The NIST Accelerated Weathering Laboratory provides researchers with well-quantified accelerated aging environments, using a unique SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) device. The SPHERE can expose materials to UV, under controlled temperature, relative humidity and strain. Development of reliable performance data requires accelerated weathering exposure equipment capable of conducting controlled, repeatable and precise accelerated aging experiments. These experiments are essential to developing performance models for service life and durability. Developing measurement science tools for service life prediction such as, validation studies, material degradation investigations and advances in weathering and durability standards and codes are essential for producing new durable materials for resilient infrastructure. This technology has reached maturity and will be modified to be transferred from NIST to industry.
Objective - To maintain, improve and expand capabilities at the NIST Accelerated Weathering Laboratory (AWL) to conduct safe, accurate and traceable aging experiments and to enable transfer of the SPHERE technology to industrial stakeholders.
What is the new technical idea? A NIST Accelerated Laboratory (AWL) has been developed to deliver the best in the world, NIST traceable weathering measurement technology to stakeholders. Current commercial technology for accelerated weathering includes design and engineering innovations to improve irradiance light exposure uniformity, airflow, temperature and relative humidity control.[ “Buyers Guide: Accelerated Weathering.” Coatings World Magazine. Online. Accessed May 15, 2017; http://www.coatingsworld.com/buyersguide/laboratory-equipment/accelerat…; “Laboratory Apparatus and Testing Equipment.” JCT Coatings Tech., November-December 2013; Atlas Material Testing Technology LLC (Chicago, Illinois); Q-Lab Corporation (Westlake, OH)] Although commercial weathering devices are dominated by xenon arc lamp systems and traditional mercury lamps, the integrating sphere technology used in NIST weathering devices provides the highest uniformity and intensity of UV irradiation and the electrode-less microwave-energized mercury arc lamp provides more stability.[ “Ultraviolet Chambers Based on Integrating SPHERES for Use in Artificial Weathering” J. W. Chin, E. Byrd, N.Embree, J.Martin, J.D. Tate, J. Coatings Tech., 2002, 74(929), 39.] Furthermore, the SPHERE has novel environmental chambers, that have precise control of temperature and relative humidity. Some NIST environmental chambers also offer mechanical stress in tension or compression.
The AWL can be used to conduct accelerated weathering experiments on material systems used in construction, support advances in weathering metrology capabilities, facilitate the transfer of UV integrating sphere exposure technology, enable service life prediction model validation and promote advances in standards and codes. The AWL is composed of the NIST 2m SPHERE, the 0.25 m sphere 6-port device, the 0.25 m strain SPHERE, and hygrothermal test chambers (no UV component). To meet the needs of researchers using the AWL (both NIST staff and external collaborators), a focus is placed on improving operational capabilities of these accelerated weathering devices. The 2m SPHERE has been operating for over 15 years and is heralded as a benchmark for the sphere technology such that its well-documented environmental conditions (temperature, UV, and relative humidity) data will be used to validate any new sphere devices. New data acquisition and access methods will be developed to improve the measurement and safety systems in the AWL. Extensive SPHERE irradiance calibration using a new spectral radiometer system will be completed to maintain accurate irradiance values for all weathering devices and provide a commercial irradiance measurement system. Statistical methods for uncertainty analysis and computational modeling will be used to systematically examine and improve the accuracy and control of all devices. Current NIST methodologies used for generating weathering data will be developed into standardized test methods and utilized to provide publicly available reference data for weathering experiments. Technology transfer consists of developing the capability of two smaller, economical SPHERE devices: 1) the 6-port Multi-port Uniform Ultraviolet Solar Irradiance Chamber (MUUSIC) system and 2) the NIST strain SPHERE. Both systems represent design improvements in SPHERE technology and support inter-laboratory testing of available weathering devices. The project will focus on developing validation protocols to confirm these two new devices performance against the current 2m SPHERE.
What is the research plan? The research plan is divided in three goals: 1) maintain and improve operation of the NIST 2m SPHERE to support current research and achieve 90 % operation time, 2) attain full operation of the 6-port MUUSIC system complete with functioning environmental chambers, and 3) attain full operation of NIST strain sphere.
The AWL will continue to improve operations by upgrading control systems and implement a maintenance logging program for the NIST 2m SPHERE and hygrothermal chambers so that internal and external projects can efficiently continue. The SPHERE needs to operate at temperatures and relative humidities up to 85 °C and 60 % RH, respectively. It was found that elements in the devices prematurely fail under these harsh conditions. Thus, solutions are needed to ensure reliability of all elements under all conditions. A validated safety system for the AWL will be developed. The safety system is a series of electronic interlocks to protect the facilities, samples, and users from over-temperature, chamber water overflow, and loss of experimental control.
Metrology and technical support for benchmarking new SPHERE devices will be provided: 6-port MUUSIC system and the NIST strain SPHERE. New instrumentation, data acquisition systems, and test fixtures will be developed and maintained, including installation and functional testing of the weathering devices and safety systems. Benchmarking and validation of the 6-port MUUSIC system and the strain sphere by accurate irradiance measurements and comparing reciprocity data with NIST 2m SPHERE at room temperature and dry conditions will also be completed.
This data is critical in validating the operation of these devices for industrial stakeholders. Furthermore, a management system for capture and sharing of environmental conditions (temperature and relative humidity(RH)) and irradiance data will be verified. Improved environmental chambers for 6-port MUUSIC system will be assembled and validated. A new system to control the temperature and RH for the strain SPHERE will be added and validated.
Finally, a database package for environmental (temperature, relative humidity and ultraviolet) data will be completed for internal and for future public use. In addition, a program for real-time sample irradiance data using the environmental database will be designed. An inter-laboratory test program of current weathering devices will be planned for a well-defined construction material.