Study Of Strength Of Composite Material Laminates With A Circular Open Hole Under Hygrothermal Conditions

With the expansion of application fields of composite material, research on composite material mechanical properties has received attention from more and more researchers. Among all mechanical problems of composite material, research on hygrothermal mechanical properties of composite material may be very difficult to deal with due to different reactions of component material under hygrothermal condition. In this paper, strength tests of open-hole composite laminates under hygrothermal condition were conducted. Then, an analytical model of open-hole composite laminates strength under hygrothermal condition was established. Hygrothermal damage propagation process of laminates under load was analyzed with this analytical model and factors which influence material hygrothermal strength were also discussed.Firstly, after moisture absorption of wet test articles was accomplished, strength tests of dry articles and wet articles were conducted under 3 different temperature and 3 different loads. Based on the test results, failure modes of samples were compared and influence of moisture and temperature on open-hole composite laminates strength was analyzed.Secondly, based on meso-structure of CFRP composite material, a non-dimensional temperature parameter was introduced into stiffness function and strength function. After introducing 3D Hashin failure criterion and stiffness reduction, a user defined material constitutive relationship subroutine UMAT was written using ABAQUS software. By imposing hygrothermal field, an analytical model was established to forecast open-hole composite laminate strength under different hygrothermal conditions and different loads. Under hygrothermal condition, damage propagation progress under tensile, compressive and squeezing load was simulated.Lastly, based on the strength forecasting model, hygrothermal effect on composite material strength was analyzed and hygrothermal degeneration curves of material tensile, compressive and bearing strength were drawn. Also, influence of laminate width-diameter ratio and bolt model in connection structure on laminate strength was discussed.