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Thermal Exposure (thermal + exposure)

Distribution by Scientific Domains

Polymers and Materials Science	72%

Selected Abstracts

Veränderungen der mechanischen Eigenschaften von Magnesium-Druckgusslegierungen nach langzeitiger thermischer Beanspruchung

MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 2 2004
D. Regener
Pressure die cast magnesium alloys; long-term annealing; microstructure; mechanical properties Abstract Die thermische Belastbarkeit von Magnesium-Druckgusslegierungen ist noch nicht ausreichend untersucht. Um die Auswirkung einer thermischen Belastung auf die Gefügestabilität und damit auf das Festigkeits- und Verformungsverhalten einschätzen zu können, werden die Legierungen AZ91, AM50 und AE42 bei 150,°C und 200,°C einer 1000 h-Langzeitglühung unterworfen. Nach der Glühung werden Zugversuche, in situ-Zugversuche und Mikrohärtemessungen bei Raumtemperatur durchgeführt und die Ergebnisse anhand der mikrostrukturellen Veränderungen diskutiert. Changes of the Mechanical Properties of Pressure Die Cast Magnesium Alloys Subjected to Long-Term Thermal Exposure The thermal resistance of pressure die cast magnesium alloys is yet not investigated sufficiently. In order to assess the effect of a thermal exposure on the microstructural stability and on the strength and deformation behaviour, the alloys AZ91, AM50 and AE42 are subjected to a long-term annealing for 1000 h at 150,°C and 200,°C. After the annealing, tensile tests, in situ tensile tests and microhardness measurements are carried out and the results are discussed on the basis of the microstructural changes. [source]

Effect of thermal exposure on the microstructure, tensile properties and the corrosion behaviour of 6061 aluminium alloy sheet

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 3 2005
R. Braun
Abstract Sheet material of the Al-Mg-Si alloy 6061 in the tempers T4 and T6 was thermally exposed at temperatures ranging from 85 to 120°C for 1000 h. The microstructure, tensile properties and the corrosion behaviour in the different heat treatment conditions were investigated using differential scanning calorimetry and transmission electron microscopy as well as performing tensile tests and various corrosion tests. The additional heat treatments, which should simulate aging during long-term service usage, caused an increase in strength of 6061-T4 sheet, associated with changes in the naturally aged microstructure. Thermal exposure at 120°C for 1000 h resulted in tensile and corrosion properties being similar to those obtained for peak-aged sheet. Alloy 6061 in the T6 temper exhibited microstructural stability when additionally heat treated at 85 and 120°C for 1000 h. No significant alterations in the microstructure, tensile properties, and corrosion performance were observed after exposure to slightly elevated temperatures. [source]

POROSITY DESTRUCTION IN CARBONATE PLATFORMS

JOURNAL OF PETROLEUM GEOLOGY, Issue 1 2006
S. N. Ehrenberg
The important thing to understand about carbonate diagenesis is not how porosity is created, but how it is destroyed. Detailed core observations from two deeply-buried carbonate platform successions (the Finnmark platform, offshore north Norway; and the Khuff Formation, offshore Iran) show that in both cases most vertical porosity variation can be accounted for by only two or three factors, namely: (1) stylolite frequency, (2) proportion of argillaceous beds, and (3) anhydrite cement. The spatial distribution of these factors is determined by the depositional distribution of clay minerals (important for localizing chemical compaction) and the occurrence of hypersaline depositional conditions and associated brine reflux (important for localizing anhydrite precipitation and dolomitisation). However, the intensity of chemical compaction and consequent porosity loss in adjacent beds by carbonate cementation also depend upon thermal exposure (temperature as a function of time). Evidence from the Finnmark platform and other examples indicate that the stratigraphic distribution of early-formed dolomite is also important for porosity preservation during burial, but this factor is not apparent in the Khuff dataset. Insofar as the Finnmark and Khuff platforms can be regarded as representative of carbonate reservoirs in general, recognition of the above porosity-controlling factors may provide the basis for general models predicting carbonate reservoir potential both locally (reservoir-model scale) and regionally (exploration-scale). Distributions of clay, anhydrite, and dolomitization should be predictable from stratigraphic architecture, whereas variations in thermal exposure can be mapped from basin analysis. In the present examples at least, factors that do not need to be considered include eogenetic carbonate cementation and dissolution, depositional facies (other than aspects related to clay and anhydrite content), and mesogenetic leaching to create late secondary porosity. [source]

Effects of Grain-Boundary Structure on the Strength, Toughness, and Cyclic-Fatigue Properties of a Monolithic Silicon Carbide

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000
Da Chen
An in situ -toughened silicon carbide (ABC-SiC) has been examined in the as-processed condition, where the grain-boundary films are predominantly amorphous, and following thermal exposure at a temperature of 1300°C, where the films become fully crystalline. Previous work has shown that, at elevated temperatures (up to 1300°C), after the grain-boundary films crystallize in situ, only a marginal reduction in strength, fracture toughness, and cyclic-fatigue crack-growth properties is observed, in comparison with those of the as-processed microstructure at 25°C. In the present study, the effect of such crystallization on the subsequent strength, toughness, and fatigue properties at 25°C is examined. Little or no degradation is observed in the room-temperature properties with the crystallized grain-boundary films/phase; in fact, although the strength shows a small reduction (,3%), the fracture toughness and fatigue-crack-growth threshold both increase by ,20%, compared with that of the as-processed structure with amorphous grain-boundary films. [source]

Effect of thermal exposure on the microstructure, tensile properties and the corrosion behaviour of 6061 aluminium alloy sheet

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 4 2005
R. Braun
See original Materials and Corrosion 2005, 56, No. 3, p. 159,165 (2005) [source]

Effect of thermal exposure on the microstructure, tensile properties and the corrosion behaviour of 6061 aluminium alloy sheet

Veränderungen der mechanischen Eigenschaften von Magnesium-Druckgusslegierungen nach langzeitiger thermischer Beanspruchung

Effect of morphology on barrier properties of poly(ethylene terephthalate),

POLYMER ENGINEERING & SCIENCE, Issue 3 2005
A.A. Natu
The effects of morphology on the barrier properties of poly(ethylene terephthalate) (PET) have been investigated. Various levels of crystallinity can be developed in PET as a result of thermal exposure, orientation, and heat setting. The morphologies of the crystalline phase are affected by the conditions of their formation. As a result of morphological differences, samples with equivalent levels of crystallinity have been found to exhibit different oxygen barrier properties. These differences are most apparent at low and intermediate levels of crystallinity. For thermally crystallized systems, at the same crystalline content, increasing superstructure size in the crystalline phase leads to greater tortuosity for the permeant molecules, resulting in lower permeability. For stretched and heat set PET, transport properties can be correlated with birefringence as well as overall orientation, measured in terms of fraction of molecules in the trans or extended chain conformation. At high levels of crystallinity, where the spherulites become volume filling, permeation takes place primarily through the interlamellar regions of the crystalline phase and is controlled by level of crystallinity, independent of the mode of crystallization. The barrier properties of PET, before spherulitic impingement occurs, are governed by the size and number of spherulites as well as by the amorphous orientation present in non-crystalline regions. POLYM. ENG. SCI., 45:400,409, 2005. © 2005 Society of Plastics Engineers [source]

A fatigue and creep study in austenitic stainless steel 316L used in exhaust pipes of naval gas turbines

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9 2004
R. F. MARTINS
ABSTRACT Exhaust pipes of naval gas turbines are made of thin wall tubing of stainless steel grade AISI 316L. The tubes are fabricated by butt welding of different sections with longitudinal and circumferential joints. The plate thickness is about 4.0 mm, and the working temperature varies between 600 °C and 400 °C in the critical zones of the pipe, in the lower and central areas, respectively. The loadings in the tube induce high-temperature fatigue and creep-fatigue cracks have nucleated and propagated in the tube near some welded joints. The paper presents FCGR data obtained in CT specimens of used material taken from the pipes and tested at RT, 335, 500 and 600 °C. Preliminary creep data obtained in tension, in thin-sheet specimens (about 4 mm thickness), also taken from the conduct wall and tested at 500, 550 and 600 °C are also given. These results are crucial to perform a fatigue-creep interaction life assessment of the critical parts of the structure in the near future. Finally, the paper presents results of research work to investigate carbide precipitation and formation in virgin thin-sheet specimens subjected to several types of thermal exposures. In some cases, 3,4 d was the time interval between exposures. Grain size measurements were carried out together with microstructural observations in the SEM. The influence of time, temperature and time interval between thermal exposures was assessed comparing the microstructures. [source]

Hyperthermic injury to adipocyte cells by selective heating of subcutaneous fat with a novel radiofrequency device: Feasibility studies

LASERS IN SURGERY AND MEDICINE, Issue 5 2010
Walfre Franco PhD
Abstract Background and Objective The main objective of the present study is to demonstrate the feasibility of utilizing a novel non-invasive radiofrequency (RF) device to induce lethal thermal damage to subcutaneous adipose tissue only by establishing a controlled electric field that heats up fat preferentially. Study Design/Materials and Methods Adipocyte cells in six-well plates were subjected to hyperthermic conditions: 45, 50, 55, 60, and 65°C during 1, 2, and 3,minutes. Cell viability was assessed 72,hours after exposure. Two groups of abdominoplasty patients were treated with the RF device during and days before their surgical procedure. Temperatures of cutaneous and subcutaneous tissues were measured during treatment (3,minutes) of the first group. The immediate tissue response to heating was assessed by acute histology. The delayed tissue response was assessed by histology analysis of the second group, 4, 9, 10, 17, and 24 days after treatment (22,minutes). A mathematical model was used to estimate treatment temperatures of the second group. The model uses patient-based diagnostic measurements as input and was validated with in vivo clinical temperature measurements. Results Cell viability dropped from 89% to 20% when temperature increased from 45 to 50°C during 1,minute exposures. Three minutes at 45°C resulted in 40% viability. In vivo, the temperature of adipose tissue at 7,12,mm depth from the surface increased to 50°C while the temperature of cutaneous tissues was <30°C during RF exposure. Acute and longitudinal histology evaluations show normal epidermal and dermal layers. Subcutaneous tissues were also normal acutely. Subcutaneous vascular alterations, starting at day 4, and fat necrosis, starting at day 9, were consistently observed within 4.5,19,mm depth from the skin surface. Subcutaneous tissue temperatures were estimated to be 43,45°C for 15,minutes. Conclusions A controlled internal electric field perpendicular to the skin,fat interface is selective in heating up fat and, consequently, has the ability to induce lethal thermal damage to subcutaneous adipose tissues while sparing overlying and underlying tissues. In vitro adipocyte cells are heat sensitive to thermal exposures of 50 and 45°C on the order of minutes, 1 and 3,minutes, respectively. In vivo, 15,minutes thermal exposures to 43,45°C result in a delayed adipocyte cellular death response,in this study, 9 days. The novel RF device presented herein effectively delivers therapeutic thermal exposures to subcutaneous adipose tissues while protecting epidermal and dermal layers. Lasers Surg. Med. 42:361,370, 2010. © 2010 Wiley,Liss, Inc. [source]