ASTM F218 Standard Test Method for Measuring Optical Retardation and Analyzing Stress in Glass

    What is ASTM F218?

    ASTM F218 is a standard test method for the quantitative evaluation of residual stress in glasses. Residual stresses develop in glasses due to process, differential thermal expansion between fused components, and inclusions. The performance of different glass products may be affected by the presence of residual process stresses, differential thermal expansion between cast components, and inclusions. The ASTM F218 (Standard Test Method for Measuring Optical Retardation and Analyzing Stress in Glass) test method guides the analysis of stress in glass using a polarimeter, and the test procedure is based on principles developed by Jessop and Friedel.                                                                                                           

    Sample Requirement and Test Procedure 

    The test sample should have a uniform thickness. In ASTM F218, the stress field is evaluated by observing the sample, then directions and signs of stress are identified by rotating the sample at 45° and 90°. For a larger retardation analysis, rotation is used to determine the stress signs & the tinted plate is removed. A monochromator filter is placed in the field to measure retardation at any point. The polarimeter is used to reveal a color pattern. To reveal a color pattern, the polarimeter is used when the full-wave plate is introduced. Standard Test Method for Measuring Optical Retardation and Analyzing Stress in Glass

    Test Results Analysis and Interpretation

    The ASTM F218 test method helps in the quantitative evaluation of stresses. The residual stress in glass samples is evaluated as a function of optical retardation. Optical retardation is expressed as the angle of rotation of an analyzing polarizer that causes extinction in the glass.

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    For ASTM F218, the optical retardation is calculated by:

     R= λ·α /180=f λ

    where: 

    R – optical retardation, 

    α – measured analyzer rotation 

    λ – wavelength of monochromatic light used in the polarimeter, and 

    f – fractional order, f = α/180

    FAQ

    Where can I get the astm f218 tested?
    You can share your astm f218 testing requirements with MaTestLab. MaTestLab has a vast network of material testing laboratories, spread across the USA and Canada. We support your all material testing needs ranging from specific astm f218 test to various testing techniques.
    Please contact us for a detailed quote for your astm f218 testing needs. Cost incurred to carry out different astm f218 testing methodology depends on the type of raw material; number of samples, coupons, or specimens; test conditions, turn around time etc. Costs of some ASTM testing methods start from $100 and the final value depends upon the factors listed above. Please contact us for the best and latest prices.
    The required number of samples or specimens should comply with the procedure given in the astm f218 standard. However, the MaTestLab operations team can assist you for your special requirements once you share your testing details with us.
    MaTestLab has a vast testing laboratory network, hence we bring you the best testing facilities in a cost-effective way. We offer considerable discounts (15-20%) to our returning customers based on test volume and frequency.
    The turnaround time for astm f218 test methodology depends upon the test procedure mentioned in the standard test document. However, we at MaTestLab understand your research requirements and hence try to get your test completed within the least possible time.
    Gokula Srinivasan Selvam
    About Author
    Gokula Srinivasan Selvam
    Gokula Srinivasan Selvam is a Material Testing Associate at MaTestLab Inc. and holds a postgraduate degree in Ceramic Engineering from IIT (BHU), Varanasi.
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