This research article presents the crashworthiness response of carbon fiber composite front bumper crush can (FBCC) assembly subjected to 40% offset frontal impact loading. Automobile manufacturers continue to strive for overall vehicle weight reduction while maintaining or enhancing safety performance. Therefore, the physical testing of lightweight materials becomes extremely important under a crash scenario in order to apply them to automotive structures to reduce the overall weight of the vehicle. In this study carbon fiber/epoxy lightweight composite material is chosen to develop frontal bumper beam crush can assemblies. Due to lack of available studies on carbon fiber composite FBCCs assemblies under frontal offset crash scenario, a new component-level experimental study is conducted in order to develop data that will provide assistance to CAE models for better correlation. A sled-on-sled testing method was utilized to perform tests in this study. 40 % offset frontal tests on FBCC structures were conducted by utilizing three high-speed cameras (HSCs), several accelerometers and load wall.
Impact histories i.e. crash pulse, force-time history, force-displacement, impact characteristics and deformation patterns from all FBCC tests were consistent. The standard deviation and coefficient of variance for the energy absorbed were very low suggesting the repeatability of the 40% offset tests. Excellent correlation was achieved between video tracking and accelerometers results for time histories of displacement and velocity. Post-impact photographs showed the progressive crushing of composite crush cans, bumper beam/crush can adhesive joint failure located on unimpacted side and breakage of the bumper beam due to the production of shear stresses as it is stretched due to its curvature after hitting the sled.
The primary focus of this investigation was to study the effect of failure modes on key energy absorption parameters including the initial peak load (P peak ), the drop in the peak load and the sustained crushing load (P avg. ) in the crushing process of unidirectional polymer matrix composite (PMC) tubes under quasi-static conditions. The failure modes of interest are the axial cracks, the transverse cracks and delamination. The roles of initiators with different radii and external constraints were carefully analyzed in the context of primary failure modes using a real time image acquisition system. The results for fiberglass/polyester tubes showed that the failure modes play a critical role on the load-deflection (P-d) response of the tubes and their corresponding specific energy absorption (SEA). In addition, it was possible to control the failure modes for better crushing performance by using external constraints combined with initiators.
The effect of different thermal cycle profiles on thermal barrier coating (TBC) spallation lifetime was investigated. Fick’s law was used to describe the thermally grown oxide (TGO) buildup. It was found that Fick’s law can be used to correlate between damage thickness and oxide thickness for different thermal cycle profiles. A critical oxide thickness of 12 μm can be associated with spallation life for the 8 wt% YSZ /PtAl/Rene N5 EB-PVD system. The importance of this correlation is that, for a given thermal cycle profile, the number of cycles to spallation can be predicted analytically using Fick’s law. The effect of maximum temperature, minimum temperature, holding time, and number of cycles were studied. It was found that by using the actual thermal cycle profile, accounting for cumulative oxide buildup throughout the complete cycle, the TBC spallation lifetime can be estimated reasonably well.
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