Effect of moisture on the mechanical properties of glass fiber reinforced polyamide composites

Abstract

The effect of moisture on the mechanical properties of glass fiber reinforced polyamide composites was investigated. The composites of short glass fiber/polyamide with different weight percent (0-30 wt%) were prepared. To investigate the effect moisture on mechanical properties of these composites, the specimens were prepared and then immersed in distilled water for a period of 60 days. The weight changes of the specimens were daily measured to determine the amount of moisture absorption of the specimens. Tensile test and flexural test were conducted based on ASTM D638-02a and ASTM D790-02, respectively. The effect of moisture on the microstructure of the composites was also investigated. The moisture absorption of the glass fiber reinforced polyamide composites could be divided into four stages: (I) the beginning stage (1-7 days), (II) the second stage (8-24 days), (III) the third stage (25-35 days) and (IV) the saturated stage (36-60 days). Yield strength, ultimate tensile strength and flexural strength of all specimens significantly decreased at the beginning stage of moisture absorption and then these mechanical properties were almost constant. The modulus of elasticity of all specimens decreased at the beginning stage and saturated stage. In addition, ductility (%Elongation) of all specimens did not change at the beginning stage. However, ductility of all specimens significantly decreased in the third stage, and then their ductility were almost constant. Based on the microstructure analysis, the results indicated that the transition of brittle to ductile properties of the glass fiber reinforced polyamide composites after moisture absorption would be attributed to the changes in their mechanical properties.