Accelerated Aging Technique Research Articles

Effects of thermo-fatigue loading, hydrostatic pressure, and heat aging on the free-volume and crystalline structure of polypropylene-co -ethylene random copolymer pipes

Plastic pipes composed of polypropylene-co-ethylene random copolymers were subjected to accelerated aging by thermo-fatigue loading (i.e., thermal cycling using hot and cold water alternately under pressure), application of hydrostatic pressure at elevated temperatures, and heat aging in an oven. The effects of these accelerated aging techniques on the molecular and crystalline structure of the material were investigated using positron annihilation lifetime spectroscopy, Fourier-transform infrared spectroscopy, and differential scanning calorimetry. It was found that all three types of applied aging techniques decreased the size of the defects in the crystalline–amorphous interphase of the material, increased the density of these defects, and had a negligible impact on the free-volume hole size and intensity of the amorphous phase. Thermo-fatigue loading resulted in decreased lamellae thickness and lamellae thickness distribution; in contrast, hydrostatic pressure loading resulted in increased lamellae thickness and lamellae thickness distribution. The effect of thermo-fatigue loading on the chemical degradation of polypropylene was more pronounced than the effects of hydrostatic pressure and heat aging. POLYM. ENG. SCI., 55:641–650, 2015. © 2014 Society of Plastics Engineers

Thermal stability and electrical properties of dodecyl-benzene-sulfonic-acid doped nanocomposites of polyaniline and multi-walled carbon nanotubes

Electrically conductive dodecyl-benzene-sulfonic-acid (DBSA) doped polyaniline (Pani) nanocomposites were prepared with multi-walled carbon nanotubes (MWCNTs) by in situ oxidative polymerization of aniline in the presence of different amounts of MWCNTs. The stability of the nanocomposites in terms of DC electrical conductivity retention was studied in ambient atmosphere by isothermal accelerated aging and cyclic accelerated aging techniques. The MWCNT/Pani nanocomposites were observed to be thermally more stable under ambient environmental conditions than Pani. Such nanocomposites with high thermal stability may find a place as future materials for the replacement for Pani.

Accelerated weathering testing principles to estimate the service life of organic PV modules

Although polymer and organic photovoltaic modules represent a promising alternative to technologies based on inorganic semiconductors in terms of versatility and cost, reliable methods to test and improve their long-term stability in end-use environments still need to be developed. To be compatible with product development cycles and time-to-market constraints, the testing should provide data quickly enough to allow for changes in formulation and/or design. Over the last decades, various established large-scale industries have been refining approaches to estimate the service life of polymer-based materials and products. State-of-the-art methodologies rely on outdoor and laboratory accelerated aging techniques that combine factors of stress in a similar way as seen in the end-use environment, though at increased levels. However, testing procedures developed by the organic electronics industry in general and OPV in particular do not systematically apply the basic principles of accelerated testing that would ensure the reproduction of failure modes seen in real life. This paper takes a close look at the crucial components of a comprehensive test program aimed at estimating the long-term durability of OPV products.

Study of UV-aging of thermoplastic polyurethane material

In the present work, the characteristics of thermoplastic polyurethane (TPU) material exposed to artificial weathering environment for different durations were studied. The influence on (i) appearance and morphology, (ii) thermal properties and (iii) mechanical properties evolution of the material were investigated during aging. For this purpose, ultraviolet (UV) chamber was used as accelerated aging technique. Optical and scanning electron microscopy (SEM) observations revealed changes in appearance and morphology of TPU material after UV-exposure. From differential scanning calorimetry (DSC) analysis, it was mainly found that thermal properties, in terms of glass transition temperature ( T g), were affected. Changes in mechanical behaviour were equally discerned using both computer-controlled tensile testing and abrasive wear tester. The mechanical properties in bulk of the studied material displayed tow steps. The elastic modulus and the stress at 200% of strain initially decreased and then increased progressively revealing an increase in crosslink density. The tribological properties, in terms of wear resistance, were affected and this degradation became more important with UV-exposure. Furthermore, our experimental results displayed prominently that there was a competition between chain scission and crosslinking mechanisms.

Effect of UV and hygrothermal aging on the mechanical performance of polyurethane elastomers

AbstractIn this study, the effects of environmental aging on the mechanical performance of elastomeric polyurethane (PU) were investigated using two accelerated aging techniques, namely, ultraviolet (UV) and hygrothermal (HT). Samples were prepared and subjected to UV and HT exposure for a period of 5 months and removed and mechanically tested at different time intervals. Differential scanning calorimetry (DSC) was performed. A noticeable change in the chemical structure of the PU after 1 month of UV exposure was found, however, that was not the case after 1 month of HT exposure. The stress and strain to failure, tearing energy, and storage modulus were evaluated at different intervals for both aging techniques. It was found that the UV exposure caused severe degradation of the PU in comparison with the HT. A reduction of more than 98% in the tearing energy was observed for the UV‐exposed samples after 5 months when compared with only a 35% reduction in the tearing energy for the HT‐exposed samples. A similar trend was observed for tear strength and storage modulus. The degradation mechanisms of the PU elastomers have been identified using SEM and correlated with the tearing energy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Evaluation of the strand in cement (SIC) test for GRCs with improved durability

Even today the durability of glass fibre reinforced concrete composites (GRC) remains a widely studied topic. The accelerated ageing technique and the strand-in-cement (SIC) test method were developed to study the durability of GRCs in the early days. Within this paper it is shown that the standard SIC specimen preparation is not always suitable to evaluate the durability of new GRCs. A modified SIC set-up is proposed and the influence of the number of tested specimens per series on the trustworthiness of the results is discussed. Moreover, the modified SIC set-up will be used within two sequences of accelerated ageing: the first sequence of series of specimens contains an ordinary Portland cement (OPC) mixture and the second series a modified matrix. The usefulness of “accelerated ageing” is discussed and commented for both series.

The Cathedral of S. Giorgio in Ragusa Ibla (Italy): characterization of construction materials and their chromatic alteration

The Cathedral of St. Giorgio in Ragusa Ibla (Sicily) is one of the most important Baroque monuments of eastern Sicily. The restoration of the monument underway has put forward notable questions regarding the stone materials used and their state of degradation. The facade appears to be made mainly of a creamy white calcarenite, and of mortars and plasters. However, detailed analysis has highlighted a more complex use of the raw material. The mortar and plaster have a different composition in regards to their architectural use while the natural stone material is distinguished not only by a creamy-white calcarenite but also by a dark coloured bituminous calcarenite (pitch rock), which now appears whiter because of superficial chromatic alterations. This process was reproduced in the laboratory using an accelerated aging technique on samples of bituminous calcarenite, which allowed the cause of the alternation to be identified as photo-oxidation of the asphaltenes. Following this process of photo-oxidation, other forms of chromatic alterations affected the facade (brown–orange-coloured patinas). FTIR, Scanning Electron Microscope and thin section microscopic observation allowed the characterization of also the products of this process to be carried out, highlighting the complex mechanism which the processes underwent.

CF8M과 SA508 용접재의 열화에 따른 파괴인성에 관한 연구

In a primary reactor cooling system(RCS), a dissimilar weld zone exists between cast stainless steel(CF8M) in a pipe and low-alloy steel(SA508 cl.3) in a nozzle. Thermal aging is observed in CF8M as the RCS is exposed for a long period of time to a reactor operating temperature between 290 and 330℃, while no effect is observed in SA508 cl.3. The specimens are prepared by an artificially accelerated aging technique maintained for 300, 1800 and 3600 hrs at 430℃, respectively. The specimens for elastic-plastic fracture toughness tests are according to the process in the thermal notch is created in the heat affected zone(HAZ) of CF8M and deposited zone. From the experiments, the JIC value notched in HAZ of CF8M presented a rapid decrease up to 300 hours at 430℃ and slowly decreased according to the process in the thermal aging time. Also, the JIC value presented a lower value than that of the CF8M base metal. And, the JIC of the deposited zone presented the lowest value of all other cases.

Fracture Toughness with Thermal Aging in CF8M/SA508 Welds

In a primary reactor cooling system, a dissimilar weld zone exists between cast stainless steel (CF8M) in a pipe and low-alloy steel (SA508 cl.3) in a nozzle. Thermal aging is observed in CF8M as the RCS is exposed for a long period of time to a reactor operating temperature between 290 and 330, while no effect is observed in SA508 cl.3. The aged specimens are prepared by an artificially accelerated aging technique maintained for 300, 1800 and 3600 hrs at 430, respectively. The specimens for elastic-plastic fracture toughness tests are prepared two types, which notch is created in the center of deposited zone and the heat affected zone of CF8M. From the experiments, the plastic-elastic fracture toughness values (JIC) with the increase of aging time decrease as the notch is created in the HAZ of CF8M, while that is different slightly as the notch is created in the deposited zone. Also, JIC values in the deposited zones are smaller than the HAZ of CF8M at all aged specimens.

Prediction of long-term corrosion and mechanical behaviors of steel in seawater by an electrochemically accelerated aging technique

Conventional corrosion testing is a time-consuming and expensive process because it requires months or years of exposure for reliable results. Thus, it is necessary to develop a simple, fast, and accurate corrosion testing method for predicting the long-term corrosion behavior of materials. In this article, the corrosion behavior of a steel specimen equivalent to that of the same specimen exposed to seawater for 90 days was reproduced in a short time (24 h) using an electrochemically accelerated aging, technique. The results indicated that the short-term accelerated aging, test yields good qualitative and quantitative agreement with a long-term immersion test in terms of weight loss, corrosion product, and type of corrosion. Furthermore, based on the experimental results, it was possible to predict the long-term mechanical behavior of the corroded structure. The tensile 1/4 of the initial strengths, respectively.

The Study on Effects of Thermal Aging of Dissimilar Weld Zone in a Primary Reactor Cooling System

In a primary reactor cooling system(RCS), a dissimilar weld zone exists between austenitic-ferritic duplex cast stainless steel(CF8M) in a pipe and low-alloy steel(SA508 cl.3) in a nozzle. Thermal aging is observed in CF8M as the RCS is exposed for a long period of time to a reactor operating temperature between 290 and 330°C, while no effect is observed in SA508 cl.3. An investigation of the effect of thermal aging on the various mechanical properties of the dissimilar weld zone is required. The purpose of the present investigation is to find the effect of thermal aging on the dissimilar weld zone. The specimens are prepared by an artificially accelerated aging technique maintained for 100, 300, 900, 1800 and 3600 hrs at 430°C, respectively. The various mechanical tests for the dissimilar weld zone are performed for virgin and aged specimens.

Gamma Irradiation of Washi. Part 2: Changes in degree of polymerization and crystallinity of cellulose

To simulate the properties of old, i.e. naturally aged paper, so that it would be suitable for the restoration of historical paper objects, modern Japanese paper (Kozo) was subjected to accelerated ageing techniques: thermal ageing at 80°C and 60% RH over periods of 1, 2, 3 and 4 weeks, and irradiation with a cobalt 60 source with doses of 49, 98, 195 and 390 kGy over a total period of 48 hours.

Effects of thermal aging on the low cycle fatigue behavior of austenitic–ferritic duplex cast stainless steel

Thermal aging is observed in a primary reactor cooling system (RCS) made of cast stainless steel. The observation occurs when the RCS is exposed for a long period of time to a reactor operating temperature between 290 and 330°C. An investigation of the effect of thermal aging on the low cycle fatigue characteristics of CF8M is required. The purpose of the present investigation is to find the effect of thermal aging of CF8M on a low cycle fatigue life. The specimen of CF8M is prepared by an artificially accelerated aging technique maintained for 300 and 1800 h at 430°C, respectively. The low cycle fatigue tests for the virgin and two aged specimens are performed at room temperature for the strain amplitudes ( ε ta) of 0.3, 0.5, 0.8, 1.0, 1.2 and 1.5%. In the experiment, it is found that the fatigue life is rapidly reduces with an increase of aging time. The experimental fatigue life estimation formula, between the virgin and two aged specimens are obtained.

Standardisation of the chromatic characteristics of sobretablas wine macerates obtained by an accelerated ageing technique using heating and oak shavings

This paper presents the results of the selection and chromatic characterisation of macerates obtained from sobretablas wines and oak shavings, aged according to the method proposed and studied by our research group. This method allows considerable shortening of the time spent in barrels and represents a viable alternative to the oxidative ageing of oloroso wines from the “Jerez-Sherry” Origin Appellation (Spain). A detailed study was undertaken of the influence on chromatic characteristics of such factors as heating, maceration and exhaustion of the shavings (using water and hydroalcoholic mixtures). By using caramel colouring additive (authorised in the European Union as E-150), colour values entirely equivalent to those of commercial wines are achieved, which are not even apparent under sensorial analysis.

Durability aspects of adhesively bonded thick adherend lap shear joints

Applications for structural adhesive in a marine environment will generally involve much thicker adherends than used in some other industries. The effect of aging on adhesively bonded joints in a wet environment is particularly important for marine applications. A major concern is the sensitivity of the adhesive to the effects of water. The durability performance of thick-adherend steel lap joints and the bulk adhesive were investigated using accelerated aging techniques (30°C, 100% relative humidity). Various simple geometric factors are shown to affect joint performance. The removal of the spew fillet, the application of a stress and the joint orientation will all significantly influence durability performance. It was found that the water affects both the adhesive and the adhesive/adherend interfacial zone.

A Study on the 43$0^{\circ}C$ Degradation Behavior of Cast Stainless Steel(CF8M)(II)-Evaluation of Low Cycle Fatigue Characteristics-

A thermal aging is observed in a primary reactor cooling system(RCS) made of a casting stainless steel when the RCS is exposed for long period at the reactor operating temperature, 290~3300C An investigation of effects of thermal aging on a low cycle fatigue characteristics included a stress variations caused by a reactor operation and trip, is required. The purpose of the present investigation is to find an effect of a thermal aging of the CF8M on a low cycle fatigue life. The specimen of CF8M are prepared by an artificially accelerated aging technique holding 300 and 1800hr at 4300C respectively. The low cycle fatigue tests for the virgin and two aged specimens are performed at the room temperature for various strain amplitudes(ta), 0.3, 0.5, 0.8, 1.0, 1.2 and 1.5% strain. Through the experiment, it is found that the fatigue life is rapidly reduced with an creasing of the aging time. The experimental fatigue life estimation formulas between the virgin and two aged specimen are obtained and are proposed to a analysis purpose.

Evaluation of the thermal oxidative stability of polyimides via TGA techniques

Thermogravimetric analysis (TGA) has been used for many years to evaluate polymer thermal stability. The objective of this study is to determine if weight-loss curves from TGA and isothermal TGA (IGA) can be used to determine degradation activation energies and thus rank the thermal stability (TS) and thermooxidative stability (TOS) for selected polyimides. Two high-temperature stable addition-cured polyimides and two aromatic condensation polyimides, all four containing fluorinated connecting linkages in the dianhydride monomers, were compared. Three TGA kinetic methods (Coats/Redfern, Ingraham/Marier, Horowitz/Metzger) were used to determine the activation energy for decomposition in air. The results were then used to rank polyimide stability compared to more traditional rankings based on long-term isothermal air aging weight-loss (IWL) studies and thermal decomposition temperatures (Td) from TGA data. Use of TGA coupled to a Fourier transform infrared (TGA–FTIR) spectrophotometer allowed for the simultaneous identification and relative quantification of evolved decomposition products (CO2, CO, ArNCO, and CHF3) of the four polyimides degraded in air or nitrogen. Isothermal TGA–FTIR (IGA–FTIR) was also done in air to determine the relative rate of product evolution at a constant temperature. Activation energies using TGA and IGA data were determined and then compared with IWL values for the degradation of the polyimide to examine for correlations of real-life thermal oxidative aging to accelerated aging techniques. The Coats/Redfern method and Td were found to best reproduce stability rankings of those from long-term, high-temperature IWL studies. Together, they may provide a time-saving technique to evaluate polyimide thermal oxidative stability. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3943–3956, 1999

Evaluation of the thermal oxidative stability of polyimides via TGA techniques

Thermogravimetric analysis (TGA) has been used for many years to evaluate polymer thermal stability. The objective of this study is to determine if weight-loss curves from TGA and isothermal TGA (IGA) can be used to determine degradation activation energies and thus rank the thermal stability (TS) and thermooxidative stability (TOS) for selected polyimides. Two high-temperature stable addition-cured polyimides and two aromatic condensation polyimides, all four containing fluorinated connecting linkages in the dianhydride monomers, were compared. Three TGA kinetic methods (Coats/Redfern, Ingraham/Marier, Horowitz/Metzger) were used to determine the activation energy for decomposition in air. The results were then used to rank polyimide stability compared to more traditional rankings based on long-term isothermal air aging weight-loss (IWL) studies and thermal decomposition temperatures (Td) from TGA data. Use of TGA coupled to a Fourier transform infrared (TGA–FTIR) spectrophotometer allowed for the simultaneous identification and relative quantification of evolved decomposition products (CO2, CO, ArNCO, and CHF3) of the four polyimides degraded in air or nitrogen. Isothermal TGA–FTIR (IGA–FTIR) was also done in air to determine the relative rate of product evolution at a constant temperature. Activation energies using TGA and IGA data were determined and then compared with IWL values for the degradation of the polyimide to examine for correlations of real-life thermal oxidative aging to accelerated aging techniques. The Coats/Redfern method and Td were found to best reproduce stability rankings of those from long-term, high-temperature IWL studies. Together, they may provide a time-saving technique to evaluate polyimide thermal oxidative stability. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3943–3956, 1999

Exhaustion Techniques in the Selection and Description of Phenolic Compounds in Jerez Wine Extracts Obtained by an Accelerated Aging Technique

This paper explains the selection and description of phenolic compounds in macerated solutions of sobretablas wines and oak shavings. The aging technique proposed and studied allows a considerably shorter stay in barrels and represents a genuine alternative to the oxidative aging to which oloroso wines from the Jerez-Xeres-Sherry are usually subjected. The influence of factors such as heating, maceration, and exhaustion of oak shavings using water/alcohol mixtures on the extraction of polyphenolic compounds affecting the organoleptic, sensory, and technological characteristics of these wines was examined. Keywords: Accelerated aging; oxidative aging; oloroso wine; phenolic compounds; Jerez-Sherry

Wheat seed ageing and embryo protein degradation

AbstractWheat seed lots of different viability were obtained by an accelerated ageing technique in which seeds were hydrated up to 12.5–14.5% on a fresh weight basis and stored at 35°C. Ageing was accompanied by a progressive delay of the onset of germination and a decrease of [35S]-methionine uptake and incorporation into soluble proteins of the imbibing embryos. A detailed analysis of newly synthesized proteins by two-dimensional polyacrylamide gel electrophoresis showed that normal protein patterns during the germination process were impaired by ageing. Only two groups of polypeptides with molecular masses of 84.9–69.5 and 66.6–60.2 kDa, respectively, were actively produced while most proteins decreased or were definitely degraded. Our results suggest that the biochemical changes required for germination are gradually opposed by a deterioration process and that some newly-synthesized polypeptides can be taken as markers in assessing seed survival of ageing stress.