ASTM B896-99

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Designation:B896–99
Standard Test Methods for
Evaluating Connectability Characteristics of Electrical
Conductor Materials
This standard is issued under the fixed designation B 896; 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.
1. Scope 3.2 Definitions of Terms Specific to This Standard:
3.2.1 connectability, n—a combination of properties deter-
1.1 These test methods define procedures for the relative
mining the ability of a material to establish and maintain stable
characterization of conductor material connectability on the
low resistance electrical contact under the influence of dete-
basis of measurements of parameters important to the design
riorating environmental and operational factors.
and performance of electrical contacts and connections to and
3.2.2 fretting, n—accelerated surface damage occurring at
with such conductors for both power and signal applications.
the interface of contacting materials subjected to small oscil-
1.2 The parameters measured are contact resistance as a
latory displacements.
function of contact force, fretting sensitivity, and compressive
relaxation.
4. Summary of Test Method
1.3 Provisionismadeformeasurementoftheconnectability
4.1 Contact Resistance—Contact resistance is measured as
parameters at elevated temperature, or corrosive ambient, or
force is increased between conductors in a crossed-rod contact
both, as may be required for evaluation for particular applica-
pair of the material(s) being tested. Held at the maximum
tions.
specified force, test contacts may be exposed to temperature
1.4 These test methods, using standardized specimen geom-
changes or corrosive environments such as high humidity to
etry and procedures, are applicable to conductor materials as
observe the effects of such changes on electrical contact
employed in an electrical connection system and may be
resistance.
adapted for evaluation of connectability of materials in the
4.2 Fretting Sensitivity—Contactresistanceofacrossed-rod
form of actual connection system components.
pair is measured at constant normal force while a microscopic
1.5 This standard does not purport to address all of the
oscillitory tangential motion is applied at the contact interface.
safety concerns, if any, associated with its use. It is the
The number of applied motion cycles required to induce
responsibility of user of this standard to establish appropriate
contact resistance instability is determined. The test may be
safety and health practices and determine the applicability of
performedatelevatedtemperatureorincorrosiveenvironment.
regulatory limitations prior to use.
4.3 Compressive Relaxation—Change of applied contact
2. Referenced Documents force with time, at fixed engagement displacement of crossed-
wire specimens, is measured. The test may be performed at
2.1 ASTM Standards:
elevated temperature.
B 539 Test Methods for Measuring Contact Resistance of
Electrical Connections (Static Contacts)
5. Significance and Use
B 542 Terminology Relating to Electrical Contacts and
2 5.1 These test methods develop comparative information
Their Use
useful for the design of stationary contacts for wire conductors.
3. Terminology 5.2 Thesetestmethodsproduceresults,whicharefreeofthe
influence of arbitrary connection systems.
3.1 Definitions—Definitions of terms used in this test
5.3 The influence of conductor surface pretreatments and
method are in accordance with Terminology B 542.
platings can be evaluated by these test methods.
5.4 The influence of environmental factors, such as high
These test methods are under the jurisdiction of ASTM Committee B-02 on
temperature and corrosive environment can be evaluated by
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee B
these test methods.
02.11 on Electrical Contact Test Methods.
Current edition approved May 10, 1999. Published July 1999.
Annual Book of ASTM Standards, Vol 03.04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B896–99
5.5 The results obtained by these test methods provide tion of the effects of long-term environmental variables, such
guidance on connection system design parameters, such as as temperature, humidity, or gaseous ambient under conditions
contact force and gas tightness requirements. whereby the contact load is influenced by stress-relaxation
effects. Fixture design for constant displacement testing must
6. Test Methods
be rigid and matched in thermal expansion characteristics to
6.1 These test methods provide for standardization of speci-
the material being tested, such as to maintain displacement
men geometry, contact loads, and other factors, which may
within 1 % of the initial value for the temperature range in
influence the results. Use of nonstandard specimens or proce-
which it is used for the duration of the test. The rigidity
dures may influence the validity of relative connectability
requirementmaybesatisfiedbyafixturewhosespringconstant
comparisons based on the test results.
(force/unit displacement) is calculated to be no less than 2003
larger than the elastic spring constant of the specimen pair
CROSSED WIRE CONTACT RESISTANCE—FIXED
when fully engaged. The specimen spring constant is deter-
LOAD
mined by measuring the displacement required to decrease the
6.2 The standard specimen shall be 2 mm (#12 AWG, .081
contact force to 1 kg from an initial 2 kg.
in.) diameter wire, at least 25 mm ( in.) long, and straight to
6.3.8 For the purpose of environmental exposure according
within 1 %. Specimens of nonstandard diameter may be used.
to 6.3.6 and 6.3.7, the fixturing shall be designed to maintain
Resulting performance data only is considered valid for com-
contact load within 62 % over the range of applied tempera-
parison with results on same-size specimens, however.
ture for the duration of the test. Fixturing shall be designed
6.3 The apparatus consists of a fixture capable of perform-
symmetrically so as to preclude introduction of shear forces in
ing as follows:
the plane of the specimen contact interface as temperature is
6.3.1 Specimens are oriented perpendicular to one another.
changed.
Contact between the specimens occurs approximately at the
6.3.9 The specific design of the apparatus may vary, pro-
center of each specimen (lengthwise).
videdthatthefunctionalrequirementsaremet.Arepresentative
6.3.2 Specimens are supported by flat or vee-groove, or
embodiment of a constant load crossed-wire fixture is provided
equivalent holders, so as to prevent bending due to applied
in Appendix X1. For constant displacement crossed-wire
contact load. Specimen support fixture shall support the speci-
testing, a variation of the stress relaxation fixture shown in
men for a length of 4D 6 0.5D, where D = specimen diameter
Appendix X3 may be used.
and shall be centered 6 0.5D with respect to the point at which
6.4 Specimen contact load, current, and potential drop shall
the crossed specimens make contact. Beyond the load support
be recorded for each specimen pair as they are brought into
region (at center of the specimens), the specimens shall be
initial contact and as the load increases. During subsequent
unsupported.
long-term testing at constant load or constant displacement,
6.3.3 Electrical connections to the ends of the specimens
specimen current and potential drop shall be measured at
shall be made by flexible leads to fixed terminals mounted on
appropriate intervals, no less frequent than ⁄10 of the duration
the fixture base.
of the test. For specimens exposed to elevated temperature, the
6.3.4 The specimens are brought into contact at a rate of 1
measurements may be performed at room temperature if
mm/min or less until contact is made.After physical contact is
required to achieve the specified accuracy.
established, the contact force is increased at a rate of 1 kg/min
FRETTING SENSITIVITY
with a maximum allowable lateral motion of 0.001 mm.
Contact force is increased until it reaches the lesser of the 6.5 Specimen size and fixturing for initial engagement shall
following: beinaccordancewith6.1-6.3.5.Additionalrequirementsareas
6.3.4.1 120 % of the force required to achieve contact follows:
resistance of 1.0 mV. 6.5.1 At a maximum force as determined in 6.3.4, the
6.3.4.2 2.0 kg (for standard specimen diameter). specimen load shall be fixed, maintaining the contact force for
6.3.4.3 2.0 3 D/2 kg (for nonstandard specimen diameter) the balance of the test.
where D = diameter in mm. 6.5.2 A cyclic motion of 20 µm amplitude at the contact
6.3.5 Instrumentation is provided for measurement of con- interface shall be imposed on one of the specimens in the
tact force, contact current, and contact voltage. The maximum direction of its longitudinal axis. The other specimen shall be
open circuit voltage shall be 10 mV and the maximum current held rigid. Fixture must be calibrated to assure the correct
shall be 100 mA. displacement at the actual contact interface between the
6.3.6 Constant load long-term testing at the maximum force specimens. Frequency of the applied motion shall be 1 cycle/
(see 6.3.3) the specimen assembly may be fixed, maintaining min.
the contact force and the physical relationship between the 6.5.3 For the purpose of environmental exposure during the
specimens so as to allow controlled evaluation of the effects of fretting sensitivity test, the fixturing shall be sufficiently
long-term environmental variables, such as temperature, hu- resis
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