Hood design-Week 2

Car bonnet is the important component which is utilized for several purposes at the front. It gives access to the engine compartment which enable the repair and maintenance of many parts namely car engine, radiator etc. Therefore, bonnet must be designed in suitable manner and it should minimize the hindrances from the disturbance caused by the external environment on the hood and its components below it. When the car is in running condition, the resisting forces from the air acting on the hood therefore the design of the bonnet should be made aerodynamic to reduce the air resistance. Hood assembly includes inner panel, outer panel, hinges, latch and reinforcements. The upper and stiffener panels arejoined through the process of hemming or both panels are joined by using the adhesive namely mastic. Spot weld can,be made where it will benecessary. Sandwich construction of the hood structure that will increases the capability of thehood’s ability to absorb the energy impacted by the external forces which are acting on the bonnet. The bonnets of the most vehicles are basically fabricated using the sheet metal structure, a good energy absorbing structure so it causes substantially a small threat.

Outer and inner stiffener panels are made or fabricated by using the of sheet metal structures therefore environment used is surface modelling. Since the hood assembly is a sheet metal component, hood structure is vulnerable to the vibrations. The source of the vibrations could be the engine generated vibrations, the vibrations due to the un-evenness in the road surface, and aerodynamic interactions of the hood surface when the vehicle is in motion. Excessive vibrations will put an impact on the passenger's ride comfort, and also make the structure susceptible to fatigue failure. Too many vibrations also affect the functioning of the locking mechanism of the bonnet, considerably risking the unlocking function and bonnet will be open up while the vehicle is in motion. Because of the many ongoing efforts are to reduce the weight of the vehicle, the thickness of the bonnet is being reduced to its possible values. This could considerably increase the severity of the vibrations that the structure is subjected to. Hence, determining the fundamental frequencies of the bonnet structure and its behaviour at those frequencies is necessary.

Safety is the most important criteria in automobile designs which concentrates on both pedestrian and occupant safety. The pedestrians are the most vulnerable road users and are at high risk of traffic accidents. The major reason for the fatality of the pedestrian in traffic accident is due to the head injury resulting from the hard impact of the head against the stiffer hood or the ground. This leads to the necessity of new inner hood panel which is less stiffer and pedestrian friendly. The head impact analysis on the present hood of the car was done to study the response of the adult head form at two different locations. Structural and modal analysis for the same present hood assembly was done to observe the local and global stiffness. In order to reduce the head injury of the pedestrian the local stiffness over the area of head impact has to be reduced thus the new design of hood inner panel was focused on that and the structural and modal analysis was done for the new design. The design with lesser local stiffness and similar global stiffness compared to the existing hood was finalized. The head impact analysis for the new design of hood inner panel was performed.