Papers by Keyword: Accelerated Testing

Abstract: The chloride diffusion coefficient indicates the capacity of a particular type of concrete to resist chloride penetration and is therefore used to predict the service life of a particular reinforced concrete structure exposed to environments containing this type of aggressive agent. Its experimental determination is time-dependent and time-consuming. For that reason, our study analyzes the characteristic behavior of the diffusion coefficient (D) of concretes in the saturated condition by testing higher NaCl concentrations and lower contamination ages than those used in standardized tests, in addition, the objective is to analyze the behavior of surface chloride concentration (Cs) over time. Therefore, it was concluded that for concrete dosed with pozzolanic cement, the Cs value varied with increasing tendency at higher ages. In addition, the D value obtained by the proposed method presented values ​​close to those obtained by standardized tests at contamination ages of 21 and 35 days.

Abstract: Several accelerated tests for high-strength aluminum alloys, such as ASTM G34, ASTM G85 Annex 2, and ASTM G110 can produce significantly different results in third generation aluminum lithium (Al-Li) alloys. In this study, the reason for this inconsistency is investigated by comparing the electrochemical kinetics for AA2060 to those of AA2090 as well as legacy alloy AA7075-T6, and by comparing the performance of AA2060 in ASTM G110 and ASTM G85. The corrosion potential of AA2060 was found to be higher than that of AA7075-T6 and AA2060-T8E41. Also, it was found that although ASTM G110 does not produce exfoliation in AA 2060-T3 as in ASTM G85, the type of attack observed in cross-section is very similar in both tests.

Abstract: Software reliability accelerated testing can achieve higher reliability requirement in a relatively less period of time, which is based on the strengthened operational profile. However, when using different strengthened operational profiles, the effects of software reliability accelerated testing are different and some risks should be considered. Based on experiments, two different kinds of strengthened operational profiles are compared, and the accelerated effectiveness and the risk between two profiles are also analyzed, which give a reference for practical application.

Abstract: For an copper-based composite friction material the accelerated testing effects was judged under three kinds of testing stress in this paper, that was, through the block design method and analysis, the forthright and functional judging method was given in certain extent for the accelerated testing designed by this paper. Meanwhile, the both methods about basic statistical analysis and basic accelerated life testing was used for discussing the statistical distribution laws on the experiment data which that the copper-based composite friction material were under three kinds of testing stress.

Abstract: Through test on compressive strength of concrete and mass changes, the effects of solution concentration and temperature on speed of concrete sulfate attack were investigated. The results show that, the speed of attack is accelerated with increasing concentration and temperature, as well as the decreasing of the size of the specimen, sulfate attack speed at 45 °C sodium sulfate solution soak with wet and dry cycle is insignificant difference with at 20 °C.It is suitable to adopt compressive strength as the assessing criterion of the sodium sulfate attack.

Abstract: Strategies for time-economic lifetime assessment of thermal barrier coatings (TBC) in service are described and discussed on the basis of experimental results, achieved on material systems with coatings applied by electron beam physical vapour deposition. Service cycles for gas turbine blades have been simulated on specimens in thermo-mechanical fatigue tests, accelerating the fatigue processes by an increase of load frequency. Time dependent changes in the material system were imposed by a separate ageing, where the samples were pre-oxidized prior to the fatigue test. Results of thermo-mechanical fatigue tests on pre-aged and as-coated specimens gave evidence of interaction between fatigue and ageing processes. An alternative approach is used, which is focused on the evolution of a failure relevant damage parameter in the TBC system. The interfacial fracture toughness was selected as a damage parameter, since one important failure mode of TBCs is the spallation near the interface between the metal and the ceramic. Fracture mechanical experiments based on indentation methods have been evaluated for monitoring the evolution of the interfacial fracture toughness as a function of ageing time. It was found that the test results were influenced by both changes of the interface (which is critical in service) and changes in the surrounding material.

Abstract: There is an increasing reliability concern of thermal stress-induced failures in multilevel coatings in recent years. This work reports investigations of cracking of NiCr coatings due to thermal cycling. The temperature cycling in accelerated testing was performed in three temperature range of 150, 175 and 200°C. The NiCr coatings were considered to have failed when the sheet resistance changed by 30% relative to an initial value. As the cyclic repetition of thermal shock increased, the sheet resistance of NiCr coatings increased. The Coffin-Manson equation was applied to the failure mechanism of cracking of NiCr coatings and the SEM observation of cracks and delamination in NiCr coatings due to thermal cycling agreed well with the failure mechanism.