ISO 8642:2008

INTERNATIONAL ISO
STANDARD 8642
Second edition
2008-09-01
Aerospace — Self-locking nuts with
maximum operating temperature greater
than 425 °C — Test methods
Aéronautique et espace — Écrous à freinage interne dont la
température maximale d'utilisation est supérieure à 425 °C — Méthodes
d'essai
Reference number
©
ISO 2008
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ii © ISO 2008 – All rights reserved

Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Inspections and tests . 1
3.1 Hardness test . 1
3.2 Bearing surface squareness test . 2
3.3 Axial load test. 4
3.4 Wrenching feature test. 5
3.5 Torque-out test. 7
3.6 Test of no rotation of the captive washer . 8
3.7 Push-out test . 9
3.8 Self-locking torque at ambient temperature . 10
3.9 Self-locking torque at ambient temperature after heat soak at maximum operating
temperature . 12
3.10 Permanent set test. 15
3.11 Vibration test . 17
3.12 Swaging test. 20

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 8642 was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee SC 4,
Aerospace fastener systems.
This second edition cancels and replaces the first edition (ISO 8642:1986) which has been technically revised.
iv © ISO 2008 – All rights reserved

INTERNATIONAL STANDARD ISO 8642:2008(E)

Aerospace — Self-locking nuts with maximum operating
temperature greater than 425 °C — Test methods
1 Scope
This International Standard specifies test methods for metric self-locking nuts with MJ threads intended for
use in aerospace construction at maximum operating temperature greater than 425 °C. It describes the test
device and the method for each test.
It applies to self-locking nuts as defined above, provided that the relevant documents (dimensional standard,
drawing, procurement specification, etc.) refer to this International Standard.
Other test devices or test methods than those specified in this International Standard may be used, but, in the
event of a dispute, the requirements laid down in this International Standard shall take precedence.
This International Standard shall be used in conjunction with ISO 8641.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 691, Assembly tools for screws and nuts — Wrench and socket openings — Tolerances for general use
ISO 5855-2, Aerospace — MJ threads — Part 2: Limit dimensions for bolts and nuts
ISO 6507-1, Metallic materials — Vickers hardness test — Part 1: Test method
ISO 6508-1, Metallic materials — Rockwell hardness test — Part 1: Test method (scales A, B, C, D, E, F, G, H,
K, N, T)
ISO 7403, Aerospace — Spline drives — Wrenching configuration — Metric series
ISO 8641, Aerospace — Self-locking nuts with maximum operating temperature greater than 425 °C —
Procurement specification
3 Inspections and tests
3.1 Hardness test
3.1.1 Procedure
The authorized procedures are:
⎯ Rockwell hardness in accordance with ISO 6508-1;
⎯ Vickers hardness HV 5 to HV 100 in accordance with ISO 6507-1;
⎯ Rockwell superficial hardness in accordance with ISO 6508-1;
⎯ microhardness.
It is strongly recommended to use the method corresponding to the hardness unit indicated. Should this not
be possible, the use of conversion charts is allowed, but, given their inaccuracy, the results obtained shall be
used warily. In the event of a dispute, the results obtained using the method corresponding to the hardness
unit indicated shall take precedence.
3.1.2 Method
This test shall be carried out at ambient temperature.
The measurement zone (bearing surface, across flats, underside of anchor nut lugs, etc.) shall satisfy the
following conditions:
a) thickness at least equal to 10 × the penetration depth;
b) parallelism with respect to bearing surface no greater than 3°.
Should this not be possible, carry out this test on a cut section after moulding the nut into a resin capable of
maintaining it in the correct position.
Remove all possible coating (protection, lubrication, paint, etc.) in the measurement zone. Align the bearing
surface to obtain the required relationship. These two operations shall not generate any heat liable to modify
the characteristics of the material constituting the nut being tested.
Carry out the test and then check conformity with the requirements of the dimensional standard or drawing.
Nuts subjected to this test shall not be used again.
3.2 Bearing surface squareness test
3.2.1 Test device
The test device is illustrated in Figure 1 and includes the following elements:
a) a threaded mandrel with end in accordance with ISO 5855-2, with the exception of the pitch diameter
which shall be in accordance with the values specified in Table 5 for the maximum mandrel;
b) a collar sliding on the plain portion of the threaded mandrel whose external diameter B is at least equal to
reference dimension A for type I, III and VI nuts in Figure 2 and equal to reference dimension A for type II,
IV and V nuts in Figure 2;
c) an appropriate feeler gauge.
3.2.2 Method
The test shall be carried out at ambient temperature.
For floating nuts, extract the nut from the cage or channel.
Lubricate the mandrel and nut threads (or threaded part) as stated in Table 1 (if necessary). Screw, with or
without using a spanner, the threaded mandrel into the nut or threaded part until it engages with the self-
locking zone.
Move the collar into contact with the bearing surface.
2 © ISO 2008 – All rights reserved

Evaluate the out-of-squareness by means of a feeler gauge whose thickness corresponds to the permissible
squareness error permitted by the dimensional standard, the drawing or the procurement specification.
For clinch nuts, the sliding collar shall have a counterbore to accommodate the shank.
Table 1 — Test bolt and lubrication
Nut to be tested Test bolt
Additional
lubrication
Material Coating Material Coating
Steel or alloy steel Any Alloy steel None
Silver or MoS None Synthetic oil
Stainless steel Stainless steel
None Silver
Key
1 sliding collar
2 threaded mandrel
3 feeler gauge
a
Pitch diameter.
Figure 1
Type I Type II Type III Type IV Type V Type VI
Wrench nuts Clinch nuts Fixed anchor nuts Floating anchor
nuts and gang
channel nuts
Figure 2
3.3 Axial load test
3.3.1 Test device
The test device is illustrated in Figure 3 and includes the following elements:
a) a steel bearing plate, heat-treated to a hardness W 40 HRC;
b) a bolt with a rolled thread and the following characteristics:
1) threads in accordance with ISO 5855-2;
2) tensile strength class greater than that of the nut under test;
3) material and coating: no specific requirement;
c) a torque wrench.
3.3.2 Method
3.3.2.1 Principle
The axial load is transmitted to the nut by the bolt, the nut resting on the bearing plate.
3.3.2.2 80 % test
This test shall be carried out at ambient temperature.
Lubricate the bolt and nut threads as stated in Table 1 (if necessary). Assemble the bearing plate on the bolt.
Assemble the nut and measure the locking torque, using the torque wrench, when the protrusion is two
pitches minimum (including chamfer).
Position the assembly on the tensile machine. Apply the load slowly and progressively. Reduce the load
slowly and progressively when the value quoted in the procurement specification has been reached.
Remove the assembly from the tensile machine. Unscrew the nut a half-turn and cease movement, then again
unscrew and measure the breakaway torque, using the torque wrench.
Remove the nut, then submit it to a visual examination and, if necessary, an examination at a magnification of
× 10 after sectioning, to check conformity with the requirements of the procurement specification.
4 © ISO 2008 – All rights reserved

Dimensions in millimetres
Wrench nuts Clinch nuts Floating anchor nuts
and non-floating anchor nuts and gang channel nuts
a
Maximum shank diameter.
b
Chamfer to suit the nut radius.
c
Hole to allow the specified float.
d
Loading direction.
Figure 3
3.3.2.3 Test at ambient temperature and test at ambient temperature after maximum operating
temperature baking (100 % test)
This test shall be carried out at ambient temperature.
If the test includes a heat soak, then heat the nut and maintain it at the temperature quoted in the procurement
specification. Take the nut from the oven and allow it to cool slowly to ambient temperature, then, in all cases,
proceed as follows.
Lubricate the bolt and nut threads as specified in Table 1 (if necessary), assemble the bearing plate on the
bolt. Assemble the nut with a protrusion of two bolt pitches minimum (including chamfer).
Position the assembly on the tensile machine and apply the load slowly and progressively. Reduce the load
slowly and progressively when the value quoted in the procurement specification has been reached.
Remove the assembly from the tensile machine. Remove the nut, then submit it to a visual examination, and if
necessary, an examination at a magnification of × 10 after sectioning to check conformity with the
requirements of the procurement specification.
Nuts subjected to this test shall not be used again.
3.4 Wrenching feature test
3.4.1 General
This test applies only to wrenchable nuts.
3.4.2 Test device
The test device is illustrated in Figure 4 and includes the following elements:
a)
...