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.     

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.     

Wechselverformungskurven und Mikrostruktur bei spannungskontrollierter Zug-Druck-Wechselbeanspruchung von Ck 45 im Temperaturbereich 295 K ≤ T ≤ 873 K

Cyclic deformation curves and microstructure of SAE 1045 after stress-controlled push-pull loading in the temperature range 295 K ≤ T ≤ 873 K Stress-controlled cyclic deformation tests were performed with normalized SAE 1045 in the temperature range 295 K ≤ T ≤ 873 K. From the measured mechanical hysteresis loops cyclic deformation curves were determined, which are characterized by temperature dependent cyclic softening and hardening processes. Due to the cyclic deformation processes at any temperature distinct dislocation structures are formed depending on the stress amplitudes and the number of cycles chosen. In the whole temperature range and for all stress amplitudes the plastic strain amplitude was proved to be a suitable parameter to describe the actual fatigue state.     

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.     

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 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.     

Relaxationsverhalten des Werkstoffs X6 CrNi 18 11 (DIN 1.4948) für den Temperaturbereich 450–650 °C

Relaxation Behaviour of the Austenitic Stainless Steel X6 CrNi 18 11 (DIN 1.4948) in the Temperature Range 450 °C to 650 °C Based upon a set of actual data from relaxation tests after tensile loading in the temperature range 450–650 °C and with test times up to 100 h, an average stress vs. time relation for relaxation behaviour is derived. The actual dataset at the temperature of 550 °C is compared with the average relation. Relaxation behaviour is numerically computed from creep data of X6 CrNi 18 11 using different hardening theories and compared with the average relation derived from actual data.     

Experimental research on bolted joint strength and dispersion in steel lattice transmission tower legs under low temperatures (−20°C to −45°C)

Cold regions with subzero temperatures (?20°C to ?45°C) have important impacts on the mechanical properties of structural steel used in lattice steel towers of overhead transmission line systems. The results from regular material tests are not appropriate for the accurate analysis of joint strength in cold weather conditions. This paper presents the tensile test results of 18 coupons of steel material and eight groups (18 specimens per group) of bolted joints with Q345 and Q420 steel under temperatures of 20°C, ?20°C, and ?45°C. The results show that the yield‐to‐ultimate strength ratio of the joints under low temperature conditions is beyond the range of 0.60 to 0.75 for Q420 structural steel. Suggestions are made on how to improve the accuracy of joint design for both the partial resistance factor and the design value of joint yield strength in cold regions.     

Spanende Bearbeitung von Hartlegierungen – Drehen und Schleifen. Teil II: Drehen von Hartlegierungen

Metal Cutting of Hard Alloys – Turning and Grinding. Part II: Turning of Hard Alloys Turning tests were carried out on selected hard alloys on iron (FeCr12C2.1, FeCr13Nb9MoTiC2.3, FeCr14Mo5WVC4.2) and cobalt basis (CoCr29W5C1.3) in a cutting speed range of between v_c = m/min and 180 m/min. Polycrystalline cubic boron nitride (PCBN) turned out to be a suitable tool material. Subsequent examinations focused on evaluating the mechanisms of chip formation, cutting tool wear and surface integrity of the workpiece. During turning of hard alloys the formation of chips is primarily influenced by the ductility and fracture toughness of the work material. While a ductile matrix enables the formation of highly deformable chips, the chips stemming from martensitically hardened alloys show low deformation. As the cutting depth increases shear and segmented chips are chiefly produced. Type and arrangement of the hard phases play a significant role. Adhesion is the main wear mechanism impacting the cutting face of the tool. Particularly, strong adhesion effects will arise during the machining of the work hardening alloy on cobalt basis. A high cobalt content of the metallic bonding phase of the PCBN cutting tool appears to be a disadvantage with this type of work material. When machining alloys on iron basis adhesion is promoted by the mechanical linking of alloy-specific hard phases to the cutting material binder. Abrasion primarily acts on the flank. The hard carbides of the work material produce typical grooves in the cutting edge zone of the tool. The flank wear increases as the carbide content goes up. As the cutting speed rises the tool wear ascertained passes through a minimum. Whereas the formation of built-up cutting edges predominates at lower speeds, a thermal softening of the PCBN binder takes place and is dominating at high cutting speeds. The location of the wear minimum depends not only on the cutting temperature but also on the strain hardening capability of the metal matrix. Raising the cutting speed will cause the cutting force to continuously reduce. The highest cutting forces are found for the Co-based alloy. The passive forces develop in line with cutting tool wear and vary with content and hardness of the hard phases involved. The selected process parameters also affect the surface near zone. With low cutting speeds and process temperatures the surface is mainly stressed mechanically. Carbides break or detach from the surrounding matrix. If the cutting speed and process temperature are increased the eutectic carbides (M₇C₃) are deformed together with the metal matrix. Microhardness profiles are indicative of near-surface strain-hardened zones after cutting of the Co-based alloy. Fe-based matrices do not show hardness changes worth mentioning. Although there are no new hardened zones noticeable even at maximum cutting speed, the matrix is nevertheless influenced thermally so that residual stresses will develop in the machined surface layer. In the lower cutting speed range the surface quality is characterized by flakes and material squeezing (Co-based alloy) and by spalling (Fe-based alloy). Only if the cutting speed is raised, a minor roughness is detected due to a potential deformation of eutectic hard phases.     

Freezing leukocytes to −40 and −20 °C under an exponential programme with original cryopreservatives

Cryoprotective solutions were developed for keeping human blood leukocytes in active and morphologically valid condition at freezing, according to an exponential programme, to −20 and −40 °C which do not require washing from the bioobject after its thawing.     

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.     

Witterungsbeständige Kunststoffe und Textilien im Automobilbau. Korrelation zwischen Frei- und Gerätebewitterung — Teil II

Weather-Resistant Plastics and Fabrics in Automotive Engineering – Correlation between Natural and Artifical Weathering – Part II Plastics and textiles used in automotive engineering are partly exposed to extreme weathering influences. These produce an ageing of the materials and components, which can become visible e.g. in the form of cracks, color changes or deformations. The first part of this report dealed with climatic variables that are important for the ageing of polymer materials and the stresses on vehicle components due to climate. In the second part test methods used to prove the weathering resistance will be presented, first the natural weathering, then some short-time testing methods of artificial weathering. Further the correlation between natural and artificial weathering will be explained using selected examples.     

Oxidation characteristics of Ti3AlC2 over the temperature range 500–900 °C

Titanium aluminium carbide (Ti₃AlC₂) displays a unique combination of characteristics of both metals and ceramics coupled with an unusual combination of mechanical, electrical and thermal properties. In this research, the oxidation characteristics of Ti₃AlC₂ over the temperature range 500–900 °C were studied by synchrotron radiation diffraction (SRD) and secondary-ion mass spectrometry (SIMS) experiments which provided elemental and phase compositional depth profiles over this range. Evidence for the outward diffusion of Al during oxidation was shown for the first time by the complementary SIMS results, which suggested the existence of amorphous Al or aluminium oxide at low temperature oxidation. At 500 °C, only anatase-TiO₂ was detected by SRD in addition to the parent Ti₃AlC₂. Transformation of anatase to rutile was observed at 600 °C and was completed by 900 °C. The crystalline phase α-Al₂O₃ was detected at 900 °C but not at lower temperatures.     

About thaumasite formation in Portland-limestone cement pastes and mortars––effect of heat treatment at 95 °C and storage at 5 °C

Owing to the presence of finely divided calcite, mortars and concretes made with Portland-limestone cements are particularly susceptible to damaging thaumasite formation during sulfate attack at lower temperatures. This work reports the results of investigations on mortars made according to DIN/EN 196 and pastes (w/c ratio of 0.5) with CEM I 42,5 R, as well as with mixtures of cement with limestone filler. Some of the samples were heat-treated at 95 °C. The length changes and resonant frequencies of the samples were measured during long-term water-storage at 20 and 5 °C. There was no evidence from X-ray diffraction data of thaumasite formation in the samples. Only for pastes containing 30 wt.% limestone filler were small areas found by SEM and X-ray microanalysis whose chemical analysis matched thaumasite or a thaumasite–ettringite solid solution.     

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.