Study On Moisture Absorption Of PMI Foam Cored Sandwich Composites

PMI foam cored sandwich composites have been widely used to manufacture the radome due to their excellent mechanical and electric properties.However,the working conditions of the radome are extremely complex,many factors,such as moisture,rain,seawater,have a significant impact on the properties of PMI foam cored sandwich composites.In view of the requirements of a new radome,the effect of moisture absorption on the properties of PMI foam sandwich composite under different conditions was studied in this paper.Firstly,panels with three different thicknesses and its corresponding PMI foam cored sandwich composites were prepared by hand lay-up.Then,the prepared composite panels and sandwich structure specimens were treated with the appropriate condition for moisture absorption.Properties of the composite panels and the PMI foam cored sandwich structure specimens were studied after moisture absorption at 60℃ and 85% RH.The results show that: With the increase of the composite panels’ s thickness,the samller the saturated moisture absorptivity of the specimens,the saturated moisture absorptivity and the moisture absorption rate of the sandwich structure specimens with the corresponding panel thickness are also lower,while the flexural stiffness and bending failure load of sandwich structure specimens drop less.The compressive properties of sandwich structure specimens are decreased after moisture absorption,but there is no obvious relationship between the panel thickness and the flat pressure properties.Properties of specimens under different humidity conditions(85% RH,95% RH and soaking water)were studied.The results indicate that: the saturated moisture absorptivity and the moisture absorption rate of specimens enhance as the humidity of the condition increases,but the descent of the wave-penetrating property of the sample becomes obvious with the increase of humidity.With the increase of the humidity,the decrease of the flaxural stiffness,flat compression strength and flat compression modulus of the sandwich structure specimens are more rapid,and the decrease are more,in addition,the bending failure load decreases more.Specimens were subjected to moisture absorption at 50 ℃,60 ℃ and 70 ℃,the results show that: Saturated moisture absorptivity of the specimens dips more at a higher temperature,while the specimens show a poorer wave-penetrating property.The flaxural stiffness,bending failure load,flat compression strength and flat compression modulus of the sandwich structure specimens are decreased obviously after the moisture absorption treatment,as the temperature increases,the flaxural properties decrease faster and more,and the compression properties are opposite.It is also found that,when specimens are treated in a relative moderate condition(below 60℃ and no soaking water)and the number of fiber layers of the panel is more than two,saturated moisture absorptivity of the PMI foam cored sandwich composite can be obtained by combining the panel and the PMI foam counterparts.