Compressive Properties Of Thermoset/thermoplastic Matrix Three-dimensional Four-directional Braided Composite Material Under Hydrothermal Aging

Carbon fiber three-dimensional four-directional braided composite material is a new type of material.Compared with traditional materials,its strength and stiffness have been greatly improved,and it also has the advantages of lower density and stable chemical properties.Therefore,it has been widely used in some important fields,such as aviation,aerospace and navigation.Carbon fiber three-dimensional four-directional braided composite materials are inevitably in a hot and humid environment during service and use.Among them,there is a difference in thermal expansion between the carbon fiber and the resin matrix,which has a greater impact on the compression performance of the material.In this thesis,the compressive properties of thermoset/thermoplastic matrix three-dimensional four-directional carbon fiber braided composites under hydrothermal environments are studied by experiments and numerical simulations.Firstly,the thermoset/thermoplastic matrix three-dimensional four-directional carbon fiber braided composite material was subjected to hydrothermal-aging tests under different hydrothermal conditions.The test results showed that the type of matrix,temperature,humidity,and weaving angle are all related to the carbon fiber three-dimensional four-directional braided composite material.The hydrothermal-aging behavior has a greater impact,mainly as follows: under the same humidity,the weight gain rate and change rate of the carbon fiber three-dimensional four-directional braided composite material increase with the increase of temperature;at the same temperature,the carbon fiber three-dimensional four-directional the weight gain rate and rate of change of braided composite materials increase with the increase of humidity;under the same hydrothermal conditions,the size and rate of change of weight gain rate of carbon fiber three-dimensional four-directional braided composite materials increase with the increase of braiding angle the three-dimensional four-directional braided composite material of thermoset carbon fiber is lower than the three-dimensional four-directional braided composite material of the thermoplastic matrix carbon fiber under the same conditions in terms of weight gain rate and size.Secondly,the axial compression test of the carbon fiber three-dimensional four-directional braided composite material after hydrothermal weight gain is carried out to obtain the corresponding mechanical parameters,and the influence of matrix type,temperature,humidity,braid angle and hydrothermal aging time on the material bearing capacity and failure mode is analyzed.From the aspect of the influence of hydrothermal weight gain on internal materials,the principle of reduced hydrothermal-aging compression performance is explained.Finally,according to the microstructure characteristics of the carbon fiber three-dimensional four-directional braided composite material,a geometric model was established,and the commercial finite element analysis software ABAQUS was used to numerically simulate the hydrothermal-aging and axial compression of the three-dimensional braided composite material.The heat conduction module simulates the weight gain and diffusion process of carbon fiber three-dimensional four-directional braided composite materials,thereby obtaining the temperature field and stress field distribution during the wet-heat aging process,and the compressive stress field distribution after the hydrothermal-aging process.Analyze the stress distribution of thermoset/thermoplastic matrix and carbon fiber at different moments,and compare the results of numerical simulation with the data obtained from experiments.The error of the two is within a reasonable range.It provides a reference for the prediction of compressive strength and failure of carbon fiber three-dimensional four-directional braided composites during use.