Surface and Sub-Surface Degradation of Carbon Fiber Reinforced Composites under Reciprocating Sliding

Carbon fiber reinforced epoxy composites consist of two parts: a matrix and a reinforcement. In this thesis the reinforcement is unidirectional carbon fiber and the matrix is a thermoset polymer called epoxy. These composites are usually not applied for tribological purposes (friction, wear), although they have inherent great potential. The nature of the carbon fiber composite wear is very important, but also the risk of debonding occurring in the interface between the matrix and the reinforcement fibers. Composite manufacturers are focusing mostly on improving the mechanical properties of such materials such as fracture toughness, hardness, and strength but little attention is given to improve their tribological properties. When applying these composites in real tribological applications in either different relative humidity or immersed in water one should bear in mind their failure process. The degradation of such materials under reciprocating sliding in different environments is still not well known and the available literature still lacks a comprehensive study of the tribological behavior of such composites. It is expected that composites respond differently with changing the counter body, sliding frequency, environment, and sliding direction which complicates their degradation behavior.This work aims at investigating the tribological behavior of carbon fiber reinforced epoxy composites in ambient air and aqueous solutions under reciprocating sliding with the goal of understanding the surface and sub-surface degradation.The principal approach adopted in this work is to establish in depth our understanding of the debonding between carbon fibers and the epoxy matrix. In a first step, a stress model is developed to get a theoretical analysis of the composite response under combined compressive and shear forces. In addition, a heat model is developed to analyze the effect of surface temperature by varying either the sliding frequency or cooling the system on water immersion. Following, experimental reciprocating sliding tests are performed to validate and explain the influence of the counter body, the sliding direction to the fiber orientation, the water immersion, and the relative humidity on the composite degradation. The knowledge acquired from theoretical and experimental analyses is used to explain the failure mechanism of carbon fiber reinforced epoxy composites in sliding contacts.Thus, for the first time carbon fiber reinforced epoxy is mechanically and thermally modelled under reciprocating sliding. It is shown that modelling is a strong tool in composite tribology which is beneficial to understand the stress concentrated region and the heat mapping of the contact area. Moreover, the sub-surface investigation is for the first time characterized in-depth by cross-sectioning the wear track by focused ion beam technique which shows clearly that debonding under reciprocating sliding takes place at the fiber/matrix interface.

Jaar van publicatie:2019

Toegankelijkheid:Open