ASTM D790-00

Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials

SCOPE
1.1 These test methods cover the determination of flexural properties of unreinforced and reinforced plastics, including high-modulus composites and electrical insulating materials in the form of rectangular bars molded directly or cut from sheets, plates, or molded shapes. These test methods are generally applicable to both rigid and semirigid materials. However, flexural strength cannot be determined for those materials that do not break or that do not fail in the outer surface of the test specimen within the 5.0 % strain limit of these test methods. These test methods utilize a three-point loading system applied to a simply supported beam. A four-point loading system method can be found in Test Method D 6272.
1.1.1 Procedure A, designed principally for materials that break at comparatively small deflections.
1.1.2 Procedure B, designed particularly for those materials that undergo large deflections during testing.
1.1.3 Procedure A, shall be used for measurement of flexural properties, particularly flexural modulus, unless the material specification states otherwise. Procedure B may be used for measurement of flexural strength only. Tangent modulus data obtained by Procedure A tends to exhibit lower standard deviations than comparable data obtained by means of Procedure B.
1.2 Comparative tests may be run in accordance with either procedure, provided that the procedure is found satisfactory for the material being tested.
1.3 The values stated in SI units are to be regarded as the standard. The values provided 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.Note 1—These test methods are not technically equivalent to ISO 178.

General Information

• Status: Historical
• Publication Date: 09-Apr-2002
• ICS: 29.035.20 - Plastics and rubber insulating materials
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.10 - Mechanical Properties

Relations

• Replaced By: ASTM D790-02 - Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
• Effective Date: 10-Apr-2002
• Referred By: ASTM E2771-11(2019) - Standard Terminology for Homeland Security Applications
• Effective Date: 10-Apr-2002
• Referred By: ASTM D1636-21 - Standard Specification for Allyl Molding Compounds
• Effective Date: 10-Apr-2002
• Referred By: ASTM F1947-21a - Standard Practice for Installation of Folded Poly(Vinyl Chloride) (PVC) Pipe into Existing Sewers and Conduits
• Effective Date: 10-Apr-2002
• Referred By: ASTM F3430-20 - Standard Specification for Closed-Cell Cellular Polypropylene (PP) Corrugated Wall Stormwater Collection Chambers
• Effective Date: 10-Apr-2002
• Referred By: ASTM F3541-22 - Standard Practice for Sectional Repair of Existing Gravity Flow, Non-Pressure Pipelines and Conduits by Pushed or Pulled-In-Place Installation of Cured-In-Place Thermosetting Resin Pipe (CIPP)
• Effective Date: 10-Apr-2002
• Referred By: ASTM D5138-23 - Standard Classification System and Basis for Specification for Liquid Crystal Polymers Molding and Extrusion Materials (LCP)
• Effective Date: 10-Apr-2002
• Referred By: ASTM F3510-21 - Standard Guide for Characterizing Fiber-Based Constructs for Tissue-Engineered Medical Products
• Effective Date: 10-Apr-2002
• Referred By: ASTM F1743-22 - Standard Practice for Rehabilitation of Existing Pipelines and Conduits by Pulled-in-Place Installation of Cured-in-Place Thermosetting Resin Pipe (CIPP)
• Effective Date: 10-Apr-2002
• Referred By: ASTM D4066-13(2019) - Standard Classification System for Nylon Injection and Extrusion Materials (PA)
• Effective Date: 10-Apr-2002
• Referred By: ASTM F3183-21 - Standard Practice for Guided Side Bend Evaluation of Polyethylene Pipe Butt Fusion Joint
• Effective Date: 10-Apr-2002
• Referred By: ASTM D4349-22 - Classification System and Basis for Specification for Polyphenylene Ether (PPE) Materials
• Effective Date: 10-Apr-2002
• Referred By: ASTM E2478-11(2022) - Standard Practice for Determining Damage-Based Design Stress for Glass Fiber Reinforced Plastic (GFRP) Materials Using Acoustic Emission
• Effective Date: 10-Apr-2002
• Referred By: ASTM F2502-17 - Standard Specification and Test Methods for Absorbable Plates and Screws for Internal Fixation Implants
• Effective Date: 10-Apr-2002
• Referred By: ASTM C1486-18(2023) - Standard Practice for Testing Chemical-Resistant Broadcast and Slurry-Broadcast Resin Monolithic Floor Surfacings
• Effective Date: 10-Apr-2002

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
An American National Standard
Designation: D 790 – 00
Standard Test Methods for
Flexural Properties of Unreinforced and Reinforced Plastics
and Electrical Insulating Materials
This standard is issued under the fixed designation D 790; 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 (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope * 2. Referenced Documents
1.1 These test methods cover the determination of flexural 2.1 ASTM Standards:
properties of unreinforced and reinforced plastics, including D 618 Practice for Conditioning Plastics and Electrical
high-modulus composites and electrical insulating materials in Insulating Materials for Testing
the form of rectangular bars molded directly or cut from sheets, D 638 Test Method for Tensile Properties of Plastics
plates, or molded shapes. These test methods are generally D 883 Terminology Relating to Plastics
applicable to both rigid and semirigid materials. However, D 4000 Classification System for Specifying Plastic Mate-
flexural strength cannot be determined for those materials that rials
do not break or that do not fail in the outer surface of the test D 5947 Test Methods for Physical Dimensions of Solid
specimen within the 5.0 % strain limit of these test methods. Plastic Specimens
These test methods utilize a three-point loading system applied D 6272 Test Method for Flexural Properties of Unrein-
to a simply supported beam. A four-point loading system forced and Reinforced Plastics and Electrical Insulating
method can be found in Test Method D 6272. Materials by Four-Point Bending
1.1.1 Procedure A, designed principally for materials that E 4 Practices for Load Verification of Testing Machines
break at comparatively small deflections. E 691 Practice for Conducting an Interlaboratory Test Pro-
1.1.2 Procedure B, designed particularly for those materials gram to Determine the Precision of Test Methods
that undergo large deflections during testing.
3. Terminology
1.1.3 Procedure A shall be used for measurement of flexural
properties, particularly flexural modulus, unless the material 3.1 Definitions—Definitions of terms applying to these test
methods appear in Terminology D 883 and Annex A1 of Test
specification states otherwise. Procedure B may be used for
measurement of flexural strength only. Tangent modulus data Method D 638.
obtained by Procedure A tends to exhibit lower standard
4. Summary of Test Method
deviations than comparable data obtained by means of Proce-
4.1 A bar of rectangular cross section rests on two supports
dure B.
and is loaded by means of a loading nose midway between the
1.2 Comparative tests may be run in accordance with either
supports (see Fig. 1). A support span-to-depth ratio of 16:1
procedure, provided that the procedure is found satisfactory for
shall be used unless there is reason to suspect that a larger
the material being tested.
span-to-depth ratio may be required, as may be the case for
1.3 The values stated in SI units are to be regarded as the
certain laminated materials (see Section 7 and Note 8 for
standard. The values provided in parentheses are for informa-
guidance).
tion only.
4.2 The specimen is deflected until rupture occurs in the
1.4 This standard does not purport to address all of the
outer surface of the test specimen or until a maximum strain
safety concerns, if any, associated with its use. It is the
(see 12.7) of 5.0 % is reached, whichever occurs first.
responsibility of the user of this standard to establish appro-
4.3 Procedure A employs a strain rate of 0.01 mm/mm/min
priate safety and health practices and determine the applica-
(0.01 in./in./min) and is the preferred procedure for this test
bility of regulatory limitations prior to use.
method, while Procedure B employs a strain rate of 0.10
NOTE 1—These test methods are not technically equivalent to ISO 178.
mm/mm/min (0.10 in./in./min).
1 2
These test methods are under the jurisdiction of ASTM Committee D20 on Annual Book of ASTM Standards, Vol 08.01.
Plastics and are the direct responsibility of Subcommittee D20.10 on Mechanical Annual Book of ASTM Standards, Vol 08.02.
Properties. Annual Book of ASTM Standards, Vol 08.03.
Current edition approved Nov. 10, 2000. Published January 2001. Originally Annual Book of ASTM Standards, Vol 03.01.
published as D 790 – 70. Last previous edition D 790 – 99. Annual Book of ASTM Standards, Vol 14.02.
*A Summary of Changes section appears at the end of this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 790
TABLE 1 Flexural Strength
Values Expressed in Units of %
of 10 psi
Material Mean, 10 psi
A B C D
V V r R
r R
ABS 9.99 1.59 6.05 4.44 17.2
DAP thermoset 14.3 6.58 6.58 18.6 18.6
Cast acrylic 16.3 1.67 11.3 4.73 32.0
GR polyester 19.5 1.43 2.14 4.05 6.08
GR polycarbonate 21.0 5.16 6.05 14.6 17.1
SMC 26.0 4.76 7.19 13.5 20.4
A
V = within-laboratory coefficient of variation for the indicated material. It is
r
obtained by first pooling the within-laboratory standard deviations of the test
2 2 2
results from all of the participating laboratories: Sr = [[(s ) +(s ) .+( s ) ]/n]
1 2 n
1/2 then V =(S divided by the overall average for the material) 3 100.
r r
B
V = between-laboratory reproducibility, expressed as the coefficient of varia-
r
2 2 1/2
tion: S ={S + S } where S is the standard deviation of laboratory means.
R r L L
Then: V =(S divided by the overall average for the material) 3 100.
R R
C
r = within-laboratory critical interval between two test results = 2.8 3 V .
r
D
R = between-laboratory critical interval between two test results = 2.8 3 V .
R
testing, or appropriate corrections shall be made. The load
indicating mechanism shall be essentially free from inertial lag
NOTE—(a) Minimum radius = 3.2 mm ( ⁄8 in.). (b) Maximum radius at the crosshead rate used. The accuracy of the testing machine
supports 1.6 times specimen depth; maximum radius loading nose = 4
shall be verified in accordance with Practices E 4.
times specimen depth.
6.2 Loading Noses and Supports—The loading nose and
FIG. 1 Allowable Range of Loading Nose and Support Radii
supports shall have cylindrical surfaces. In order to avoid
excessive indentation, or failure due to stress concentration
directly under the loading nose, the radii of the loading nose
5. Significance and Use
and supports shall be 5.0 6 0.1 mm (0.197 6 0.004 in.) unless
5.1 Flexural properties as determined by these test methods
otherwise specified or agreed upon between the interested
are especially useful for quality control and specification
clients. When other loading noses and supports are used they
purposes.
must comply with the following requirements: they shall have
5.2 Materials that do not fail by the maximum strain
a minimum radius of 3.2 mm ( ⁄8 in.) for all specimens, and for
allowed under these test methods (3-point bend) may be more
specimens 3.2 mm or greater in depth, the radius of the
suited to a 4-point bend test. The basic difference between the
supports may be up to 1.6 times the specimen depth. They shall
two test methods is in the location of the maximum bending
be this large if significant indentation or compressive failure
moment and maximum axial fiber stresses. The maximum axial
occurs. The arc of the loading nose in contact with the
fiber stresses occur on a line under the loading nose in 3-point
specimen shall be sufficiently large to prevent contact of the
bending and over the area between the loading noses in 4-point
specimen with the sides of the nose (see Fig. 1). The maximum
bending.
radius of the loading nose shall be no more than 4 times the
5.3 Flexural properties may vary with specimen depth,
specimen depth.
temperature, atmospheric conditions, and the difference in rate
NOTE 2—Test data have shown that the loading nose and support
of straining as specified in Procedures A and B (see also Note
dimensions can influence the flexural modulus and flexural strength
8).
values. The loading nose dimension has the greater influence. Dimensions
5.4 Before proceeding with these test methods, reference
of the loading nose and supports must be specified in the material
should be made to the specification of the material being tested.
specification.
Any test specimen preparation, conditioning, dimensions, or
6.3 Micrometers— Suitable micrometers for measuring the
testing parameters, or combination thereof, covered in the
width and thickness of the test specimen to an incremental
materials specification shall take precedence over those men-
discrimination of at least 0.025 mm (0.001 in.) should be used.
tioned in these test methods. If there are no material specifi-
All width and thickness measurements of rigid and semirigid
cations, then the default conditions apply. Table 1 in Classifi-
plastics may be measured with a hand micrometer with ratchet.
cation System D 4000 lists the ASTM materials standards that
A suitable instrument for measuring the thickness of nonrigid
currently exist for plastics.
test specimens shall have: a contact measuring pressure of
25 6 2.5 kPa (3.6 6 0.36 psi), a movable circular contact foot
6. Apparatus
6.35 6 0.025 mm (0.250 6 0.001 in.) in diameter and a lower
6.1 Testing Machine— A properly calibrated testing ma-
fixed anvil large enough to extend beyond the contact foot in
chine that can be operated at constant rates of crosshead motion
all directions and being parallel to the contact foot within 0.005
over the range indicated, and in which the error in the load
mm (0.002 in.) over the entire foot area. Flatness of foot and
measuring system shall not exceed 61 % of the maximum load
anvil shall conform to the portion of the Calibration section of
expected to be measured. It shall be equipped with a deflection
Test Methods D 5947.
measuring device. The stiffness of the testing machine shall be
7. Test Specimens
such that the total elastic deformation of the system does not
exceed 1 % of the total deflection of the test specimen during 7.1 The specimens may be cut from sheets, plates, or
D 790
molded shapes, or may be molded to the desired finished be necessary (32:1 or 40:1 are recommended). When laminated
dimensions. The actual dimensions used in Section 4.2, Cal- materials exhibit low compressive strength perpendicular to the
culation, shall be measured in accordance with Test Methods laminations, they shall be loaded with a large radius loading
D 5947. nose (up to four times the specimen depth to prevent premature
damage to the outer fibers.
NOTE 3—Any necessary polishing of specimens shall be done only in
7.4 Molding Materials (Thermoplastics and Thermosets)—
the lengthwise direction of the specimen.
The recommended specimen for molding materials is 127 by
7.2 Sheet Materials (Except Laminated Thermosetting Ma-
1 1
12.7 by 3.2 mm (5 by ⁄2by ⁄8 in.) tested flatwise on a support
terials and Certain Materials Used for Electrical Insulation,
span, resulting in a support span-to-depth ratio of 16 (tolerance
Including Vulcanized Fiber and Glass Bonded Mica):
61). Thicker specimens should be avoided if they exhibit
7.2.1 Materials 1.6 mm ( ⁄16 in.) or Greater in Thickness—
significant shrink marks or bubbles when molded.
For flatwise tests, the depth of the specimen shall be the
7.5 High-Strength Reinforced Composites, Including Highly
thickness of the material. For edgewise tests, the width of the
Orthotropic Laminates—The span-to-depth ratio shall be cho-
specimen shall be the thickness of the sheet, and the depth shall
sen such that failure occurs in the outer fibers of the specimens
not exceed the width (see Notes 4 and 5). For all tests, the
and is due only to the bending moment (see Note 8). A
support span shall be 16 (tolerance 61) times the depth of the
span-to-depth ratio larger than 16:1 may be necessary (32:1 or
beam. Specimen width shall not exceed one fourth of the
40:1 are recommended). For some highly anisotropic compos-
support span for specimens greater than 3.2 mm ( ⁄8 in.) in
ites, shear deformation can significantly influence modulus
depth. Specimens 3.2 mm or less in depth shall be 12.7 mm ( ⁄2
measurements, even at span-to-depth ratios as high as 40:1.
in.) in width. The specimen shall be long enough to allow for
Hence, for these materials, an increase in the span-to-depth
overhanging on each end of at least 10 % of the support span,
ratio to 60:1 is recommended to eliminate shear effects when
but in no case less than 6.4 mm ( ⁄4 in.) on each end. Overhang
modulus data are required, it should also be noted that the
shall be sufficient to prevent the specimen from slipping
flexural modulus of highly anisotropic laminates is a strong
through the supports.
function of ply-stacking sequence and will not necessarily
correlate with tensile modulus, which is not stacking-sequence
NOTE 4—Whenever possible, the original surface of the sheet shall be
unaltered. However, where testing machine limitations make it impossible dependent.
to follow the above criterion on the unaltered sheet, one or both surfaces
NOTE 8—As a general rule, support span-to-depth ratios of 16:1 are
shall be machined to provide the desired dimensions, and the location of
satisfactory when the ratio of the tensile strength to shear strength is less
the specimens with reference to the total depth shall be noted. The value
than 8 to 1, but the support span-to-depth ratio must be increased for
obtained on specimens with machined surfaces may differ from those
composite laminates having relatively low shear strength in the plane of
obtained on specimens with original surfaces. Consequently, any specifi-
the laminate and relatively high tensile strength parallel to the support
cations for flexural properties on thicker sheets must state whether the
span.
original surfaces are to be retained or not. When only one surface was
machined, it must be stated whether the machined surface was on the
8. Number of Test Specimens
tension or compression side of the beam.
NOTE 5—Edgewise tests are not applicable for sheets that are so thin 8.1 Test at least five specimens for each sample in the case
that specimens meeting these requirements cannot be cut. If specimen
of isotropic materials or molded specimens.
depth exceeds the width, buckling may occur.
8.2 For each sample of anisotropic material in sheet form,
test at least five specimens for each of the following conditions.
7.2.2 Materials Less than 1.6 mm
...