Composite laminates are susceptible to impact events during use and maintenance, affecting their safety performance. Edge-on impact is a more significant threat to laminates than central impact. In this work, the edge-on impact damage mechanism and residual strength in compression were investigated using experimental and simulation methods by considering variations in impact energy, stitching, and stitching density. The damage to the composite laminate after edge-on impact was detected in the test by visual inspection, electron microscopic observation, and X-ray computed tomography techniques. The fiber and matrix damage were determined according to the Hashin stress criterion, while the cohesive element was used to simulate the interlaminar damage. An improved Camanho nonlinear stiffness discount was proposed to describe the stiffness degradation of the material. The numerical prediction results matched well with the experimental values. The findings show that the stitching technique could improve the damage tolerance and residual strength of the laminate. It can also effectively inhibit crack expansion, and the effect increases with increasing suture density.

Based on the effects of natural cooling on the warpage of the injection-molded parts, a concept of total warpage deformation was proposed. A three-dimensional numerical model of total warpage for the injection-molded parts of short-glass-fiber-reinforced polypropylene (PP) composites was established using coupled finite element method (FEM). The total warpage deformation is composed of two parts: stress-induced deformation during injection molding and thermally induced shrinkage deformation after ejection. The residual stress, temperature, and anisotropic thermal and mechanical properties formed in injection molding were subsequently transferred into the thermal stress analysis package as initial conditions. On account of the difference between the fluid and structural mesh, the tetrahedral and hexahedral mesh types were used in injection molding simulation and thermal stress analysis, respectively. The comparison between the simulation and experimental results showed that the simulated warpage deformation agreed well with the experimental measurements quantitatively and qualitatively, suggesting the validation of the proposed numerical model.

Micro-tubes have small diameters and thin wall thicknesses. When using double-layer gas-assisted extrusion (DGAE) technology to process micro-tubes, due to the influence of flow resistance, airflow from the inner gas-assisted layer cannot flow into the atmosphere through the lumen. Over time, it will inflate or even fracture the micro-tubes intermittently and periodically. To solve this problem, a new double-layer micro-tube gas-assisted extrusion die was designed in this study. Its mandrel has an independent airway leading to the lumen of the extrudate, with which the gas flow into the lumen of the extrudate can be regulated by employing forced exhaust. Using the new die, we carried out extrusion experiments and numerical calculations. The results show a significant positive correlation between micro-tube deformation and gas flow rate in the lumen of a micro-tube. Without considering the refrigerant distortion of the microtube, the flow rate of forced exhaust should be set equal to that of the gas from the inner gas-assisted layer flow into the micro-tube lumen. By doing this, the problem of the micro-tube being inflated can be eliminated without causing other problems.