A New Test Facility for Measuring the Coefficient of Moisture Expansion of Advanced Composite Materials

Abstract

A new test facility is here described; it has been designed to measure carefully the coefficient of moisture expansion (CME) in specimens made of advanced composite materials. The facility is basically composed of a thermostat, contained in a vacuum chamber, in which five carbon fiber-reinforced plastic (CFRP) samples, one Invar sample, and six displacement transducers are enclosed. The CFRP specimens are first subjected to an accelerated absorption cycle and, later on, placed into the vacuum environment (10−3 Pa) of the thermostat at a temperature of 330K, controlled within ±0.1K. The measurement of dimensional variations are carried out using very accurate inductive displacement transducers mounted on Invar frames (5 × 10−8 m is the typical accuracy). One of the specimens tested is made by Invar, with a zero CME, to have a stable length reference during the simultaneous measurement of the five CFRP samples. About 100 h are usually necessary for the test. A coefficient of moisture expansion of 3.85 × 10−5 and 3.1 × 10−3 (ΔM/M)%−1 was obtained along the fiber direction and normal to the fiber direction, respectively. A maximum standard deviation of 5 × 10−6 (ΔM/M)%−1 in the CME along the fiber direction has been confirmed.