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The high-speed ice-ball impact damage research of epoxy resin/carbon fiber 3D four-way braided composites was carried out. Using the air gun impact test system, ice balls with three different impact velocities were used to conduct impact tests. After the test, industrial CT scans were performed on the main damage positions of the test pieces, and the internal damage forms were observed. The composite macro constitutive model based on surface unit-cell and interior unit-cell and a strain rate related material model of the ice were used to establish the finite element model. The simulation model was compared with the test. The results show that the damage of the matrix in the surface unit-cell area is more serious than that in the interior unit-cell area, the damage area of the front surface is generally larger than that of the back surface, the oblique impact angle has an influence on the damage area and damage location. As the impact angle decreases, the damage area of the composite material also decreases. Increasing the thickness of plate can improve the ability to absorb energy and reduce the damage area of the material. [ABSTRACT FROM AUTHOR]

The longitudinal compressive behavior of the three-dimensional four-step braided composites after cyclic hygrothermal aging was investigated using a split Hopkinson pressure bar (SHPB) apparatus under high strain rates (1100~1250 s−1, 1400~1600 s−1, 1700~1850 s−1, respectively). The SEM micrographs were examined to the damage evolution of the composites after cyclic hygrothermal aging. A high-speed camera was employed to capture the progressive damage process for the composites. The results indicate that the saturated moisture absorption of the composites was not reached during the whole 210 cyclic hygrothermal aging days. The composites mainly underwent epoxy hydrolysis and interfaces debonding during continuous cyclic hygrothermal aging time. The peak stress of the composites still behaved as a strain rate effect after different cyclic hygrothermal aging days, but the dynamic stiffness modulus clearly had no specific regularity. In addition, the peak stress and the dynamic stiffness modulus of the composites after 210 cyclic hygrothermal aging days almost decreased by half when subjected to longitudinal compression. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) structures used in aviation are typically exposed to cyclic hygrothermal environments in which they may be subjected to impact loads that threaten flight safety. Although the effects of hygrothermal aging on the mechanical behavior of FRPs have been extensively explored, few authors have discussed the impact-induced behavior of composites after long-term hygrothermal aging, and hardly any study has examined the effect of the strain rate of neat epoxy resin after hygrothermal aging. This study examines the quasi-static and dynamic tensile properties of TDE86 epoxy resin under cyclic hygrothermal aging for the first time. The resin specimens were aged for 0, 1, 7, 14, 28, 56, 70, and 140 days, representing specimens that were unaged, and had been in service for one month, six months, one year, two years, four years, five years, and 10 years respectively. The strain rate at which they were tested ranged from 7.5 × 10−6 s−1 to 1000 s−1. This yielded the hygroscopic law, the process of evolution of crack-induced damage, and the viscoelastic behavior of the specimens, including the hygrothermal effect and the effect of the strain rate of the epoxy resin. This information can be used to predict the hygrothermal behavior of FRPs based on the micromechanics method. [ABSTRACT FROM AUTHOR]

Epoxy resin composite materials are increasingly used in the aerospace field. The dynamic mechanical behavior of the resin matrix is of great significance in studying the impact response of composites. In the current study, the quasi-static and dynamic compression properties of TDE86 epoxy are studied at different temperatures, and the influence of the temperature and strain rate on the mechanical properties of epoxy are analyzed. The quasi-static and dynamic compression stress–strain curves are used to fit the parameters of the Zhu–Wang–Tang (ZWT) constitutive equation at different temperatures. A subroutine for the ZWT constitutive model is developed in ABAQUS, and numerical simulations of split Hopkinson pressure bar tests are performed. The results show that, at low strain rates, the elastic modulus, yield stress, and yield strain of the epoxy increase as the strain rate increases and decrease as the temperature increases. The dynamic stress–strain curve of the epoxy can be divided into four stages, namely the initial elastic, yield, strain softening, and unloading stages. There is no distinct relationship between the yield strain and the logarithmic strain rate under high strain rates, although the yield strain is generally smaller than that under low strain rates. The yield stress increases linearly with the logarithmic strain rate. Under the same strain rate, the yield stress decreases as the temperature increases, whereas the yield strain does not change monotonically. By comparing the stress–strain curves obtained by simulations with the test results, the developed subroutine is validated and the applicability of the ZWT constitutive model at different temperatures is verified. • Epoxy exhibits initial elasticity, yield, and strain softening during quasi-static compression. • Elastic modulus, yield stress, and yield strain decrease significantly with increasing temperature. • ZWT model could describe the stress-strain relationship of epoxy resin below 8% strain at different strain rates. [ABSTRACT FROM AUTHOR]