The presence of voids and delamination are common structural defects in the manufacturing process of carbon fiber‐reinforced plastics (CFRPs) structures. The reduction of manufacturing quality and mechanical properties caused by such defects will restrict the extensive application of composite materials in engineering field. Therefore, this work reports the experimental research and analysis on the effect of random vibration applied to the curing system of CFRP laminates, mainly aiming at the reduction of the void content and improvement of mechanical performances under low cure pressures. Range of vibration acceleration was from 5 to 20 g, for different periods of random vibration. For the sake of porosity and property comparison, the autoclave process with different cure pressures was designed as the experimental control groups. Based on the method of mathematical statistics, the content, equivalent diameter and aspect ratio of the voids in the specimens were calculated, and the effect of vibration on the morphological characteristics of pores was clarified. All composite laminates were subjected to the short‐beam three point bending test to determine their interlaminar shear strength (ILSS). Then the influence of random mechanical vibration on the ILSS between the composite layers was analyzed. The research showed that the low porosity and high quality CFRP laminates could be produced at low cure pressures by introducing the random vibration into the forming process. POLYM. COMPOS., 40:3122–3130, 2019. © 2018 Society of Plastics Engineers

Compared with the conventional composite curing processes, high-pressure microwave curing is a promising technology. In this study, a set of devices for high-pressure microwave curing was built and equipped with real-time temperature measurement capability and a microwave input control system. The orthogonal experimental method was applied to optimize three process parameters, including the heating rate, curing temperature, and holding time, for the high-pressure microwave curing of T800/X850 composites. The effects of the three parameters on the curing quality were studied by measuring the interlaminar shear strength (ILSS) and conducting differential scanning calorimeter tests. The fracture surface of the samples was also examined by scanning electron microscopy. The results showed that the heating rate had a significant effect on the ILSS of the laminates, and the degree of cure of all samples was more than 95% in the tests. Furthermore, the optimal process parameters were determined as follows: heat up to 170°C with a heating rate of 6°C min−1 and a holding time of 90 min. The total curing time of the sample was 42.4%, and the ILSS of the sample was slightly enhanced by 0.31% compared with standard thermal curing. These results could serve to make trade-offs between reducing manufacturing time and preserving the mechanical properties of microwave-cured composites.

In the manufacturing process of carbon fiber-reinforced plastics composites, if the cure pressure that can form the hydrostatic pressure of resin is transferred inhomogeneously to the interior of composite structures, the critical imperfections such as voids and delamination which damage the mechanical properties and restrict subsequent use will be formed. Therefore, the present work reports the experimental research and analysis on the effect of random vibration applied to the curing system of carbon fiber-reinforced plastic laminates, mainly aiming at the reduction of the void content and improvement of mechanical performance under the vacuum pressure. The range of acceleration of vibrations was covered from 5 g to 15 g, for different periods of random vibration. Conducting a facile thermogravimetric analysis-based methodology, the influence of random vibration on the composite density, fiber volume fraction and void content of carbon fiber reinforced plastic laminates was analyzed. And the influence of voids on the interlaminar shear strength of materials was compared in terms of the initiation and propagation of interlaminar failure. In addition, the scanning electron microscopy was employed to observe the fracture surfaces of the composite specimens, which confirmed the different behaviors of fiber–matrix interface of various curing processes. The major benefits of the current research are that, the application of random vibration during the curing process can better wet through fibers by resin and increase the fiber volume fraction while reducing the bubbles and volatile gas of composite laminates at the same time.

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Voids and delamination are viewed as significant defects in the manufacturing process of carbon fiber-reinforced plastics structures and have been demonstrated to reduce the final performance of composites. Vibration is increasingly applied in new processing technologies for reducing void content and improving performance under low cure pressures. Therefore, this study investigates the effect of random vibration on the formation of voids during the curing process and the final interfacial properties of composite laminates. A 10 g random vibration was applied in the curing cycle, and a no-vibration cure cycle was designed as the experimental control group. The cure cycles were interrupted at pre-defined stages for each process to enable the in situ behavior of void content and growth of voids to be studied. Then the short-beam three-point bending test was employed to determine the interlaminar shear strength of composite samples. And the interlaminar cracks and fracture surfaces of tested specimens were captured by scanning electron microscopy. Besides, the interfacial shear strength of composite samples was measured by single-fiber push-in test. Compared with static group, the major benefits of the current research are that the growth of voids was impeded and void content was decreased obviously at each stage in composite samples produced by random vibration-assisted vacuum processing. In addition, the final interfacial properties were improved at the macro and micro levels due to adequate adhesion of the fiber–matrix interface when random vibration was introduced into the curing cycle.