Stress redistributions in adhesively bonded double-lap joints, with elastic–perfectly plastic adhesive behavior, subjected to axial lap-shear cyclic loading

A shear-lag model is developed in order to evaluate stress redistributions in double-lap joints under axial (tensile) lap-shear cyclic loading. The adherend materials exhibit linear elastic behavior, whereas the material of the adhesive layer satisfies the elastic–perfectly plastic shear stress–strain constitutive relation. The reference state (from which the stresses are redistributed) is based on the standard elastic–perfectly plastic shear-lag analysis for double-lap joints. The main conclusion of the current analysis is that, during unloading, shear stresses of opposite sign may develop in the plastic zones of the adhesive layer, at the ends of the overlap, without reversing the direction of the applied load. A simple model for evaluating the variation of the maximum peel stress in the adhesive layer, based on the variation of the peak shear stress, demonstrates that the sign of peel stresses may alternate, as well. Under cyclic (fatigue) loading, the range of the peak stresses in the adhesive layer is the basic parameter for the evaluation of the variation of the energy release rate and the associated crack growth rate in the overlap. In this framework, the current simplified analysis may provide a reference model for comparisons with experimental data or with results which are based on more complex numerical models. The current model can be readily extended to cover the cases of development of plastic zones in the adhesive layer with shear stresses and plastic strains of opposite sign (during unloading or during load direction change).     

Application of activated charcoal in the downstream processing of bacterial olefinic poly(3-hydroxyalkanoates)

Medium chain length poly(hydroxyalkanoates) (mcl-PHAs) are bacterial thermoplastic elastomers with a large potential in medical applications. The present study provides a novel process to isolate and purify poly([R]-3-hydroxy-omega-undecenoate-co-3-hydroxy-omega-nonenoate-co-3-hydroxy-omega-heptenoate) (PHUE) and poly([R]-3-hydroxy-omega-undecenoate-co-3-hydroxy-omega-nonenoate-co-3-hydroxyoctanoate-co-3-hydroxy-omega-heptenoate-co-3-hydroxyhexanoate) (PHOUE) from Pseudomonas putida species. Three different types of activated charcoal were compared with regard to their capability to selectively remove impurities. The product 'Charcoal activated, powder, pure' from Merck was found to be most suitable. Using ethyl acetate as solvent, the polyesters were extracted from freeze-dried biomass at room temperature and simultaneously purified by addition of activated charcoal at the beginning of the extraction. The period of extraction was one hour and the ratio solvent to biomass was 15:1 (vol/wt). After extraction, the solids were separated by pressure filtration through a metallic lace tissue. The filtrate was again passed through the previously accumulated filter cake, followed by a second filtration through a 0.45 microm membrane to remove finest coal particles. The resulting filtrate was concentrated, thus yielding polyesters whose quality and yield depended on the quantity of activated charcoal applied. For highly pure PHUE and PHOUE with low endotoxin levels, the optimum ratio of activated charcoal to solvent for extraction (V/V) was found to be 0.5 for PHUE and 0.25 for PHOUE. The yields with regard to the raw polymers amounted to 55 wt% for PHUE and 75 wt% for PHOUE, which are acceptable for polymers that can be used for medical applications.     

Coating the inner walls of metal tubes with carbon films by physical vapor deposition at low temperature

Tubes are often required to exhibit better performance in corrosion and wear behavior than the material the tube is made of can offer. The situation can be improved when the tube is coated with a protective film. This can be achieved by sputter coating with an ion beam. A sputter target is located inside the tube. Energetic ions are accelerated into the tube and impinge onto the target. Thus, material is sputtered from the target onto the inner walls of the tube. Two apparatus for coating tubes of different lengths and diameters are described. Aluminum and stainless steel tubes were coated with amorphous carbon films. Results on adhesion, corrosion performance in aqueous media and thickness uniformity are shown.     

Nanofabrication with Pulsed Lasers

An overview of pulsed laser-assisted methods for nanofabrication, which are currently developed in our Institute (LP3), is presented. The methods compass a variety of possibilities for material nanostructuring offered by laser–matter interactions and imply either the nanostructuring of the laser-illuminated surface itself, as in cases of direct laser ablation or laser plasma-assisted treatment of semiconductors to form light-absorbing and light-emitting nano-architectures, as well as periodic nanoarrays, or laser-assisted production of nanoclusters and their controlled growth in gaseous or liquid medium to form nanostructured films or colloidal nanoparticles. Nanomaterials synthesized by laser-assisted methods have a variety of unique properties, not reproducible by any other route, and are of importance for photovoltaics, optoelectronics, biological sensing, imaging and therapeutics.     

Systematics of salt precipitation in complexes of polyethylene oxide and alkali metal iodides

Conductivity measurements in PEO₃₀MI polymer electrolytes with M=Li, Na, K, Rb, or Cs over the temperature range from about 65 to 200 °C show an increasing tendency for salt precipitation with increasing cation size. The salt precipitation in these complexes upon heating is revealed by the decrease of the dc conductivity starting at a critical temperature T_c. Whereas LiI and NaI complexes do not show precipitation effects, T_c monotonically decreases from about 140 to 65 °C when changing the salt component from KI via RbI to CsI. For the PEO-RbI system, precipitation is further investigated by nuclear magnetic resonance (NMR) and tracer diffusion experiments. NMR analysis unambiguously demonstrates the onset of RbI salt precipitation and the increase of the precipitate fraction with increasing temperature. In diffusion experiments on PEO₃₀RbI with the radiotracers and , the precipitation effect is manifested by anomalous features in the penetration profiles, however, without noticeable changes in their depth range. Combining the resulting tracer diffusion coefficients with the dc conductivity data enables us to assess crucial parameters characterizing ionic transport in PEO₃₀RbI.     

The Influence of Heavy Metal Ions on Beer Flavour Stability

In this study, the importance of iron and copper ions and their radical formation via the respective Fenton and Haber‐Weiss reactions was confirmed. Of the other heavy metals present in the brewing process in relevant concentrations, the impact of manganese ions on beer flavour stability has been elucidated. In contrast to iron and copper, manganese ions are not removed from wort or beer to any great extent during the process. Additionally, manganese shows a similar radical‐promoting effect to that seen with iron and copper. Its reactivity, and typically higher concentration than the other two metals in beer, appear to make manganese an especially potent pro‐oxidant in beer. The results of the investigation clearly indicate that there are other heavy metals influencing the stale flavour characteristics of beer, in addition to the well‐known metals, iron and copper. In contrast to the aforementioned ions, manganese does not enter the product by being leached out of a tank or from piping materials, but rather comes from the cereals employed in brewing. This finding, concerning the importance of manganese as a redox system in beer staling, can serve as a basis for a different approach in the choice of raw materials.     

Quantitative relationships between composition, particle size, triple phase boundary length and surface area in nickel-cermet anodes for Solid Oxide Fuel Cells

The present study is focusing on the elaboration of the quantitative relationships between the primary microstructural parameters (i.e. the phase volume fractions Φ, the particle and pore sizes and the corresponding size distributions PSD) with the more complex topological features (triple phase boundary length TPB_L, and specific surface area SSA) in porous Ni-cermet anodes. These relationships are crucial for the microstructure optimization and for the improvement of the corresponding electrode performance.In the first part of the study a pristine anode material with a graded microstructure is analyzed. The results from the different zonations indicate that the TPB_L correlates well with the volume fraction of the coarsest phase which is nickel. However the volume fractions also correlate with the particle size after sintering due to stronger particle coalescence at higher nickel volume fractions. Since the larger particle size leads to a decrease of the TPB_L this coarsening effect partly neutralizes the advantage of a higher nickel volume fraction. Furthermore, the TPB_L is also linked with the nickel surface area and with the corresponding pore-nickel interface area. The pore-nickel interface is the least abundant internal surface and therefore it represents the microstructural feature which predominantly limits the TPB formation in our nickel-cermet anode.In the second part the effects of microstructural degradation during exposure in a humid gas environment at 950 °C are investigated. During the early period (<200 h) the rapid decrease of the TPB_L is directly linked with the kinetics of nickel grain growth. At longer periods (>1000 h) the nickel coarsening ceases whereas the decrease of the TPB_L continues at a lower rate. During longer exposure time the reduction of TPB_L is most probably caused by a slight volatilization of the nickel phase and by the formation of continuous CGO layers which are shielding the surface of the nickel grains.     

金属注射成形的数值模拟和高效算法

金属注射烧结成形的注射模拟不同于普通的塑料注射工艺。注入模具的是金属粉末和塑性流动剂构成的均匀混合喂料。除流动本构显著不同外，注射结果的匀质性分析是一项重要内容。混合理论的应用和高效显式算法的开发与研究，是解决这一问题的关键。对模拟结果与试验结果进行了比较和对照，验证了该方法的有效性。     

Solar ICS systems with two cylindrical storage tanks

Two types of ICS solar water heaters designed, constructed and tested. The systems consist of two cylindrical storage tanks, which are connected in series and are horizontally incorporated in a stationary asymmetric CPC type mirror. The efficient operation of the system is due to the thermal losses suppression of the two inverted cylindrical surfaces and the effective use of the two tanks during sunshine period. Low cost and durable materials are used to construct the systems. The mean daily efficiency and the thermal performance of the hot water storage during night are calculated from outdoor experimental data. The results show that the proposed ICS systems are efficient and suitable for practical use as DHW systems.     

On the influence of non‐enzymatic crosslinking of caseins on the gel strength of yoghurt

After storage of UHT milk at 37°C resp. 50°C, yoghurt was prepared. For a storage temperature of 37°C, breaking strength of the yoghurt samples increased from 2.7 to 5.8 N with increasing storage duration of the UHT milk. A plateau is reached after 17 days of storage. This increase in breaking strength correlates with a significant increase in non‐reducible casein oligomerization from 14% for fresh UHT milk to 25% measured using size exclusion chromatography under reducing and denaturing conditions and calculated as sum of predominantly formed dimers and trimers at the total casein fraction. At a storage temperature of 50°C, a less increase in breaking strength from 2.7 to 4.6 N with a plateau after 17 days was observed while casein oligomerization increased to 63%. After acid hydrolysis, only lysinoalanine and histidinoalanine were detected in the caseinate samples via amino acid analysis. The quantified concentration of lysinoalanine and histidinoalanine could not explain the observed casein oligomerization. Thus, unknown crosslinked amino acids must have been formed during storage, inducing significant changes in the functional properties of milk proteins.