Zur Tragfähigkeit schwingend beanspruchter Hochtemperatur-Lötverbindungen

Fatigue strength of high-temperature brazed joints. Starting from an extensive review of literature the fatigue strength of high-temperature brazed joints is investigated and the results are evaluted statistically. NiCr 20 TiAl- and X 8 CrCoNiMo 10 6-joints are brazed in vacuum by inductive heating with AuNi 18 or PdNi 40. The heat-treatment after brazing and the test-temperature are alternated systematically; in some cases additionally the surface preparation is varied. The typical ruptures of joints are shown by micrographs.     

Horizontaltragfähigkeit von zusammengesetzten Mauerwerksquerschnitten

Zusammengesetzte Schubwandquerschnitte weisen unter kombinierter Beanspruchung aus Normalkraft und Schub mit Scheibenbiegung bezüglich der Steifigkeit und Tragfähigkeit ein deutlich günstigeres Verhalten auf als gerade Wandabschnitte ohne entsprechende Flansche. Insbesondere im Hinblick auf Erdbeben beanspruchungen wurde an der Technischen Universität München ein Versuchsprogramm an im Grundriss T‐förmigen Schubwandbauteilen unter realistischen Randbedingungen durchgeführt und mit rechnerischen Untersuchungen begleitet. Der Beitrag stellt die Ergebnisse auszugsweise dar, insbesondere im Hinblick auf numerische Vergleichsberechnungen. Masonry shear walls with flanges: Behaviour under combined loadings. Concering the load bearing capacity and the stiffness characteristics of shear walls with flanges, a significant better behaviour under combined shear loadings, compared to walls with rectangular shape, can be found. Within a research project, several tests on full‐scale walls with T‐shaped ground plan view and different execution detaillings (e. g. connection between shear wall and intersecting wall with shear ties or interlocking) under combined N‐M‐V loadings (static‐cyclic and pseudo‐dynamic) have been performed. In the following some results of the tests and numerical investigations are presented.     

Zur Aussagefähigkeit der Härtemessung von Thermoplasten

On the Efficiency of Information of Thermoplastics' Hardness Measurements In the present study results of penetration depth measurements as a function of (loading) time are given for 10 thermoplastics using an automated test appliance. The specimens' temperatures have been varied at several stages between room temperature and 100°C. At each stage time-dependent hardness curves H (t) have been derived. The findings permit a more efficient classification of the material's behaviour than it is possible by the aid of conventional hardness testing (so-called ?one-point-measurement”?). So the concept of hardness curves H (t) ought to be taken into consideration on the occasion of future revision of hardness test standards.     

Zur Aussagefähigkeit der Almenintensität als Kennwert bei der gezielten Eigenspannungserzeugung durch Kugelstrahlen

The Significance of Almen Intensity for the Generation of Shot Peening Residual Stresses In practice, shot peening operations are characterized by almen intensity and coverage applied as well as by specifications of type and hardness of the material and the shot peening medium respectively. However, this is not unambigous and consequently not sufficient in all cases. This is outlined and discussed using experimental investigations about the influence of almen intensity and shot diameter on near surface residual stress distributions, taking energy exchanges into account.     

Zur Ermittlung der Abscheidungseigenspannungen und verbleibenden Eigenspannungen in galvanisch hergestellten Nickelschichten nach der Spiralkontraktometer- und Streifendehnungs-Methode

Concerning Investigation of Internal Electrodeposition Stress and Residual Internal Stress in Electrodeposited Nickel Coatings by Spiral Contractometer and “Strip Dilatometer” Methods . For assessing the affect of material and plating conditions on internal stress in electrodeposited coatings and its influence on material strength of plated parts it is better knowing internal stress in thin, just deposited layers (while plating process continuous) and also the course of internal stress in the coating (after plating has been finished) instead of investigating an average stress in the coating. In order to get this more substantial information on internal stresses in electrodeposited coatings a deposition model – gradual composition of the coating – and stress calculation methods were developed for Spiral Contractometer and “Strip Dilatometer”. Both methods were applied on measurements in a Watts-Nickel electrolyte.     

Zur Frage der drucklosen Messung der elektrischen Leitfähigkeit von pulverförmigen Werkstoffen

Contribution to the Problem of Pressure-less Measurements of the Electric Conductivity of Powder Materials Two authors (1, 2) proposed to use the electric conductivity of a loosely packed powder bed as the electric characteristics of the power material. The authors got reproducible and intercomparable results applying their method on various oxide powders, e.g. reduced MnO₂ and mixed oxides. This is in contradiction to the common experience that in the range of small pressure, reliable results hardly can be obtained. Obviously, some special conditions have made the good results possible. Here below, the pressure-less method has been applied to four different powders: a species of MnO₂, copper, Cd(OH)₂ and PbO₂. As the principal result, it has to be stated that the pressure-less method delivers reliable results only in the case of such powders, whose grain core resistance doesn't have to be neglected against the contact resistance between the grains. This condition is fulfilled here only in the case of manganese dioxide. Probably, the oxide powders under study in (1, 2) also have been in the correct range. In spite of this, the pressure-less method may not be applied on metal powders or on the metal-likek PbO₂ powder. Also in the case of Cd(OH)₂ masses, severe objections exist.     

Die Bruchmechanik und ihre Anwendung auf Fragen der Bauteilzähigkeit

Linear Elastic Fracture Mechanics and its Application to Structural Components . The first part deals with some theoretical aspects of linear elastic fracture mechanics and their application to thick-walled structural components. One of the prerequisites are plane strain conditions in both the fracture mechanics specimens and in the structural components. The types of specimens, the experimental procedure for the investigation of stress intensity factors K_Ic and some difficulties in practice are discussed together with examples illustrating the application of fracture mechanics technology to heavy section pressure vessel components.     

Zur Zähigkeit von Vergütungsstählen

On Toughness of Quenched and Tempered Steels Toughness as consumed fracture energy is dependent on fracture mechanism. Grain size and loading conditions influence the transition from ductile dimple fracture to brittle cleavage fracture. In quenched and tempered steels packet size and particle distribution are of importance as well as brittle intergranular fracture modes by grain boundary segregation of impurities in ferrite (temper embrittlement) or precipitates in austenite. Anisotropy of toughness arises from banded structures.     

Zur Ermittlung verformungsbedingter Makro- und Mikroeigenspannungen durch mechanische und röntgenographische Eigenspannungsanalysen

Analysis of deformation induced residual macro-and microstresses by mechanical and X-ray methods Residual stress distributions in plastically deformed tensile and bending specimens of perlitic steel were analysed using X-ray diffraction technique and incremental holedrilling method. After tensile loading compressive residual stresses are measured by X-ray analysis in the ferrite phase. Consequently X-ray analysis detects compressive microstresses. In the case of bending specimens residual macrostresses are superposed with residual microstresses after unloading. In no case identical residual stress values were measured by X-ray and hole drilling methods. Microstresses can be separated combining both measurement methods. Microstresses after tensile loading were found to be greater than in surface layers of respective bending samples subjected to the same amount of plastic strain.     

Rechnerischer Festigkeitsnachweis der Ermüdungstragfähigkeit von vergüteten und einsatzgehärteten Stirnrädern

The work presents a calculative proof of strength for compensated and case hardened spur gears taking into account the different stress conditions in the tooth root and on the tooth flank. The basis of the proof of stregth is the local comparision of the occured stresses and the allowed stresses in the spur gear. The complex stress condition on the tooth flank is illustrated. On the flank occours a three dimensional stress condition with turnig principial stress systems. Furthermore the influences on this stress condition of residual stresses and of the contact of technical surfaces are discussed. Especially the described complex stress condition on the tooth flank asks for a calculation with an adequate criterion of failure. For this purpose a variant of the Schubspannungsintensitätshypothese (SIH) is proposed. The applicability of the proposed model is verified with numerous results of experiments. Some of the calculations are presented here. Altogether there is a good conformity between the test results and the calculated results especially for the ammount of the fatigue limit, the kind of damage (e.g. tooth root breackage, pitting, tooth breackage in the region of the flank) and the position of the beginning of the damage.     

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.