ASTM E990-21

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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: E990 − 13 E990 − 21
Standard Specification for
Core-Splice Adhesive for Honeycomb Sandwich Structural
Panels
This standard is issued under the fixed designation E990; 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
1.1 This specification covers core-splice adhesive for use with nonmetallic honeycomb cores in the fabrication of honeycomb
sandwich panels used in relocatable structures. The adhesive shall be used for new production or depot repair. The adhesive shall
be suitable for forming bonds that can withstand long combinations of stress, temperature, and relative humidity expected to be
encountered in service. The adhesive shall be used for bonding core segments and for bonding core segments to edge members
and to integral members in a honeycomb sandwich panel. The adhesive shall not allow the transfer of water from one part of the
panel to another either through or along the line of the adhesive.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.after
SI units are provided for information only and are not considered standard.
1.3 The following precautionary caveat pertains only to the test method portion, Section 6, of this specification: 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 safety, health, and healthenvironmental practices and determine the applicability of
regulatory limitations prior to use.
1.4 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
2.1 ASTM Standards:
B209 Specification for Aluminum and Aluminum-Alloy Sheet and Plate
C393/C393M Test Method for Core Shear Properties of Sandwich Constructions by Beam Flexure
D792 Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement
E631 Terminology of Building Constructions
E864 Practice for Surface Preparation of Aluminum Alloys to Be Adhesively Bonded in Honeycomb Shelter Panels
E865 Specification for Structural Film Adhesives for Honeycomb Sandwich Panels
E874 Practice for Adhesive Bonding of Aluminum Facings to Nonmetallic Honeycomb Core for Shelter Panels
E1091 Specification for Nonmetallic Honeycomb Core for Use in Shelter Panels
This specification is under the jurisdiction of ASTM Committee E06 on Performance of Buildings and is the direct responsibility of Subcommittee E06.53 on Materials
and Processes for Durable Rigidwall Relocatable Structures.
Current edition approved Oct. 1, 2013Feb. 1, 2021. Published February 2014February 2021. Originally approved in 1984. Last previous edition approved in 20092013
as E990 – 09.E990 – 13. DOI: 10.1520/E0990-13.10.1520/E0990-21.
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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E990 − 21
E1749 Terminology Relating to Rigid Wall Relocatable Shelters
2.2 Federal Standards:
QQ-A-250/4 Aluminum Alloy 2024, Plate and Sheet
QQ-A-250/8d Aluminum Alloy 5052H34, Plate and Sheet
QQ-A-250/11d Aluminum Alloy 6061T6, Plate and Sheet
2.3 Military Standards:
MIL-S-8802 Sealing Compound, Temperature-Resistant, Integral Fuel Tanks, and Fuel Cell Cavities, High-Adhesion
Available from DLA Document Services, Building 4/D, 700 Robbins Avenue, Philadelphia, PA 19111-5094, http://quicksearch.dla.mil/.
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3. Terminology
3.1 DefinitionsDefinitions:—See
3.1.1 For definitions of general terms related to building construction used in this specification, refer to Terminology E631, and
for general terms related to rigid wall relocatable shelters, refer to Terminology E1749. Terminologies E631 and E1749 for
definitions of general terms used in this specification.
4. Materials and Manufacture
4.1 The adhesive shall be free of foreign materials, be noncorrosive to the metal parts, and have the structural integrity equal to
or better than that of an unspliced panel section as specified in Table 1, Flexural Sheer.
5. Requirements
5.1 Material—The adhesive shall be thermosetting and when tested in accordance with Section 6, shall meet the requirements of
Table 1. The adhesive shall not have a deleterious effect on the panel nor on its component parts over the range of temperature
at which the adhesive will be used. This adhesive shall be compatible and capable of co-curing with the structural film adhesive
(Specification E865) used to fabricate the panel.
5.2 Form—The adhesive shall be of film form either 1.27 mm (0.051 in.) or 2.54 mm (0.100 in.) thick and shall be capable of
expanding to at least 1.75 times its original thickness.
5.3 Working Characteristics:
5.3.1 Application—The adhesive shall be suitable for application to core material, edge members, and integral parts in accordance
with the manufacturer’s instructions at temperatures from 1818 °C to 30°C (6530 °C (65 °F to 85°F)85 °F) and at relative
humidities of up to 50 %.
5.3.2 Curing—The time, temperature, and pressure used to cure the adhesive shall be as specified herein.
5.3.2.1 Curing Time and Temperature—The adhesive shall meet the requirements of this specification when cured in accordance
with manufacturer’s recommendation so long as the time and bondline temperature do not exceed 1 h or 145°C (293°F).145 °C
(293 °F).
5.3.2.2 Curing Pressure—The pressure required for curing the adhesive shall be contact.
5.4 Storage Life—The adhesive shall have a minimum storage life of 3 months from the date of receipt at the fabricator facility
TABLE 1 Physical Properties Qualification Requirements
Reference
Table Requirements
Paragraph
Water migration 6.1 Not more than the volume of
the cavity (in cell)
Volatility 6.2 1 % maximum
Expansion 6.3 1.75 minimum ratio
Sag for 1.27 mm (0.05 in.) 6.4 3.8 mm (0.15 in.) maximum
uncured thickness
Sag for 2.54 mm (0.1 in.) 6.4 12.7 mm (0.500 in.) maximum
uncured thickness
3 3
Density (cured) 6.5 0.8 g per cm (50 lb/ft )
maximum
3 3
Density (cured) 6.5 0.8 g per cm (50 lb ⁄ft )
maximum
Flexural shear (assembly 6.6 Same as honeycomb core,
compatibility) minimum 1.24 MPa (180 psi)
L-direction
Tube shear (core splice 6.7 Minimum average 4.13 MPa
integrity) (600 psi)
Minimum individual 3.1 MPa
(450 psi)
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when stored at −17.8°C (0°F)at −17.8 °C (0 °F) or below. Under conditions in accordance with 5.3.1, the adhesive shall have a
cumulative out-life of at least 5 days at 2424 °C 6 3°C (753 °C (75 °F 6 5°F).5 °F).
5.5 Properties—The properties of the test specimens prepared and tested as described herein shall conform to the requirements
of Table 1.
6. Test Methods
6.1 Water Migration Test:
6.1.1 The core Splice Adhesive Mold is illustrated in Fig. 1 (Note 1). Apply a mold release agent to both the interior of the female
portion and the exterior of the male portion of the mold. Install a layer of adhesive (Note 2) on the entire length of the 19.05 mm
diameter part of the male portion of the mold so that the layer of adhesive overlaps along a vertical seam. Close the mold by
lowering the female portion over the male portion until it seats against the base of the male portion. A press may be used to help
close the mold. Remove the mold from the press and place in an oven. Cure in the oven at 121121 °C 6 5.6°C (2505.6 °C (250 °F
6 10°F)10 °F) for 1 h minimum. Remove cured adhesive from the mold.
NOTE 1—The mold may be made of aluminum, acrylic plastic, or other suitable material. The outer shell may be fabricated as a split mold.
NOTE 2—Depending on the expansion ratio and the unexpanded thickness of the material being tested, it may be necessary to install more than one layer
3 3
of adhesive. The size of the adhesive shall be calculated as follows: Length × width × thickness = 1.65 cm (0.65 in. ).
6.1.2 Prepare the sample (approximately 38 mm (1 ⁄2 in.) long) by cutting the cylinder of cured adhesive and visually check to
ensure that there are no cracks, pin holes, and so forth.
6.1.3 Cover a piece of aluminum (approx. 50 × 50 × 650 mm × 50 mm × 6 mm) (2 × 2 × (2 in. × 2 in. × ⁄4 in.) with MIL-S-8802,
1 1
Class B-2 Sealant, or equivalent, to a depth of 33 mm to 6 mm ( ⁄8 in. to ⁄4 in.). Use a “dam,” such as vacuum-bagging putty or
an aluminum foil tray, around the edge of the aluminum to prevent the sealant from running off (see Fig. 2).
6.1.4 Place the prepared sample of adhesive (6.1.2) on the sealant and seat it gently into the sealer. Allow the sealant to cure at
room temperature overnight.
FIG. 1 Core Splice Adhesive Mold
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FIG. 2 Water Migration Test Specimen Assembly
1 3
6.1.5 Install a glass tube approximately 38 mm (1 ⁄2 in.) long approximately 19 mm ( ⁄4 in.) down into the hole in the top of the
specimen, and seal between the glass tube and the test specimen with MIL-S-8802, Class B-2 sealant, or equivalent. Allow the
sealant to cure at room temperature overnight.
6.1.6 Fill the cell in the sample through the glass tube with distilled water using a hypodermic needle. Inject the water at the
bottom to ensure that the cell is full and that no air is entrapped. Measure the volume required to fill the cell.
6.1.7 Connect a buret filled with distilled water to the glass tube using a clear polyethylene tubing (see Fig. 3). Adjust the buret
to a height of 914.4 mm (36 in.) above the top of the test specimen and ensure that there is no entrapped air.
6.1.8 The water migration through the adhesive tube specimen shall not exceed the number of millilitres required to fill the cavity
(approximately 12 mL (0.4 oz)) when subjected to a 915 mm (36-in.)(36 in.) head for 24 h.
6.2 Volatile Test—Volatility of the film adhesive shall be tested in accordance with the procedure in 6.2.1 – 6.2.9.
6.2.1 Cut the adhesive into three one-ply test specimens. Each specimen is to be a 51-mm (2-in.)51 mm (2 in.) diameter disk or
5151 mm by 51-mm (251 mm (2 in. by 2-in.)2 in.) square.
6.2.2 Weigh the containers that will be used in the cure of the test specimens cut in 6.2.1. Each container shall be an aluminum
moisture dish, of sufficient size to allow the specimen to lie in the bottom without the edges of the specimen touching the side of
the container. (W = weight of container.)
6.2.3 Place each specimen in a container, then place the containers in a desiccator that contains a desiccant such as dryerite for
2 h 6 10 min at room temperature, 2424 °C 6 3°C (753 °C (75 °F 6 5°F).5 °F).
6.2.4 Remove the container and specimen from the desiccator and weigh. This weight shall be designated as W . (W = weight
2 2
of container plus weight of uncured adhesive.)
6.2.5 Cure the specimens in a forced-air circulating oven. The time and temperature shall be in accordance with 5.3.2.1. When
a cure temperature range is specified, the volatility test shall be conducted at the maximum curing temperature.
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FIG. 3 Water Migration Test
6.2.6 Remove the containers and cured specimens from the oven while at cure temperature, and place in a desiccator and cool to
room temperature, 2424 °C 6 2.8°C (752.8 °C (75 °F 6 5°F).5 °F).
6.2.7 Remove the cooled containers and specimens from the desiccator and reweigh. This weight shall be designated as W .
(W = weight of cured adhesive and container.)
6.2.8 The percent weight loss shall be calculated as follows:
W 2 W
2 3
V 5 3100 (1)
W 2 W
2 1
where:
V = weight loss (volatility), %,
W = weight of container, g (oz),
W = weight of container plus weight of uncured adhesive, g (oz), and
W = weight of cured adhesive and container, g (oz).
6.2.9 The percent of weight loss of three specimens shall be averaged and reported as volatility.
6.3 Expansion Test—Cut three specimens of the core splice adhesive (approx. 102 × 102102 mm × 102 mm) (4 × 4(4 in. × 4 in.)
with the liners intact. Record the average thickness (at least three readings per sp
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