In this study, a progressive damage model was developed for the mechanical response and damage evolution of carbon fiber stitched composite laminates under low-velocity impact (LVI). The three-dimensional Hashin and Hou failure criteria were used to identify fiber and matrix damage. The cohesive zone model was adopted to simulate the delamination damage, combined with the linear degradation discounting of the equivalent displacement method to characterize the stiffness degradation of the material, and the corresponding user material subroutine VUMAT was coded. The finite element analysis of the LVI of stitched composite laminates under different energies was finished in Abaqus/Explicit. Furthermore, the simulation predictions matched well with the results of the experimental tests. Based on this, composite laminates’ mechanical response and damage forms with different thicknesses and stitch densities were analyzed. The findings show that the main damages of composite laminates were matrix tensile damage and delamination. The stitching process could improve the impact tolerance of composite laminates, inhibiting delamination and reducing the area of the delamination damage. The higher the density of the stitching, the more noticeable its inhibition would be. The thickness of the laminate also had a more significant effect on the damage to the laminate. Thin plates were more prone to matrix tensile damage due to their lower flexural rigidity, whereas thick plates were more susceptible to delamination because of their higher flexural rigidity.

Research based on numerical simulation with the CFD software ANSYS POLYFLOW is conducted on the mixing properties for the wave screw elements, as well as barrier screw elements, by using statistical tools. Then, the investigation is conducted in detail on the relationship between pressure, maximum shear rate, mixing index and other flow field characteristics of the two above screws under the same simulation conditions. It is found that polymer melt flow in the wave screw possesses various advantages compared with the normal barrier screw, such as acquiring larger pressure, stronger shearing and stretching action, better mixing and efficiency, which mainly result from the periodic depth change design in the screw groove. On the other hand, the increased wave bulge in the wave screw lessens the space for the polymer melt to be conveyed forward, which can greatly reduce the original function of the secondary flight. Also, the convergent and divergent zones in the wave screw groove produce a much stronger stress favoring the shear and elongation rates, and also lead to a sharp increase of the axial force load on the wave screw. Consequently, for the optimization of the wave screw configuration it is suggested to reduce the axial force without decreasing the effect of the excellent distributive and dispersive mixing.

Numerous vibration-assisted methods have been adopted to solve problems in polymer processing, but the introduction of vibration fields is typically done on small extruders or injectors in school laboratories and industrial research rooms, which profoundly limits the application of vibration technology. The purpose of this study is to put forward a simple vibration excitation method for all scale extruders or injection molding machines. To recover the mixing performance of that excitation method, a numerical investigation was carried out using the CFD software ANSYS POLYFLOW 19.2, and the analysis and comparison were made between the mixing performance of a simplified screw element with and without a sinusoidal pulsating speed field. The results showed that not all dynamic states with the superimposed excitation field have better mixing performance than the steady state without any pulsating field. Nevertheless, the introduction of a pulsating speed field under certain parameters setting can indeed enhance the stretching rate, reduce the separation scale, increase the mixing efficiency, and lower the screw force. These findings are of great importance and provide valuable references for the development and application of vibration-assisted molding technology in plastics machinery.

A novel speed sinusoidal pulsating system is designed by applying differential drive, which is loaded on the plasticizing screw in an extruder or in an injection molding machine. With the CFD software ANSYS POLYFLOW 19.2, this paper builds simplified physical and mesh models for the double wave screw unit, carries out numerical simulation by using particle tracing manner, and finally analyses comparatively the mixing behavior of the wave screw mixing unit with and without sinusoidal pulsating field. It is found that the mixing screw unit with the superimposed excitation field takes on lower transportation efficiency and a descending melt pressure, while there are different reactions on the various pulsating amplitude and frequency for the max shear rate and mixing index. On the other hand, the introducing pulsating field can strengthen the shear field and gain a higher mixing efficiency. The results are of great importance and reference for improving the plasticizing performance and engineering application of the speed pulsating system.

Vibration-assisted technology has been employed to satisfy various requirements for different polymeric products due to its excellent performance, but because of the large inertia of the vibration excitation system, these attempts are strictly limited to several fixed vibration amplitudes and frequencies in small extruders or injectors. The purpose of this study is to carry out a numerical investigation via smoothed particle hydrodynamics (SPH) and to perform a comparative analysis of physical parameters among different cases from various perspectives on the fluid channel in twin-screw extruders (TSEs). The results demonstrate that certain combinations of larger vibration amplitudes and frequencies can significantly enhance the velocity, pressure, and particle distribution characteristics within the flow channel. However, no monotonic (i.e., strictly increasing or decreasing) trends are observed with respect to either amplitude or frequency alone. These findings are in excellent agreement with previously reported experimental studies and confirm that the meshless smoothed particle hydrodynamics (SPH) method is a robust and effective computational tool for investigating how various vibrational parameters influence flow behavior in twin-screw extruders (TSEs). Moreover, the results underscore that optimal amplitude and frequency selections must be tailored to the specific rheological and thermal properties of the polymer being processed. This work establishes a solid theoretical and numerical foundation for integrating superimposed vibration-assisted technology into the design optimization of TSE systems.

Vibration-assisted methods are playing a more and more important role in processing polymers for twin screw extruders (TSEs) in order to satisfy the increasing requirements for polymetric products in various applications, but existing vibrating technologies are usually restricted in school laboratories and industrial research rooms because of their drawbacks. The purpose of this study is to design a novel vibration method for TSEs. Numerical simulation was performed based on a meshless method, namely smoothed particle hydrodynamics (SPH). The velocity distribution, particle distribution, and pressure of particles in a co-rotating twin screw component in the conveying zone of a TSE are investigated in detail to recover the influence of the rotational speed excitation on the flow properties of both fully filled and partially filled states. The results show that cases under superimposed excitation can produce a more variable physical effect, thus enhancing and weakening the velocity field and the pressure field alternately. And on the whole, that effect could improve the particle distribution in according cases. These findings can lay a solid foundation for further study on the development and application of superimposed excitation technology in the polymer processing of TSEs.