CETR Friction and Electrical Testing of One-Finger and Three-Finger Electric Connectors
Service Requested
Item 1, Insertion Test. Measuring both friction force and electric contact resistance of one-finger and three-finger electric connectors during their insertion.
Item 2, Fretting Test. Measuring both friction force and electric resistance of one-finger and three-finger electric connectors during 1-mm-stroke fretting.
Status:
Item 1 was done and repeated, results are very repeatable.
Item 2 was done and repeated, results are very repeatable.
Part I – INTRODUCTION
1.1. Objective:
This work was requested by a major customer to evaluate the CETR Micro-Tribometer for electrical contact durability measurements. It should be considered not the final stage, but a very successful beginning of a work to establish a correct database of advanced tribo-metrological and electrical parameters of various connectors and switches. Such database can later be used for design, evaluation, optimization and routine control of electrical connectors and switches.
CETR will gladly support the electric contact projects, by providing both laboratory support and the most advanced test equipment. When any special piece of test and measurement equipment will be required for either R&D or Quality Control or Incoming Inspection purposes, CETR will be happy to either modify the micro-tribometer or develop new custom testers, including on confidential basis.
1.2. Equipment:
Micro-Tribometer model UMT-2 is a highly precision, fully automated instrument. It can provide both rotational and/or linear motions to various parts and assemblies, in both vertical and horizontal directions, and thus simulate the dynamics in the real machines. It can measure numerous tribological parameters, including:
- friction force, torque and coefficient,
- in-situ wear depth and wear rate,
- contact acoustic emission,
- contact electrical resistance and capacitance,
- digital video.
A general view of this instrument is presented below.
Part II - INSERTING AND FRETTING TESTS
2.1 Samples:
Inserting and fretting experiments were conducted for two types of connectors, namely one-finger and three-finger connectors.
2.2. Experimental Procedures:
Inserting Experiment: a one-finger or a three-finger connector was inserted into a bus bar for about 7 mm to make electric contacts with the bus bar. Both friction force and electric contact resistance were measured continuously during the inserting.
Fretting Experiment: after the inserting procedure, a one-finger or a three-finger connector was oscillated between 7 mm and 8 mm contact depth. Both friction force and electric contact resistance were measured continuously.
2.3. Experimental Results:
Test results for the insertion tests are shown in Figures 1 and 2 for one-finger connectors and Figures 3 and 4 for three-finger connectors.
Test results for the fretting are shown in Figures 5 and 6 for one-finger connectors and Figure 7 and 8 for three-finger connectors.
Figure 1, Insertion test for one-finger connector.
Figure 1, inserting depth (Z1, in white), friction force (Fz, in red) and electric contact resistance (I2, in brown) are shown as a function of inserting time from 5 to 75 seconds for one-finger connectors. The first 5 seconds was for initial stability. The friction force reached a maximum value of about 120 N at about 25 seconds, at an insertion depth of about 2 mm; at the same time the electric contact resistance reached a minimum value of 20 mOhm. The friction force then dropped, and the contact electric resistance increased, during further insertion, for more than 2 mm inserting depth. This behavior was quite repeatable, as demonstrated in Figure 2 for a repeat run.
Figure 2, Repeat run as for Figure 1 (insertion test for one-finger connector).
Figure 3, Inserting test for three-finger connector.
Figure 3, inserting depth (Z1, in white), friction force (Fz, in red) and electric contact resistance (I2, in brown) are shown as a function of insertion time from 5 to 75 seconds for three-finger connectors. The first 5 seconds were for initial stability. The friction force reached a maximum value of about 120 N at about 10 seconds, at an insertion depth of 2 mm; at that time the electric contact resistance reached a minimum value of 10 mOhm. With further insertion, friction force dropped while contact electric resistance remained small for more than 1 mm insertion depth. This behavior was very repeatable, as demonstrated in Figure 4 for a repeat run.
Comparing Figures 1 and 2 with Figures 3 and 4, one can see that the electric contact resistance of the three-finger connector reached the minimum value faster and the minimum value was only half of that for the one-finger connectors.
Figure 4, Repeat run as for Figure 3 (inserting test for three-finger connector).
Figure 5, Fretting test for one-finger connector.
Figure 5, fretting displacement (Z1, in white), friction force (Fz, in red) and electric contact resistance (I2, in brown) are shown as a function of fretting time from 5 to 95 seconds for one-finger connectors. The first 5 seconds were for initial stability. The friction force progressively increased with fretting time, whereas the electric contact resistance progressively decreased. This indicates that surface conditions were continuously changed as the two surfaces rubbed against each other. This behavior was very repeatable, as demonstrated in Figure 6 for a repeat run.
Figure 6, repeat run as for Figure 5 (fretting test for one-finger connector).
Figure 7, Fretting test for three-finger connector.
Figure 7, fretting displacement (Z1, in black), friction force (Fz, in red) and electric resistance (I2, in brown) are shown as a function of fretting time from 5 to 65 seconds for three-finger connectors. The first 5 seconds were for initial stability. The friction force progressively increased with fretting time, whereas the electric contact resistance progressively decreased with fretting time. Again, this indicates that surface conditions were continuously changed as the two surfaces rubbed against each other. This behavior was very repeatable, as demonstrated in Figure 8 for a repeat run.
Figure 8, repeat run as for Figure 7 (fretting test for three-finger connector).
Comparing Figures 5 and 6 with Figures 7 and 8, one can see that the contact electric resistance of three-finger connector was only half of that for one-finger connectors. In addition, it appears that three-finger connectors reached the steady state faster than one-finger connectors in the fretting tests.
PART III. CONCLUSIONS
A. The Micro-Tribometer is confirmed to be capable of electric contact testing with both friction force and electric contact resistance measured in various testing modes.
B. The contact electric resistance of three-finger connectors reached the minimum value faster, and the minimum value was only half of that for one-finger connectors.
C. In the fretting tests, the contact electric resistance of three-finger connectors was only half of that of one-finger connectors, at the same friction force. In addition, it appears that three-finger connectors reached the steady state faster than one-finger connectors.