Reusable constant force spring force bands (CFSB) M32628/ 01-10 thru 13 (ISOTDS1 thru 4) shield termination bands were evaluated for tensile strength performance as described in SAE AS85049™ and AS85049/128™. The M32628/01 shield termination bands are employed on shielded wire harness constructions to secure the shield on to the connector accessory/back-shell banding platform in order to protect the wires in the bundle from electromagnetic interference (EMI).

Figure 1. Test Setup

Four sizes of constant force spring bands were tested applied to eight shell sizes of connector accessories/backshells. The CFSBs were installed on A-A-59569 shield braid of suitable width, on shell size A- H of M85049/88™ backshells, mated to interface connector fixtures. The M85049/ 88™ backshells mate to the Mil-Dtl-38999 Series 3 connectors. The braid retention/tensile test requirements are per AS85049/ 128F™, para 2a. To pass the test, the M32628/01-10 thru -13 constant force spring band test articles may not shift, loosen, break or slip after exposure to the prescribed linear force.

For the band termination test, a 6-inch braid was clamped by each specimen to the accessory. The braid shell was tin coated copper in accordance with a-a-59569 with a 90% coverage. Two specimens each were clamped to an m85049/82-10*03, m85049/82-18*03, and m85049/82-28*03 accessory respectively.

For the braid retention test, the braid was pulled at a rate of 1 inch per minute to a force of 100 pounds minimum for braid .50 inch and under and 150 pounds minimum for braid over .50 inch. The braid could not pull out, and band slippage could not exceed .025 inch when measured from a fixed point on the adapter. Braid breakage due to tensile load was not viewed as a failure.

The AS85049/128F™ para 2a test was performed to assess the tensile strength performance characteristics of the M32628/10-10 thru -13 (ISOTDS1 thru 4) reusable constant force shield bands when installed on the legacy Mil-Dtl-38999 Series III compatible M85049/ 88™ EMI accessory. All shell sizes were tested, versus only the three called out in the AS85049/128F™ para 2.

Figure 2. Test Article Before Tensile Testing

All backshells tested were M85049/ 88™, size -9 thru -23 (A-H). They were aluminum base metal, with W=Cadmium plating per AS85049™ with the suitable cable entry sizes.

Specimens were tested using an electromechanical 100 KN MTS load frame. A smaller 10 KN load cell was utilized to minimize error in the test data. Specimens were fixtured using a mechanical wedge grip and fittings that were manufactured to interface with the different connector assemblies.

The tensile test setup was programmed to apply a tensile load by increasing the displacement between fixed ends of the assembly using a rate of 1 inch per minute until the desired load was reached. For accessory shell sizes 9 thru 19 connectors, a minimum force of 100 pounds was the required load while using .50 inch or less width braid. For the shell sizes 21 and 23, the minimum force applied was 150 pounds as the braid was wider than .50 inches (one inch). Once the maximum force requirement was reached, the applied force dwell/hold was one minute on average.

This work was done by Oliviu (Ollie) Muja and Matthew Stanley for the Naval Air Warfare Center Aircraft Division. For more information, download the Technical Support Package (free white paper) below. NAWC-0004

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This article first appeared in the September, 2021 issue of Aerospace & Defense Technology Magazine.

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