Abstract
Foreign object damage (FOD) behavior of two commercial gas-turbine-grade silicon nitrides, AS800, SN282, was determined at ambient temperature through postimpact strength testing of target disks impacted by steel ball projectiles with a diameter of 1.59 mm in a velocity range from 115 to 440 m/s. AS800 silicon nitride exhibited a greater FOD resistance than SN282, primarily due to its greater value of fracture toughness (KIc). The critical impact velocity Vc for which the corresponding postimpact strength was the lowest was Vc ≈ 440, 300 m/s for AS800, SN282, respectively. A unique lower strength regime was typified for both silicon nitrides depending on impact velocity, was attributed to significant radial cracking. The damage generated by projectile impact was typically in the form of ring, radial, cone cracks with their severity, combination being dependent on impact velocity. Unlike the thick (3 mm) flexure bar target specimens used in previous studies, the thin (2 mm) disk target specimens exhibited a unique back-side radial cracking on the reverse side just beneath the impact sites at, above impact velocities of 160 m/s for SN282, 220 m/s for AS800.
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