Accelerated Aging Studies Research Articles

Analyses on Electrical-Mechanical Characteristics of Environment-friendly Transformer Insulating Material by Accelerated Thermal Aging

Aging of transformer insulating material in natural ester insulating oil is compared to that in conventional transformer oil. Aging of insulating paper and insulating oil have been studied by performing accelerated thermal aging test. Sealed aging test vessels containing cooper, laminated core, Kraft paper and insulating oil(natural oil or mineral oil) were aged at for 500, 1000, 1500 and 2000 hours. Insulating oils after aging are investigated with total acid number, breakdown voltage and viscosity. Also, degradation of insulating paper after aging is determined using breakdown voltage and mechanical strength. Accelerated aging studies demonstrate a slower aging rate for natural ester insulating oil compared to the rate for conventional mineral oil.

Predicting the lifetime of fluorosilicone o-rings

Long-term (up to 1000 days) accelerated oven-aging studies on a commercial fluorosilicone o-ring seal are used to predict the sealing lifetime at room temperature (23 °C). The study follows force decay (relaxation) on squeezed o-ring material using isothermal compression stress relaxation (CSR) techniques. The relaxation is normally a complex mix of reversible physical effects and non-reversible chemical effects but we utilize an over-strain approach to quickly achieve physical equilibrium. This allows us to concentrate the measurements on the chemical relaxation effects of primary interest to lifetime assessment. The long-term studies allow us to access a fairly broad temperature range (80–138 °C) which results in improved modeling of the temperature dependence of the accelerated data. Non-Arrhenius behavior is observed with evidence of a significant lowering of the activation energy at the lowest accelerated aging temperature (80 °C). This observation is consistent with numerous recent accelerated aging studies that probed temperature ranges large enough to observe similar non-Arrhenius behavior. The extrapolated predictions imply that significant loss of sealing force requires on the order of 50–100 years at 23 °C. Field aging results out to ∼25 years at 23 °C are shown to be in reasonable accord with the significant change in Arrhenius slope observed from the accelerated aging study.

Decay of electrical conductivity in p-toluene sulfonate doped polypyrrole films

Long term performance of conductivity of p-toluene sulfonic acid (pTSA) doped electrochemically synthesized polypyrrole (PPy) films was estimated from accelerated aging studies between 80 °C and 120 °C. Conductivity decay experiments indicated that overall aging behavior of PPy films deviated from first order kinetics at prolonged aging times at elevated temperatures. However, an approximate value for the activation energy of the conductivity decay of PPy was calculated as E=47.4 kJ/mol, enabling an estimate of a rate constant of k=8.35×10−6/min at 20 °C. The rate of decrease of conductivity was not only temperature dependent but also influenced by the dopant concentration. A concentration of 0.005 M pTSA in the electrolyte resulted in a conductive film and when this film was exposed to 120 °C for a period of 40 h, the conductivity decayed to about 1/20 of its original value. The concentration of pTSA was increased to 0.05 mol/l and when the resulting film was aged in the same way, it showed a decrease in the conductivity to about 1/3 of its original value. Both microwave transmission and dc conductivity data revealed that highly doped films were considerably more electrically stable than lightly doped films. The dopant had a preserving effect on the electrical properties of PPy.

Neuro-detector Based on Coherence Analysis for Stator Insulation in Electric Motors

This research describes the monitoring of the fundamental spectral features of stator insulation damage through accelerated aging studies for induction motors with a power rating of 5 HP. In order to accomplish this goal, even-harmonic values of the line frequency defined between the 4th and the 16th harmonics, which are computed by the coherence approach between the stator currents and vibration signals, are determined as indicators of stator insulation damage. After this determination, a neuro-detector based on the auto-associative neural structure is trained in the frequency domain. This uses coherence variations and even-harmonic values as indicators of the insulation damage of an induction motor by observing the changes in the errors (residuals) generated by the neural net.

A 4-Month Accelerated Aging Study of Geomembranes Exposed to Landfill Leachate

The accelerated aging of High Density Polyethylene geomembranes exposed to the leachate obtained from the municipal landfill of a suburb of Athens (Ano Liosia), was studied at 50°C for 4 months. The change of properties as a function of aging was assessed after 30, 60, 90, and 120 days immersion, via Tensile testing, Differential Scanning Calorimetry, ATR Spectroscopy, Hardness, and Melt Flow Index measurements. From the obtained results, it appeared that minor changes of the above properties take place under the experimental conditions of our study.

Accelerated aging study of ultra high molecular weight polyethylene yarn and unidirectional composites for ballistic applications.

Accelerated aging study of ultra high molecular weight polyethylene yarn and unidirectional composites for ballistic applications.

Compact Disc Service Life Studies by the Library of Congress

This paper reports on research studies conducted by the Library of Congress (LC) on the factors affecting the service life of compact discs.A natural aging pilot study was initiated in 1996 as part of a plan to formulate a strategy to preserve the Library's growing collection of music on CD by periodic monitoring of the condition of the discs. After 10 years of testing the original sample set of 125 discs at selected intervals the study was expanded to include 1050 more discs to achieve a more representative sampling of the Library's collection to date. Sampling, testing, storage, and data analysis for both studies are discussed.Two accelerated aging studies were conducted to explore the mechanisms of optical disc degradation. The first study used a single stress condition to evaluate the effect of security labels on CDs. The second study used multiple elevated stress conditions to observe the differences in disc failure rates in a heterogeneous population, and to evaluate the effect of laser engraving a property stamp on the disc. The initial Block Error Rate (BLER) and its rate of change was used as the indicator of service life, with the value of 220 per second signaling the end-of-life. Observations of physical degradation on both a macro and micro scale and their effect on disc life are included.Aluminum oxidation is widely considered to be the primary cause of disc deterioration. Results of the accelerated aging studies suggest that several factors are at work. Initial work to correlate life expectancy with chemical composition is described.

Lifetime predictions for semi-crystalline cable insulation materials: I. Mechanical properties and oxygen consumption measurements on EPR materials

Long-term accelerated aging studies (up to 7 years of aging) were conducted on four typical EPR materials used as cable insulation in nuclear power plant safety applications with the goal of establishing lifetime estimates at typical aging conditions of ∼50 °C. The four materials showed slow to moderate changes in mechanical properties (tensile elongation) until just before failure where abrupt changes occurred (so-called “induction-time” behavior). Time–temperature superposition was applied to derive shift factors and probe for Arrhenius behavior. Three of the materials showed reasonable time–temperature superposition with the empirically derived shift factors yielding an approximate Arrhenius dependence on temperature. Since the elongation results for the fourth material could not be successfully superposed, consistency with Arrhenius assumptions was impossible. For this material the early part of the mechanical degradation appeared to have an Arrhenius activation energy E a of ∼100 kJ/mol (24 kcal/mol) whereas the post-induction degradation data had an E a of ∼128 kJ/mol. Oxygen consumption measurements were used to confirm the 100 kJ/mol E a found from early-time elongation results and to show that the chemistry responsible before the induction time is likely to remain unchanged down to 50 °C. Reasonable extrapolations of the induction-time results indicated 50 °C lifetimes exceeding 300 years for all four materials.

Nylon 6.6 accelerated aging studies: thermal–oxidative degradation and its interaction with hydrolysis

Accelerated aging of Nylon 6.6 fibers used in parachutes has been conducted by following the tensile strength loss under both thermal–oxidative and 100% relative humidity conditions. Thermal–oxidative studies (air circulating ovens) were performed for time periods of weeks to years at temperatures ranging from 37 °C to 138 °C. Accelerated aging humidity experiments (100% RH) were performed under both an argon atmosphere to examine the ‘pure’ hydrolysis pathway, and under an oxygen atmosphere (oxygen partial pressure close to that occurring in air) to mimic true aging conditions. As expected the results indicated that degradation caused by humidity is much more important than thermal–oxidative degradation. Surprisingly when both oxygen and humidity were present the rate of degradation was dramatically enhanced relative to humidity aging in the absence of oxygen. This significant and previously unknown phenomena underscores the importance of careful accelerated aging that truly mimics real world storage conditions.

Accelerated-Aging Studies of Chirped Bragg Gratings Written in Deuterium-Loaded Germano-Silicate Fibers

Accelerated-aging studies of chirped Bragg gratings written in deuterium-loaded germano-silicate fibers were carried out using isothermal and continuous isochronal anneal methods. The master aging curve obtained from the isothermal decay is explained using the Arrhenius-rate-model-based equation. An empirical polynomial function was used to fit the continuous isochronal anneal data. The estimated attempt frequency (n) values from the two anneal methods were found to agree well within error. Further, the model-based calculations were found to predict postanneal long-term behavior of the gratings extremely well. Implications of the two anneal methods to accurately predict the thermal stability of chirped fiber Bragg gratings are discussed in light of rapid and reliable qualification of different types of gratings written in different fibers.

Studies of the thermal degradation of acetaminophen using a conventional HPLC approach and electrospray ionization-mass spectrometry.

The thermal degradation of acetaminophen is studied via conventional accelerated aging studies by initially thermally stressing the compound at temperatures between 160 degrees C and 190 degrees C and measuring the rate of decomposition by reversed-phase high-performance liquid chromatography. Rates of decomposition of the compound in the dry state and the activation energy for the process are determined and compared with previously published kinetic and thermodynamic data for the degradation of acetaminophen in solution. In addition, the thermal fragmentation of acetaminophen under electrospray ionization (ESI) conditions using an interface with a heated capillary inlet is studied and the apparent activation energy for this process also is characterized. A comparison of the data shows that acetaminophen is significantly more stable in the dry state than in solution. However, the gas-phase fragmentation of acetaminophen under ESI conditions occurs more readily than either dry- or solution-state degradation. Although the resulting electrospray fragmentation mimics the breakdown product that is formed when the compound undergoes either acid or base catalyzed hydrolysis in aqueous solutions, the mechanism that produces the fragment ion appears to involve a two-step process. Initially, the parent ion forms of the analyte are produced in the spray region of the interface followed by wall-catalyzed decomposition and re-ionization in the heated inlet capillary of the spectrometer.

SuperLig ® 644 resin accelerated aging study

SuperLig® 644 resin was exposed to simulated Hanford waste solution under air atmosphere or in protated inert environment, and in 0.5M HNO3 solution for 15 days and 45 °C. The degradation was evaluated by cesium batch distribution measurement.

Shelf Life Prediction of Propellants Using a Reaction Severity Index

Shelf life predictions for solid rocket propellant formulations depend upon the existence of a reliable and efficient accelerated aging method. Results presented in this paper demonstrate the failure of simple models like Arrhenius to predict the aging behavior of some composite propellants. This work proposes a new approach for accelerated aging studies of the degradation of the polymeric binder in such propellant formulations. Using a reaction severity index, simple kinetic models have been demonstrated to adequately model the degradation behavior of various propellants submitted to isothermal aging. Furthermore, the versatility of the method allows shelf life predictions for samples experiencing temperature cycles during aging.

The influence of inert packaging on the shelf ageing of gamma-irradiation sterilised ultra-high molecular weight polyethylene

Ultra-high molecular weight polyethylene (UHMWPE) is used for wear applications in total hip prostheses and total knee prostheses. Sterilisation of these prostheses is commonly by gamma-irradiation. This process creates reactive free radicals in the UHMWPE, greatly increasing its susceptibility to oxidative degradation. This study has investigated the influence of air and vacuum packaging on the properties of gamma-irradiated UHMWPE (GUR1050) following 3 years of shelf ageing. The findings indicate that vacuum packaging minimises oxidative degradation reactions that occur for UHMWPE during shelf ageing. However, gamma-irradiation of vacuum-packaged UHMWPE promotes a degree of cross-linking. It is proposed that this may enhance the wear performance of UHMWPE. Accelerated ageing studies indicate that 3 years of shelf ageing would also seem to reduce the susceptibility of gamma-irradiated UHMWPE to oxidative degradation upon removal from its vacuum packaging.

Accelerated aging studies of UHMWPE. II. Virgin UHMWPE is not immune to oxidative degradation.

In Part I of this series, we showed that aging at elevated oxygen pressure is more successful at increasing the depth to which degradation occurs although it, too, generally causes greater degradation at the surface than at the subsurface. Therefore we hypothesized that thermal degradation alone, in the absence of free radicals, could be sufficient to artificially age UHMWPE in a manner analogous to natural aging. In the present study, virgin and air-irradiated UHMWPE (extruded GUR 1050 and compression-molded 1900) were aged up to 4 weeks at elevated oxygen pressure, and the mechanical behavior at the surface and subsurface was examined. All the materials were substantially degraded following 4 weeks of aging, but the spatial variations in the nonirradiated materials more closely mimicked the previously observed subsurface peak of degradation seen in naturally aged UHMWPE following irradiation in air. This aged material could provide a more realistic model for subsurface mechanical degradation, making it suitable for further mechanical testing in venues such as wear simulation.

Accelerated aging studies of UHMWPE. I. Effect of resin, processing, and radiation environment on resistance to mechanical degradation.

The resin and processing route have been identified as potential variables influencing the mechanical behavior, and hence the clinical performance, of ultra-high molecular weight polyethylene (UHMWPE) orthopedic components. Researchers have reported that components fabricated from 1900 resin may oxidize to a lesser extent than components fabricated from GUR resin during shelf aging after gamma sterilization in air. Conflicting reports on the oxidation resistance for 1900 raise the question of whether resin or manufacturing method, or an interaction between resin and manufacturing method, influences the mechanical behavior of UHMWPE. We conducted a series of accelerated aging studies (no aging, aging in oxygen or in nitrogen) to systematically examine the influence of resin (GUR or 1900), manufacturing method (bulk compression molding or extrusion), and sterilization method (none, in air, or in nitrogen) on the mechanical behavior of UHMWPE. The small punch testing technique was used to evaluate the mechanical behavior of the materials, and Fourier transform infrared spectroscopy was used to characterize the oxidation in selected samples. Our study showed that the sterilization environment, aging condition, and specimen location (surface or subsurface) significantly affected the mechanical behavior of UHMWPE. Each of the three polyethylenes evaluated seem to degrade according to a similar pathway after artificial aging in oxygen and gamma irradiation in air. The initial ability of the materials to exhibit post-yield strain hardening was significantly compromised by degradation. In general, there were only minor differences in the aging behavior of molded and extruded GUR 1050, whereas the molded 1900 material seemed to degrade slightly faster than either of the 1050 materials.

Evaluation of Desorption/Ionization Mass Spectrometric Methods in the Forensic Applications of the Analysis of Inks on Paper

Fast atom bombardment and laser desorption mass spectrometry (LDMS) provide molecular level information concerning an ink's composition. Two ink-jet printer inks, Ink A containing the cationic dye Methyl Violet 2B, and Ink B containing the anionic dye, Solvent Black, were studied. Both positive and negative ion detection modes of the mass spectrometer were used. LD may be used for the analysis of inks on paper. Once on paper, the ink's solvent system has evaporated, leaving mainly the dyes behind, which are detected using LDMS. An ink fades with time, indicating that the dyes are degrading. Preliminary results from an accelerated aging study of ballpoint pen ink using UV irradiation confirm that dye degradation products are formed. The degradation chemistry follows an oxidative demethylation process for which all products formed are detected using LDMS. Results suggest that LDMS may be developed to determine the relative age of inks.

Stroke Risk Profile Predicts Brain Volume and Cognitive Function in Stroke-free Subjects: The Framingham Study

30 Background: The contribution of stroke risk factors to the pervasive brain atrophy and cognitive impairment seen with aging is controversial. This is partly due to a paucity of longitudinal data in stroke-free subjects. We hypothesize, that even in subjects who remain free of clinical stroke, exposure to stroke risk factors may adversely impact brain volume. Objective: To prospectively examine the association of Framingham Stroke Risk Profile (FSRP) scores at baseline with MRI brain volume on follow-up, and to further evaluate the association of brain volume with cognitive function, in a population-based cohort of stroke- and dementia-free subjects. Methods: Framingham Offspring Study subjects were evaluated for stroke risk factors at exam 5 (1991–1995). A sex-specific, composite FSRP score was calculated for each subject, as validated in prior studies. 909 subjects (age range 42–82, mean age: 61 years, 427 men), who remained free of clinical dementia and stroke, underwent quantitative MRI imaging and neuropsychological evaluation, 4 to 9 years later (1999–2000). Using linear regression models adjusted for age and sex, we examined the association between the FSRP score and Total Cerebral Brain Volume- TCBV (expressed as a ratio of total cranial volume). We also evaluated the association of TCBV with age- and education- adjusted scores on a battery of neuropsychological tests administered at the time of imaging. Results: There was a strong inverse association between TCBV and the FSRP score (p=0.002). TCBV also showed a significant positive association with performance on tests of manual dexterity (e.g. finger tapping; p 0.05). Conclusion: An adverse stroke risk profile predicted lower MRI brain volume, which in turn was associated with poorer performance on specific neuropsychological tests suggestive of vascular cognitive impairment. Pathogenetic mechanisms for these associations in stroke-free subjects could include various vascular causes for accelerated brain aging and merit further study.

Accelerated aging studies of multi-section tunable GCSR lasers for dense WDM applications

The first accelerated aging study of wavelength tunable packaged sampled grating reflector (GCSR) lasers is reported. Stable power and SMSR were observed during the 5000 hours of operation at elevated temperatures. Frequency shifts of the selected lasing channels were characterized to access potential failures in an optical network. A longer burn-in was found to significantly reduce the amount of the observed shifts, and hence increase the reliability of the device. The effective room-temperature lifetime of GCSR is estimated to be 13.4 y. A new end-of-life criteria is also proposed.

Accelerated aging of annealed proton-exchanged waveguides

Low temperature hydrogen diffusion in annealed proton-exchanged (APE) waveguides has the potential of degrading device performance over a period of several years. An accelerated aging study was performed in order to determine its impact on device performance. The effect of aging was modeled as a second anneal. Both planar waveguides and Y-fed balanced-bridge modulator (YBBM) devices were aged at elevated temperatures. The hydrogen concentration profile of the planar waveguides was measured after aging with secondary ion mass spectrometry (SIMS) and compared to the profile from a control sample. The YBBM characteristics were measured as a function of aging time as well. Measured activation energies indicate that hydrogen diffusion is the dominant aging mechanism in the YBBM. Extrapolations indicate that device degradation is negligible at temperatures of 95/spl deg/C or below. An operating/storage temperature as high as 125/spl deg/C can be sustained for 13 years with little effect. A method for determining the effect of aging on any device is outlined.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>