MIL-DTL-83528 – Design Detail Specifications for Conductive Elastomers

elastomers

MIL-DTL-83528 is a U.S. military detail specification for design requirements of conductive elastomers such as the materials used, the performance of the material/part, and limitations of the part/material. Having conductive elastomer materials approved for manufacture by the U.S. Department of Defense signifies that it has passed the inspections and tests of MIL-DTL-83528. The testing and inspection methods have their own requirements and standards as documented in their corroborating MIL or ASTM testing spec.

The following will briefly describe the test method to qualify the material

Volume Resistivity

  • A sample sheet of material is placed onto a nonconductive surface and tested with a two-point probe connected to an ohmmeter. The measurements are calculated to determine the volume resistivity.

Shielding Effectiveness

  • The attenuation (shielding effectiveness) is measured for each material by applying a 1” wide frame gasket of the material to the perimeter of a metallic cover plate. The cover plate is bolted to the opening of a shielded enclosure that contains a receiver or spectrum analyzer so that it covers the opening. A transmitter antenna is placed outside of the shielding enclosure and pointed in line with the cover plate and receiver/spectrum analyzer.

Specific Gravity

  • The mass of a sample of material is measured in air, then the mass is determined when it is immersed in a liquid of a precise density.

Hardness (Shore A)

  • The hardness of the material is measured through indenting/penetrating a sample piece of material using a set amount of force and time. The corresponding indention/penetration depth is the durometer of the material.

Tensile Strength

  • A barbell sample of material is stretched through tension and the amount of force required to break the material is measured.

Elongation

  • The percent of change in length of the barbell sample before the material fractures.

Tear Strength

  • Test pieces of material are pulled in a direction 45° to the 90° center angle and measured until this force causes a deformation.

Compression Set

  • Samples of material are compressed for a set amount of time and force. The percentage of change from the original material thickness is measured.

Heat Aging

  • Material samples are heated to the upper operating temperature for 1000 hours, cooled for an hour, rinsed in isopropyl alcohol, dried for an hour, and then its volume resistivity is measured

Lower Operating Temperature

  • This temperature is the point when material a specimen retracts 10% in a methanol bath.

Electrical Stability During Vibration

  • A test gasket (frame) is clamped between two metal plates, a tightened central faster is applying the clamping force which needs to deflect the gasket 5-10 percent of its thickness. This apparatus is mounted to a vibration shaker and the resistance of the material is measured during and after vibration.

Electrical Stability After Break

  • Measurement of volume resistivity taken up to 30 minutes after breaking the material from tension.

Fluid Immersion

  • The materials are exposed to various fluids and measured for maximum volume swelling (25%) and maximum change in hardness (15 shore A units). If the measurement exceeds the maximum limit it is given a grade of non-survive, otherwise, survive.

EMP Survivability

  • Rectangle cross section washers are clamped between tin-plated aluminum plates until they are deflected 10 percent. The gasket/plate apparatus is installed in an EMP simulator and exposed to 0.9 kA/in EMP, after exposure the volume resistivity is measured.

Military Detail Specification MIL-DTL-83528E, Gasketing Material, Conductive, Shielding Gasket, Electronic, Elastomer, EMI/RFI General Specification For, revision E (DOD, 13 August 2012)