Multi cornered thin wall sections for crashworthiness and occupant protection

摘要

The desire to improve crashworthiness of a passenger vehicle for enhanced occupant safety has been a major challenge for decades. When a crash is unavoidable, it is the crash energy and the manner in which vehicle occupants experience the associated forces that will determine the extent of injury to those occupants. Axial collapse of the thin walled structures has been studied in detail over decades and the understanding was limited primarily to circular and square tubes. This research extended the knowledge beyond Square/Cylindrical shapes towards complex sections along with further exploratory works applicable to practical aspects. The hands on tools for designers to act as comparators for exercising flexibility in design decisions that are missing is addressed in this research study. Since axial crush mode is dominant in vehicle frontal crash and rear impact, dynamic and quasi-static, axial crush characterization has been developed with various cross-sections across different designs within the constrained packaging space. A new strategy has been proposed to improve energy absorption efficiency of thin-walled columns by designing extra stable corners in the cross-section. Several profiles of multi-corner thin-walled columns obtained through this strategy were presented and their crashworthiness capacities under axial crush loading were investigated analytically, experimentally, and numerically. Super Folding Element (SFE) concept was used in characterizing the collapse behaviour and parameters acting as comparators for designers were developed. The methodology was then utilized to develop a new 12-Edge section with better packaging at edge corners for robust collapse in asymmetric/inextensional mode with good corner angle and high energy absorption capacity. Thorough analysis of the results data from the crush tests both physical and numerical lead to an important conclusion that the maximation of edge corners with right packaging and favourable corner angles provided higher capacity to absorb the initial crash kinetic energy with good weight effectiveness. The 12-edge section’s dominance over the pack of other sections was widely analysed and established through the crush responses. A new methodology of design sensitivity analyses using DOE (design of experiments) based on Taguchi method was also proposed and performed to identify dominant characteristics. Analytical expressions for design parameters like Mean crushing force (Pm), Specific Energy Absorption(SEA), Solidity ratio(ϕ)and Collapse Efficiencies are derived while new design parameters of Weight effectiveness (WE), and structural effectiveness ( ) along with their application are proposed. The understanding and characterization developed at component and subsystem level fit well into the domain of upfront energy absorption motive and would not be complete if their ultimate responses are analysed at a full vehicle level in terms of their capacitance for crash energy absorption. The foundational dominance of 12-edge section at component level maturity and as applied to full automotive dynamic vehicle crash test resulted in achieving overall reduction in parameters reflecting Femur and chest injury of the occupants. Thus indicative of the potential of the multi-cornered sections for enhancement in crashworthiness of Automtive vehicles and reduction in occupant fatalities in severe crash events.