Residual Stresses Depending on Changes of Temperature and Water Absorption in Carbon Fiber/Epoxy Single-Fiber Model Composites

Abstract

The axial stresses of the fiber in single carbon fiber/epoxy resin model composites under change of surroundings, e.g., temperature and water, have been measured by micro-Raman spectroscopy. The specimens were soaked in hot air, water and hot water, and returned to the beginning state to cause cyclic changes of temperature and water absorption :(1) heating and cooling at atmospheric environment, (2) immersing in the water of the room temperature and drying, and (3) immersing in the hot water of 80 and drying at the room temperature. In the case of ( 1) and ( 2), the fiber axial stresses after the cyclic change of the surroundings recover almost the same before the heating or the immersion. On the other hand, the fiber axial stress after the drying is more compressive than that before the hygrothermal exposure in the case of (3). Hygrothermal effects on the residual stress are discussed based on fiber stresses caused at elevated temperature over the glass transition temperature of the epoxy resin.