Effect of Water Absorption on Time–Temperature Dependent Strength of Unidirectional CFRP

Abstract

Static strengths for four typical directions of unidirectional CFRP were measured under various temperatures at a single loading rate for dry and wet specimens. The four directions were longitudinal tension and bending, transverse bending, and compression. Water absorption effects on temperature dependence of these static strengths of unidirectional CFRP were assessed. Results show that the static strengths in these four directions of unidirectional CFRP as well as the viscoelastic coefficient of matrix resin decrease concomitantly with increasing temperature and water absorption. Each of four static strengths of CFRP laminates is determined uniquely by the viscoelastic coefficient of matrix resin. Therefore, the master curves of four static strengths against the reduced time at a reference temperature can be constructed and formulated using the time–temperature shift factor for the viscoelastic coefficient of matrix resin based on the time–temperature superposition principle. These master curves of four static strengths clarify that the long-term lives for four directions decrease with water absorption.