ASTM F2156-17
(Test Method)Standard Test Method for Measuring Optical Distortion in Transparent Parts Using Grid Line Slope
Standard Test Method for Measuring Optical Distortion in Transparent Parts Using Grid Line Slope
SIGNIFICANCE AND USE
5.1 Transparent parts, such as aircraft windshields, canopies, cabin windows, and visors, shall be measured for compliance with optical distortion specifications using this test method. This test method is suitable for assessing optical distortion of transparent parts as it relates to the visual perception of distortion. It is not suitable for assessing distortion as it relates to pure angular deviation of light as it passes through the part. Either Test Method F801 or Practice F733 is appropriate and shall be used for this latter application. This test method is not recommended for raw material.
SCOPE
1.1 When an observer looks through an aerospace transparency, relative optical distortion results, specifically in thick, highly angled, multilayered plastic parts. Distortion occurs in all transparencies but is especially critical to aerospace applications such as combat and commercial aircraft windscreens, canopies, or cabin windows. This is especially true during operations such as takeoff, landing, and aerial refueling. It is critical to be able to quantify optical distortion for procurement activities.
1.2 This test method covers the apparatus and procedures that are suitable for measuring the grid line slope (GLS) of transparent parts, including those that are small or large, thin or thick, flat or curved, or already installed. This test method is not recommended for raw material.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3.1 Exception—The values given in parentheses are for information only.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation: F2156 − 17
Standard Test Method for
Measuring Optical Distortion in Transparent Parts Using
1
Grid Line Slope
This standard is issued under the fixed designation F2156; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2
1.1 When an observer looks through an aerospace 2.1 ASTM Standards:
transparency, relative optical distortion results, specifically in E177 Practice for Use of the Terms Precision and Bias in
thick, highly angled, multilayered plastic parts. Distortion ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to
occurs in all transparencies but is especially critical to aero-
space applications such as combat and commercial aircraft Determine the Precision of a Test Method
F733 Practice for Optical Distortion and Deviation of Trans-
windscreens, canopies, or cabin windows. This is especially
true during operations such as takeoff, landing, and aerial parent Parts Using the Double-Exposure Method
F801 Test Method for Measuring OpticalAngular Deviation
refueling. It is critical to be able to quantify optical distortion
for procurement activities. of Transparent Parts
1.2 This test method covers the apparatus and procedures
3. Terminology
that are suitable for measuring the grid line slope (GLS) of
3.1 Definitions of Terms Specific to This Standard:
transparent parts, including those that are small or large, thin or
3.1.1 design eye, n—the reference point in aircraft design
thick, flat or curved, or already installed. This test method is
from which all anthropometrical design considerations are
not recommended for raw material.
taken.
1.3 The values stated in SI units are to be regarded as
3.1.2 distortion, n—the rate of change of deviation resulting
standard. No other units of measurement are included in this
from an irregularity in a transparent part.
standard.
3.1.2.1 Discussion—Distortion shall be expressed as the
1.3.1 Exception—The values given in parentheses are for
slope of the angle of localized grid line bending, for example,
information only.
1 in 5 (see Fig. 1).
1.4 This standard does not purport to address all of the
3.1.3 grid board, n—an optical evaluation tool used to
safety concerns, if any, associated with its use. It is the
detect the presence of distortion in transparent parts.
responsibility of the user of this standard to establish appro-
3.1.3.1 Discussion—The grid board is usually, but not
priate safety and health practices and determine the applica-
always, a vertical rectangular backboard with horizontal and
bility of regulatory limitations prior to use.
vertical intersecting lines with maximum contrast between the
1.5 This international standard was developed in accor-
white lines and the black background.
dance with internationally recognized principles on standard-
3.1.4 grid line slope, n—an optical distortion evaluation
ization established in the Decision on Principles for the
parameterthatcomparestheslopeofadeviatedgridlinetothat
Development of International Standards, Guides and Recom-
of a nondeviated grid line.
mendations issued by the World Trade Organization Technical
3.1.4.1 Discussion—The degree of deviation shall be indi-
Barriers to Trade (TBT) Committee.
cated by a ratio, for example, 1 in 2, 1 in 8, or 1 in 20 (the
visual optical quality improves as the second number gets
larger.)
1
This test method is under the jurisdiction of ASTM Committee F07 on
Aerospace andAircraft, and is the direct responsibility of Subcommittee F07.08 on
2
Transparent Enclosures and Materials. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved June 1, 2017. Published June 2017. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2001. Last previous edition approved in 2011 as F2156 - 11. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/F2156-17.
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
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F2156 − 17
3.1.6.1 Discussion—in terms of this test method, approxi-
mately 95 % of all pairs of replications from the same
evaluator and the same photo differ in absolute value by less
than the rL.
3.1.7 reproducibility limit (RL), n—from Practice E177,
27.3.3, “approximately 95 % of all pairs of test results from
laboratories similar to those in the study are expected to differ
in absolute value by less than 1.960√2s (about 2.0√2s) = 2.77s
(or abou
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F2156 − 11 F2156 − 17
Standard Test Method for
Measuring Optical Distortion in Transparent Parts Using
1
Grid Line Slope
This standard is issued under the fixed designation F2156; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 When an observer looks through an aerospace transparency, relative optical distortion results, specifically in thick, highly
angled, multilayered plastic parts. Distortion occurs in all transparencies but is especially critical to aerospace applications such
as combat and commercial aircraft windscreens, canopies, or cabin windows. This is especially true during operations such as
takeoff, landing, and aerial refueling. It is critical to be able to quantify optical distortion for procurement activities.
1.2 This test method covers the apparatus and procedures that are suitable for measuring the grid line slope (GLS) of transparent
parts, including those that are small or large, thin or thick, flat or curved, or already installed. This test method is not recommended
for raw material.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3.1 Exception—The values given in parentheses are for information only.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2
2.1 ASTM Standards:
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
F733 Practice for Optical Distortion and Deviation of Transparent Parts Using the Double-Exposure Method
F801 Test Method for Measuring Optical Angular Deviation of Transparent Parts
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 design eye, n—the reference point in aircraft design from which all anthropometrical design considerations are taken.
3.1.2 distortion, n—the rate of change of deviation resulting from an irregularity in a transparent part.
1
This test method is under the jurisdiction of ASTM Committee F07 on Aerospace and Aircraft, and is the direct responsibility of Subcommittee F07.08 on Transparent
Enclosures and Materials.
Current edition approved Dec. 1, 2011June 1, 2017. Published January 2012June 2017. Originally approved in 2001. Last previous edition approved in 20062011 as
F2156 - 06.F2156 - 11. DOI: 10.1520/F2156-11.10.1520/F2156-17.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
3.1.2.1 Discussion—
Distortion shall be expressed as the slope of the angle of localized grid line bending, for example, 1 in 5 (see Fig. 1).
3.1.3 grid board, n—an optical evaluation tool used to detect the presence of distortion in transparent parts.
3.1.3.1 Discussion—
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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F2156 − 17
FIG. 1 Optical Distortion Represented By Tangent
The grid board is usually, but not always, a vertical rectangular backboard with horizontal and vertical intersecting lines with
maximum contrast between the white lines and the black background.
3.1.4 grid line slope, n—an optical distortion evaluation parameter that compares the slope of a deviated grid line to that of a
nondeviated grid line.
3.1.4.1 Discussion—
The degree of deviation shall be indicated by a ratio, for example, 1 in 2, 1 in 8, or 1 in 20 (the visual optical quality improves
as the second number gets larger.)
3.1.5 installed angle, n—the transparency orient
...
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