Zeitstandprüfung von Polypropylen bei 120 °C

Long Term Creep Tests of Polypropylene at 120 °C The mechanism of damage in the pipe wall during the internal pressure creep test of polypropylene-pipes at a test temperature of 120° is described. The resulting consequences from the investigations relating to the test method are shown and a test station with automatic recording of the time of damage is presented. Further on solutions are explained to eliminate the security risks during the tests of big pipes. A practical performance is described. On the basis of the time-temperature-correlation of the long term behavior of polypropylene the mathematical basis to interpolate minimum requirements for quality control are presented.     

Eine Probeneinspann- und Heizvorrichtung für Dauerschwingversuche im Temperaturbereich 20 °C < T < 600 °C

Grip °and Specimen Heating-System for Fatigue Tests at the Temperature-Range 20 °C < T < 600 °C A grip and specimen heating system for fatigue tests is presented. The equipment is easily to handle, long-time stable and available up to a test-temperature of 600 °C also with inert environment. Specimens can be fixed without bending moments.     

Ermittlung des Versagensverhaltens thermisch gespritzter MCrAlY/IN617-Verbundwerkstoffe im Zugversuch bei Temperaturen bis 800 °C im Rasterelektronenmikroskop

Fracture mechanisms of Thermally Sprayed MCrAlY/lN617 Composite Materials during Tensile Tests up to 800 °C Tensile strength of thermally sprayed MCrAlY/IN617 composite materials has been prooved at temperatures up to 800 °C in a SEM. For these investigations two different qualities of composite materials have been developed. One sort of composite material had been produced with a good quality, the other one was produced with defects in the coating layer. The tensile strength of the good homogeneous material shows no dependence with increasing temperature, whereas the inhomogeneous composite materials develop better strength values with increasing temperature. The inhomogeneous coating always breaks in the near of the defect.     

Kriech-Ermüdungsverhalten der Titanlegierung IMI 834 bei 600 °C

Creep-Fatigue Behaviour of the Titanium Alloy IMI 834 at 600 °C In the present study the creep-fatigue behaviour of the Titanium alloy IMI 834 at 600°C was investigated. A comparison of the crack initiation life behaviour and of the crack propagation as caused by different types of complex creep-fatigue cycles (with hold times into tension and/or into compression direction and with different loading rates into tension and/or into compression direction) showed, that a slow increase of the loadings into tension reduced the life and increased the crack velocity more than hold times at the maximum load. Furthermore, there existed environmental influences. On the basis of the experimental investigations the prediction capability of convenient crack initiation life prediction methods was evaluated. It turned out that the prediction capability of the Strain Range Partitioning Method could be improved if it was frequency modified. The prediction capability of the Frequency Modification Method could also be improved, if mean stresses in the cycles were explicitly accounted for. In the short and long crack stage the propagation behaviour could be correlated well if the effective cyclic J-Integral was used. This is of importance for damage tolerance considerations. Because the strains and the stresses at the crack tip are most important for the crack propagation behaviour, they were analysed on the basis of the Finite Element Method. It was found that the strains and stresses differed for different types of creep-fatigue cycles.     

Spektralfotometrische Messungen bei 60° Einfallswinkel

Spectrophotometric measurements at 60° incidence angle A measurement VN‐accessory for characterisation and quality control of optical coatings using absolute measurements of transmittance and reflectance for s‐ and p‐polarised light at 60° incidence angle has been developed. In the common case of nearly normal incidence, the polarisation state of the incident light is of low relevance. In the case of 45° incidence angle the Abeles relation holds. Therefore, in both cases, changing the polarisation will add no further information. The use of larger angles, as 60° in our case, is common in ellipsometry. At this large angle of incidence, when measuring thick samples, unwanted effects such as transmission beam offset and further beam splitting caused by multiple internal reflections become significant. Therefore, glass substrates with different thickness have been included into the evaluation process of the 60°‐VN‐accessory. An excellent agreement between theory and measurement could be established for sample thicknesses up to 2.5 mm.     

Das Spannungs-Dehnungs-Verhalten von PTFE-Schälfolie im Temperaturbereich zwischen +25°C und −80°C und dessen Beeinflussung durch Kerben

Stress/strain properties of PTFE skived film over a temperature range of +25 °C to ?80 °C and the problem of notch effect Chemical plant under severe corrosive stress can be protected with “made-to-measure” liners welded up from PTFE skived film. For correct manufacture, handling and use of these chemical plant linings, a thorough knowledge of the semi-finished product and particularly of its load/deformation properties over a wide temperature range is required. The present paper deals with questions of strength and ductility and with the problem of notch effect at temperatures below + 25 °C. It is based on tensile tests carried out on PTFE skived film. Defined punched and cut notches were used to obtain information on notch sensitivity below room temperature. As the tests relate to two very different skived films, the reasons for these differences are analysed. The part played by the degree of crystallinity in determining many property differences is examined more closely with special reference to its effect on ultimate tensile strength, ductility and notch sensitivity. The aim of this study is not to determine material constants for PTFE but to identify tendencies in the behaviour of the semi-finished product, PTFE skived film, and so to gain useful information for its use in chemical plant lining.     

Quasistatisches Verformungsverhalten reiner Sintereisen im Temperaturbereich von –184 bis 600°C

Quasistatic deformation behaviour of pure sintered iron in the temperature range between –184 and 600°C The deformation behaviour of pure sintered iron materials with densities between 6,88 und 7,57 g/cm³ was investigated in tension tests in the temperature range of –184 and 600°C. Supplementary compression tests were carried out at 20°C. Increasing density leads to increasing material resistances and ductility properties due to the increase of the bearing specimen cross sections as well as due to smaller numbers of pores, more spherical pores with smaller notch effects and smaller numbers of mircocracks, which are initiated at pores. After equal deformations, due to pore closing effects and the impediment of crack initation, the flow stresses of compressively deformed specimens are larger than those of tensily deformed. The deformation behaviour is dominated at low temperatures by thermal activated glide processes of dislocations and their interactions with short range obstacles, at middle temperatures by dynamic strain ageing due to elastic interactions of glide dislocations and diffusing carbon atoms and at high temperatures by recovery controlled dislocation creep processes.     

Eine Cermet-Glasschmiermittelkombination für Reibpaarungen bei Arbeitstemperaturen von 650–1100°C

A cermet/lubricating glass-combination for friction pairs at working temperatures 650–1100°C The function and the efficency of technical plants are limited by the used materials and their behaviour under working conditions. At elevated temperatures, the corrosion and wear resistance and the thermal shock behaviour are as necessary as mechanical stability at high operating temperatures. Metals and ceramics often cannot meet the conditions. Dynamic applications may require lubricatings, metals surfaces may be too soft and not very oxidation-resistant. Metal-ceramic materials, -cerments-, use a combination of the properties of their microstructural parts. This paper shows a combination of a cermet and a lubricating glass with interesting aspects for high temperature operation.     

Spannungsrißbildung und Spannungsrißkorrosion bei Kunststoffen

Environmental stress cracking and stress-corrosion cracking in plastics Plastics are being used to an increasing extent in fields which have hitherto been the reserve of other, usually metallic, materials. Owing to their good processability and chemical resistance, plastics engineering materials are for example employed for vessels, pipes, valves and fittings, blowers, pumps and gear wheels. In these applications they are not only exposed to liquid media but, are also subjected to occasional or continuous mechanical stress. The trouble is that there are media to which plastics in the stress-free state are absolutely immune, but that, when tensile stresses are present, cracking may occur; this phenomenon is called environmental stress cracking. It is therefore necessary for the design engineer both to know whether the medium to be handled causes environmental stress cracking, and to be familiar with the other properties of the material. The following article describes the most important methods of detecting environmental stress cracking and the most important media which cause this form of cracking in common plastics materials.     

Effect of minor alloying with Al on oxidation behaviour of MoSi2 at 1200°C

Effect of Al alloying in small concentrations on oxidation behaviour of molybdenum di-silicide (MoSi₂) at 1200°C has been investigated. MoSi₂–2.8 and 5.5 at.% Al alloys possessed 0.5, and 2.5 at.% Al in solid solution, respectively, and dispersoids of -Al₂O₃. On the other hand, MoSi₂–9 at.% Al alloy possessed 3.1 at.% in solid solution in MoSi₂ and Mo(Si,Al)₂ phase, besides -Al₂O₃ dispersoids. The kinetics of oxidation of all the alloys followed a parabolic rate law. The oxidation rate was higher in the MoSi₂–Al alloys in comparison to MoSi₂, with weight gain values varying by an order of magnitude. The MoSi₂–5.5 and 9 at.% alloys demonstrated closely related oxidation characteristics and proved to be more resistant to oxidation than MoSi₂–2.8 at.% Al alloy. The oxide scale comprised of SiO₂ in MoSi₂, mixture of SiO₂ and -Al₂O₃ in MoSi₂–2.8 at.% Al alloy, and -Al₂O₃ in case of MoSi₂–5.5 and 9 at.% Al alloys. The mechanism of oxidation has been analysed using thermodynamic and kinetic considerations.     

Zusammenwirken von Spannungsrißkorrosion und Ermüdung bei der Schwingungsrißkorrosion eines hochfesten Stahles

Conjoint Action of Stress Corrosion Cracking and Fatigue on Corrosion Fatigue of a High Strength Steel The corrosion fatigue characteristics of a high strength, martensitic steel in 0.5 n NaCl solution is investigated with regard to the fatigue and stress corrosion cracking behaviour of the material. Test parameters are stress ratio and frequency, testing is carried out with fracture mechanics methods, the crack surfaces are examined fractographically. An analysis of the results reveals that corrosion fatigue in high strength steel is caused by fatigue or by stress corrosion cracking, depending on the kinetics of the two processes. Fatigue and stress corrosion cracking do not act cumulative or additive. Instead, the kinetically faster process causes crack advance. The crack growth characteristics are interpreted with respect to the fractographic appearance of the crack surfaces. Corrosion fatigue cracks propagate either intergranular relative to the prior austenite grain boundaries as stress corrosion cracks do or transgranular like fatigue cracks, depending on the crack growth rates of the two processes. Fatigue and stress corrosion cracking do not interact, at least in a measurable degree, because of the different crack path of the two fracture processes. Results can be assessed quantitatively with the “process competition model”.     

Physical mechanisms of dielectric breakdown in SiO2 for the range of −150°C to 150°C

This paper explains the physical nature of breakdown for 10 nm oxide in the range of −150°C to 150°C for N- and P-channel devices (NFETs and PFETs). At 30°C, two mechanisms occur: trap creation and impact ionization; at lower temperatures, the trap creation is significantly suppressed with a corresponding decrease in activation energy. Using the physical model, the reliability of NFETs is compared with what the PFETs relative to processing conditions.     

Bruchmechanische Untersuchungen an einer Schweißverbindung von 90 mm Dicke aus Almg 4,5 Mn bei Raumtemperatur und bei −196 °C

Toughness Evaluation for a Thick Weld Joint of AlMg 4,5 Mn at ?196 °C To asses the toughness of a 90 mm thick MIG-weld joint of Al Mg 4.5 Mn fracture mechanics and charpy impact material parameters have been determined at 20 °C and ?196 °C. Additional to the mechanical tests extensive metallographic and fractographic tests on specimens of the weld material and base material were done. The results of the fracture mechanics tests and the fracture analysis show, that now brittle fracture will occur at ?196 °C. The further conclusions are, that charpy energy values are no meaningful basis for a toughness evaluation of such an aluminium weld joint. The joint can be used without restrictions at ?196 °C.     

Hot-wire thin-film transistors on PET at 100 °C

Bottom-gate amorphous silicon thin-film transistors were fabricated using active layers deposited by r.f. and hot-wire (HW) chemical vapor deposition on polyethylene terephthalate (PET) and polyimide (PI) substrates. The maximum processing temperature was 100 °C for PET and 250 °C for PI. For transistors deposited at 100 °C by r.f. on PET and at 175 °C by HW on PI the transistor characteristics are comparable, although still inferior, to those of standard amorphous silicon transistors fabricated on glass substrates at 250 °C. HW transistors fabricated at 100 °C showed poor device characteristics. For devices fabricated at 100 °C, an extended anneal at this temperature was required to improve the transistor characteristics, independently of the film deposition technique used.     

Mechanische Verträglichkeit bei Verbundwerkstoffen – Naßkorrosion

Mechanical compatibility of metallic composites . Corrosion in aqueous media. As a main condition for corrosion in aqueous media between components of a composite material, both components have to be touched by an invironmental wed atmosphere or of a fluid. If this condition is given contact corrosion can take place with any composite, independent of the mechanical compatibility of the components. Crevice corrosion is possible too if mechanical incompatibility (or extern loads) causes cracks between the components; stress corrosion cracking is possible as well. Stainless steel vires, for instance, can not reinforce the composit if attached by SCC. The other kinds of corrosion mostly dammage the matrix, which also reduces properties of the composit. Examples are given of possible kinds of corrosion for some fiber reinforced metallic composites and for metal laminates.