Interaction of slip‐ and flame‐spray coated carbon‐bonded alumina filters with steel melts

Ceramic foam filters play an essential role in the quest for cleanliness of cast steel parts as they facilitate turbulence reduction during mold filling as well as removal of nonmetallic inclusions. A coating on these filters is able to increase their strength and filtration efficiency by improving the adhesion of inclusions to the filter strands. In this study, Al₂O₃‐C filters were coated with an alumina slip via slip and flame spraying. The phase composition and the microstructure of the coatings were investigated before and after immersion into molten steel contained in a metal casting simulator. After contact with molten steel, Al₂O₃‐C reference filter shows intense decarburization which often influence the quality of cast steel parts due to formation of gas bubbles. Slip‐sprayed alumina coatings on such a filter promote the deposition of inclusions due to formation of a vitreous alumina layer but will also cause gas bubble formation as they exhibit a high porosity. Flame‐spray coatings have low porosity and hence, prevent formation of gas bubbles. Furthermore, they showed the highest reactivity toward the steel melt and hence, are recommended for filtration of cast products with a high demand on cleanliness.     

Stability of milling with non-uniform pitch and variable helix Tools

We study mechanical vibrations in milling with non-uniform pitch and variable helix tools. The process is modeled by a periodic delay differential equation with distributed delay, which takes into account, for example, the nonlinear cutting force behavior, the effect of runout, and the exact delay distribution due to the unequally spaced flutes. We present a new method for the identification of the chatter stability lobes from the linearized system that is based on the multifrequency solution. We give detailed remarks on the truncation of the resulting infinite dimensional matrices and the efficient numerical implementation of the method. Cutting tests for steel milling with a customary end mill with non-uniform pitch and variable helix angle and a conventional end mill with uniform pitch and constant helix angle are performed. The numerical and experimental results coincide well. They reveal a significant increase of the limiting depth of cut for the variable helix tool compared to the conventional tool. Moreover, we show that in contrast to conventional tools, for non-uniform pitch and variable helix tools, an exact model with time-varying coefficients, nonlinear cutting force behavior, and runout is necessary for an accurate prediction of the stability lobes.     

Fabrication of a transversal multilayer thermoelectric generator with substituted calcium manganite

The sintering behavior and thermoelectric performance of Ca_0.99Gd_0.01Mn_0.99W_0.01O₃ was studied, and a multilayer thermoelectric generator was fabricated. The addition of CuO as sintering additive was found to be effective for the reduction in the sintering temperature from 1300°C to about 1000°C‐1050°C. Dense samples were obtained after firing at 1050°C, whereas some porosity remained after firing at 1000°C. Samples sintered at reduced temperature exhibit lower electrical conductivity, whereas the Seebeck coefficient S = ?150 μV/K at 100°C is not affected by lowering the sintering temperature. The figure of merit is ZT = 0.12 at 700°C for samples sintered at 1300°C; ZT = 0.08 and 0.03 were obtained for multilayer laminates sintered at 1050°C and 1000°C, respectively. A transversal multilayer thermoelectric generator (TMLTEG) was built by stacking layers of substituted CaMnO₃ green tapes, and printing AgPd conductor stripes onto the thermoelectric layers at an angle of 30° relative to the direction of the heat flow. The multilayer stack was co‐fired at 1000°C. The TMLTEG has a power output of 2.5 mW at ?T= 200 K in the temperature interval of 25°C‐300°C. A meander‐like generator with larger power output comprising six TMTEGs is also presented.     

Compositional minimisation of finite state systems using interface specifications

We present a method for thecompositional construction of theminimal transition system that represents the semantics of a given distributed system. Our aim is to control thestate explosion caused by the interleavings of actions of communicating parallel components byreduction steps that exploitglobal communication constraints given in terms ofinterface specifications. Theeffect of the method, which is developed forbisimulation semantics here, depends on the structure of the distributed system under consideration, and theaccuracy of the interface specifications. However, itscorrectness is independent of the correctness of the interface specifications provided by the program designer.A preliminary version appeared inProceedings of CAV'90 — Second International Workshop on Computer-Aided Verification, Vol. 531Lecture Notes in Computer Science, Springer, pp. 186–196, June 1990.     

Transparent cubic-ZrO2 ceramics for application as optical lenses

Optical transparent polycrystalline ZrO₂ ceramics were fabricated by solid-state sintering process using first vacuum sintering followed by hot isostatic pressing. In the visible wavelength range (400–800 nm), the in-line transmittance of 5.6-mm thick samples reaches 68% at exemplary wavelength 600 nm (corresponding to an in-line absorbance based on 10 of A₁₀ = 0.08 cm^?1), which is approximately 90% of theoretical limit. The refractive indices of the ZrO₂ optoceramics at 630 nm (n_d) are varying between 2.10 and 2.20, depending on TiO₂ contents, the latter being used as sintering aid. The appearance of birefringence is strongly correlated to the addition of TiO₂ as sintering additive in the ceramic samples, whereas addition of TiO₂ and simultaneous increase in Y₂O₃ content resulted in a decrease of birefringence.     

Computations of fatigue crack growth with strain gradient plasticity and an irreversible cohesive zone model

Computations of fatigue crack growth with a first-order strain gradient plasticity (SGP) model and an irreversible cohesive zone model are reported. SGP plays a significant role in the model predictions and leads to increased fatigue crack growth rates relative to predictions with classical plasticity. Increased magnitudes of tractions and material separation at the crack tip together with reduced crack closure appear as the cause for accelerated crack growth in SGP. Under plane strain conditions SGP appears as an essential feature of the development of the crack closure zone. Size effects are explored relative to changes in internal material length scale as well as to structural length scales.