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The objective of this study is to characterize the tensile properties and interfacial adhesion of chopped glass fiber semipreg reinforced polymer composites. Tensile testing was used to investigate the resistance to tension of composites. Differential Scanning Calorimetry (DSC) was also used to determine the thermal behavior of composites. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) analysis were conducted to determine the microstructure and morphology of the composite polymers. The tensile testing results indicated that the tensile strength and Young's modulus were respectively improved by 23.45% and 53.77% for the CR-6/PA6 but decreased by 36.49% and 11.39% for CR-6/PA6GF30. DSC results revealed that crystallinity of PA6GF30 and PA6 surface of composites specimen was lower than those of PA6GF30 and PA6 specimens. SEM micrographs of CR-6/PA6 and CR-6/PA6GF30 fractured surfaces depicted good adhesion at the interface between CR-6 and injected PA6 or PA6GF30. XRD results showed that PA6 and PA6GF30 have different crystalline forms. The crystallizability of CR-6/PA6 and CR-6/PA6GF30 was promoted by the presence of CR-6. Introduction of glass fiber was shown to be helpful for formation of a more stable α-phase of PA6 and PA6GF30. [ABSTRACT FROM AUTHOR]

Safety requirements and lightweight have been the primary considerations in designing automotive parts. The selection of materials with high specific strength, energy absorption, and specific stiffness properties, such as aluminum and fiber-reinforced composites, paves the way to resolving this challenge. This study investigates and compares the energy absorption characteristics and pedestrian protection of the automotive front bumper beam made of aluminum, carbon fiber-reinforced epoxy (CFRE), and glass fiber-reinforced epoxy (GFRE) with the steel counterpart. The baseline steel bumper beam under a high-velocity frontal crash to a rigid wall at 50 km/h was first analyzed using finite element analysis through LS-DYNA. The bumper beams of other lightweight materials were designed with identical energy absorption capacity. They were then assessed through the low-velocity crashes according to UN-ECE R42 regulation and Euro NCAP pedestrian testing protocol. Although the aluminum bumper beam deformed less in crash tests, it possessed the lowest specific energy absorption (SEA) and the highest peak force. The quasi-isotropic CFRE and GFRE composite beams attained higher SEA because the stresses could be efficiently distributed in the beams, as observed from more extensive damage areas, especially in the ±45°-plies. From a proposed effective parameter weighted from the peak force, maximum deformation, energy absorption, mass, and cost, the GFRE bumper was recommended for modern car bumper beams. The optimal design of the GFRE bumper beam could substantially improve crashworthiness compared to the baseline steel beam with a weight reduction of 67.7%, a 101.8% increase in the SEA, and a 59.8% decrease in the peak force. Furthermore, the pedestrian's lower leg protection was further achieved by adjusting the beam's position. [ABSTRACT FROM AUTHOR]

Crash box is the main component of the crumple zone to absorb impact energy. Therefore, it requires the highest energy absorbing performance under axial and oblique impact loads at different angles. This study presents an optimal solution for the hexagonal crash box design with a functionally graded thickness (FGT) honeycomb filler. The crash box finite element model was firstly validated with the experimental impact test. Layer sensitivity analysis of the FGT model showed that using 41 layers along the crash box axis was sufficient to obtain accurate results. The multi-objective optimization was adopted to obtain the optimal grading exponents of the FGT crash box that maximize specific energy absorption (SEA) and minimize initial peak crash force (IPF) at the 0-, 10-, 20-, and 30-degree impact angles based on the Particle Swarm Optimization technique. The optimal FGT design could decrease the IPF in all design cases compared to the crash with uniform thickness (UT), while the SEA of the FGT crash box demonstrated better crashworthiness at the 30-degree impact angle. Furthermore, the FGT crash box exhibited the progressive failure mode at the oblique impact angles, which resulted in higher energy absorbing capability than the bending failure mode observed in the UT crash box. [ABSTRACT FROM AUTHOR]