REINFORCEMENTS

The reinforcement fabrication process shall be those most suitable for the particular joint needs.

Metal reinforcements are either thin or thick, the difference having an influence on the possible method of fabrication. Thin reinforcements are defined as reinforcements that can be fabricated by hydro-forming or spinning and will be used in joints with limiting axial compression requirement. Hydro formed reinforcements are recommended for research or small development programs. Spun reinforcements are recommended for production programs. For both types, the forming should be made with the material in a normalized condition, and the material should be heat treated to the required properties prior to final machining.

Thick reinforcements should be machined from plates for research or small development programs. The plate should be normalized for rough machining and heat treated to the required properties prior to final machining. For production programs, thick reinforcements should be stamped to the required shape with the material in the normalized condition, and then heat treated to the required properties prior to final machining.

Heat treatment will cause some distortion of the reinforcements. This distortion should be considered in the assembly of a joint by inspecting the reinforcements for high and low spots and then assembling the reinforcements so that all the high spots are aligned and the elastomer thickness will be circumferential uniform.

Although composite reinforcements have been fabricated by winding and molding, lay-up and molding, and molding with a mixture a chopped fiber and resin, it is recommended for all production programs that composite reinforcements be fabricated by laying resin impregnated cloth cut into specific patterns into a matched metal mold and curing under pressure at a temperature and time suitable for the resin. However, in research or development programs, consideration should be given to compression molding with a be  fabricated   as in integral part of reinforcement.

JOINT ADHESIVE SYSTEM

The joint adhesive system shall not fail before the elastomer material.

The joint adhesive system must be evaluated prior to joint fabrication by use of quadruple-lap shear specimens; an acceptable system must fail cohesively. The specimens must duplicate the thickness and cure condition of the elastomer and bond system in the joint. Fabricated joint should be bench tested at least to ultimate pressure and vectoring conditions to demonstrate the structural capability of the adhesive bond system.

Failures can occur when the bond system is either too chick or too thin. To control the thickness, the viscosity of the primer and the adhesive, the rate at which these materials are sprayed on the reinforcements, and the time for spraying should be monitored; limits on these items should be included in the joint fabrication specification.