Effects of moisture ingression on the impact damage resistance and damage tolerance of alumina based oxide/oxide ceramic matrix composites

In this study the effects of moisture ingression on the impact damage resistance and damage tolerance of Nextel (TM) 610/alumina-silicate ceramic matrix composites were experimentally evaluated. Thin and thick composite laminates with balanced and symmetric layups were placed inside an environmental chamber at 80 degrees C and 85% relative humidity till moisture saturation was reached. The laminates were then subjected to low velocity impacts using a hemispherical steel impactor at energy levels of 2.5 J and 10 J for the thin and thick laminates, respectively. This resulted in similar damage depths on the impactor side between the two sets of laminates. The resultant damage was characterized non-destructively with the damage metrics of external dent area, dent depth and planar internal damage area quantitatively determined. Impacted laminates were subject to in-plane compression loading and the residual strengths were evaluated. Planar internal damage area was larger for the moisture exposed laminates in comparison to their pristine counterparts for both the thin and thick laminates. Also, larger internal damage area resulted in lower compression-after-impact strength and thus, less damage tolerant laminates. This was true for the pristine and moisture exposed cases for both the laminate thicknesses.