The effects of the content and position of shape memory alloy (SMA) wires on the mechanical properties and interlaminar fracture toughness of glassfiber-reinforced epoxy (GF/epoxy) composite laminates are investigated. For this purpose, varying numbers of SMA wires are embedded in GF/epoxy composite laminates in different stacking sequences. The specimens are prepared by vacuum-assisted resin infusion (VARI) processing and are subjected to static tensile and three-point-bending tests. The results show that specimens with two SMA wires in the stacking sequence of [GF 2 /SMA/ GF 1 /SMA/GF 2 ] and four SMA wires in the stacking sequence of [GF 4 /SMA/ GF 2 /SMA/GF 4 ] exhibit optimal performance. The flexural strength of the optimal four-SMA-wire composite is lower than that of the pure GF/epoxy composite by 5.76% on average, and the flexural modulus is improved by 5.19%. Mode-I and II interlaminar fracture toughness tests using the SMA/ GF/epoxy composite laminates in the stacking sequence of [GF 4 /SMA/GF 2 / SMA/GF 4 ] are conducted to evaluate the mechanism responsible for decreasing the mechanical properties. Scanning electron microscopy (SEM) observations reveal that the main damage modes are matrix delamination, interfacial debonding, and fiber pullout.
Direct numerical simulation (DNS) of a hypersonic compressible flow over a blunt wedge with fast acoustic disturbances in freestream is performed. The receptivity characteristics of boundary layer to freestream pulse acoustic disturbances are numerically investigated at Mach 6, and the frequency effects of freestream pulse wave on boundary layer receptivity are discussed. Results show that there are several main disturbance mode clusters in boundary layer under acoustic pulse wave, and the number of main disturbance clusters decreases along the streamwise. As disturbance wave propagates from upstream to downstream direction, the component of the modes below fundamental frequency decreases, and the component of the modes above second harmonic components increases quickly in general. There are competition and disturbance energy transfer between different boundary layer modes. The nose boundary layer is dominated by the nearby mode of fundamental frequency. The number of the main disturbance mode clusters decreases as the freestream disturbance frequency increases. The frequency range with larger growth narrows along the streamwise. In general, the amplitudes of both fundamental mode and harmonics become larger with the decreasing of freestream disturbance frequency. High frequency freestream disturbance accelerates the decay of disturbance wave in downstream boundary layer.
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