A stochastic microstructure model for particle reinforced aluminium matrix composites.

Metal matrix composites are complex materials consisting of various phases which can display largely different mechanical properties. The deformation behaviour of these composites cannot be sufficiently modelled by averages or simple particle shapes due to the local stresses that occur on the particle edges. Therefore, a sophisticated model of the microstructure is needed. We introduce a method for stochastic modelling of a silicon carbide (SiC) particle reinforced aluminium matrix composite. The SiC particles are modelled by Laguerre polyhedra generated by densely packed spheres. The shape factors of the polyhedra have been fitted to the particle shapes observed in three-dimensional images. Particle elongation in extrusion direction and the observed log-normal volume distribution of the particles are included in the model by suitable scaling. An outlook is presented on how to model the grains of the polycrystalline aluminium matrix and intermetallic precipitates, which result from the strengthening mechanism of the matrix. LAY DESCRIPTION: Metal matrix composites are complex materials consisting of different phases which can display largely different mechanical properties. The deformation behaviour of these composites cannot be sufficiently modelled by averages or simple particle shapes due to the local stresses that occur on the particle edges. Therefore, a sophisticated model of the microstructure is needed. We introduce a method of stochastic modelling of a silicon carbide (SiC) particle reinforced aluminium matrix composite. The SiC particles are modelled by Laguerre polyhedra generated by densely packed spheres. The shape factors of the polyhedra have been fitted to the SiC shapes observed in three-dimensional images. Additionally, the polyhedra are scaled anisotropically to account for orientation anisotropy and to obtain a log-normal volume distribution. An outlook is presented on how to model the aluminium phase's grains and intermetallic precipitates, which result from the strengthening mechanism of the aluminium matrix alloy.

[The effectiveness of an individual mandibular advancement splint (MAS) in subjects with obstructive tongue-base-snoring]. / Effektivität der individuell adjustierbaren Protusionsschiene bei Patienten mit obstruktivem Zungengrundschnarchen.

OBJECTIVE: Besides operation the mandibular advancement splint (MAS) is one of the main options for treatment of snoring. Especially the MAS by Hinz, which exclusively blocks mandibular retrusion, has been established as an effective alternative. The aim of this study is to examine the effectiveness of this MAS and to evaluate the role of obstruction at the level of the tongue base as a successful pretherapeutic predictor by using the sleep nasal endoscopy. SUBJECTS AND METHODS: From August 2001 until August 2006 we have examined over 450 patients with sleep disorders at our hospital. All patients have had an ENT examination, a standardized polysomnography and a sleep nasal endoscopy with therapy simulation. The application of a MAS is indicated if an obstruction at the level of the tongue base is detected and the RDI (respiratory disturbance index) is below 10/h. 10 patients are examined by PSG and partly by sleep nasal endoscopy before and after adjustment of the MAS. The patient group is classified in three velum- (n = 3), isolated tongue base-snorers, five combined tongue base-/velum- and two tongue base-/epiglottis-snorers. RESULTS: The subjective sleep recovery and the snoring-intensity can be improved by the MAS in eight of ten patients. In addition the long-term acceptance of this therapy is very high. CONCLUSIONS: According to our experiences the MAS by Hinz is an effective treatment option for patients with an obstruction level at the tongue base confirmed by sleep nasal endoscopy.