The tensile and impact properties of polytetrafluorethylene (PTFE)/Al/W reactive energetic composites were investigated using a universal materials testing machine and an improved pendulum impact tester at room temperature. Samples of four types, all containing W, of differing composition and particle size were prepared by cold pressing and sintering. With increasing W content in the PTFE/Al/W samples, the mass loss during sintering and the density of the materials obtained increased. The addition of microlevel W led to the tensile strength decreasing from 25.3 to 19.8 MPa, while the elongation changed little, but substituting nanolevel W for 5 wt% Al yields a maximal strength of 31.4 MPa. The failure behavior of PTFE/Al/W includes deformation, fracture, disorganization and reaction, in four steps. The addition of 30 wt% of coarse W particles improved the impact strength of the material, but the reactive activity increased and the perfectability of the reaction decreased.
Carbon fiber reinforced polymer (CFRP) after low-velocity impact is detected using infrared thermography, and different damages in the impacted composites are analyzed in the thermal maps. The thermal conductivity under pulse stimulation, frictional heating and thermal conductivity under ultrasonic stimulation of CFRP containing low-velocity impact damage are simulated using numerical simulation method. Then, the specimens successively exposed to the low-velocity impact are respectively detected using the pulse infrared thermography and ultrasonic infrared thermography. Through the numerical simulation and experimental investigation, the results obtained show that the combination of the above two detection methods can greatly improve the capability for detecting and evaluating the impact damage in CFRP. Different damages correspond to different infrared thermal images. The delamination damage, matrix cracking and fiber breakage are characterized as the block-shape hot spot, line-shape hot spot, and "工" shape hot spot respectively.
This paper reports the transverse impact responses of 3-D braided composite I-beam from experiment and finite element analysis (FEA). The transverse impact tests were conducted on a modified split Hopkinson pressure bar (SHPB). Three different impact gas pressures were set to research the effect of the impact velocity on the transverse impact behaviors of the I-beams. A microstructure geometric model was established to model the real structure of 3-D braided composite I-beam. The mechanical responses including load-time history, displacement-time history and energy absorption were obtained. Damage process and stress distribution were analyzed from the FEA result. From the result, the complex braided structure remarkably affected the stress state of different braiding yarns. Finally, the fracture morphologies obtained from FEA and experimental results showed a good agreement which validated the established model.
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