Volume 53, Issue 9

Kurzfassung Experimentell ermittelte Wöhlerlinien bilden häufig die Grundlage eines Ermüdungsfestigkeitsnachweises. Der vorliegende Beitrag soll zum einen den Anwender dafür sensibilisieren, dass trotz präziser Fertigungsverfahren, exakter Prüftechnik, gleicher Chargen usw. Versuchsergebnisse streuen und somit immer nur eine Schätzung der Wöhlerlinie vorliegt. Zum anderen werden die Einflussgrößen auf die Vorhersagegenauigkeit von Wöhlerlinien im Zeitfestigkeitsbereich untersucht. Insbesondere wird auf den notwendigen Stichprobenumfang, die Aufteilung der zur Verfügung stehenden Prüfkörper und die Versuchsauswertung eingegangen. Die Fortpflanzung der Schätzfehler wird mit einer anschließenden Schadensakkumulationsrechnung bewertet. Aus den Untersuchungen werden Hinweise für die Versuchsdurchführung und Auswertung von Schwingfestigkeitsversuchen im Zeitfestigkeitsbereich abgeleitet. Teil 1 behandelt die Schätzung von 50%-Wöhlerlinien; in Teil 2 wird auf die Schätzung der Streuung näher eingegangen.

Kurzfassung Die Auslegung schwingend beanspruchter Bauteile setzt häufig experimentell ermittelte Wöhlerlinien voraus. Diese werden aus Einstufenschwingversuchen bestimmt. Die Auswertung solcher Versuche erfordert statistische Verfahren. Neben der mittleren 50%-Wöhlerlinie muss auch das Streuverhalten der Experimente analysiert werden. Der vorliegende Beitrag gibt Hinweise zur Abschätzung der Standardabweichung aus einer Stichprobe von Wöhlerversuchen. Zur Korrektur der systematischen Unterschätzung der Standardabweichung bei geringen Stichprobenumfängen werden Näherungslösungen angegeben. Dabei wird zwischen Versuchen nach dem Horizonten- und dem Perlenschnurverfahren unterschieden.

For differentiating the applicability of various numerical welding simulation methods as well as unifying the prerequisites and the steps to be taken in simulation, normative codes are required for the user. Since any standard-like documents are currently still lacking in this field, the DIN German Institute for Standardization in partnership with the Research Association of DVS German Welding Society have set up a standards committee dealing with the preparation of respective documents. This article focuses on the presentation of the new DIN Spec 32534-1 explaining the major simulation steps and specifying the application fields and the key terms of welding simulation. In addition, a generally valid simulation structure has been established which is intended to serve as a recommendation for customers and suppliers in formulating and handling a service order as well as for persons who start doing welding simulation for the first time. It additionally gives an overview of the other subject areas dealt with in the standards committee as well as of the international activities in this field.

Fractures of denture base polymer material are one of the most frequent reasons for repair of removable dentures. The aim of this study was to determine the influence of depth alignment of glass fiber reinforcements onto denture base polymer flexural obtained with the “short beam” testing method. The study showed higher values of flexural strength when reinforcements were placed 1mm from specimen surface (130,63 to 158,55MPa) compared to 0,5mm distance from specimen surface (117,83 to 153,68MPa). Specimens tested after polymerization had higher flexural strength values than specimens tested after storage in water, while thermocycled specimens unexpectedly revealed the highest values. It could be concluded that fiber reinforcements should be positioned more than 0,5mm (up to 1mm) from the base surface of dental prostheses since lesser distance would diminish the reinforcing effect.

Magnesium-based alloys as biodegradable orthopedic implants have been successful for their high degradation rates in the physiological environment and the consequent loss in the mechanical integrity. Casting method used in production of magnesium-based alloys influences the microstructure of implants due to cooling conditions. In this study, the effects of casting method (permanent mold casting and sand mold casting) on the degradation of AZ91D magnesium alloy in Hank's simulated body fluid at 36.5 ± 0.5°C have been investigated using immersion technique of cylindrical specimens. The specimens were subjected to simulated body fluid for 8 h and 24 h. The results have shown that the cooling rate from melt and grain size have great influence on the degradation rate of magnesium alloy.

Mechanical properties of discontinuities are different from those of a whole rock. In particular, shear strength of a discontinuity is closely related to its morphological characteristics. Study on mechanical behavior and its failure mechanism of jointed rocks under shear stresses is of great theoretical significance. This paper presents a fundamental research on mechanical properties of the regular jugged discontinuity under various normal stresses. The strength and roughness of discontinuity under shear stress are investigated by analysis of the shear test data. An empirical formula between slope ratio and roughness coefficient of discontinuity are proposed to calculate shear stiffness, and an empirical formula is finally established to evaluate shear strength of discontinuity.

Kurzfassung In der Studie für diesen Beitrag wurde das Eindringen von Al-Schmelze in hochtonerdehaltige Feuerfest-Materialien auf Basis Aluminium-Silikat untersucht. Die Wirkung des flüssigen Aluminiums — legiert mit 5 wt.-% Magnesium und folglich Bildung einer aggressiven Umgebung — auf hoch tonerdehaltige feuerfeste Steine wurde untersucht. Die Steine wurden bei 825°C getempert oder bei 1350°C gebrannt. Die Untersuchung bezüglich des Eindringens beruhte auf dem Tiegeltest gemäß DIN 51069. Hier wurden Proben mit Zusätzen von Phosphorsäure, Phosphorsäure und Bariumsulfat, Phosphorsäure und Bariumsulfat und Borsäure physikalisch und analytisch untersucht. Diese Arbeit fokussiert sich auf das Thema, wie Zusätze von Phosphorsäure, Baryt und Borsäure, phosphatgebundene, hoch tonerdehaltige Feuerfest-Steine beeinflussen und gegen das Eindringen von Al schützen. Für die Eindringenstests wurden hoch tonerdehaltige feuerfeste Materialien auf Bauxit-Basis als Referenzsteine verwendet.

In this study surface finish and dimensional charactersitics of castings produced with gypsum bonded block investment moulds were investigated. Commercial and laboratory made gypsum bonded investment moulds were used for investment casting mould making. To compare the casting quality of the investment powders, wax patterns for surface roughness specimens and linear dimension measurement specimens were designed and produced with special geometry. Wax trees were assembled with these patterns, cylindrical stainless steel perforated flasks were settled around the trees and gypsum bonded investment slurries were filled into flasks. Conventional tin bronze and sterling silver were subsequently cast into these moulds by vacuum assisted and vacuum pressure casting processes, respectively. Afterwards, surface roughness of specimens were measured and linear dimensions of wax patterns and cast specimens were compared to determine percentage of dimensional change.

The merge of materials science with the biological sciences has produced some advanced materials which are called functionally graded materials (FGMs) in order to provide the desired material characteristics. The FGMs concept originates in Japan in 1984 during the space plan project. FGMs are materials or structures in which the material properties vary with location in such a way as to optimize some functions of the overall FGMs. It is well known that the main inorganic component of natural bone is hydroxyapatite (HAP) and that the main organic component is collagen (Col). Hydroxyapatite HAP implants are not bioabsorbable, and because induction of bone into and around the artificially made HAP is not always satisfactory, loosening or breakage of HAP implants may occur after implantation in the clinical application. The development of a new material which is bioabsorbable and which has osteoconductive activity is needed. Therefore, the aim of the current investigation is to design an implant, in the presence of cancellous bone as a thin layer around it, from functionally graded material. In this study, a novel biomaterial, collagen/hydroxyapatite (Col/HAP) as a functionally graded material (FGM), was developed using the finite element and optimization techniques which are available in the ANSYS package. These materials have a self-organized character similar to that of natural bone. The investigations have shown that the maximum stress in the cortical bone and cancellous bone for the Col/HAP functionally graded implant has been reduced by about 40% and 19% respectively compared to currently used titanium dental implants.

In the present study, spectral analysis of ultrasonic signals and measurements of the velocity of longitudinal ultrasonic waves have been carried out on a duplex stainless steel type 2205. Specimens were annealed at 875°C in time periods between 1800 and 86400 s in order to promote microstructural changes associated to σ-phase formation. Transducers with frequencies of 5, 10 and 17 MHz were used to obtain power spectra. The spectra corresponding to long time treatments showed a high attenuation of the ultrasonic waves, which is attributed to the precipitation of σ-phase and secondary austenite. Furthermore, overall results suggest that spectra obtained at frequencies of 10 and 17 MHz allow, with acceptable accuracy, distinguishing the microstructural changes that take place in this duplex steel for prolonged aging times.