Verhalten von Druckgasflaschen unter Wasserstoff bei schwellender Beanspruchung mit geringen Frequenzen

Behaviour of Gas Cylinders Periodically Pressurized with Hydrogen at Low Frequencies In the course of a three years research project, commercial gas cylinders manufactured from quenched and tempered steel 34 CrMo 4 had been the subject of internal hydrogen pressurization cycles under near service conditions. Since hydrogen facilitates the initiation and propagation of fatigue cracks, the low cycle fatigue life of these cylinders is generally reduced as compared to identical tests in oil. Following the results of parallel experiments applying acoustic emission techniques and from the fractographic analysis of the fracture surfaces produced, a model has been presented describing the individual steps taking place in the development of a hydrogen induced vessel failure. Apart from the role which is played by service stresses and metallurgical factors, the results lead to the conclusion that the possible development of a failure is basically controlled by the state of the internal surface of the cylinder. From the experimental results it is possible to predict the safe service life of frequently filled hydrogen cylinders and pressure vessels. Provided that they are manufactured according to current specifications and guidelines, these cylinders and pressure vessels can be expected to operate safely over long periods.     

Das Verhalten rostfreier Stahlgußlegierungen unter gleichzeitiger mechanischer und korrosiver Belastung

Behaviour of stainless cast alloys under combined mechanical and corrosive attack In media with 3000 mg B/1 (as boric acid, H₃BO₃) and varying chloride contents down to 1 mg Cl^?/1 13%-Cr-steels show pitting. Under constant load cracks appear simultaneously. As can be expected, 17%-Cr-steels are more resistant and duplex ferritic austenitic steels exhibit no corrosion cracking in 3% NaCl-solution even after 10 000 hrs. Generally, corrosion resistance improves with increasing contents of ferrite forming elements. Corrosion cracks are interpreted in termes of anodic stress corrosion cracking. Notch impact bending tests with hydrogen charged specimens show that deformability is reduced.     

Beanspruchung von Hohlzylindern mit exzentrisch eingeschweißten Stutzenrohren unter Innendruck

Internal Pressure Loading of Hollow Cylinders with excentric welded-in Nozzles Investigations were carried out on nozzles welded on to the basic pipe with a V-seam without counter welded root; the material was of St 35 and WB 36. Flat specimens St 37 and BH 51 with a cross seam were delivered for comparative fatigue tests. The highest stressed part was established on the hole edge in the base material for nearly all types during static measurements (with and without longitudinal force compensation). The stress concentration factor α_K, plastic support factor n_0,2 and weakening factor v_0,2 were determined for the highest stressed part on samples of St 35 (exception WB 36). Stresses with longitudinal force compensation were somewhat larger than without, that means the results of internal pressure pulsating tests can be regarded as the lower limit of loading types. With internal pressure pulsating, cracks were predominantly on the hole edge in the base material, i. e. the negative influence of the (ground) seam was mostly smaller than the differences in maximum strains between hole edge and weldment. Compared with the test results of polished test bars, a surface factor f₀ would be defined. As far as the crack was within the range of the weld a “weld factor” f_S could be added so that the fatigue can be calculated with the total factor f_ges - f₀ × f_S from the strain amplitude of the polished bar. When utilizing the static design basis it turns out that the higher strength of WB 36 as against St 35 allows only a factor 2 ÷ 10 lower fatigue life (pulsating loading).     

Grenzflächenpressung von Eisenwerkstoffen und Leichtmetallen unter kontinuierlicher Beanspruchung

Limiting surface pressure under continued pressure of ferrous and lightweight metals In this article the results of tests examining the limiting surface pressure of ferrous and light weight metals are presented. The tests were carried out under consistent conditions using a standardised test procedure.     

Versuchs- und Rechendaten zur Dauerschwingfestigkeit von metallischen Werkstoffen unter mehrachsiger Beanspruchung

Experimental Data and Calculated Results about the Fatigue Endurance Limit of Metals under Multiaxial Alternating Load An extensive catalogue of present available experimental data about the fatigue endurance limit of metallic materials under multiaxial loading conditions and thereupon determined deviation ratios between experimental results (long life fatigue tests) and calculated values by five newer computation methods is demonstrated (a further showed statistical analysis of these devations indicates, that in relation to the other failure criterions the ?Quadratische Versagenshypothese”? QVH is preferably recommended for a reliable application). The tabulated data-catalogue totally includes 530 referenced loading cases (limited to various biaxial states of combined normal and torsional alternating stress with sinusoidal synchronous or out-of-phase amplitudes and superimposed mean stresses) with experimental results (probability of survival of P_S = 50%) on metallic materials (unalloyed and alloy steels, non-ferrous metals and wrought aluminium alloys, cast irons and sintered metals).     

Kurzzeitschwingfestigkeit von duktilen Stählen unter mehrachsiger Beanspruchung

Low-Cycle Fatigue of Ductile Steels under Multiaxial Deformations To investigate the fatigue behaviour of cyclically softening and hardening steels under multiaxial elastic-plastic strains, axial strain and shear strain controlled fatigue tests under constant amplitude loading were carried out. S-N curves under axial strain and torsional pure shear as well as under combined axial strain and shear, in and out of phase, were obtained for the cyclically softening tempered steel 30 CrNiMo 8 (similar to AlSI-Type 4340) and the cyclically hardening quenched stainless steel X 10 CrNiTi 189 (AISI-Type 321) in the region of low-cycle fatigue. For both steels, used in the design of vessels, pipings, shafts, etc. the fatigue life to crack initiation is reduced by an out of phase (δ = 90°) shearing of the strained specimens in comparison to the in phase loading. The decrease of fatigue life under out of phase strains is caused by changing direction of principal strains resulting in an interaction of the deformations in all directions of the surface. This interaction is taken into account by a calculation procedure deriving an equivalent strain and predicting the fatigue life under combined strain on the base of S-N curves for unaxial strain.     

Rißfortschritt in ultrafesten Stählen und deren Schweißverbindungen bei dynamischer Beanspruchung

Crack propagation in ultra-high-strength steels and their welded joints under dynamic loading . Reported are results of investigation into the propagation of cracks in the base metal and weld metal of an ultra-high-strength steel. The material used in the investigations was a Ni? Co? Mo? alloy maraging steel with a yield point of 170 kp/mm². The steel was arc welded and TIG welded. The joints exhibited a drop of static strength in the range of 5 to 8 percent related to the base metal. Under zero-to-tension stress cycles the fatigue strength corresponded that of other high-strength steels, under tension-compression stress cycles the steel exhibited a higher fatigue strength. It was possible to show striations with the aid of scanning microscopy. Comparing the track propagation calculated in the microscopic range with the results obtained from the crack growth curves produced approximate agreement.     

Beitrag zum Nachweis von Rissen infolge Spannungsrißkorrosion mit Ultraschall

Contribution concerning the ultrasonic detection of cracks due to stress corrosion . Topic of the present report: Experimental examinations concerning ultrasonic crack detection, carried out on compressedgas bottles showing different stress-corrosion damages. Following the discussion of the test results hints are given with respect to the practical test performance.     

Untersuchungen zur Deutung des Dauerschwingverhaltens von CoCrMo-Gußlegierung,dargestellt an Brüchen von Endoprothesen

Studies for the Interpretation of Fatigue Behavior of CoCrMo Cast Alloy Presented on Fatigue Failures of Endoprotheses Examinations were preformed on the fractured surfaces of appliances made from CoCrMo cast alloy, which were broken in fatigue failures and used in prothetical surgery as endoprotheses. The examinations were performed on behalf of scanning electron microscope. During the examinations of three appliances which were broken in patients, it was found that for the failure of endoprotheses broken in fatigue, the number and distribution of microporosity was also responsible.     

Mechanisches Verhalten des Schutzschicht-Grundwerkstoff-Verbundes von Gasturbinenschaufeln unter betriebsähnlicher zyklischer Beanspruchung

Mechanical behaviour of the coating-substrate-compound of gas turbine blades under service-type cyclic loading With a special test technique developed for the investigation of the thermo-mechanical loading of materials for gas turbines, aniso-thermal service-type strain cycle tests with different coating-substrate-combinations were carried out. For comparison isothermal standard strain cycle tests with one selected coating-substrate combination were carried out. With this combination also the coating-load was calculated with finite-element-calculation.     

Klebflächenvorbehandlung von Aluminiumoberflächen mit Haftvermittler

Surface pretreatment for adhesive bonding of aluminum with adhesive mediator The influence of three steps pretreatment degreasing, blasting and primer and the two steps pretreatment degreasing and blasting on the adhesive behaviour of aluminum alloy AlMg4,5Mn0,5 were investigated. The investigations were preformed using two cold hardening two‐components epoxy adhesives, one hot hardening one‐component epoxy adhesive and one cold hardening two‐components polyurethane adhesive. The three steps pretreatment indicate that the adhesion bonding strength by epoxy adhesives are higher than that by two steps pretreatment. On the other hand, the adhesion bonding strength was similar by using polyurethane adhesive independence of the pretreatment method. Leaving out the pretreatment step degreasing after corund blasting caused by using, PU, EP 2 and EP 3 adhesives a significant decreasing of the bonding strength in comparison with the only degreased specimen. This degreasing process was used to remove the residual blasting medium from the aluminum surfaces after blasting. The topographical structure of the surfaces after corund blasting was covered by further pretreatment with primer as a consequence of higher primer viscosity, which causes a decreasing in the surface roughness. The chemical composition of pretreated surfaces by three steps was different from that by two steps.     

Verhalten von Hüftgelenks-Endoprothesen bei quasi statischer und dynamischer Belastung

Behaviour of Hip – Joint Endoprostheses under quasi-static and dynamic Load Clinical experience with total-hip endoprostheses has shown that the following problems take priority: – Loosening of the socket (acetabular cup) and the femoral prosthesis – Fracture of the femoral prosthesis – Loosing due to deep infection. Accordingly aims the research at locating the biological and mechanical reasons for the failures as well as testing alternative solutions such as – methods of fixation – construction of protheses – new materials and finishing methods. This publication concerns areas of the mechanical side of the problem. The comparison between the original system of proximal femur and acetabulum and the implanted prosthetic system shows changes in the stiffness of the systems depending on the different types of implanted endoprostheses. The influence of the frequency of loading on the deformation of the system is investigated in a frequency range between quasi-static and dynamically changing loads. The movements between implanted cup and neighbouring pelvic bone during cyclic load is measured. The results of these examinations give clues concerning qualitative and quantitative repercussions from the different endoprosthetic systems under conditions optimal in view of true comparison, and possible or desirable alternative solutions of the problem in view of construction and material.     

Klebflächenvorbehandlung von Aluminiumoberflächen mit SIP‐Haftvermittler

Surface pretreatment for adhesive bonding of aluminium with adhesive mediator SIP The present contribution describes the influence of different surface pretreatments including adhesive mediator SIP for adhesive bonding of aluminium alloy AlMg4,5Mn0,4. The investigations were performed using two cold hardening two‐components epoxy‐adhesives, one hot hardening one‐component epoxy‐adhesive and one cold hardening two‐components polyurethane‐adhesive. The adhesive bonds with epoxy‐adhesives show after three‐step pretreatment degreasing + corundblasting + SIP coating the highest adhesive strength values whereas adhesive bonds with polyurethane‐adhesive showed a decrease of bond strength as compared with the delivering surface condition.