A comprehensive investigation of plastic, elastomeric, ceramic, glass, metallic, and composite materials for short exposure time—rain erosion resistance at velocities of Mach 1.5, 2.0, 2.5, 3.0, and 4.0 has been accomplished.

Wedge-shaped holders capable of exposing multiple materials specimens at five different impact angles were designed, fabricated, calibrated, and successfully employed for 65 supersonic firings on the rocket sled track at Holloman Air Force Base, N. Mex.

Droplet breakup effects on the wedge because of shock-wave-droplet interactions have been analyzed and found to influence a portion of the data. Quantitative data in the form of weight loss per unit area and mean depth of penetration rate (MDPR) were determined for the various materials, and an equation for relating the erosion rate (MDPR) with the normal component of the velocity (V sinθ) was developed as follows: MDPRsinθ=K(Vsinθ)α Values of K and α have been determined for all of the materials.

The relationship of erosion rate-velocity dependence for numerous materials at powers of five or greater for the velocity exponent has been confirmed at velocities up to three times as great as previously conducted.

The values for the velocity exponent (α) have been determined as 6 to 10 for bulk ceramics, 5 to 7 for bulk plastics and fiber-reinforced plastic composites, 6 to 8 for glasses, and 7 for aluminum indicating a very strong erosion rate-velocity dependence at speeds up to Mach 4.0.