Effect of relative humidity and full immersion in water on friction, wear and debonding of unidirectional carbon fiber reinforced epoxy under reciprocating sliding

Abstract

Unidirectional carbon fiber reinforced epoxy was tested in ambient air at three different levels of relative humidity and under full immersion in demineralized water. Reciprocating sliding tests were performed at 23 °C against either stainless steel or alumina balls moving in parallel or anti-parallel direction to the fibers. We demonstrate in this work that humidity and water immersion affect significantly the fiber debonding. Under sliding against stainless steel or alumina at low relative humidity, fiber debonding is more pronounced than at high relative humidity and at water immersion. The wear depth increases with increasing relative humidity when sliding against stainless steel, whereas it remains practically constant against alumina. For all test conditions, the wear depth is larger when tested against stainless steel than against alumina. It was found that the thin moisture film formed at the surface of the stainless steel counter body leads to a higher corrosive risk than water immersion. More precisely, we demonstrate that high humidity leads to the production of oxide debris originated from the stainless steel ball which increases markedly the wear by abrasion. These debris lead to a high fluctuation of the coefficient of friction measured on carbon fiber reinforced epoxy composite sliding against stainless steel at 85% RH, whereas a steady state coefficient of friction is noticed against alumina.