Application Note | Wire Fatigue
Fatigue Testing of Wire with Electrical Conductance Apparatus
Detecting the Exact Point of Wire Failure by Gauge with a Multimeter on a Linear Reciprocating Tribometer
Research & Experimental Testing
Frank Liu
Visual Design & Editorial
Andrew Shore
Introduction
Electrical wires are the most common form of interconnects between electrical devices. Wires are usually made of copper (and sometimes aluminum) due to copper’s ability to conduct electricity very well, ability to bend, and its cheap cost. Outside of material, wires can also be assembled in different ways. Wires can be obtained in different sizes, usually denoted by gauges. As the wire diameter increases, the wire gauge decreases. Longevity of the wire will change with wire gauge. The difference in longevity can be compared by conducting a reciprocating linear test with the NANOVEA Tribometer to simulate fatigue.
Importance of Fatigue Testing of Wire
For reliability of electrical devices, the wires must have high durability. A single wire can be the reason the whole device becomes non-functional. As a result, finding critical conditions when wires begin to fail is important to prevent device failure. Fatigue testing is done to simulate real life conditions to better understand how failure occurs. To identify failure for an electrical component, a multimeter was augmented to the NANOVEA Tribometer. The addition of the multimeter helps precisely identify the point of failure compared to other methods, such as visual inspection.
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Measurement Objective
Three different wire gauges were tested with the NANOVEA Tribometer with a reciprocating linear test module. The resistance of the wire was continuously measured during the test to identify the point of critical failure. To avoid electrical contact, an insulating aluminum oxide ball bearing was used. Each test was conducted in the same manner to compare the durability between wires.
NANOVEA T2000 High Load
Pneumatic Tribometer
Test Procedure
| Test parameter | Value |
|---|---|
| Test module | Linear reciprocating |
| Normal force | 15 N |
| Rotational speed | 50 rpm |
| Wear track amplitude | 20 mm |
| Ball material | Al2O3 |
| Ball diameter | 6 mm |
Table 1: Test parameters for fatigue testing on wire.
Results and Discussion
The three wire gauges all failed at different times. The higher gauge (smaller wire diameter) showed failure much faster than the lower gauge.
The selection of the point of failure was found when the resistance began reading infinity (no electrical current flowing through the wire). This meant the metal in the wire became discontinuous due to the fatigue testing. Continuity may be briefly restored from the internal wires brushing each other. To combat this inconsistency, the point of failure was selected from the first occurrence of discontinuity.
| Sample | Revolutions | Minutes | Distance (m) |
|---|---|---|---|
| 16 gauge | 1404 | 28.08 | 56.16 |
| 18 gauge | 308 | 6.16 | 12.32 |
| 20 gauge | 130 | 2.60 | 5.20 |
Table 2: Point of failure for wires in revolutions, minutes, and distance.
Figure 5 shows the results from the fatigue testing. Each wire failed in different ways. The 16-gauge wire failed when the metallic wires were worn through. The 18-gauge wire had its sheath remain intact, but the metallic wires were still damaged. The use of the multimeter allowed detection of failure, even when internal. The 20-gauge wire was torn through and completely separated into two pieces under similar testing conditions.
Conclusion
Three different wire gauges underwent fatigue testing under the same conditions. The 16-, 18-, 20-gauge wires lasted 28.08, 6.16, and 2.60 minutes respectively. Lower gauge wires have shown to last much longer than higher gauge wires under these testing conditions. Each wire has shown different failures under similar test conditions. The use of the multimeter to record electrical conductance allowed for a consistent way to identify failure. This proved especially useful for the 18-gauge wire since it failed before visual damage can be seen.
The NANOVEA Tribometer offers precise and repeatable wear and friction testing using ISO and ASTM compliant rotative and linear modes, with optional high temperature wear, lubrication and tribo-corrosion modules available in one pre-integrated system. An optional 3D non-contact profiler is available for simple in-situ depth measurements or high-resolution 3D imaging of wear tracks in addition to other surface measurements such as roughness.
Frequently Asked Questions About Wire Fatigue Testing
How can a tribometer test wire fatigue?
A linear reciprocating test repeatedly loads the wire under a ball, simulating fatigue under the same conditions for every sample, so wires of different gauges can be compared.
How is the point of failure detected?
A multimeter added to the tribometer measures the wire’s resistance throughout the test. Failure is taken at the first reading of infinite resistance, when no current flows because the metal has become discontinuous.
Why not rely on visual inspection?
Failure can be internal. The 18-gauge wire kept its sheath intact while its metal wires were damaged; the resistance reading caught the failure before any visual damage could be seen.
How long did each gauge last?
Under 15 N at 50 rpm over a 20 mm stroke, the 16-gauge wire failed after 28.08 minutes (56.16 m), the 18-gauge after 6.16 minutes (12.32 m) and the 20-gauge after 2.60 minutes (5.20 m).
Why use an aluminum oxide ball?
Al2O3 is an electrical insulator, so the ball does not make electrical contact with the wire and the resistance measurement reflects only the wire itself.
Which instrument was used?
The NANOVEA Tribometer with a linear reciprocating module, augmented with a multimeter to record electrical conductance during the test.
