Mechanism of effect of processing parameters on stress wave propagation characteristics during automated fiber placement

The internal defects in the material structure and their distributions could effectively be identified by using stress wave characteristics. In order to identify the internal defects of the preform by using processing loads that act as a stress wave excitation source, the effect of the processing parameters on the stress wave propagation characteristics in the laying process should be first studied to determine the position of the stress sensor. In this paper, the thermo-mechanical coupling model of the laying process was constructed by using the finite element method (FEM). The relationship between the stress wave characteristic parameters and the processing parameters was analyzed, and the experimental verification was then carried out. In order to explain the effect of the processing parameters on the stress wave characteristics from the perspective of microscopic energy, molecular dynamics (MD) method was used to establish the molecular model of the prepreg interface, and the energy parameters such as total energy, surface energy of fibers, and internal energy of matrix were calculated. Furthermore, the driving energy of stress wave and its contribution ratio under different processing parameters were identified and evaluated to reveal the energy effect mechanism of the processing parameters on the stress wave characteristics. The results show that the lateral waves driven by the internal energy of matrix have a significant relationship with the processing parameters. The effect of the formation of internal defects on the waveform is easy to identify under the different processing parameters. This conclusion could be used as a reference for stress sensor placement.