ASTM D790-17
(Test Method)Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
SIGNIFICANCE AND USE
5.1 Flexural properties as determined by this test method are especially useful for quality control and specification purposes. They include:
5.1.1 Flexural Stress (σf)—When a homogeneous elastic material is tested in flexure as a simple beam supported at two points and loaded at the midpoint, the maximum stress in the outer surface of the test specimen occurs at the midpoint. Flexural stress is calculated for any point on the load-deflection curve using equation (Eq 3) in Section 12 (see Notes 5 and 6).
Note 5: Eq 3 applies strictly to materials for which stress is linearly proportional to strain up to the point of rupture and for which the strains are small. Since this is not always the case, a slight error will be introduced if Eq 3 is used to calculate stress for materials that are not true Hookean materials. The equation is valid for obtaining comparison data and for specification purposes, but only up to a maximum fiber strain of 5 % in the outer surface of the test specimen for specimens tested by the procedures described herein.
Note 6: When testing highly orthotropic laminates, the maximum stress may not always occur in the outer surface of the test specimen.4 Laminated beam theory must be applied to determine the maximum tensile stress at failure. If Eq 3 is used to calculate stress, it will yield an apparent strength based on homogeneous beam theory. This apparent strength is highly dependent on the ply-stacking sequence of highly orthotropic laminates.
5.1.2 Flexural Stress for Beams Tested at Large Support Spans (σf)—If support span-to-depth ratios greater than 16 to 1 are used such that deflections in excess of 10 % of the support span occur, the stress in the outer surface of the specimen for a simple beam is reasonably approximated using equation (Eq 4) in 12.3 (see Note 7).
Note 7: When large support span-to-depth ratios are used, significant end forces are developed at the support noses which will affect the moment in a simple supported...
SCOPE
1.1 These test methods are used to determine the flexural properties of unreinforced and reinforced plastics, including high modulus composites and electrical insulating materials utilizing a three-point loading system to apply a load to a simply supported beam (specimen). The method is generally applicable to both rigid and semi-rigid materials, but flexural strength cannot be determined for those materials that do not break or yield in the outer surface of the test specimen within the 5.0 % strain limit.
1.2 Test specimens of rectangular cross section are injection molded or, cut from molded or extruded sheets or plates, or cut from molded or extruded shapes. Specimens must be solid and uniformly rectangular. The specimen rests on two supports and is loaded by means of a loading nose midway between the supports.
1.3 Measure deflection in one of two ways; using crosshead position or a deflectometer. Please note that studies have shown that deflection data obtained with a deflectometer will differ from data obtained using crosshead position. The method of deflection measurement shall be reported.
Note 1: Requirements for quality control in production environments are usually met by measuring deflection using crosshead position. However, more accurate measurement may be obtained by using an deflection indicator such as a deflectometer.
Note 2: Materials that do not rupture by the maximum strain allowed under this test method may be more suited to a 4-point bend test. The basic difference between the two test methods is in the location of the maximum bending moment and maximum axial fiber stresses. The maximum axial fiber stresses occur on a line under the loading nose in 3-point bending and over the area between the loading noses in 4-point bending. A four-point loading system method can be found in Test Method D6272.
1.4 The values stated in SI units are to be regarded as the standard. The values provided i...
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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.
Designation: D790 − 17
Standard Test Methods for
Flexural Properties of Unreinforced and Reinforced Plastics
1
and Electrical Insulating Materials
This standard is issued under the fixed designation D790; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 1.5 The text of this standard references notes and footnotes
that provide explanatory material. These notes and footnotes
1.1 These test methods are used to determine the flexural
(excluding those in tables and figures) shall not be considered
properties of unreinforced and reinforced plastics, including
as requirements of the standard.
high modulus composites and electrical insulating materials
1.6 This standard does not purport to address all of the
utilizing a three-point loading system to apply a load to a
safety concerns, if any, associated with its use. It is the
simply supported beam (specimen). The method is generally
responsibility of the user of this standard to establish appro-
applicable to both rigid and semi-rigid materials, but flexural
priate safety and health practices and determine the applica-
strength cannot be determined for those materials that do not
bility of regulatory limitations prior to use.
break or yield in the outer surface of the test specimen within
the 5.0 % strain limit.
NOTE 3—This standard and ISO 178 address the same subject matter,
but differ in technical content.
1.2 Test specimens of rectangular cross section are injection
molded or, cut from molded or extruded sheets or plates, or cut 1.7 This international standard was developed in accor-
from molded or extruded shapes. Specimens must be solid and dance with internationally recognized principles on standard-
uniformly rectangular.The specimen rests on two supports and ization established in the Decision on Principles for the
is loaded by means of a loading nose midway between the Development of International Standards, Guides and Recom-
supports. mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.3 Measure deflection in one of two ways; using crosshead
positionoradeflectometer.Pleasenotethatstudieshaveshown
2. Referenced Documents
that deflection data obtained with a deflectometer will differ
2
from data obtained using crosshead position. The method of 2.1 ASTM Standards:
deflection measurement shall be reported. D618 Practice for Conditioning Plastics for Testing
D638 Test Method for Tensile Properties of Plastics
NOTE 1—Requirements for quality control in production environments
D883 Terminology Relating to Plastics
are usually met by measuring deflection using crosshead position.
D4000 Classification System for Specifying Plastic Materi-
However, more accurate measurement may be obtained by using an
deflection indicator such as a deflectometer.
als
NOTE 2—Materials that do not rupture by the maximum strain allowed
D4101 Specification for Polypropylene Injection and Extru-
underthistestmethodmaybemoresuitedtoa4-pointbendtest.Thebasic
sion Materials
differencebetweenthetwotestmethodsisinthelocationofthemaximum
D5947 Test Methods for Physical Dimensions of Solid
bending moment and maximum axial fiber stresses. The maximum axial
Plastics Specimens
fiberstressesoccuronalineundertheloadingnosein3-pointbendingand
over the area between the loading noses in 4-point bending. A four-point
D6272 Test Method for Flexural Properties of Unreinforced
loading system method can be found in Test Method D6272.
and Reinforced Plastics and Electrical Insulating Materi-
1.4 The values stated in SI units are to be regarded as the
als by Four-Point Bending
standard. The values provided in parentheses are for informa- E4 Practices for Force Verification of Testing Machines
tion only.
E83 Practice for Verification and Classification of Exten-
someter Systems
1
These test methods are under the jurisdiction of ASTM Committee D20 on
Plastics and are the direct responsibility of Subcommittee D20.10 on Mechanical
2
Properties. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved July 1, 2017. Published July 2017. Originally approved contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ɛ2
in 1970. Last previous edition approved in 2015 as D790 – 15 . DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D079
...
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.
´2
Designation: D790 − 15 D790 − 17
Standard Test Methods for
Flexural Properties of Unreinforced and Reinforced Plastics
1
and Electrical Insulating Materials
This standard is issued under the fixed designation D790; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1
ε NOTE—Editorially corrected 4.3 in January 2016.
2
ε NOTE—Editorial corrections were made in February 2016.
1. Scope*
1.1 These test methods are used to determine the flexural properties of unreinforced and reinforced plastics, including high
modulus composites and electrical insulating materials utilizing a three-point loading system to apply a load to a simply supported
beam (specimen). The method is generally applicable to both rigid and semi-rigid materials, but flexural strength cannot be
determined for those materials that do not break or yield in the outer surface of the test specimen within the 5.0 % strain limit.
1.2 Test specimens of rectangular cross section are injection molded or, cut from molded or extruded sheets or plates, or cut
from molded or extruded shapes. Specimens must be solid and uniformly rectangular. The specimen rests on two supports and is
loaded by means of a loading nose midway between the supports.
1.3 Measure deflection in one of two ways; using crosshead position or a deflectometer. Please note that studies have shown
that deflection data obtained with a deflectometer will differ from data obtained using crosshead position. The method of deflection
measurement shall be reported.
NOTE 1—Requirements for quality control in production environments are usually met by measuring deflection using crosshead position. However,
more accurate measurement may be obtained by using an deflection indicator such as a deflectometer.
NOTE 2—Materials that do not rupture by the maximum strain allowed under this test method may be more suited to a 4-point bend test. The basic
difference between the two test methods is in the location of the maximum bending moment and maximum axial fiber stresses. The maximum axial fiber
stresses occur on a line under the loading nose in 3-point bending and over the area between the loading noses in 4-point bending. A four-point loading
system method can be found in Test Method D6272.
1.4 The values stated in SI units are to be regarded as the standard. The values provided in parentheses are for information only.
1.5 The text of this standard references notes and footnotes that provide explanatory material. These notes and footnotes
(excluding those in tables and figures) shall not be considered as requirements of the standard.
1.6 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.
NOTE 3—This standard and ISO 178 address the same subject matter, but differ in technical content.
1.7 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:
D618 Practice for Conditioning Plastics for Testing
D638 Test Method for Tensile Properties of Plastics
1
These test methods are under the jurisdiction of ASTM Committee D20 on Plastics and are the direct responsibility of Subcommittee D20.10 on Mechanical Properties.
Current edition approved Dec. 1, 2015July 1, 2017. Published January 2016July 2017. Originally approved in 1970. Last previous edition approved in 20102015 as
ɛ2
D790 – 10.D790 – 15 . DOI: 10.1520/D0790-15E02.10.1520/D0790-17.
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.
*A Summary of Changes section appears at the end of this standard
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