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The presentation will discuss the difference between EU and US standards for the determination of explosion (flammability) limits and limiting oxygen concentration. Small differences observed in measured values can be traced back to the different test apparatuses and criteria. The discrepancies can be much greater in the case of limiting oxygen concentration because of the high amount of inert gases and the corresponding low laminar burning velocities. The paper describes some examples and the influence of the chosen criteria on the results. The European and US standards use the criteria of flame propagation in open test vessels and of pressure rise in closed ones. The examples discussed show that flame propagation is still possible at very small pressure rise values, as observed much below the pressure rise criterion of usual standards. However, flame propagation in a process plant can cause an accident or explosion and must be avoided. Therefore, the flame propagation criterion is recommended to be used in chemical safety engineering. The European safety database CHEMSAFE contains expertevaluated safety data for cases where the determination method and criteria are known. Flammability characteristics based on the pressure rise criterion may suffice in certain cases, e.g. for explosion protection in closed vessels without any connecting pipes.
IGUS is the International Group of Experts on the Explosion Risks of Unstable Substances. Today, the aim of the group is to exchange information on the behavior of unstable substances and to improve safety in production, storage, transport, and use of these substances. Full members of IGUS work for governments and independent research organizations. Experts from industry can and do attend meetings by invitation. IGUS's 50th anniversary in 2012 gives reason to have a closer look at the questions of how IGUS came to be, what IGUS's aims and objectives were, and how it is organized and working today.
Thermo-mechanical fatigue (TMF) testing plays an increasingly important role in the design, the reliability assessment and the lifecycle management of safety critical components used, for instance, for power generation, in the process industry and in aeronautical and automotive applications, with a view to increasing the fuel efficiency, safety and service intervals, while reducing production (and material) costs. In a European Commission funded research project (acronym: TMF-Standard) of the 5th Framework Programme, 20 European laboratories have undertaken a joint research effort to establish a validated code-of-practice (CoP) for strain-controlled TMF testing. Starting from a survey of the testing protocols and procedures previously used by the partners, a comprehensive pre-normative research activity into various issues has been completed, addressing the dynamic temperature control, the effects of deviations in nominal temperatures and phase angles, the influences of temperature gradients, as well as the practicalities of test interruption and restart procedures. Meaningful allowable tolerances for the various test parameters were identified and practical recommendations as to the test techniques were formulated. From this a preliminary CoP was compiled and used to guide an extensive round robin exercise among the project partners. From the statistical analysis of that exercise, a validated CoP was derived dealing with strain-controlled constant amplitude TMF of nominally homogeneous metallic materials subjected to spatially uniform temperature fields and uniaxial mechanical loading. It is intended to give advice and guidance on the appropriate test setup, testing procedures and the analysis of results, in particular for newcomers in the field of strain-controlled TMF. This paper highlights some of the results of the TMF-Standard project. Moreover, commonalities and differences of the present CoP with respect to the standard documents for strain-controlled TMF, which have been developed at ISO and ASTM levels, are presented in this paper.
A major international inter-comparison exercise on strain-controlled thermo-mechanical fatigue (TMF) has been undertaken to validate a new European Code of Practice for TMF Testing and to provide underpinning information for an ISO Standard. This paper focuses on (a) distribution of samples of Nimonic 90, (b) the establishment of a protocol for testing and reporting results, and (c) the analysis of the results. Participants in the inter-comparison exercise comprised eight inner-circle partners who primarily used test pieces which were all manufactured at the same workshop, albeit of three different test piece geometries, and ten outer-circle participants who manufactured their own test pieces, of their own in-house geometry. Each participant undertook three repeat in-phase (IP) tests and three repeat out-of-phase (OP) tests. The tests were conducted at temperatures cycling between 400 °C and 850 °C, with a strain range selected to give a failure life of approximately 1000 cycles, resulting in a stress range of up to ~1000 MPa. The testing conditions were chosen following a preliminary evaluation of critical testing parameters. Results from solid circular and solid flat test piece geometries, together with hollow tubular test pieces have been compared. The influence of temperature measurement using different types of temperature sensors has also been investigated. In-house repeatability has been assessed, together with inter-laboratory reproducibility. The results have been correlated with modulus and thermal expansion data for individual tests. Initially, the largest contribution to scatter in the results was attributed to human errors in reporting the results, compounded by computer assisted cut-and-paste errors. Once these obvious discrepancies had been corrected, it was possible to use the data sets to point to some recommendations regarding testing procedures that can be incorporated into the Code of Testing Practice [Hähner P et al. Code of practice for thermo-mechanical fatigue testing TMF-Standard-Work Package 6 Report, September 2005] and provide technical underpinning for the ISO Standard. The results and the procedures used for analysis are presented.
Geosynthetic clay liners (GCLs) often have a sandwich-like multilayer structure, e.g. bentonite encased between two geotextile layers connected by fibers or yarns, either by needle-punching or stitch-bonding. Therefore, the internal shear strength of the GCL depends on the strength of reinforcing fiber bundles or yarns and their anchoring strength in the cover and carrier geotextiles. When used on long and steep slopes and covered with thick soil layers, the GCL is permanently exposed to a combined action of compressive and shear stress. Such load conditions are characteristic for landfill covers and the slope stability of the overall cover system in the long run strongly depends on the long-term internal shear strength of the GCL. A new test method was developed to study this long-term shear behavior. The focus was not only on creep, as it is normally done, but on aging effects. The shear test devices allow the measurement of creep curves and times-to-failure at elevated temperatures in different media (tap water and de-ionized water). In this publication, the main findings of the experiments on needle-punched GCLs with and without thermal treatment are summarized. Tap water as a test medium was essential to ensure sodium to calcium ion exchange in the bentonite layer. Under this condition extremely long test durations without failure were achieved. Sliding failure occurred when de-ionized water was used. Two failure modes were observed: brittle failure of the GCLs with thermal treatment and slow disentanglement of fiber bundles for untreated GCLs. Short-term shear strength (e.g. peel strength) is unrelated to the actual long-term shear strength, i.e. to the times-to-failure achieved in long-term shear strength test. Hence, short-term shear strength alone will not provide reliable dimensioning data for product design and choice of resins. Therefore, the often suggested approach, namely, restriction to short-term tests only and application of factors of safety, is challenged by these results.
Data are reported from oven aging in circulating air and water immersion tests at 80°C on various polyolefin (polyethylene (PE) and polypropylene (PP)) needle-punched nonwoven geotextiles (GTnws) and the results of these long-term tests are compared with the oxidative resistance of high-density PE geomembranes (HDPE GMs) described in a preceding paper (Polym. Degr. Stability 79(1) (2003) 161). Polyolefin fibers used in geotextiles are typically less stabilized, have a very high surface-to-volume ratio and an oriented morphology compared with HDPE GMs. Therefore, significant differences in the oxidation behavior of these products are expected which may affect their durability. Two general results can be obtained from our measurements: Firstly, while the lifetime of the HDPE GM is essentially determined by the slow loss of stabilizers, for all GTnws a rapid reduction in the oxidative induction time (OIT) and, as we conclude, in the amount of stabilizer was observed during water immersion and air aging. Secondly, the mechanical property degradation of the GTnws depended strongly on the oxidation conditions: the induction period prior to the degradation was much longer for immersion in water than for oven aging in circulating air. After antioxidant depletion, an induction time of the oxidation reaction, which depends on the draw ratio of the stretched fibers and the oxygen supply, might substantially contribute to the induction period of the mechanical property degradation of GTnws. For one PP GTnw product, a sudden reduction in the mechanical strength occurred after onset of degradation which continued rapidly until complete deterioration. For other PP samples as well as for all PE GTnws the reduction in mechanical strength proceeded slowly. Best fits were obtained by modeling the degradation process of the PE GTnws by a second-order kinetic. Using an activation energy of 60 kJ/mol (Geotextiles, Geomembranes and Related Products, Balkema, Rotterdam, 1990; Conference Proceedings of the Sixth International Conference on Geosynthetics, Industrial Fabrics Association International (IFAI), Atlanta, USA, 1998, pp. 683690; Clay Geosynthetic Barriers, Balkema, Lisse, The Netherlands, 2002, pp. 8796), lower limits of the half-live of the degradation at worst case field conditions were obtained in the range 3083 years. Some decades have to be added for the overall induction time. However, under field conditions with limited oxygen supply, the expected service lifetime might be at least half an order of magnitude longer.
Fundamentals of Tribotesting
(2000)
Tribology is an experiment-oriented branch of a complex, interdisciplinary science, in which testing plays a major role in the solution of technical problems, in the field as well as in the development of tribomaterials. Various test methods are used for this purpose, and the results are sensitive to the choice of test method and test conditions.
In this paper, the effects of test parameters on friction and wear results are considered, some selected results of model tests with different types of materials are presented, and guidelines are derived, that help improve the reliability and level of confidence of tribological tests performed in laboratories.