contain higher contents of 226Ra (radium), especially in combination with low air exchange rates. For a realistic estimation of indoor radon
concentrations, it is helpful to carry out measurements of radon exhalation rates from relevant materials using emission test chambers. In Germany, it is aspired to limit the total indoor radon concentration to 100 Bq/m3, whereby building materials should contribute at most 20 Bq/m3. Within a project financed by the German Institute for Construction Technology (DIBt), a practical oriented measurement procedure of the radon exhalation of building materials in accordance to ISO 16000-9 was developed to have a means for the assessment of these materials with respect to their indoor use. Test chambers with different volumes were used. The tested materials were mainly used for wall constructions (e.g., bricks, light-weight concrete) and have known specific radium activities and radon exhalation rates.
In 1882, the East-West suburban train viaduct was built through Berlin as part of the public traffic solution in the late 19th Century. Today, the only left over iron arch bridge is a pair of two arches Crossing the Spree river in the middle of Berlin. Before dismantling the former parallel two original pairs of iron arches and rebuilding new arches for the high-speed railway line through Berlin in 1997, BAM was involved in an extensive test program of the heritage iron arch structure. Especially the estimation of accumulated damage in critical details and the verification of the old material properties at early stage was important information to the bridge owners. The testing program included two strain and displacement measurement campaigns, non-destructive testing, materials testing and microscale metallographic analysis of critical details. The measured strain cycles were significant lower in number and size than expected. Most of the cycles were compression stress cycles only. The work was planned in Cooperation with the Berlin consultancy Professor Hilbers that was responsible for the design and calculation of the reconstruction measures. Additionally, after calculation of the possible reuse of the old arches, we compared measured data from strain measurements with the results from calculation.
The measured data and the calculated data show a good qualitative correlation.
Beside such well approved residues like fly ash, blast fumace slag, silica fume and crushed concrete orbrick, other materials, like waste incineration bottom ash, steel slag, biomass ash, industrial sludge or mixed demolition waste, bear the potential to be used in high-grade mineral building materials. However, sophisticated Processing technologies and progressive applications ofthe waste products are needed. The material efficiency has to be improved by further R&D activities. This paper Shows the activities ofthe working group “Saving Resources by Material Recycling” and presents research about the use of residues from industry, incineration processes and deconstruction for the production of high-grade mineral building materials.
For the design of gas explosion venting systems for confinements only little guidance is given when considering the constructional boundary conditions or process conditions. For this reason conservative assumptions are prevalent in practice and in many cases the protective Systems become significantly oversized. Such safety margins in venting areas can lead to a critical acceleration of the pressure rise. Finally, a gas explosion at turbulent conditions caused by oversizing of the venting area rather leads to an under-sized system and supports the deflagration to detonation transition (DDT). The present investigation was focused especially on the influence of certain obstacles as well as the effect of the initial pressures on the explosion venting behavior of methane-air-mixtures and of hydrogen-air-mixtures.
Ultrashort pulses lasers are tools of choice for functionalizing the bulk of transparent materials. In particular, direct photoinscription of simple photonic functions have been demonstrated. Those elementary functions rely on the local refractive index change induced when focusing an ultrashort pulse in the volume of a transparent material. The range of possibilities offered by direct photoinscription is still under investigation. To help understanding, optimizing and assessing the full potential of this method, we developed a time-resolved phase contrast microscopy setup. The imaginary part (absorption) and the real part of the laser-induced complex refractive index can be visualized in the irradiated region. The setup is based on a commercially available phase contrast microscope extended into a pump-probe scheme. The originality of our approach is that the illumination is performed by using a pulsed laser source (i.e. a probe beam). Speckle-related issues are solved by employing adequate sets of diffusers. This laser-microscopy technique has a spatial resolution of 650 nm, and the impulse response is about 300 fs. The laser-induced refractive index changes can be tracked up to milliseconds after the energy deposition. The excitation beam (the pump) is focused with a microscope objective (numerical aperture of 0.45) into the bulk of an a-SiO2 sample. The pump beam can be temporally shaped with a SLM-based pulse shaping unit. This additional degree of flexibility allows for observing different interaction regimes. For instance, bulk material processing with femtosecond and picosecond duration pulses will be studied.
The notched impact strength at -30 °C is one of the selected properties, together with the corresponding test method and tolerances, for a comparison of polyethylene grades of one design type in the procedural rule on suitability proof for alternative plastic resins used for packagings and intermediate bulk containers (IBCs) for the transport of dangerous goods.
The marginal drop heights determined with the drop test at -18 °C after pre-storage of the test samples with 55 % nitric acid at 40 °C only partly related to the notched impact strength at -30 °C. The Charpy method is only suitable for classifying the grade in relation to toughness behavior and using this classification for comparison with other grades. Notched impact strength can provide a qualitative indication if the test samples fail under shock forces.
Conditioning the design types with 55 % nitric acid for 21 days at 40 °C causes an increase in the marginal drop heights of the design types in drop tests at -18 °C when compared with design types without pre-storage. Post-crosslinking of the grades increases stiffness because of the acidic influence.
With CO2 being one reason for climate change carbon capture and storage (CCS) is discussed to mitigate climate change. When emission gases are compressed into deep geological layers CO2-corrosion can easily cause failure of injection pipes. Different steels 42CrMo4, X46Cr13 and X20Cr13 were tested as well as X35CrMo17 and X5CrNiCuNb16-4 in a laboratory Environment similar to the conditions of the CCS engineering site at the Northern German Bassin. Samples were exposed to synthetic aquifer water saturated with technical CO2 at a flow rate of 3 NL/h.
Corrosion rates obtained via mass loss vary in a wide range (0,005 to 2.5 mm/year). The precipitations within the corrosion scale revealed a complicated multiphase layer containing siderite FeCO3, goethite α-FeOOH, lepidocrocite γ-FeOOH, mackinawite FeS and akaganeite Fe8O8(OH)8Cl1,34 and spinelphases of various compositions.
The Konrad repository for not heat generating radioactive wastes was licensed first in 2002. But due to legal actions this license has not been finally confirmed before 2007. Subsequently, the Federal Office for Radiation Protection (BfS) began scheduling backfitting of the former iron ore mine into a repository. The licensed repository volume is 303,000 m3 based on estimations of expected waste volumes to be disposed off although the mine itself would offer a much larger volume. Once the repository is ready for Operation, waste packages can be disposed, but this is not expected before the end of this decade. Nevertheless, there is already today a great interest in qualified and certified waste conditioning and packaging for disposal requiring Containers, tested, evaluated and certified by BAM and BfS.
Key points of the Konrad license concern comprehensive requirements for waste products and Containers. Details are described in BfS reports, which constitute the basic documents for the license. Following the final license confirmation a revision of these documents has been requested in order to include considerations of water poisoning substances. This work is currently done by BfS in Cooperation with the NLWKN of Lower Saxony and the Institute for Safety Technology (ISTec). Concerning the specification for Containers themselves no or only minor changes are expected.
Concrete containing lightweight aggregates has been known since ancient times. To reduce weight, natural aggregates of volcanic origin, such as crushed lava or pumice, were used in construction purposes, for example for the Pyramids during the Mayan period in Mexico or for monumental structures in the Roman Empire. The most famous examples of this first application of lightweight aggregate concrete (LWAC) in Europe are certainly the Colosseum and the Pantheon. The Roman constructors used natural as well as artificial aggregates, such as pumice, crushed lava and crushed brick, to realise lightweight concrete applications in parts of these buildings. Still today, pumice is used in Germany, Italy, Japan and Iceland as aggregate for structural lightweight concrete.
Self-ignition behavior of mixtures of methane and oxygen was investigated in a temperature range from 600 to 800°C. Variations of mixture composition, inert gas content, temperature and filling rate of the ignition autoclave were carried out in order to establish process boundaries for high temperature partial oxidation processes. The tests show that considerably high methane contents are needed to avoid an ignition. Heating-up tests show that ignition is possible at surprisingly low temperatures. This can be attributed to pre-ignition reactions that produce more instable intermediates.
In contrast to other simulation fields like forming simulation, welding simulation is still not widely used in industrial environments. A high user expertise, a high time-to-solution and the result accuracy are the most important problems that hinder its extensively application. Different modeling approaches influence these aspects and an analysis of their implementation is of interest especially for the automotive industry as a key user for production Simulation.
Concrete is by far the most common building material in the world. Due to its good durability it is widely used in building envelopes. One major part of the embodied energy in concrete comes from the production of Portland cement that consumes around 3,500 MJ energy per each ton of cement. Globally 2.6 billion tons of Portland cement is produced and the consumption is increasing. Since concrete will be used as main building material also in future construction, it is reasonable to develop concrete building components with lower embodied energy.Using the example of an ultra-high performance concrete (UHPC) façade element, it is demonstrated how the embodied energy can be reduced by application of hydrothermal curing.
The influence of paper type and state of degradation on laser cleaning of artificially soiled paper
(2011)
Lasers can be a supplemental tool for restorers to overcome some of the limitations of traditional dry cleaning techniques for works of art on paper. The laser working range has to be optimized allowing for safe removal of contamination and limitation of damage to the substrate. This paper addresses the influence of paper type and state of degradation on laser working range. Three types of new paper (pure cellulose, bleached pulp paper, rag paper) were degraded and characterized with respect their degree of polymerization. Laser-induced damage thresholds of new and degraded paper were determined using SEM and viscometry. Additionally, artificially soiled model samples were made using two kinds of soiling, namely pulverized charcoal and soot-blackened standard test dust. Cleaning thresholds of soiled paper samples were evaluated. A working range for all combinations of paper and soiling between 0.05 J/cm2 and 0.5 J/cm2 was found for the application of 8-ns laser pulses at 532 nm wavelength.
The strength of laminates distinctly depends on the transverse strength of the laminas. The transverse failure is dominated by the adhesion between fiber and matrix. Usual strength criteria however do not take into account the adhesive strength explicitly. The determination of the interface strength is performed on the micromechanical scale using single fiber specimens. The fibers are loaded under off-axis loading while the debonding is monitored under a microscope. The stresses acting in the Interface are calculated by finite element analyses. It is found that for off-axial angles up to 35° interfacial debonding is the dominant failure mode while fiber breakage takes place at lower angles. The occurrence of fiber breakage and debonding under off-axis loading shows that the restriction to two potential failure planes - perpendicular or parallel to the fibers - as applied in common failure criteria has to be put in question.
Ingress of moisture and harmful ions (e.g. Chloride, sulfate) into cementitious materials is one of the major factors in defining their durability. Modifications of building materials by targeted deposition of surface functional agents that make the surface hydro- and/or oleophobic aim to minimize moisture and ion ingress, and thus extend Service life of the cement based structures. Water repellent and easy-to-clean coatings for inorganic Substrates have gained strong attention during the last few years and various formulations based on silicones or alkylpolysiloxanes have been developed. Cementitious building materials are highly complex Systems with many components and changing properties in the course of a building’s Service life. The interactions between the Chemical agents and the cement based materials depend on many factors. The Chemical properties of the material Substrate appear to be the most important but in the context of their influence on the functionality of silanes and/or siloxanes these characteristics have not been well understood yet. The aim of this study was to evaluate the effect of different blended cements on water repellent agents’ performance. Two organosilicon compounds
were applied on fresh blended cements containing limestone (L), fly ash (F), slag (S) and trass (T), and investigated in terms of their functionality.
The surface properties of functionalized blended cements were studied based on wettability, i.e. contact angle measurements, before and after exposure to artificial and natural weathering. The first results indicate that slag and trass more distinctly affect the water repellent Surface performance after aging.
The goal of this study was to find a correlation between cleaning efficacy of substrates protected with anti-graffiti systems (AGS) and their porosity, surface roughness, and composition as well as usability of the Technical Testing Guideline for Anti-Graffiti Systems (TP-AGS, issued by BASt) for natural stone and brick/clinker masonry. The results showed that the cleaning efficacy mainly depends on the porosity of the substrate and the type of AGS. Also, higher surface roughness contributed to a lower cleaning efficacy. The results showed also that concrete panels and cement joints in masonry represented the worst case. The color change of all substrate materials compared to concrete was mostly within acceptable limits. Gloss changes were significant for a number of substrates. In particular, several of the wax-treated low-porosity substrates exceeded the threshold value of 10. The limit of water vapor permeability of the AGS prescribed in the TP-AGS might be too high for natural stone substrates. In general, the TP-AGS is useful for the determination of the efficiency factor of anti-graffiti agents on various substrates.
Although identified on the basis of so-called instationaiy creep-tests the constifrvtive model of Eurocode 3 (EN 1993-1-2, 2010) - hereinafter refened to as EC3 - represents a non-linear rateindependent relationship between stress and meclianical strain. I.e. the experimentally observed phenomenou of creep at constant stress but linear time varying temperature is described only through the temperature dependence of the material parameters characterizing the EC3 constitutive model. As a consequence some important phenomena cannot properly be described: E.g. creep or relaxation at constant temperature, creep or relaxation at non-monotonic temperature rates or sensitivity of the instationary creep process on the temperatme rate.
The concept and technical details of the implementation of the developed integrated monitoring system within the IMO-WIND project are presented. The tasks of the components of the system and its requirements are described. Selected results from the continuous monitoring during operation of the plant M5000_2 regarding the task design verification and dynamic structural analysis are given.
Main topics of the research project BEGLARES are the restoration of "dalle de verre" concrete Windows and the development of repair techniques and mortars. This project is executed in Cooperation between Glasmalerei Peters GmbH, the University of York and the BAM Federal Institute for Materials Research and Testing. It is funded by the Federal Ministry of Economics and Technology. The main mechanism of damages, the development of repair mortar and special test specimens are presented.
Paper is one of the most important materials representing and witnessing human culture particularly as a carrier medium for text and image. As soiling hampers the reception of information, paper cleaning techniques are needed. Traditional mechanical and chemical cleaning methods are used by conservator-restorers. In some cases, a classical cleaning procedure of paper objects yields unsatisfactory results or a conventional treatment is even impossible. Especially, fragile paper objects cause problems due to mechanical instabilities. Laser cleaning as a non-contact method might be a way to overcome some of the limitations of classical cleaning techniques. Laser parameters have to be chosen to achieve removal of the soiling without influencing the artwork. Any immediate as well as long-term effects causing an irreversible change of the artwork have to be avoided. At present, most laser applications are found in stone and metal conservation, while laser treatment of complex organic materials like paper is still not fully developed for application in conservators' workshops. This contribution describes recent work of pulsed laser cleaning of soiled model samples. Pure cellulose, rag paper and wood-pulp paper were mechanically soiled with pulverized charcoal in a standardized procedure to make model samples representing essential characteristics of contaminated real-world artworks. Afterwards, model samples were cleaned using short and ultrashort laser pulses in the nanosecond and femtosecond time domain, respectively. An extensive analysis of the model samples after laser treatment using an optical microscope and a multi-spectral imaging system allows a comparison of the cleaning results obtained with both laser sources.
The 9 meter drop onto an unyielding target is one of the important mechanical tests within the safety assessment of transport casks for radioactive material. In general, the cask is equipped with impact limiters to reduce the dynamic load on the cask body by absorbing a major part of the kinetic energy. The impact limiters are often made of wood or aluminium. In this study an elastic-plastic material model with volume change was used to describe the stress-strain behaviour of wood found in crush tests. For aluminium, an elastic-incremental plastic material model with Cowper-Symonds parameters for strain rate depending material hardening was used to model the adiabatic stress-strain relations measured at specimens at constant ambient temperature. Hereafter simulations with a sophisticated finite element model were carried out and compared with different drop tests. Four drop tests of a half-scale cask model equipped with wood and aluminium impact limiters with different drop positions were selected to investigate the impact limiter behaviour during a 9 meter drop test. All drop tests were simulated with the same FE mesh but under different boundary and initial conditions.
This paper describes a structural reliability analysis utilizing monitoring data in the ultimate limit state with consideration of the uncertainties of the monitoring procedure. For this purpose the uncertainties of the monitoring data are modeled utilizing a new framework for the determination of measurement uncertainties. The approach is based on a process equation and Statistical models of observations for the derivation of a posterior measurement uncertainty by Bayesian updating. This facilitates the quantification of a measurement uncertainty using all available data of the measurement process. For the reliability analysis in the ultimate limit state, monitoring data can be utilized as a loading model Information and as proof loading, i.e. resistance model Information. Both approaches are discussed with generic examples and it is shown that the modeling of monitoring data in a reliability analysis can result in a reduction of uncertainties and as a consequence in the reduction of the probability of failure. Furthermore, the proof loading concept is developed further to account for the uncertain characteristic of proof loading due to the measurement uncertainties which is consistent with the framework for the determination of measurement uncertainties. These approaches and findings can be utilized for the assessment of structures for life cycle extension and the design of monitoring Systems.