Numerical Investigation of Water Drop Erosion Mechanisms in Infrared-Transparent Materials.

摘要

Numerical techniques were used to investigate the response of IR window materials to subsonic impacts (675 and 1100 fps) of water drops. Tensile crack initiation and propagation were treated, and the final predicted crack patterns were used to measure damage. Target damage sensitivity to elastic and tensile failure properties, impact velocity, density, and variations in numerical cell size were studied for 21 cases. The concept of using a rigid surface as an intermediary between water drop impact and window response was validated. An increase in the critical failure tensile stress, sigma subtau, to 8000 psi from the nominal 6500 psi causes a 60% reduction in target damage, while a decrease to 5000 psi increases target damage by over 1000%. The tensile strength of the target is the most sensitive macromechanical physical characteristic in determining target damage. Target damage decreases with an increase in Young's Modulus or Poisson's Ratio and with a decrease in density. The approximate relationship of the macromechanical property sigma sub tau to a fundamental micromechanical property (the stress intensity factor (K sub I) in terms of the numerical calculation cell size (Delta x) is as follows: K sub I = sq. root of (pi(Delta x)) sigma sub tau.