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Crimp test standards and methods

Background

Variety of crimped wire terminalsThe quality of a crimp joint depends on the mechanical strength of the joint as well as its electrical conductivity. If results from pull force tests are within an allowed range, it assures that the proper crimp force has been applied during crimping. This is crucial as, when making a crimp, enough force must be applied to break down the layer of non-conductive oxides that may build up on the stripped conductor and the plating on the inside of the terminal. This is necessary to provide a good metal-to-metal contact. If this does not occur, electrical resistance can increase. Overcrimping a crimp termination will reduce the circular area of the conductor and thereby increase electrical resistance.

Crimp joint testing (also known as "pull testing") ensures the integrity of the final product but, more importantly, it ensures the effectiveness of the crimping tool itself, since it can be calibrated according to test results. Calibration is best carried out in response to Statistical Process Control (SPC) analysis which can be gathered from data obtained by pull testers.

Standards and methods

International and industry standards all prescribe procedures for testing wire terminal strength in a repeatable manner.It is essential that there is no jerking or sudden application of force so this is the reason why standards state that there should be a 'constant rate of pull' and most define a speed at which tests should be performed. The only practical way to achieve repeatability for pull-out tests is to use a motorised test system such as the CrimpTest-1 or the WTST range of testers.

Although standards define a minimum pull-out force limit according to the wire diameter and AWG conductor size, it is of greater importance to the manufacturer and user to know that joints can definitely sustain higher loads. So the actual force at which the termination will break is measured. Directly pulling the wire joint until destruction at a constant rate, typically 25 to 50 mm/min, is the  most commonly adopted test method and performed by using a motorised test system. The peak force to separate the terminal from the wire is measured and is compared to the table of minimum pull-out forces in the standard to determine a pass or fail.

Other tests call for a steadily increasing load to a specific limit which is then held for a defined period of time before the test continues until a break of the joint is achieved.

This test method establishes the requirements for a standardized method of evaluating the quality of crimped-type electrical connections to solid or stranded conductors. This test method applies to 16-gauge and smaller diameter copper wire, coated or uncoated. Evaluation testing is designed to ensure that a particular design crimped connection system consisting of conductor and component and associated tooling is capable of achieving a reliable electrical and mechanical connection.
This standard establishes a test method to determine the axial tensile load that can be applied to a mated pair of connectors, and the holding effect of a connector cable clamp without causing any detrimental effects upon the cable or connector when subjected to inadvertent axial tensile loads.  Load is increased to a specified level for the connector or conductor, and held for 1 hour, whilst electrical continuity at 100 mA is measured.
Provides updated tests and test requirements for crimped joints with copper, copper alloy, aluminium and aluminium alloy conductors.
- 408 Elements of electrical and optical connection: Describes a procedure for measuring the mating and unmating forces for elements of connection.
- 412 Elements of electrical and optical connection: Describes a procedure for measuring the contact insertion and extraction forces.
- 417 Elements of electrical and optical connection: Defines a method of determining the tensile strength of crimped connections.
This standard for aircraft wiring, specifies a method of determining the forces required to insert and extract the contact pin into and out of the terminal socket of the signal contact.
Describes methods for tensile strength and pull-out testing.
Def Stan 59-71 specifies the mechanical and electrical performance requirements for crimped electrical connections onto copper conductors for use in MOD equipment and systems. It details the Qualification Approval requirements for crimping tools, the Capability Approval requirements for crimp terminals, splices and connector contacts and the crimp evaluation tests which shall be met by a Capability Approved terminal, splice or connector contact when crimped to a copper conductor by a Qualification.
Describes the design requirements and tests for the crimping of insulated and non-insulated terminations to general purpose cables, with conductors of copper, copper alloy, aluminium or aluminium alloy, in locations in which the stabilized conductor temperature does not exceed the values specified for the relevant type, i. e. 105 °C, 190 °C or 260 °C. 
This standard sets out requirements for interconnecting cable and harness assemblies that connect electrical/electronic and electromechanical components and is applicable to NASA programs involving interconnecting cable and wire harnesses for flight hardware and mission critical ground support equipment. 
SAE (Society for Automotive Engineers) standard AS7928 includes pull testing of crimped terminals, lugs, splices and conductors.
USCAR (US Council for Automotive Research) standard 21 includes  pull testing of solderless crimped connectors. 
486-A, 486-B issued 2013.  This safety standard relates to wire connectors and soldering lugs. Section 9.3.4 covers the 'pull out' test method.
486-C issued 2013.  This safety standard relates to splicing wire connectors. Section 9.3.4 covers the 'pull out' test method. Section 9.6 covers 'secureness of insulation'
Issued 2009.  This automotive company standard relates to crimp connectors. Section 4.5.1 covers the 'conductor extraction force' test method.

Related standards

This standard covers non-destructive testing of individual wire bonds made by either ultrasonic, thermal compression or thermosonic techniques. The test is intended to reveal (by breaking) non-acceptable wire bonds but is designed to avoid damage to acceptable wire bonds.
Specifies requirements for metallic, non-metallic and composite cable ties and their associated fixing devices used for the management and support of wiring systems in electrical installations. Includes method for testing loop tensile strength cable ties of metallic and non-metallic types, and test conditions.
Defines a method for loop tensile strength testing of cable ties for use in aerospace applications, using a split-round mandrel of defined dimensions.