Research On Mechanical Properties Of Composite Foam Sandwich Structures In Humid And Hot Environment

Fiber reinforced polymers(FRP)has emerged in structural reinforcement at the end of the last century because of its advantages of light weight,high strength and corrosion resistance.after more than 20 years of development,it has basically repla ced steel as the preferred material for structural reinforcement,and has been widely used in the practical engineering of strengthening concrete structures such as houses,bridges and so on.However,the working environment of concrete is more complex,such as dams,piers and other concrete structures are in a flooding environment for a long time,which are prone to environmental corrosion,concrete cracking,floating impact and so on in the course of service.as a protective structure of concrete,the water resistance and strength of composite materials are related to the safety of the structure,so it is particularly important to study its moisture absorption and anti-fail-ure mechanical properties in the service environment.In this paper,the moisture absorption and mechanical properties of composite foam sandwich structure are studied.The specific research contents are as follows:1.Vinyl resin laminate with 8 layers of glass fiber(GF)and rigid polyurethane foam(RPUF)sandwich structure were prepared by VARI process,and several main technical parameters in the preparation process were put forward.2.The constant temperature water immersion moisture absorption tests of GF resin base plywood and GF/RPUF sandwich structure specimens were carried out at25℃,40℃,55℃ and 70℃.Combined with Arrhenius formula and FICK’s second law,the water diffusivity and saturated hygroscopicity of the specimens at different temperatures and their relationship with temperature were obtained,and the water diffusion coefficient and saturated hygroscopicity of the specimens at any flooding temperature in the range of 25℃ to70 ℃ were constructed.A moisture absorption model which can predict the water diffusion coefficient and saturated moisture absorption of the material in the first stage of moisture absorption.3.The static mechanical properties of GF laminates and GF/RPUF sandwich structures after hygrothermal treatment were studied,including the tensile properties of GF laminates and the buckling properties of GF/RPUF sandwich structures.The morphological changes of the failure interface and the degradation of mechanical properties of the specimens treated under different hygrothermal conditions were analyzed.4.The low-velocity impact tests of GF/RPUF sandwich structure specimen with different energy of 12 J,18J and 24 J were carried out,and the damage appearance changes and low-velocity impact response parameters of foam-cored sandwich structure treated under different impact energy and different hygrothermal conditions were discussed.The results show that the hydrolysis of vinyl is the main factor leading to the mechanical properties of the composites in hygrothermal environment,and glass fiber has good corrosion resistance in hygrothermal environment.