Measuring and testing – Simulated environment
Reexamination Certificate
2000-03-09
2003-08-12
Noland, Thomas P. (Department: 2856)
Measuring and testing
Simulated environment
C126S685000, C359S001000, C359S720000, C359S726000, C359S733000, C359S742000, C359S853000, C374S057000
Reexamination Certificate
active
06604436
ABSTRACT:
BACKGROUND
1. Field of the Invention
The invention relates to a process for subjecting materials to accelerated irradiance exposure factors that permit about a year's worth of representative weathering to be accumulated in a period from about 3 to 10 days, under controlled weathering conditions that include several concurrent levels of temperature and/or relative humility at very high levels of natural sunlight.
In the invention process, a solar concentrator [which may include a High Flux Solar Furnace (HFSF) and an Irradiance Redistribution Guide (IRG)] is used to obtain elevated levels (25-100×) of concentrated sunlight for accelerated testing of material samples. When an IRG is used, it provides the capability of being able to modify (redistribute) the Gaussian-shaped beam from the HFSF into a more uniform profile on a sample exposure plane.
Also encompassed in the invention process for obtaining ultra-accelerated natural sunlight exposure testing is the use of reflective apparatus such as multi-step and multi-faceted concentrators and refractive apparatus such as Fresnel lens concentrators, holographic concentrators, 2D or 3D micro lens arrays, and an array of Fresnel lens facets to obtain elevated levels (25-100×) of concentrated sunlight for accelerated natural sunlight testing of material samples.
By adequately controlling sample temperatures and demonstrating that reciprocity relationships are obeyed (i.e., the level of applied accelerated stresses does not change the failure/degradation mechanism), this novel capability allows materials to be subjected to accelerated irradiance exposure factors of 25-100×, thereby permitting a year's worth of representative weathering (in terms of natural sunlight exposure) to be accumulated in from about 3 to about 10 days.
2. Description of the Prior Art
U.S. Pat. No. 4,817,447 discloses a weathering chamber using lamps and sample temperature control using cooling air. Uniform sample irradiance at accelerated levels of up to 10 suns (within the UV bandwidth) appears attainable.
A test apparatus incorporating a mirror, which rejects infrared, is disclosed in U.S. Pat. No. 4,012,954. In the '954 patent, convective cooling air and a conductively cooled substrate are also incorporated. However, although convective cooling is used, the air movement is not used to deliver humidity to the samples during exposure; rather, humidity is provided by floating the sample substrate in a water bath. Further, as in the case of U.S. Pat. No. 4,817,477, the '954 patent uses artifical light sources for exposure of the samples.
U.S. Pat. No. 3,686,940 discloses a water-cooled cylindrical mirror, which rejects infrared radiation in an ultraviolet test apparatus. In the '940 patent, natural sunlight is not used.
A solar weathering device with control of sample temperature by cooling air is disclosed in U.S. Pat. No. 4,807,247. While this patent uses natural sunlight, a sample irradiance at accelerated levels of only up to 8 suns across the complete solar spectrum is employed.
U.S. Pat. No. 5,138,892 discloses accelerated light fastness testing of materials with xenon lamps and sample temperature control using airflow. Sample irradiance at accelerated UV levels of up to 8 suns (180 W/m
2
between 300-400 nm) are attainable. This patent does not utilize natural sunlight in its testing of materials.
A weather test machine using xenon lamps and sample temperature and humidity control using airflow is disclosed in U.S. Pat. No. 5,646,358. Uniform sample irradiance at accelerated levels up to 1-3 suns (within the UV bandwidth) is attainable. This patent does not utilize natural sunlight in its weather test machine.
U.S. Pat. No. 5,153,780 discloses a dish reflector and method for concentrating moderate solar flux uniformly on a target plane, said dish having stepped reflective surface characterized by a plurality of ring-like segments arranged about a common axis, each segment having a concave spherical configuration.
3. The Need for Capabilities Beyond the Prior Art
There is a need for devising facilities for ultra-accelerated natural sunlight exposure testing of materials and devices under controlled weathering conditions that include several concurrent levels of temperature and/or relative humidity at very high levels of natural sunlight. This need is associated with the desirability to be able to predict the in-service lifetimes of said materials and devices from correlation's derived between such realistically accelerated test results and those obtained during normal use conditions. Further, there is a need to conduct these ultra-accelerated exposure tests at irradiance exposure factors of from about 25 to 100 suns, wherein the irradiance is highly uniform. The need to conduct these ultra-accelerated natural sunlight exposure tests of materials and devices should exclude artificial light sources which invariably introduce uncertainties regarding realistic spectral content of the irradiance stress on samples being exposed. For example, the use of artificial light leads to unrealistic degradation mechanisms and failure modes of exposed materials caused by low wavelength (<300 nm) photons that are not present in terrestrial solar spectra.
SUMMARY OF THE INVENTION
In light of the drawbacks of the foregoing prior art, a general object of the present invention is to provide the unique capability to carry out ultra-accelerated exposure testing of materials and devices under controlled conditions that include several concurrent levels of temperature and/or relative humidity at very high levels of natural sunlight, thereby permitting about a year's worth of representative weathering, in terms of natural sunlight exposure, to be accumulated in from about 3 to about 10 days.
A further object of the present invention is to provide ultra accelerated exposure testing of materials and devices by controlling sample temperatures and humidities and demonstrating that reciprocity relationships are obeyed (i.e., level of applied accelerated stress does not change failure/degradation mechanism).
A yet further object of the present invention is to provide ultra-accelerated exposure testing of materials and devices that allows materials to be subjected to accelerated irradiance exposure factors of 25-100× to provide about a year's worth of representative weathering, in terms of natural sunlight exposure, to be accumulated in from about 3 to about 10 days.
A still further object of the invention is to provide a method of carrying out ultra-accelerated exposure testing of materials and devices utilizing a sample chamber that allows control of temperature and humidity during light exposure; wherein concentrated sunlight enters the chamber through an appropriate window, which may include quartz.
A further object yet still of the invention is to provide a method for carrying out ultra-accelerated exposure testing of materials and devices utilizing a cold mirror as a filter that reflects the ultraviolet/visible (UV/VIS) and transmits the near infrared (NIR) part of the solar spectrum, since the short wavelength (UV) light has been shown to be the predominant deleterious stress experienced by materials and devices during outdoor weathering.
Another object of the present invention is to provide a method of carrying out ultra-accelerated exposure testing of materials and devices under controlled weathering conditions, wherein conductive cooling of sample materials is provided by a water cooled substrate on to which samples are placed, and convective cooling is provided by blowing moist or dry air over the top surface of the samples, to provide high or low humidity to the samples during exposure of redirected concentrated sunlight into the exposure chamber to reduce the thermal load on the samples.
The invention is accomplished by the steps of: utilizing a solar concentrator to obtain elevated levels (25-100×) of concentrated sunlight with a uniform flux profile on the materials or samples being tested; sp
Jorgensen Gary J.
Lewandowski Allan A.
Midwest Research Institute
Noland Thomas P.
White Paul J.
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