Accelerated aging

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A climatic chamber, used in accelerated aging Climatic chambers.jpg
A climatic chamber, used in accelerated aging

Accelerated aging is testing that uses aggravated conditions of heat, humidity, oxygen, sunlight, vibration, etc. to speed up the normal aging processes of items. It is used to help determine the long-term effects of expected levels of stress within a shorter time, usually in a laboratory by controlled standard test methods. It is used to estimate the useful lifespan of a product or its shelf life when actual lifespan data is unavailable. This occurs with products that have not existed long enough to have gone through their useful lifespan: for example, a new type of car engine or a new polymer for replacement joints.

Contents

Physical testing or chemical testing is carried out by subjecting the product to

Mechanical parts are run at very high speed, far in excess of what they would receive in normal usage. Polymers are often kept at elevated temperatures, in order to accelerate chemical breakdown. Environmental chambers are often used.

Also, the device or material under test can be exposed to rapid (but controlled) changes in temperature, humidity, pressure, strain, etc. For example, cycles of heat and cold can simulate the effect of day and night for a few hours or minutes.

Techniques and methods

Accelerated aging employs a variety of controlled methods to replicate and speed up the effects of natural aging. These methods vary depending on the type of product, material, or environmental condition being simulated. Below are the most commonly used techniques:

Environmental Stress testing

Temperature cycling

Samples are exposed to repeated cycles of extreme heat and cold, mimicking daily or seasonal temperature fluctuations. For example, in the automotive industry, components like engines and braking systems are tested using temperature cycling to simulate real-world conditions such as hot desert climates during the day and freezing temperatures at night. In electronics, printed circuit boards (PCBs) are subjected to rapid temperature shifts to evaluate solder joint reliability and material resilience.

Thermal shock

Thermal shock refers to the rapid exposure of materials or components to extreme temperature differences over a very short period. Unlike temperature cycling, which involves gradual changes between high and low temperatures, thermal shock imposes abrupt transitions that can lead to immediate stresses within a material. This method is often used to evaluate a product's resistance to cracking, warping, or other forms of failure caused by sudden thermal gradients. [1] For example, glass or ceramic components in aerospace applications are subjected to thermal shock tests to ensure durability under high-speed atmospheric reentry conditions.

Humidity testing

- Humidity testing involves subjecting materials or products to high levels of moisture or fluctuating humidity conditions to simulate exposure to tropical, coastal, or industrial environments. This method is used to evaluate the effects of moisture on material degradation, corrosion, swelling, and overall performance. [2]

- For example, electronic devices undergo humidity testing to ensure their enclosures and seals can prevent moisture ingress, while construction materials such as wood or adhesives are tested to evaluate resistance to warping or delamination.

- Humidity testing is often conducted in combination with elevated temperatures to accelerate the effects of moisture exposure, particularly for materials like polymers, metals, and composites.

UV exposure

UV testing is a component of aging tests designed to simulate the long-term effects of ultraviolet (UV) radiation exposure on materials, products, and coatings. [3] UV radiation, a component of sunlight, is one of the primary contributors to material degradation over time. UV testing helps assess the durability and performance of materials under prolonged exposure to UV light, providing insights into their expected lifespan and identifying potential vulnerabilities.

Purpose and Applications: The primary purpose of UV testing is to evaluate the resistance of materials to photodegradation, including fading, discoloration, cracking, embrittlement, or loss of mechanical properties.

Common applications of UV testing include:

Plastics and Polymers: Assessing the weatherability of polymers used in outdoor products.
Coatings and Paints: Ensuring the durability of protective and decorative coatings exposed to sunlight.
Textiles: Evaluating the fade resistance of fabrics and dyes.


Testing Methods: Accelerated UV Testing: This approach uses specialized equipment, such as xenon arc or fluorescent UV lamps, to simulate UV radiation in a controlled environment. Common standards include ASTM G154 (fluorescent UV lamps) and ASTM G155 (xenon arc lamps). [4] [5]

Oxygen and pollutant exposure

Samples are exposed to controlled concentrations of oxygen or atmospheric pollutants (e.g., ozone or sulfur dioxide) to simulate oxidative degradation or corrosion.

Mechanical stress testing

High-speed operation

Vibration testing

Chemical stability testing

Thermal aging

Chemical exposure

Simulated use conditions

Pressure cycling

Strain testing

Combined stress testing

Validation of results

Applications

Library and archival preservation science

Accelerated aging is also used in library and archival preservation science. In this context, a material, usually paper, is subjected to extreme conditions in an effort to speed up the natural aging process. Usually, the extreme conditions consist of elevated temperature, but tests making use of concentrated pollutants or intense light also exist. [6] These tests may be used for several purposes.

There is no single recommended set of conditions at which these tests should be performed. In fact, temperatures from 22 to 160 degrees Celsius, relative humidities from 1% to 100%, and test durations from one hour to 180 days have all been used. [6] ISO 5630-3 recommends accelerated aging at 80 degrees Celsius and 65% relative humidity [7] when using a fixed set of conditions.

Besides variations in the conditions to which the papers are subjected, there are also multiple ways in which the test can be set up. For instance, rather than simply placing single sheets in a climate controlled chamber, the Library of Congress recommends sealing samples in an air-tight glass tube and aging the papers in stacks, which more closely resembles the way in which they are likely to age under normal circumstances, rather than in single sheets. [8]

Limitations and criticisms

Accelerated aging techniques, particularly those using the Arrhenius equation, have frequently been criticized in recent decades. While some researchers claim that the Arrhenius equation can be used to quantitatively predict the lifespan of tested papers, [9] other researchers disagree. Many argue that this method cannot predict an exact lifespan for the tested papers, but that it can be used to rank papers by permanence. [10] [11] A few researchers claim that even such rankings can be deceptive, and that these types of accelerated aging tests can only be used to determine whether a particular treatment or paper quality has a positive or negative effect on the paper's permanence. [12]

There are several reasons for this skepticism. One argument is that entirely different chemical processes take place at higher temperatures than at lower temperatures, which means the accelerated aging process and natural aging process are not parallel. [6] [12] [13] Another is that paper is a "complex system" [10] and the Arrhenius equation only applicable to elementary reactions. Other researchers criticize the ways in which deterioration is measured during these experiments. Some point out that there is no standard point at which a paper is considered unusable for library and archival purposes. [13] Others claim that the degree of correlation between macroscopic, mechanical properties of paper and molecular, chemical deterioration has not been convincingly proven. [10] [14] Reservations about the utility of this method in the automotive industry as a method for assessing corrosion performance have been documented [15] [16]

In an effort to improve the quality of accelerated aging tests, some researchers have begun comparing materials which have undergone accelerated aging to materials which have undergone natural aging. [17] The Library of Congress, for instance, began a long-term experiment in 2000 to compare artificially aged materials to materials allowed to undergo natural aging for a hundred years. [18]

History

The technique of artificially accelerating the deterioration of paper through heat was known by 1899, when it was described by W. Herzberg. [6] Accelerated aging was further refined during the 1920s, with tests using sunlight and elevated temperatures being used to rank the permanence of various papers in the United States and Sweden. In 1929, a frequently used method in which 72 hours at 100 degrees Celsius is considered equivalent to 18–25 years of natural aging was established by R. H. Rasch. [6]

In the 1950s, researchers began to question the validity of accelerated aging tests which relied on dry heat and a single temperature, pointing out that relative humidity affects the chemical processes which produce paper degradation and that the reactions which cause degradation have different activation energies. This led researchers like Baer and Lindström to advocate accelerated aging techniques using the Arrhenius equation and a realistic relative humidity. [6]

See also

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References

  1. ↑ John B. Wachtman (1996). Thermal Shock and Thermal Fatigue Behavior of Advanced Ceramics. Springer. doi:10.1007/978-94-015-8200-1. ISBN   978-94-015-8200-1.
  2. ↑ {Enriquez, R. and Gillen, K. T. (2005). Review of accelerated ageing methods and lifetime prediction techniques for polymeric materials (PDF) (Report). National Physical Laboratory. Retrieved 16 January 2025.{{cite report}}: CS1 maint: multiple names: authors list (link)
  3. ↑ Rabek, J.F., ed. (2016). Handbook of UV Degradation and Stabilization. Elsevier. ISBN   978-1927885574.
  4. ↑ "ASTM G154-16: Standard Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Nonmetallic Materials". ASTM International. Retrieved 18 January 2025.
  5. ↑ "ASTM G155-13: Standard Practice for Operating Xenon Arc Light Apparatus for Exposure of Non-Metallic Materials". ASTM International. Retrieved 18 January 2025.
  6. 1 2 3 4 5 6 7 8 9 "Archived copy". Archived from the original on 29 November 2014. Retrieved 19 November 2014.{{cite web}}: CS1 maint: archived copy as title (link), Porck, H. J. (2000). Rate of paper degradation: The predictive value of artificial aging tests. Amsterdam: European Commission on Preservation and Access.
  7. ↑ Bansa, H. (1992). Accelerated aging tests in conservation research: Some ideas for a future method. Restaurator 13.3, 114-137.
  8. ↑ "Accelerated Aging of Paper: A New Test (Preservation, Library of Congress)". Library of Congress . Archived from the original on 27 July 2009. Retrieved 11 August 2009., Library of Congress (2006). Accelerated aging of paper: A new test. The Library of Congress: Preservation. Retrieved 8 August 2009.
  9. ↑ Zou, X.; Uesaka, T; & Gurnagul, G. (1996). Predication of paper permanence by accelerated aging I. Kinetic analysis of the aging process. Cellulose 3, 243-267.
  10. 1 2 3 Strofer-Hua, E. (1990). Experimental measurement: Interpreting extrapolation and prediction by accelerated aging. Restaurator 11, 254-266.
  11. ↑ Bégin, P. L. & Kaminska, E. (2002). Thermal accelerated ageing test method development. Restaurator 23, 89-105.
  12. 1 2 Bansa, H. (2002). Accelerated aging of paper: Some ideas on its practical benefit. Restaurator 23, 106-117.
  13. 1 2 Bansa, H. (1989). Artificial aging as a predictor of paper's future useful life. The Abbey Newsletter Monograph Supplement 1.
  14. ↑ Calvini, P. & Gorassini, A. (2006). On the rate of paper degradation: Lessons from the past. Restaurator 27, 275-290.
  15. ↑ Hunt, Gregory (3 April 2018). "New Perspectives on Lubricant Additive Corrosion: Comparison of Methods and Metallurgy". SAE Technical Paper Series. Vol. 1. pp. 2018–01–0656. doi:10.4271/2018-01-0656.
  16. ↑ Hunt, Gregory (4 April 2017). "New Perspectives on the Temperature Dependence of Lubricant Additives on Copper Corrosion". SAE International Journal of Fuels and Lubricants. Vol. 10. pp. 2017–01–0891. doi:10.4271/2017-01-0891.
  17. ↑ Batterham, I & Rai, R. (2008). A comparison of artificial ageing with 27 years of natural ageing. 2008 AICCM Book, Paper and Photographic Materials Symposium, 81-89.
  18. ↑ , Library of Congress (2008). 100-year paper natural aging project. The Library of Congress: Preservation. Retrieved 8 August 2009.
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