The Influence Of Interface Property On Impact Energy Absorption Of Aramid/Expoxy Composite

Fiber-reinforced composites will dissipate energy by all sorts of damage when they are subject to low-velocity impact. The damage in the composites influences the mechanical properties of the composites, including bending strength and compressive strength. The mechanisms of failure process are complicated and influenced by many factors. Fiber-matrix interface plays a major role in the impact performance of composites because it mainly transfers mechanical loads from matrix to fiber during impacting. The effect of interface on impact performance varies when different fiber/matrix systems are studied. The objective of this thesis is to investigate the influence of interface performance on low-velocity impact performance of aramid/matrix composite.Aramid filaments are treated by a low-temperature plasma with different treatment times. The surface of filaments is observed by SEM and the results show that the filament surface is smooth before the treatment and becomes more rough if filaments are treated for 6 minutes. In addition, it is found that the filament peels after 9 minutes of plasma treatment.The tensile properties of aramid filament are examined by a tensile tester and verify the data by means of statistics. The results show that the tensile strength, initial modulus and elongation at rapture of the filaments reduce slightly with the time of treatment.Filament pull-out test is used to evaluate the influence of the plasma treatment on the interfacial properties. The results show that the interfacial shear strength increases after plasma treatment and reaches a maximum value, 16.22% greater than that before the treatment, when the filament is treated for 6 minutes. After thaat, the interfacial shear strength decreases. Moreover, when the filaments are treated for 12 minutes, the interfacial shear stress will be lower than that treated for 6 minutes.Izod pendulum is used to test the influence of the fiber/matrix bond strength on the low velocity impact responses of the composites. The curves of energy-time, force-time and velocity-time are obtained by a data acquisition system. The force-timecurves are then converted to force-displacement curves to calculate the energy associated with different impact phase. The results show that the maximum load of the composites with non plasma treatment filament is low and the absorption is also low in the initial crack phase. However, the energies associated with the crack propagation are relatively high. After the filaments are treated by plasma for 6 minutes, the maximum load increases and initial energy is greater than 18.57%. At the same time, the energy absorbed in the crack propagation phase decreases relatively that lead to overall energy absorption of the composites increases slightly, it is greater than 12.89%.By observing the appearance of the damage area, it can be found that the mode of damage is influenced by the interfacial shear strength. If the interfacial shear strength is low, fiber pull-out is the primary energy-absorbing mechanisms, whereas the dominant energy-absorbing mechanisms changes into fiber/matrix debonding and delamination when the interfacial shear strength is stronger.