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Long-term Tests (long-term + test)

Distribution by Scientific Domains

Polymers and Materials Science	60%
Engineering	20%
Chemistry	20%

Selected Abstracts

Predicting creep crack initiation in austenitic and ferritic steels using the creep toughness parameter and time-dependent failure assessment diagram

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2009
C. M. DAVIES
ABSTRACT Methods for evaluating the creep toughness parameter, Kmatc, are reviewed and Kmatc data are determined for a ferritic P22 steel from creep crack growth tests on compact tension, C(T), specimens of homogenous parent material (PM) and heterogeneous specimen weldments at 565 °C and compared to similar tests on austenitic type 316H stainless steel at 550 °C. Appropriate relations describing the time dependency of Kmatc are determined accounting for data scatter. Considerable differences are observed in the form of the Kmatc data and the time-dependent failure assessment diagrams (TDFADs) for both the 316H and P22 steel. The TDFAD for P22 shows a strong time dependency, but is insensitive to time for 316H. Creep crack initiation (CCI) time predictions are obtained using the TDFAD approach and compared to experimental results from C(T) specimens and feature components. The TDFAD based on parent material properties can be used to obtain conservative predictions of CCI on weldments. Conservative predictions are almost always obtained when lower bound Kmatc values are employed. Long-term test are generally more relevant to industrial component lifetimes. The different trends between long- and short-term CCI time and growth data indicate that additional long-term test are required to further validate the procedure to predict the lifetimes of high temperature components. [source]

Damage Phenomena Observed on PVD Coatings Submitted to Repeated Impact Tests

PLASMA PROCESSES AND POLYMERS, Issue S1 2007
Florent Ledrappier
Abstract Thin hard coatings obtained by PVD process are widely used to improve the mechanical and friction behaviour of industrial parts. Depending on the friction conditions, the failure mechanisms and resulting selection criteria may be very different. This study aims to investigate the endurance life of some PVD coatings under repeated impact conditions. Impact tests at controlled impact energy have been performed using a hemispherical tip. Long-term tests have been done to determine the coating endurance life while short tests enable us to identify the damage phenomena. Depending on the nature of the PVD coating, cracks, blisters or spalling may be observed under impact. These phenomena may worsen until the complete film rupture occurs. [source]

Predicting creep crack initiation in austenitic and ferritic steels using the creep toughness parameter and time-dependent failure assessment diagram

Long-term study of a portable field robot in urban terrain

JOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 8-9 2007
Carl Lundberg
The armed forces have a considerable amount of experience in using robots for bomb removal and mine clearing. Emerging technology also enables the targeting of other applications. To evaluate if real deployment of new technology is justified, tactical advantages gained have to be compared to drawbacks imposed. Evaluation calls for realistic tests which in turn require methods dictating how to deploy the new features. The present study has had two objectives: first, to gain a comprehensive view of a potential user of man-portable robots; second, to embed a robot system with users for assessment of present technology in real deployment. In this project we investigated an army company specialized in urban operations performing their tasks with the support of the iRobot Packbot Scout. The robot was integrated and deployed as an ordinary piece of equipment which required modifying and retraining a number of standard behaviors. The reported results were acquired through a long-term test ranging over a period of six months. This paper focuses on the characteristics of the users and their current ways of operation; how the robot was implemented and deployed. Additionally, this paper describes benefits and drawbacks from the users' perspective. A number of limitations in current robot technology are also identified. The findings show that the military relies on precise and thoroughly trained actions that can be executed with a minimum of ambiguity. To make use of robots, new behavioral schemes, which call for tactical optimization over several years, are needed. The most common application during the trials was reconnaissance inside buildings with uncertain enemy presence when time was not critical. Deploying the robot took more time than completing the task by traditional means, but in return kept the soldiers out of harm's way and enabled them to decrease weapon deployment. The range of the radio link, limited video feedback, and the bulky operator control unit were the features constraining the system's overall performance the most. On the other hand, did properties of the system, such as ruggedness, size, weight, terrain ability, and endurance, prove to match the application. The users were of the opinion that robots such as the Packbot Scout would be a valuable standard feature in urban intervention. © 2007 Wiley Periodicals, Inc. [source]

Limitation of immunoaffinity column for the removal of abundant proteins from plasma in quantitative plasma proteomics

BIOMEDICAL CHROMATOGRAPHY, Issue 5 2009
Tomoko Ichibangase
Abstract In plasma proteomics, before a proteome analysis, it is essential to prepare protein samples without high-abundance proteins, including albumin, via specific preparation techniques, such as immunoaffinity capture. However, our preliminary experiments suggested that functional changes with use alter the ability of the immunoaffinity column. Thus, in this study, to evaluate the changes of the removal ability of abundant proteins from plasma by the immunoaffinity column, plasma proteome analysis was performed for the long-term test for the reproducibility of the affinity column using the fluorogenic derivatization,liquid chromatography,tandem mass spectrometry method combined with an IgY column. The specific adsorption for albumin decreased with an increase in the number of the column usage before its expiration date. Moreover, it was demonstrated that hydrophobic high molecular weight compounds in plasma adsorbed onto the column materials surface contributed to the functional changes from specific immunoaffinity adsorption into hydrophobic interaction. These results suggested that, in quantitative plasma proteomics studies, it is important to keep in mind the risk of not only the nonselective loss but also the changes in the adsorption ability of the immunoafinity column. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Ceramic Matrix Composites: A Challenge in Space-Propulsion Technology Applications

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2005
Stephan Schmidt
Various technology programs in Europe are concerned, besides developing reliable and rugged, low-cost, throwaway equipment, with preparing for future reusable propulsion technologies. One of the key roles for realizing reusable engine components is the use of modern and innovative materials. One of the key technologies that concerns various engine manufacturers worldwide is the development of fiber-reinforced ceramics,CMCs (ceramic matrix composites). The advantages for the developers are obvious,the low specific weight, the high specific strength over a large temperature range, and their great damage tolerance compared with monolithic ceramics make this material class extremely interesting as a construction material. Over the past few years, the EADS-ST Company (formerly DASA) has, together with various partners, worked intensively on developing components for hypersonic engines and liquid rocket propulsion systems. In the year 2000, various hot-firing tests with subscale (scale 1:5) and full-scale nozzle extensions were conducted. In this year, a further decisive milestone was achieved in the sector of small thrusters, and long-term tests served to demonstrate the extraordinary stability of the C/SiC material. Besides developing and testing radiation-cooled nozzle components and small-thruster combustion chambers, EADS-ST worked on the preliminary development of actively cooled structures for future reusable propulsion systems. In order to get one step nearer to this objective, the development of a new fiber composite was commenced within the framework of a regionally sponsored program. The objective here is to create multidirectional (3D) textile structures combined with a cost-effective infiltration process. Besides material and process development, the project also encompasses the development of special metal/ceramic and ceramic/ceramic joining techniques as well as studying and verifying nondestructive investigation processes for the purpose of testing components. [source]

DSC as a valuable tool for the grease laboratory

LUBRICATION SCIENCE, Issue 3 2000
Martin Josef Pohlen
Abstract There is a need to reduce both the time and cost involved in research and development for lubricating greases. Most of the normal test methods used to characterise a grease are long-term tests, but it is important to develop screening tests that also give reliable information. Thermal analysis is one such way to fulfil these requirements. In the present work, a differential scanning calorimeter (DSC) with a normal pressure cell was used in a grease laboratory. By varying the atmosphere and the heating rate, different tests were worked out. The effects of changing physical parameters, such as viscosity and thickener structure, or chemical parameters, such as additives and thickener types, were examined. These methods can be used for controlling raw materials, improvement of grease formulations and production processes, development of new products, as a replacement for the oxidation bomb (ASTM D-942, DIN 51 808), and as a screening test for the FE9 life (DIN 51 821) test rig. [source]

Long-Term Properties of Butt-Welded Poly(propylene)

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2003
Ernst Schmachtenberg
Abstract It is still not clear why the long-term properties of plastic weld seams can only be differentiated by the very expensive medium tensile creep tests. One hypothesis for justifying this is based on the change in the structure of the weld seam surroundings, another cites the consumption of antioxidants and the following ageing in the weld seam area to be responsible for this. Butt-welded weld seams made of poly(propylene) were systematically produced under different process parameters. Corresponding to the particular hypothesis, these weld seams were then analyzed in various ways to find correlations or to prove one of the hypotheses. Regarding their short-term weld seam quality, the analyzed weld seams could not be differentiated through short-term tensile or short-term bend test. However, the medium tensile creep tests showed significant differences in both time until failure and long-term weld seam quality. Under long-term loading, the start of the brittle crack could be detected in most weld seams in the fine spherulite-zone or between this zone and the area of the flow lines. This demonstrated again that only long-term tests are suitable for examining different weld seam qualities. Depending on the welding parameters, times until failure decline with increasing heated-tool temperature and heating time. Though these parameters lead to a higher consumption of antioxidants in the weld seam, a degradation was not detected in the breaking area. In fact, increasing heated-tool temperatures and heating times, as well as higher joining pressures lead to a change in the internal structure of the material. This can be seen in morphological structure analyses in the larger bend of the entire weld seam area. A larger bend, however, correlates with higher residual stresses in the weld seam. In the medium tensile creep tests, these residual stresses as well as the tensile stress in the border region and the compressive stress in the middle are superimposed by the tensile stress resulting from the test stress. Thus a greater bend of the weld seam area and higher residual stresses in the weld seam itself lead to shorter times until failure in medium tensile creep tests. Schematic representation of the formation of residual stresses in a weld seam and residual stresses in the different bended weld seam areas. [source]

Tensile creep of a long-fibre glass mat thermoplastic (GMT) composite.

POLYMER COMPOSITES, Issue 9 2009

In Part I of this article, the short-term tensile creep of a 3-mm-thick continuous long-fibre glass mat thermoplastic composite was characterized and found to be linear viscoelastic up to 20 MPa. Subsequently, a nonlinear viscoelastic model has been developed for stresses up to 60 MPa for relatively short creep durations. The creep response was also compared with the same composite material having twice the thickness for a lower stress range. Here in Part II, the work has been extended to characterize and model longer term creep and recovery in the 3-mm composite for stresses up to near failure. Long-term creep tests consisting of 1-day loading followed by recovery were carried out in the nonlinear viscoelastic stress range of the material, i.e., 20,80 MPa in increments of 10 MPa. The material exhibited tertiary creep at 80 MPa and hence data up-to 70 MPa has been used for model development. It was found that viscoplastic strains of about 10% of the instantaneous strains were developed under load. Hence, a non-linear viscoelastic,viscoplastic constitutive model has been developed to represent the considerable plastic strains for the long-term tests. Findley's model which is the reduced form of the Schapery non-linear viscoelastic model was found to be sufficient to model the viscoelastic behavior. The viscoplastic strains were modeled using the Zapas and Crissman viscoplastic model. A parameter estimation method which isolates the viscoelastic component from the viscoplastic part of the nonlinear model has been developed. The model predictions were found to be in good agreement with the average experimental curves. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source]

Efficient Synthesis of Dimethyl Ether over HZSM-5 Supported on Medium-Surface-Area ,-SiC Foam

CHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 10 2008
Svetlana Ivanova Dr.
Abstract In this study, we aimed to produce a highly selective and stable catalyst for the production of dimethyl ether by methanol dehydration. The activities were compared of different active phases of the employed system, zeolite HZSM-5 or , -alumina, supported on silicon carbide as foam, and it was found that the supported zeolite catalysts are more active than and as selective as the alumina-based catalysts. The as-prepared zeolite/SiC composites reveal good stability in long-term tests in the presence or absence of steam. The high stability is attributed to the presence of highly dispersed micrometer-sized zeolite particles, which make the active sites more accessible to the reactants and promote the quick transfer of the desired product, dimethyl ether, out of the catalyst bed, minimizing deactivation of the catalyst. [source]