Inherent variability in accelerated weathering devices

Fischer, Richard M.; Ketola, Warren D.; Murray, William

doi:10.1016/0033-0655(91)80005-4

Cited by 27 publications

(8 citation statements)

References 3 publications

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“…For example, the temperature governing the rate of degradation of a polymeric material is the temperature of the test specimen and not ambient temperature. Although it is relatively simple to monitor specimen temperature in the laboratory, such direct measurements are seldom practical in the field (an exception to this is the work of Fischer et al [1991a]). As shown by eq (33) in section 4.2.2, the temperature of a coated specimen is not directly related to ambient temperature [Saunders et al, 1990], the most common variable used in characterizing temperature in outdoor environments.…”

Section: 4mentioning

confidence: 99%

Methodologies for predicting the service lives of coating systems

Martin¹

1994

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EXECUTIVE SUMMARYOver the last two decades, the organic coatings industry has undergone rapid technological and structural changes. These changes have been induced by legislative actions such as restrictions pertaining to hazardous chemicals, toxic effluents, and volatile organic compounds. The consequence of these changes has been the displacement of almost all commercially-important, well-established coatings (largely highsolvent coatings) by newer systems, the formulation and application of which arc based on different chemistries and technologies. Unlike the displaced coatings, however, the new coatings do not have performance histories and the only accepted method for generating performance data is through an extensive outdoor exposure program. Since outdoor exposure results typically take five years to obtain, a desperate need exists for a methodology which is capable of generating timely, accurate, and reliable service life estimates of a coating system. This report reviews the attributes of the service life prediction problem which are common to all materials, components, and systems in an effort to establish a set of criteria for assessing the adequacy of existing or proposed service life prediction methodology for coating systems. The current durability methodology and the reliability-based methodology are then evaluated against these criteria.The proposed cnteria include the ability to 1) handle high variability in the time-to-failure data for nominally identical coated panels exposed in the same service environment, 2) analyze multivariate and censored time-to-failure data, 3) establish a connection between laboratory and field exposure results, and 4) quantitatively predict the service life of a coating system exposed in its intended service environment.The current durability methodology was developed prior to the recognition of the proposed criteria and, as such, was not designed to satisfy these criteria. Efforts to correct its deficiencies have been made over the last 80 years, but success has been elusive. The failure of the current methodology has generally been ascribed to inadequacies in laboratory-based aging tests, specifically, the inability to simulate weathering conditions in the laboratory. However, we suggest that the failure of the current methodology can be attributed to its being based on faulty premises, inadequacies in experimental design, and the lack of reproducibility of the weather over any time scale.An alternative, reliability-based methodology is reviewed and assessed. This methodology has a strong theoretical basis plus a history of successful applications in the electronics, medical, aeronautical, and nuclear industries. A number of experiments with coatings has already been conducted using this methodology. The results indicate that this methodology can be applied in predicting the service life of coating systems and that it satisfies the proposed service life prediction criteria. Implementation of a reliability-based methodology will require substantial changes in the cu...

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Section: 4mentioning

confidence: 99%

Methodologies for predicting the service lives of coating systems

Martin¹

1994

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“…In contrast, this form for relative humidity dependence is one of many forms of equal probability of being correct [16]. Furthermore, as shown in [1] and [2], humidity may have no effect, a large positive effect, or a negative effect on degradation rates for paints and coatings. If the degradation process produces water as a byproduct in the rate-determining step, the presence of moisture can actually slow down degradation [17].…”

Section: B Uv Aging 1) Modeling Fit Equationsmentioning

confidence: 99%

“…For temperature and irradiance, the Arrhenius form used here is very common and it requires atypically accurate and comprehensive data to be able to determine that a different form is more appropriate [1]. In contrast, this form for relative humidity dependence is one of many forms of equal probability of being correct [16].…”

Section: B Uv Aging 1) Modeling Fit Equationsmentioning

confidence: 99%

Highly Accelerated UV Stress Testing for Transparent Flexible Frontsheets

Kempe

Hacke

Morse

et al. 2023

IEEE J. Photovoltaics

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For flexible photovoltaic (PV) applications, the dominant material for the frontsheet is poly(ethylene-cotetrafluoroethylene). As a fluoropolymer, it resists soiling by letting the water run off easily, is resistant to degradation by exposure to ultraviolet light, and is more mechanically durable than most fluoropolymers. To keep costs down, less expensive alternative polymers are desirable. In this study, highly accelerated ultraviolet light and heat stresses are applied to candidate materials, and the degradation kinetics are determined to provide information to evaluate their suitability for use in a PV application. Because of the uncertainty in service life prediction, the acceleration parameters are instead used primarily to evaluate the relevance of the applied stresses. Here, we find that the best materials are fluoropolymer based and that even when exposed to high irradiance at high temperatures, relatively little degradation is seen. For the 15 materials tested here, we found the Arrhenius activation energy for various degradation processes to be 39 ± 22 kJ/mol with a power law dependence on irradiance of 0.49 ± 0.22 with a negative correlation coefficient of −0.606 (i.e., more highly thermally activated processes are less dependent on the irradiance level). For frontside exposure, the most severe conditions used here (4 W/m 2 /nm @340 nm, 70 °C, for 4000 h) were on average equal to about 11.4 y in Riyadh, Saudi Arabia when mounted with insulation on the backside. Thus, to get relevant amounts of ultraviolet exposure with unmodified commercial equipment (∼0.8 W/m 2 /nm @340 nm) requires extraordinarily long exposure times, especially if conducted at lower irradiance levels.

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“…Differences in the spectral power distribution of the light source, surface temperature, and moisture stresses, both within and between (17). Variability in laboratory-accelerated exposure testing is not limited to carbonarc exposures or to graphic or retroreflective sheetings.…”

Section: Variability In Laboratory-accelerated Weathering Tests Of Rementioning

confidence: 99%

“…Paper No. 99-0702 67 different devices running the same test cycle, are major sources of variability in laboratory-accelerated exposure tests (17). Variability in laboratory-accelerated exposure testing is not limited to carbonarc exposures or to graphic or retroreflective sheetings.…”

Section: Ketolamentioning

confidence: 99%

Laboratory-Accelerated Versus Outdoor Weathering for Retroreflective Sheeting Specifications

Ketola

1999

Transportation Research Record: Journal of the Transportation R

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Laboratory-accelerated weathering tests are used instead of outdoor weathering tests in specifications for products intended for long-term outdoor use because they provide fast results. These accelerated tests are used as a measure of acceptable weathering performance for a material. Acceptance of results from laboratory-accelerated tests in product specifications is based on two major assumptions: (a) materials that pass the requirements of the laboratory-accelerated test meet outdoor durability requirements, and (b) results from laboratory-accelerated tests are much more consistent than those from outdoor exposures. Numerous examples illustrate the errors that occur when these assumptions are wrong. Material with good outdoor durability can fail to meet the requirements of a specified laboratory-accelerated test, or material with poor outdoor durability will pass the requirements of the specified laboratory-accelerated test. Between-lab variability can cause a product to be rejected by a specifier although the same test run by the supplier produced acceptable results. For retroreflective sheeting, outdoor exposures are actually more consistent than the laboratory-accelerated exposure most commonly used in specifications. To assure minimum acceptable durability, 36-mo outdoor exposures are recommended for most retroreflective sheeting specifications. However, results from these exposure tests do not predict the ultimate service life of retroreflective sheetings.

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Inherent variability in accelerated weathering devices

Cited by 27 publications

References 3 publications

Methodologies for predicting the service lives of coating systems

Methodologies for predicting the service lives of coating systems

Highly Accelerated UV Stress Testing for Transparent Flexible Frontsheets

Laboratory-Accelerated Versus Outdoor Weathering for Retroreflective Sheeting Specifications

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