Shiyu Wang

Induction welding of thermoplastic (CFRP) composites is one of the most promising welding techniques due to its high efficiency, flexibility, and selectivity of the heat area. However, the nonuniformity of the temperature field in the welding area poses a challenge to welding quality. In this paper, a multifactor optimization method devoted to the quality and efficient bonding of carbon fiber‐reinforced polycarbonate (CF/PC) composites was presented. A transient three‐dimensional finite element model was developed and validated to analyze the heating characteristics during the welding process. The mapping relationship between process parameters—equilibrium temperature and relative effective area were established to optimize the weld quality applying the response surface method. The single lap shear experiment was carried out to evaluate the mechanical properties of the welded joints, focusing on micro appearances and welding defects. The results show that the optimal process parameters are a current of 100A and a coil distance from the surface of 3.6 mm. Under the process parameter, the effective welding area is 0.3823 with an error of 4.25%.Highlights: The transient three‐dimensional finite element (FE) model was established. The evaluation indicators for welding quality were proposed. The multifactor optimization method for process parameters was developed. The mechanical property and welding defects of welded joints is evaluated.

The automated fiber placement (AFP) process faces a crucial challenge: the emergence of out-of-plane buckling in thermoplastic prepreg tows during steering, significantly impeding the quality of composite layup. In response, this study introduces a novel approach: the development of equations for wrinkle-free fiber placement within composite pressure vessels. The investigation encompasses a detailed analysis of prepreg trajectories in relation to shell geometry, accompanied by an in-depth understanding of the underlying causes of wrinkling on dome surfaces. Moreover, a comprehensive model for shell coverage, grounded in placement parameters, is meticulously established. To validate the approach, a simulation tool is devised to calculate press roller motions, ensuring the uniform fiber dispersion on the mandrel and achieving flawless coverage of the shell without wrinkles. This innovative strategy not only optimizes the AFP process for composite layup but also remarkably enhances the overall quality of composite shells. As such, this research carries significant implications for the advancement of composite manufacturing techniques and the concurrent improvement in material performance.

The dynamic mechanical response of high-performance thermoplastic composites over a wide range of strain rates is a challenging research topic for extreme environmental survivability in the field of aerospace engineering. This paper investigates the evolution of the dynamic properties of woven thermoplastic composites with strain rate and damage process at elevated temperatures. Out-of-plane dynamic-compression tests of glass-fiber (GF)- and carbon-fiber (CF)-reinforced polyphenylene sulfide (PPS) composites were performed using a split Hopkinson pressure bar (SHPB). Results showed that thermoplastic composites possess strain-rate strengthening effects and high-temperature weakening dependence. GF/PPS and CF/PPS composites had the same strain-rate sensitivity (SRS) below the threshold strain rate. The softening of the matrix at elevated temperatures decreased the modulus but had little effect on strength. Some empirical formulations, including strain-rate and temperature effects, are proposed for more accurately predicting the out-of-plane dynamic-compression behavior of thermoplastic composites. Lastly, the final failure of the specimens was examined by scanning electron microscopy (SEM) to explore potential failure mechanisms, such as fiber-bundle shear fracture at high strain rates and stretch break at elevated temperatures.

The characteristics of the bandwidth and impedance changes of the antenna are analyzed, and the NiZn ferrite transmission-line transformer is applied to the six-meter spiral whip antenna to solve the problem of narrow bandwidth, and the influences of taking the conventional transformation ratio or the unconventional transformation ratio of transmission-line transformer are analyzed, and the influences of the bandwidth and reflection coefficient of the antenna are analyzed, and the suitable transmission-line transformer is determined.