Quasi-static perforation response of inter-ply hybrid polypropylene composites at various temperatures

This study is motivated by the lack of knowledge in the research of mechanical characterization of thermoplastic composites (TPCs) with additional fiber hybridization. To enhance the mechanical properties of long glass fiber-reinforced polypropylene (PP) composite, hybridization via alkaline-treated aramid and carbon fabrics is performed. High performance fabrics modified with 10 wt.% sodium hydroxide (NaOH) aqueous solution are incorporated into the PP composite as reinforcements. Herewith, four arrangements (hybrid composites) for two different reinforcements and two different stacking configurations and the monolithic composite are separately investigated in terms of quasi-static perforation behavior. Failure mechanisms are also evaluated at macro level by visual observations and micro scales through a scanning electron microscopy (SEM). The experimental results provide a basis for selecting fiber-enabled hybridization and lay-up configuration with improved perforation resistance. Moreover, the influence of test temperature is reported for three different values as 20°C, 60°C, and 100°C. Based upon the results, the maximum penetration force of hybrid configuration with single-layered aramid fabric reinforcements is approximately 15.5% higher than that of single-layered carbon fabric reinforcements at 60°C test temperature. It is further observed that the absorbed energy improves as the number of fabrics is increased in both aramid and carbon reinforcements. The test temperatures significantly affect the failure mechanisms of TPCs. A smaller damaged area at the penetrated faces of the hybrid structures is obtained by comparison with the monolithic TPCs.

The Low Breaking Fiber Mechanism and Its Effect on the Behavior of the Melt Flow of Injection Molded Ultra-Long Glass Fiber Reinforced Polypropylene Composites

In this study, fiber breaking behavior, fiber orientation, length variation, and changes in melt flow ability of long glass fiber reinforced polypropylene (L-FRP) composites under different mold cavity geometry, melt fill path, and plasticization parameters were investigated. The matrix material used was polypropylene and the reinforcement fibers were 25 mm long. An ultra-long-fiber composite injection molding machine (with a three-stage plunger and injection mechanism design) was used with different mold cavity geometry and plasticization parameters. Different screw speeds were used to explore the changes in fiber length and to provide a reference for setting fiber length and parameter combinations. Flow-length specimen molds with different specimen thickness, melt fill path, and gate design were used to observe the effect of plasticizing properties on the flow ability of the L-FRP composite materials. The experimental results showed that the use of an injection molding machine with a mechanism that reduced the amount of fiber breakage was advantageous. It was also found that an increase in screw speed increased fiber breakage, and 25 mm long fibers were shortened by an average of 50% (to 10 mm). Long fibers were more resistant to melt filling than short fibers. In addition, the thickness of the specimen and the gate design were also found to affect the filling process. The rounded angle gate and thick wall product decreased the flow resistance and assisted the flow ability and fiber distribution of the L-FRP injection molding.

Influence of low-fracture-fiber mechanism on fiber/melt-flow behavior and tensile properties of ultra-long-glass-fiber-reinforced polypropylene composites injection molding

In this study, an injection molding machine with a low-fracture-fiber mechanism was designed with three stages: a plasticizing stage, an injection stage, and a packing stage. The fiber-fracture behavior is observed under the screw (plasticizing stage) of low-compression/shear ratio for the ultra-long fiber during the molding process. The molding material employed in this study was 25-mm-ultra-long-glass-fiber-reinforced polypropylene (PP/U-LGF). In addition, a thickness of 3 mm and a width of 12 mm spiral-flow-mold were constructed for studying the melt flow length and flow-length ratio through an experiment. The experimental results showed that the use of an injection molding machine with a three-stage mechanism decreased the fiber length when the screw speed was increased. On average, each fiber was shortened by 50% (>15 mm on average) from its original length of 25 mm. Longer glass fibers were more resistant to melt filling, and as the fiber length was reduced, the mixing between the melt and glass fibers was improved. Thus, the melt fluidity and fiber ratios were increased. In addition, the mixing/flow direction of the melt had an impact on the dispersion and arrangement of glass fibers, thus the tensile strength of PP/U-LGF increased.

Effects of Different Cooling Methods After Demoulding on the Cornering Fatigue Resistance of the Injection-Molded Long-Glass-Fiber Reinforced Thermoplastic Composite Wheel

As an un-sprung rotary part of the vehicle, the wheel has a significant effect on reducing fuel consumption and emission for conventional fuel vehicles and increasing the mileage of electric vehicles, which is significantly higher than that of a spring-loaded non-rotating part. The high-performance long fiber reinforced thermoplastic composite is used to manufacture wheel through the injection molding, which not only can achieve wheel weight reduction but also provides a new way to promote wheel lightweight due to its advantages of fast molding, easy to achieve mass production, easy to recycle materials and so on. The wheel is a key safety component of a vehicle, and its performance is one of the most important factors that affect the safety of the vehicle. Therefore, the wheel made of long fiber reinforced thermoplastic composite must meet the requirements of cornering fatigue test, radial fatigue test and 13° bench impact test. In this paper, aiming at the cornering fatigue property of the composite wheel, the influence of different cooling methods on this performance of the composite wheel after demoulding are studied. The injection molding of passenger car wheels (type 5.5J × 15), composed of long-glass-fiber (LGF) reinforced thermoplastic composite (PA66+50 wt. % LGF), are fabricated under the same injection process conditions. The two cooling methods, water-cooling and air-cooling, are used to cool composite wheel to room temperature under atmospheric pressure respectively. The cornering fatigue test is carried out on the cooled composite wheels, and attain the variation curves of the maximum principal strain and the minimum principal strain with time in different directions at the test points of the spoke root of the composite wheel, respectively. In addition, during the process of cornering fatigue test of the composite wheel, the temperature change of the spokes is monitored in real-time with the aid of infrared thermal imager, and obtain the temperature distribution and change of the spokes under different load cycles. The effect of different cooling methods on the cornering fatigue performance of composite wheels is compared and analyzed based on the maximum number of cycles, the strain test results of spoke root and temperature distribution and change of composite wheel. The results show that after demouling, air cooling mode is more beneficial to improving the composite wheel cornering fatigue performance than water cooling mode. This rule is also applicable to composite wheels that are injection molded with composite materials provided by another manufacturer. The research results provide some guidance for the processing of the wheel made of long-glass-fiber reinforced thermoplastic composite.

Mold-Face Heating Mechanism, Overflow-Well Design, and Their Effect on Surface Weldline and Tensile Strength of Long-Glass-Fiber-Reinforced Polypropylene Injection Molding

Long-fiber polymers offer the advantage of a lower production cost because specific tool designs are required for conventional injection molding equipment to produce long-fiber polymer parts. The use of long fibers allows relatively high fiber aspect ratios to be obtained, thereby enhancing composite stiffness, strength, creep endurance, and fatigue endurance. However, the multigate design of the injection-molded part can result in weldline formation during the molding process, which reduces the structural strength of the molded part. Therefore, in this study, the surface quality, fiber compatibility, and structural strength of long-glass-fiber-reinforced polypropylene (PP/LGF) injection-molded samples were compared in the use versus nonuse of a mold-cavity overflow-well area and the mold-face infrared heating method. The experimental results indicate that the mold-cavity overflow-well area more greatly improved the surface roughness of the PP/LGF molded samples. Moreover, the infrared heating of the mold-face decreased the weldline depth of the samples. Optical-microscopy images and mold-cavity pressure distributions indicated that the weldline tensile strength and the interface compatibility between fibers and melts at the weldline region during the molding stage were higher in the use than in the nonuse of the mold-cavity overflow-well and mold-face infrared heating method.