Page 38 - 2019 Mil/Aero eBook
P. 38

1. Mating Cycles
Mating cycles vary considerably from application to application. Mating cycle benchmarks are born out of military specification norms and are typically de-rated from the mating pair’s actual capabilities. Some systems require interconnects to be mated for testing and acceptance but, once engaged on the platform, are only unmated and mated again due to an issue or an upgrade. Other systems require mating and unmating on a regular basis, and those that are dedicated to test systems require continual mating and unmating.
Mating cycles mechanically wear interconnects’ coupling devices and contact interfaces and can expose the base materials of these components, which can be susceptible to corrosion in humid or salt laden environments. Extreme cases of wear can increase the mating and unmating torques of coupling systems or even break the continuity of a mated pair of contacts. The number of mating cycles that test harness interconnects are subjected to should be carefully monitored, as wear on a test harness interconnect could damage the interconnects on the tested product.
Interconnects can be optimized for tens of mates to tens of thousands of mates. Material selection, finish, surface roughness, the contact system, and lubrication all play a significant role in the number of mating cycles an interconnect can reliably perform.
The two primary points of concern for end-users are the performance of the coupling nut (or other mechanical mating technology) over time, which is obviously less of a concern in push-pull connectors, and changes in contact electrical performance due to fretting or other forms of contact wear. For this reason, rugged systems almost always use mil-qualified contacts (e.g., M39029) with regulated dimensional and plating specifications. When properly engineered into a connector, mil-spec contacts can support many thousands of cycles without issue.
Avnet stocks Glenair’s Series 23 SuperNine® MIL-DTL-38999 Series III Type Connectors, which feature advanced plating and sealing materials, integrated EMI shielding, and a high-reliability anti-vibration coupling mechanism; are available in an extensive line of PC tail configurations, as well as with hermetically sealed crimp contacts and with accessories including backshells, protective covers, and shrink boots; and are rated for 1,500 mating cycles.
2. Coupling Style
Interconnect coupling systems facilitate mating and unmating processes. Simple threaded coupling systems are generally adequate for converting torque into axial displacement, but often require multiple rotations of the coupling nut to fully engage the connectors. Multi-start threaded coupling systems can reduce the number of rotations required to fully engage connectors, and thus enable quicker mating and unmating. One shortcoming of threaded coupling systems is that there is often no clear indication that the connectors have been fully mated.
Bayonet and lever-style coupling systems have the advantage of locking into a detent at full mate, which provides users with some tactile, visual, and/or audible affirmation of full mate. The primary drawback of these systems is that all of the load associated with mating and unmating is focused on the bayonet pins, which requires them to be made of potentially weightier and/or costlier wear-resistant materials, unlike threaded systems, which distribute the load across the threaded surfaces and avoid the types of concentrated force or stress that causes wear. Another drawback is the backlash or back-off in the axial engagement due to the need to overcome the detent in the engagement ramp, which facilitates the locking of the coupling mechanism. In this way, push-pull systems are similar to the bayonet design, as their coupling system also needs to overcome a detent for proper mating and locking.

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