Effects of temperature, seawater and impact on the strength, stiffness, and life of sandwich composites

A study was conducted to determine the effects of subzero temperatures, seawater saturation, and low velocity impact on the flexural strength, stiffness, and life of sandwich composites. Specimens were tested statically and in fatigue using a four-point bending arrangement that included a combined metal and rubber load pad that spanned the inner loading heads and which prevented any local crushing damage. Both undamaged and impact damaged specimens were tested in room temperature (RT) dry, RT seawater saturated, -20°C dry, and -20°C seawater saturated environments. The impact energy level was chosen to produce damage that was observable, yet did not produce excessive permanent deformation. The primary results were that reducing the temperature tended to increase stiffness, strength, and fatigue life. Seawater saturation had minimal effects on strength, stiffness, or life, but influenced the static failure mode. Impact damage had little effect on the static results, but caused a significant loss in fatigue life. These results demonstrate that static test results cannot be used to infer fatigue behaviors, and indicate the need for the accurate determination of material and structural responses across the full range of expected usage environments.