ASTM D3929-03(2015)

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of the standard as published by ASTM is to be considered the official document.
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Designation: D3929 − 03 (Reapproved 2010) D3929 − 03 (Reapproved 2015)
Standard Test Method for
Evaluating Stress Cracking of Plastics by Adhesives Using
the Bent-Beam Method
This standard is issued under the fixed designation D3929; 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.
ε NOTE—Captions of Figures 3, 4, 5, and 6 were corrected editorially in April 2010.
1. Scope
1.1 This test method describes a procedure for determining the compatibility of adhesives with plastics based on whether the
adhesive causes cracking of stressed samples.
1.2 Specimen configurations and test fixture designs are given.
1.3 This test method is suitable for products in the form of sheet or strip. It can also be used on injection molded tensile
specimens or flexural bars.
1.4 The values stated in SI units are to be regarded as the standard. The inch-pound units given in parentheses are for
information only.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
D638 Test Method for Tensile Properties of Plastics
D790 Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
D907 Terminology of Adhesives
3. Terminology
3.1 Definitions—Many of the terms in this test method are defined in Terminology D907.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 cracking, n—a continuous localized failure of the plastic, leading to loss of structural integrity.
3.2.2 crazing, n—apparent fine cracks at or under the surface of a plastic.
This test method is under the jurisdiction of ASTM Committee D14 on Adhesives and is the direct responsibility of Subcommittee D14.40 on Adhesives for Plastics.
Current edition approved April 1, 2010Sept. 1, 2015. Published April 2010September 2015. Originally approved in 1980. Last previous edition approved in 20032010 as
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D3929 – 03.D3929 – 03 (2010) . DOI: 10.1520/D3929-03R10E01.10.1520/D3929-03R15.
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’sstandard’s Document Summary page on the ASTM website.
3.2.2.1 Discussion—
This is a form of localized yielding of the plastic due to the combined action of stress and an attacking medium. Initial crazing
may be detectable only by inspection under magnification.
3.2.3 failure, n—an arbitrary point defined by the initial detection of cracks or crazes.
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D3929 − 03 (2015)
4. Summary of Test Method
4.1 This test method involves the qualitative determination of the compatibility of adhesives with plastics by observing the
effect of adhesives applied in the liquid state on stressed plastic specimens. Bars of plastic are bent in a three-point loading fixture
to cause a predetermined initial tensile stress on the surface of the bar. The liquid adhesive is then applied to the area of maximum
stress which is checked periodically for crazing or cracking.
4.1.1 Due to the stress relaxation behavior of certain plastics, initial stress only can be determined and the stress level may
decrease significantly during the course of the test.
5. Significance and Use
5.1 This test method is designed for obtaining a qualitative estimate of the compatibility of plastics and adhesives. Due to the
many process variables associated with the fabrication of plastic parts, it is not possible to use this test as a substitute for
compatibility tests on actual parts.
5.2 The detection of cracks or crazes may be determined with or without optical aid. Make comparisons only among tests
employing crack detection methods of equivalent sensitivity.
6. Apparatus
6.1 Test Fixtures—Bent beam test fixtures (see Fig. 1) are designed to place the specimen in three-point bending. The amount
of deflection is adjustable as well as the loading span. Other fixtures may be used as long as specimen deflection is known.
6.2 The amount of deflection on the specimen is measured by use of a dial gage indicator or a vernier caliper having a depth
indicator (see Fig. 2). Use a measuring device capable of reading to 0.025 mm (0.001 in.).
7. Test Specimen
7.1 The preferred specimen is a flexural bar designed in accordance with Test Methods D790.
Depth 6.4 mm ( ⁄4 in.)
Width 13 mm ( ⁄2 in.)
Length 130 mm (5 in.)
Loading Span 100 mm (4 in.)
L/d 16/1
Tensile bars, such as Type I in Test Method D638, can also be used. Specimens of rectangular section may also be cut from sheets
or molded plastic articles.
7.2 Mold specimens in a low-stress condition or anneal so that molded-in stresses will not have a significant effect.
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Detailed drawings are shown in Figs. 3–5. Also necessary to complete the test fixture are the following parts: 2 pieces at 6 by 38 mm ( ⁄4 by 1 ⁄2-in.) dowel pins and
2 pieces of M4–0.7 (8–32 unc) by 32 mm (1 ⁄4-in.) socket head cap screws.
FIG. 1 Test Fixture with Plastic Bar in Place
D3929 − 03 (2015)
FIG. 2 Measurement of Test Bar Deflection with Depth Gage of Vernier Caliper
FIG. 3 Test Fixture Frame
(All dimensions in mm (in.) unless otherwise stated.)
7.3 Carefully cut or machine specimens in accordance with the plastic manufacturers’manufacturers’ recommended procedures
to avoid introducing stresses at machined surfaces.
8. Procedure
8.1 Place the plastic test specimen in the test fixture at the required loading (
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