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The serious damage caused to 3D braided carbon fiber (CF)/epoxy (EP) composites in high-energy irradiation environments is a pressing research topic that has not yet been reported. This study analyzed the γ-irradiation multi-scale damage of the matrix, interfaces, and near-interface regions in 3D braided CF/EP composites with three different braiding angles (18°, 28°, 38°) at atomic, microscopic, and macroscopic scales. The molecular structure and atomic charge information alterations of epoxy matrix were characterized using soft X-ray absorption spectroscopy (sXAS). When the irradiation dose reached 1000 KGy, the compressive strength of composites decreased by 20.88 %, 18.07 %, and 16.60 %, respectively, with an increase in the braiding angle. Micro-CT observation, along with statistical computing, confirmed that irradiation causes interface damage and increases the defect volume of 3D braided composites. Nanoindentation was used to compare the modulus of carbon fiber, interface, near-interface regions and matrix in irradiated composites and the function of CF/resin interface as an irradiation defect capture site in the irradiation resistance of resin-matrix composites has been newly established. In addition, the mechanism behind the effect of braiding angle on macroscopic properties was also analyzed. [Display omitted] • The braided structures exhibited varying responses to irradiation, with 3D-38° showing the highest performance retention. • Soft X-ray absorption spectrometry was developed to characterize the valence changes of oxygen and carbon in irradiated resin. • Interface as an irradiation defect capture site consumes most of the energy and reduces the damage of resin near the interface. [ABSTRACT FROM AUTHOR]

Abstract The understanding of dynamic damage and failure of thermo-oxidative aged 3D carbon fiber/epoxy braided composite is critical to its durability design. Here we aim at a fine description of damage and failure of aged composites under impact compression by means of experiment and finite element analysis (FEA). The composites and epoxy resins were aged in air at 110 °C, 130 °C and 150 °C for prescribed time, respectively. The failure processes were recorded with high-speed camera. We found that with the increase of ageing temperature, the interface damage becomes more serious and the epoxy resins tend to a rubbery behavior. For the composites aged at lower temperature (110 °C), the impact resistance degradation is mainly attributed to the degradation of epoxy resin. While interface degradation is found to be the dominant degradation mechanism when the composites aged at higher temperature (130 °C, 150 °C). FEA results showed that in the process of impact, the plastic deformation induced temperature and thermal stress of the aged composites decrease compared with the unaged composite. For the unaged composites and the composites aged at lower temperature, the damage of reins is the main factor that affects the energy absorption of fiber tows. The interface damage plays a more important role in the energy absorption of fiber tows when the composites aged at higher temperature. [ABSTRACT FROM AUTHOR]

Abstract When serving as a lightweight structural member in many areas, the dynamic mechanical behavior of fiber-reinforced polymeric matrix composites, especially under different strain rates, means a lot to the optimization of structure design as to high-speed impact. Under different loading rates and directions, we experimentally and numerically investigated the strain rate effect on the impact compressive behavior of 3-D angle-interlock woven composites (3-D AWCs) composed of carbon fiber and epoxy resin. Based on the factual geometrical architecture of 3-D AWC, the meso-scale model, which considers the interfacial damage between the reinforcements and matrix, was established to visually characterize the deformation history and damage morphologies of 3-D AWCs during impact compression process. Further, we performed high strain rate compressive tests on the split Hopkinson pressure bar (SHPB) apparatus integrated with a high-speed photography system for capturing images of progressive damage process to validate the proposed mesoscopic model. The stress-strain curves of various strain rates show strain rate effect varies depending on loading direction. The rate sensitivity on the compressive failure strength exists at weft direction and through-thickness direction except for warp direction. Moreover, both from images and finite element model results, the localized adiabatic shear band induced by intense plastic strain, initiates mainly from epoxy resin matrix and propagates along the interface at all three loading directions. [ABSTRACT FROM AUTHOR]