Mechanical Design

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Browsing Mechanical Design by Author "Alazar, Mulugeta"

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    Investigation on Crashworthiness of Locally Manufactured Bus Structural Frame by using Numerical Approach
    (Addis Ababa University, 2021-12) Alazar, Mulugeta; Haileleoul, Sahle (PhD)
    The thesis aimed to investigate the crashing behavior of locally manufactured 60 seated bus structural frames in case of frontal and side impacts. In addition to studying the crashworthiness of current structure, the most severe impact condition was identified by referring to crash test and an improvement on structure for a better crash performance for that impact condition was proposed. A full frontal and an offset impact position were used for frontal impact testing while analysis for side impact a perpendicular and angled/oblique impact position were used. Full-frontal crash analysis was done according to the ECE-R29 involving a frontal crash pendulum test in which impacting energy is set to 55 kJ and safe space between steering model and manikin is checked. while for offset frontal impact a simulation of bus structure impacting a rigid wall with an initial velocity of 56km/hr was done to check structures response to such kind of accidents. For sideimpact, residual space specified on ECE-R60 was used to check side frame deformation in case of perpendicular and angled/oblique impact. An impacting trolley with an initial speed of 48 km/hr was used for the side-impact test. Commercial software CATIA and ABAQUS were used for geometrical modelling and analysis. The study focused on identifying the crashworthiness of the bus structure by analyzing the structural deformation, crash pulse, crash force efficiency, HIC, and energy absorbing capacity. The results showed that the current structure had failed to meet regulation in the case of both frontal impacts and side perpendicular impact. In full frontal impact an intrusion of 17.32 mm in to manikin is seen and side frame has intruded residual space by 8.22 mm. Amongst the tests most severe impact damages was observed in the case of full-frontal and off-set frontal crash tests. For improving crashworthiness of the structure, three models were proposed and tested according to ECE-R29, the first two were based on increasing the thickness of frames and the last was by adding a reinforcement profile. The simulation results for improved models showed, by adding a reinforcement profile has improved the crashworthiness of the bus by creating a space between manikin and steering model of 36.33 mm structure and meets with regulation.