Model updating of crash box structures for crashworthiness study / Muhammad Nur Arif Bin Mohamad Asri

Faculty of Mechanical and Automotive Engineering Technology

Thesis (Master of Science) -- Universiti Malaysia Pahang – 2023

Includes bibliographical references

structure. It absorbs the kinetic energy during the event of a collision by plastically deform to absorb the impact energy efficiently. Various designs are applied towards the structure with different materials, configurations, and imperfections or trigger mechanisms. Crash box with trigger mechanisms is often a subject in crashworthiness studies, however, this research will have an approach to dealing with the structure with modal testing through experimental and computational analysis due to the location of the structure that exposed to vehicle vibration as well. As discrepancies occur, the model updating technique is utilised to identify and update the sensitive parameters that cause the discrepancies. The parameters are then used in the crashworthiness analyses to determine their effect towards the crashworthiness output of the crash box structure. The crash box structures are modelled in finite elements before being analysed with the normal mode analysis in MSC Patran and MSC Nastran and quasi-static analysis in Abaqus. Five different fabricated structures are made up of two parts attached using a spot weld with different designs of trigger mechanisms. Three approaches to joining elements are used for the finite element model: CWELD, CBEAM, and CBAR. The modal behaviour for all modelling is identified by using SOL 103, while the experimental modal analyses are conducted with the use of an impact hammer test with the roving hammer method to obtain the modal responses. The model updating method was conducted to reduce the discrepancies between the experimental and the computational data. Sensitivity analyses are executed to find the most sensitive model updating parameters. The results obtained by this study demonstrate that the use of CBAR joining element is the best to replicate the spot weld joining, where for all five types of crash box structures, the CBAR elements did show a significant percentage of error compared to CWELD and CBEAM for all types of crash box structures, while the most sensitive parameters that affect the modal behaviour of the structures are Young’s modulus of AA-6061, followed by the density of AA-6061 and Young’s modulus of spot welded joint. In terms of crashworthiness analyses, it is identified that the use of updated parameters in crashworthiness analyses compared to the initial results of crashworthiness output did show a small change where the crashworthiness output of the structure is slightly higher for both primary and secondary peaks as well as for the magnitude of the absorbed energy. The outcome of this research will contribute towards the field of mechanical vibration and crashworthiness, especially in the automotive industry, in which this research focuses on the optimization method of the modelling to improve the accuracy and reliability of the computational prediction.