Schäden an Bauteilen mit Verschleißschutzschichten

Damage of Components with Wear Resistant Coatings The appearance of wear happened to assorted components with different wear resistant coatings is described with the aid of metallographic microstructural investigation leading to the recognition of the cause of damage. Nitrided and reinforced extruder parts have suffered from sliding wear and abrasion. Thermally sprayed coatings consisting of oxides failed because of productional defects resp. taking the wrong material. The quality of thermally sprayed coatings can be proved by tearing tests without destroying the component.     

Schäden durch kerbinduzierte Schwingbrüche

Failures by notch induced fatigue fractures Notches produce local stress concentrations and promote the formation of fatigue cracks. Characteristic types of notches as a result of design, manufacturing and operation are presented and remedial measures are discussed. Examples demonstrate the effect of different kinds of notches on various components.     

Einsatz moderner Berechnungsverfahren zur Analyse und Abwehr von Schäden

Improved Methods of Stress Analysis to Analyze and Prevent Failures The continuous rising demands on productivity and economy of modern processes, for example in the chemical or power generating industries, cause a tendency for permanent rise of the process parameters pressure and temperature. But for the engineer of a project rising process parameters mean an unproportional increase of the number of mechanical/thermal/chemical induced load collectives. During the basic design phase of a plant this aspect has to be taken into account with respect to the materials choice and the analysis of all mechanical, thermal and chemical induced load cases. In this article modern computer based stress analysis methods for the complex simulation of combined mechanical/thermal load cases are discussed using the example of pipe work. The emphasis was focussed on ?pipe work”? with respect to the new German pressure vessel code of April, 21 st., 1989. Since then within the framework of this code the integrity of pipe work has to be verified. Due to this demand a general discussion was initiated to validate the appropriate analysis method. In this article different examples were chosen to demonstrate the influence of complex load situations on the total stress level, for example the combination of external bending moments with stresses due to the mismatch of the physical properties of a selected material combination. Another goal of this paper is to show the demand for further investigations to transfer brand new scientific results to common engineering praxis. This aspect is discussed examining the failure behaviour of heat resistant steels under complex mechanical/thermal loading. It must be emphasized that the discussed analysis methods are not a paragraph in the German pressure vessel code. But these methods are necessary to assist the code in effective analysis and prevention of failures.     

Schäden wälzbeanspruchter DLC‐Schichten auf Stahlsubstraten unterschiedlicher Härte

Damages of slip‐rolling tested DLC coatings on steel substrates of different hardness Extremely hard diamond coatings on hard SSiC substrates, various hard DLC coatings on 100Cr6 substrates (HRC60) as well as selected DLC coatings on unhardened steel substrates (HRC20) were tested under slip‐rolling conditions. Unadditivated paraffin oil was used as a lubricant. The tests were carried out in an Amsler type twin disc tester at initial maximum pressures of P₀=2.3 GPa according to Hertz. The tests were terminated after n=1.000.000 revolutions (endurance tests: n=10.000.000 revolutions) or if a coherent damaged area of A>1 mm² occurred. The slip‐rolling tests showed that the SSiC had a supportive influence on the diamond coatings which, however, failed due to fractures in the substrate. At least two of the DLC coatings on 100Cr6 substrates (HRC60) withstood the slip‐rolling test for up to n=10.000.000 revolutions with nearly no visible damage. These coatings deposited onto a soft, nitrogen alloyed steel (HRC20) were able to adjust to the deformation of the substrate without major damaged areas (A>1 mm²).     

Verhalten von Mauerwerksbauten unter Erdbebeneinwirkung: Auswertung der Schäden des Albstadt‐Erdbebens vom 3. September 1978

Numerische Untersuchungen zum Verhalten von Mauerwerksbauten unter Erdbebeneinwirkung führen oft zu pessimistischen Schadensprognosen, welche im Gegensatz zu den Beobachtungen stehen. Um diesen Widerspruch aufzulösen, werden erfahrungsbasierte Verletzbarkeitsfunktionen für typische Mauerwerksgebäude auf der Grundlage der durch das Erdbeben vom 3. September 1978 bei Albstadt (mit einer Lokalmagnitude M_L von 5,7 und Epizentralintensität I₀ = VII—VIII) verursachten Schäden entwickelt. Anhand des Bauwerksbestandes von 1978 erfolgt die Einordnung der beobachteten Schäden in Schadensgrade auf Basis der European Macroseismic Scale EMS‐98 [1]. Die für den Bauwerksbestand repräsentativen Bauweisen werden herausgearbeitet; für die vorherrschenden Gebäude aus unbewehrtem Mauerwerk ist eine weitere Unterscheidung nach Baualter, Geschosszahl und phänomenologischen Gesichtspunkten möglich. Vulnerability of masonry structures under seismic action: Damage analysis of the September 3, 1978 Albstadt earthquake. Numerical studies of the earthquake behavior of masonry buildings in Central Europe based on national building codes acc. to the Eurocode 8 lead to pessimistic damage prognoses, which are in contradiction to the observed behavior. In order to eliminate this discrepancy realistic experience‐based vulnerability and displacement functions for typical masonry constructions are developed. Because of the rather limited number of earthquake damage observations, the Magnitude M_L 5.7 Albstadt earthquake from September 3, 1978 (intensity VII—VIII) in South Germany also based on its excellent documentation is reconstructed with the building stock existing at that time. The prevailing building types and for these the characteristic damage cases are investigated in close cooperation with the local authorities. The presented unreinforced masonry structures are divided by year of construction, number of storeys and phenomenological aspects.     

Fließfläche metallischer Schäume

Yield surface of metallic foam In this examination the parameters of a simple phenomenological material model are experimentally determined. Afterwards the energy which is absorbed by the metallic foam at plastic deformation is estimated.     

Sztynort Palace – Damage,repair and contemporary adaptations / Schloss Steinort – Schäden,Sicherung und modellhafte Adaption

The model project financed by the Deutsche Bundesstiftung Umwelt (German Federal Environmental Foundation) to repair anthropogenic foundation damage to Sztynort Palace was implemented in 2014/15 with the active participation of the Chair for Structural Design of the TU Dresden and thus achieved an exemplary adaptation of the house to future changes of environmental conditions. In addition to securing of the masonry of the northwest tower, which had been severely damaged by settlement, and further technically challenging refurbishment works to the partially collapsed cellar vaults, above all innovative solutions were planned, optimized and implemented to install an effective and modern drainage and rain water management system to the historic house with its complex construction.     

Untersuchung des Schädigungsablaufes in kohlenstoffaserverstärkten Kunststoffen

Acoustic Emission Investigations on Failure Mechanisms in Carbon Fibre Reinforced Plastics For a reliable application of modern high-strength materials such as carbon fibre reinforced plastics the knowledges of failure mechanisms as well as detailed informations about the influence of defects occuring during the manufacturing process are necessary. To study the damage progression in fibrous composites a non destructive manner, a very sensitive test failure processes in the laminate have only microscopic dimensions. In our investigations the damage progression was studied by means of acoustic emission analysis (AEA) for different types of ply orientated containing several artifical defects, as cut-through fibres, disbonded fibres and porous matrix. In a further step internally pressurized tubes were tested to investigate the applicability of AE-results to real components. Additionally, fractographic investigations improve the interpretation of the acoustic emission data. It is shown, that AEA succeeds in monitoring damages already at a very early state of damage. At increasing loads the different types of defect emit characteristic AE, which is correlated with a void-type dependent damage progression in the laminate. These knowledges of the failure mechanisms and their typical acoustic emission allow a classification of the different types of manufacturing defects concerning their influence. So, especially the porous matrix could be shown to be the most significant failure type as it causes the largest decrease of strength. The onset of AE at porous materials, however, was found at very low load levels, so that this type of defect can be detected properly.     

Schädigungsentwicklung bei Ermüdung verschiedener CFK-Laminate

Fatigue Damage Development of Various CFRP-Laminates The behaviour of a woven carbon-fibre reinforced laminate in a balanced eight-shaft satin weave style was compared to non-woven laminates with an equivalent cross-ply lay-up (50% of the fibres in the 0° and 50% in the 90° direction) Two types of non-woven laminates were investigated consisting of continuous fibres and aligned discontinuous fibres, both produced from carbon fibre prepregs. The static strength and the fatigue behaviour was measured. Stiffness reduction was monitored during fatigue loading as a damage analogue to which the mechanisms of damage could be associated. Similarities and differences in the fatigue behaviour and damage development of the three laminates will be discussed.     

Künstliche und natürliche Verbundwerkstoffe für den Einsatz bei hohen Temperaturen

Artificial and Natural Composites for High Temperature Application. Artificial composites are made by embedding reinforcing fibers into a metallic matrix f. i. by means of powder metallurgy. Natural composites are defined by the thermodynamic equilibrium: directional solidified eutectics as natural composites of high stability at high temperatures. Composites will probably replace conventional superalloys as turbine blades in jet engines allowing higher temperatures of combustion and therefore resulting in higher efficiency. Examples of such composites as materials for engine design are discussed. New processing methods (high energy rate forming and directional casting) and some recent results are described. Practical examples are mentioned and an outlook given for use in the near future.