| dc.description.abstract | To achieve the emission and fuel efficiency targets proposed by various regulatory bodies around the world, automotive manufacturers have shifted towards utilization of advanced lightweight materials for automotive structural applications. Owing to high specific mechanical properties and energy absorption characteristics, fiber-reinforced plastic (FRP) composites possess a high potential to replace current steel and aluminum structures in automobiles. Recent developments in cost effective unidirectional (UD) non-crimp fabrics (NCFs), rapid curing resins and automated fabrication processes such as high-pressure resin transfer molding (HP-RTM) or liquid compression molding (LCM) may accelerate the integration of FRP composites into the structures of high volume production vehicles. This thesis investigates the application of carbon fiber reinforced plastic (CFRP) composites in automotive primary frontal crash structures for energy management and light weighting applications. A robust computational modelling strategy was developed for predicting the crash performance of UD-NCF composite components and validated by utilizing available experimental data. The suitability of using NCF CFRP composite materials for a developed front-end energy absorbing technology demonstrator was numerically evaluated based on the New Car Assessment Program (NCAP) test configurations. To numerically evaluate the performance of an NCF composite material, two macroscale constitutive models were chosen from the composite material library available in the commercial finite element software LS-DYNA (Livermore Software Technology Corporation, Stuttgart). In addition to calibrating ply-level material properties, the existing material models rely on non-physical parameters that must be calibrated using component-level test data. In this study, an NCF composite hat channel component fabricated using HP-RTM was used for this purpose. A stacking sequence of [0/±45/90]s was used for the hat channel component, which was subjected to an axial crush force under dynamic loading rate. The numerically predicted force-displacement profile was evaluated until a good correlation was obtained with the experimental test data. To validate the calibrated material models, a similar hat channel component with a [±45/02]s stacking sequence subjected to an axial crush force under dynamic loading rate was simulated and compared against corresponding experimental test data. Two additional simulations were conducted for the same hat channel components with the same stacking sequences under quasi-static condition to further validate the impact simulation model. A good correlation was obtained between the predicted and experimental crush response, crush force and energy absorption. The next step in the study utilized the validated impact simulation model to design a vehicle frontal crash structure technology demonstrator comprised of the HP-RTM NCF composite material. Using a full-frontal steel structure from a production vehicle as a baseline, a simplified laboratory scale technology demonstrator of 525 mm length was developed, which comprised of redesigned frontal sub-assembly components to accommodate the design of the composite crush rails. Four different technology demonstrator concepts were designed based on the manufacturing feasibility, and the impact performance of each design concept was numerically simulated. Evaluating the performance of the designed composite technology demonstrator against the baseline hot stamped steel by considering overall deformation mode, crush force, energy absorption and deceleration profiles demonstrated that NCF composites provided increased energy absorption capabilities. Furthermore, the effect of stacking sequence and total laminate thickness for the chassis frame were shown to have a notable influence on the predicted crash performance and energy absorption, with similar crush response. Finally, the laminate of the chassis frame was tailored by considering a variation in the numbers of plies across the part by invoking a ply drop off scheme, resulting in a thinner crushable region for energy absorption and a thicker region with high rigidity for intrusion resistance. The crash performance evaluated, and results supported the suitability of composites in energy absorbing and intrusion management of composites in automotive frontal crash applications. These numerical models predicted that NCF composite structure was 29% (1.6 kg) lighter than the hot-stamped steel structure and 48% (3.7 kg) lighter than a conventional baseline steel structure. In addition to weight savings, the proposed composite primary chassis frame reduced the number of components from three to two. In future work, different loading conditions and experimental tests will be conducted to support the numerical simulations of this thesis. | en |
