Residual strengths of composite structures subjected to ballistic impact

Abstract

Fibre-reinforced polymer composite materials are increasingly used on aircraft. Unlike civil operations, military aircraft are vulnerable to ballistic impact damage. Knowledge about ballistic damage to the carbon fibre polymer composite materials is important for military aircraft design, operation, and battle-damage repairs. Very limited research has been reported in measurement of residual strengths of composite structures subject to ballistic damage.Projectiles with 7.62mm, 12.7mm and 20.0mm calibres were used in the ballistic testing with relatively low and high impact velocities between 200m/s and 1000m/s. Tap test, ultrasonic A-scan and flash thermography non-destructive inspection techniques were used to examine the extent of damage caused by ballistic impact on the specimens.Tensile, compression, and shear specimens were manufactured and tested. The results showed that with the impact velocity clearly above the ballistic limit, though the overall damage area is significantly larger than the projectile calibre size, the residual strength of the specimen with ballistic damage was not significantly lower than that of a specimen with a machined hole of the same diameter as the projectile calibre. A modified characteristic length model well fitted the measured results. FEM analysis was also conducted that provided insight understanding about the failure mechanism.