Experimentelle Verifizierung einer neuer Modellgleichung für die voraussage des Elastizitätsmoduls eines Verbundwerkstoffes

Experimental Verification of a New Enquation for the Youngs Modulus of Composite Materials A recently proposed model equation for the prediction of Youngs modulus of elasticity of composite materials has been compared with extensive experimental data from the literature. As the derivation of the equation assumes a definite matrix-type microstructure with spheroidal inclusions, only composites containing particulate inclusions of different geometries were considered, including data on ceramic, glass and polymer matrix composites. A quantitative good agreement between theory and experiment was found, specially when the inclusion shape and orientation, being the microstructural parameters entering in the equation, were accurately known. The microstructural parameters involved in the equation can be obtained from real microstructural data via quantitative microstructural analysis and sterology, no fitting is involved. This fact makes the proposed equation substantial also for practical applications.     

Genaue Bestimmung der Dichte von Gasen aus Messungen des Brechungsindex

Ohne Zusammenfassung The online version of the original article can be found at     

Verformungen und Spannungen im Bereich der plastischen Zone nahe der Rißspitze angerissener Proben aus Ck 45

Strains and Stresses in the Area of the Plastic Zone Near the Crack Tip of Precracked Steel Specimens. Models for shape and dimension of the plastic zone near the crack tip of precracked specimens are described and discussed. Using idealized assumptions an area of influence of the plastic zone is postulated in accordance with the shape of the plastic zone observed. In this area an estimation of the stress distribution has been made. X-ray stress measurements have been done in and near the plastic zone.     

Elastizitätstheoretische Lösung des kreisförmigen Einschlusses in unendlicher Scheibe mittels der Beziehungen zwischen Loch‐ und Einschlussproblem

The method applied for the derivation of an elastic solution of an infinite plate with a circular inclusion of mismatching stiffness under uniform remote tension stress is based on the special deformation characteristic of this inclusion geometry. Outgoing from the analysis of the plate with a circular hole is the exact solution of the general inclusion problem obtained by superposition of a specific inner stress field.     

Bestimmung der Bahnelemente von Satelliten aus Dopplermessungen

The iteration algorithm for the determination of all orbital elements of Kepler orbits using Doppler measurements from a ground station is derived. For this purpose we determine analytically the Jacobian of the radial velocity, depending on all six orbital elements. This is performed for the general cases of elliptic, hyperbolic and parabolic orbits. Numerical examples show good approximations of the orbital elements with only a few steps of iteration. This method can be applied for the traditional determination of orbital elements as well as for board-autonomous determination of satellite orbits and for radio science experiments in interplanetary space.     

Bewertung von Spannungszuständen bei der experimentellen Bestimmung des Schubmoduls an zellularen Materialien

Evaluation of stress states for the experimental determination of the shear modulus of cellular materials The experimental determination of the shear modulus of materials proves to be problematic in practice. The different methods do not only preduce the desired pure shear stress state. In this paper, starting from several experimental implementations of the shear test, possible sources of errors in determination of the shear modulus are discussed. An estimation of the possible error is calculated by numerical simulations. Two examples from the field of cellular metals are given to illustrate the effect of just an approximate realization of the pure shear stress state.     

Röntgenographische Elastizitätskonstanten teilkristalliner Polymerwerkstoffe

X-ray elastic constants of semicrystalline polymers The X-ray elastic constants (XEC) of Polyethylen (PE) were calculated from single crystal stiffnesses. The results are compared with published experimental data of different PE-materials. The studies reveal the possibility to take into account the structure of the different PE-modifications considering the Young's modulus of the material. Additionally the published experimental results on Polypropylen (PP) and Polybutylenterephthalat (PBT) are discussed.     

Chevronproben zur näherungsweisen Bestimmung der Bruchzähigkeit

Chevron Specimen for the Estimation of Fracture Toughness Fracture toughness is a material property which is presently used in many industrial areas, either as material selection criteria or as material quality requirement. In some areas, nuclear power plants and aerospace, it is also a design parameter for design against catastrophic failures. Determination of the fracture toughness in accordance with ASTM E 399 is relatively elaborate. Depending on the material concerned, a certain minimum material cross section is required to obtain the necessary size of the specimen. Many semi-finished product forms of the different materials can not be tested for fracture toughness due to the specimen size requirements. For these reasons, alternative test methods were sought of which testing of chevron-notched specimens is one method. In the work to be presented, the test method to determine fracture toughness via chevron-notched specimens is briefly described. The most frequently used chevron-notched specimens are shown together with loading grips to be used in conjunctions with universal testing machines. Certain effects associated with some of the chevronnotched specimens are pointed out which result in a large difference between the fracture toughness determined in accordance with ASTM E 399 and that obtained via chevron-notched specimens. The aim of our research effort is to develop a chevron-notched specimen geometry which furnishes fracture toughness values compatible with K_Ic values without complicating the test method. Such a chevronnotched specimen is presented and the fracture toughness values obtained from these specimens of 7475-T 7351 and different Ti-alloys are compared to the K_Ic values obtained in accordance with ASTM E 399 for the same materials.     

Leichte Turbolader-Verdichterräder aus Aluminium- und Magnesium-Feinguß

Light turbocharger compressor wheels from aluminium and magnesium investment casting Within the scope of a team work between Kühnle, Kopp & Kausch AG, Volkswagen AG, Sterling International Technologies Ltd. and the Fraunhofer Institute for Strength of Structures under Operational Conditions LBF compressor wheels of aluminium and magnesium investment casting were developed and tested. Strength and fatigue tests, overspeed and field tests as well as metallographic checks were made in addition to the finite element calculations to optimize the stress under centrifugal force in an appropriate way for the materials involved. The results and the knowledge gathered are to clarify whether magnesium alloys are an appropriate replacement for the proven standard aluminium alloy for turbochargers.     

Schwindungsgleichung: Bestimmung der Koeffizienten aus Sinterversuchen – mit Hilfe mehrfacher Regression

Sintering Equation: Determination of its coefficients by experiments – using multiple Regression Sintering is a method for volume-compression (or volume-contraction) of powdered or grained material applying high temperature (less than the melting point of the material). Mäkipirtti tried in ([2]) to find an equation which describes the process of sintering by its main parameters sintering time, sintering temperature and volume contracting. Such equation is called a sintering equation. It also contains some coefficients which characterise the behaviour of the material during the process of sintering. These coefficients have to be determined by experiments. Here we show that some linear regressions will produce wrong coefficients, but multiple regression results in an useful sintering equation.     

Ein neuartiges Eindringtiefenmeßverfahren zur Bestimmung der Orientierung von spritzgegossenen Teilen aus Polystyrol

The Determination of Orientation of moulded Polystyrene by means of a special indentation hardness test The orientation of molecules of injection moulded Polystyrene type PS 168 N (BASF) was qualitatively measured by means of a special hardness testing device. With increasing orientation there was a decrease of indentation normal of the orientation and vice versa. Moulded parts showed no orientation-dependant indentation after quenching.     

Verbesserung des Vakuums in Isoliergefäßen aus Glas

Improving the vacuum would increase the insulation capacity of commercially available glass containers by a factor of about two. To do this, pressures of 10^?4 mbar must be attained. Different approaches were taken to meet this objective. As an alternative to today's commonly practiced sealing method, three possibilities are introduced which eliminate the necessity of pump stub narrowing which causes reduced conductance. Furthermore, depending on the sealing process used, the gases occuring during sealing are either avoided completly or they can at least be reduced by having the chance of exact temperature control resp. by a lower separation temperature. A completly different approach was taken by using Getters, of which a metal hydride on a TiVMn base proved especially suitable. It is activated by heat and can be integrated into the normal production process without any problem. Aside from a shorter pump period, the added advantage here is the containment of the gasses occuring during sealing as well as that of the longterm gasses.     

Zur Übertragbarkeit der Schwingfestigkeit aus einachsigen Begleitprobenversuchen auf Bauteile aus Tiefziehstählen

Fatigue strength of deepdraw steel structural parts: Transferability of uniaxial test results In the course of further reducing the weight of structural parts, constantly growing importance is being attributed to the analysis of fatigue strength. Due to the possibilities of numerical stress analysis the so-called local concept [1, 3, 4] has become popular besides the nominal approach. This article wants to show the difficulties occuring with fatigue-life predictions according to the local concept for hot-rolled deepdraw steel structural parts. The fatigue-life of the structural parts has been predicted through elasto-plastic finite element calculations using uniaxial fatigue tests of smooth specimens. An important prerequisite for the local approach is the transferability of the uniaxial fatigue strength to the structural parts. Therefore, a highly ductile, hot-rolled deepdraw steel has been used in this example to show in what respect transferability of fatigue strength is given from uniaxial tests to structural components. Thereby, the notch root strain has been proved to be insufficient for the transferability.     

Bestimmung der Streckgrenze und der Hall‐Petch‐Konstanten des Vergütungsstahles 42CrMo4 unterschiedlichen Gefüges mittels Eindruckprüfungen

Determination of yield stress and Hall‐Petch coefficients of the tempering steel 42CrMo4 with different microstructure by means of indentation testing Yield stress of steels can be determined by tensile tests or by indentation testing. Indentation tests offer the advantage of measuring the yield stress of certain parts that otherwise could not be used to withdraw tensile samples. Furthermore, measurements in parts with a varying yield stress e.g. surface hardened steels can be carried out. This work investigates several methods of indentation tests to measure the yield stress of the tempering steel 42CrMo4. The yield stress of different microstructures is compared to results of tensile tests. Using the indentation test according to GOST 22762‐77 the Hall‐Petch coefficients of microstructures consisting of perlite and ferrite are determined. Thus the influence of grain size and distance of perlite lamellas on the yield stress can be taken into account.     

Elastizität und mechanische Dämpfung eines unidirektional SiC-kurzfaserverstärkten Alkali-Kalk-Silicatglases

Elasticity and mechanical damping of an unidirectional SiC-short-fibre reinforced alkali-lime-silicate-glass The embedment of short-fibres in inorganic glasses enables as is well know a considerable improvement of the strength as well as the fracture toughness of these materials. Still not investigated is the influence of the fibre-reinforcement on the mechanical damping of the composites. In this paper the dynamic mechanical thermal analysis is presented, which was used to determine mechanical damping and elasticity of not reinforced and unidirectional SiC-short-fibre reinforced AR-glass as a function of temperature and fibre volume fraction. The results show that the composite specimens exhibit - besides a glass-typical temperature dependence of the damping - an additional damping part, which can be attributed to the fibre reinforcement. This damping part is just as the specimen elasticity to a large extent dependent on the fibre volume fraction and is mainly associated with sliding processes in the fibre-matrix-interface under the vibrating stress. Specimens with a fibre volume fraction of 10% and a temperature of 15°C show-in comparison to non-reinforced AR-glass - an about 100% increased damping value connected with a nearly 50% decreased Youngs modulus.