Vehicle crashworthiness is crucial for passenger safety and presents significant design challenges during the vehicle development phase. Energy absorption of the vehicle structure and integrity of the passenger compartment are key factors in ensuring optimal protection of occupants in a crash event. Meeting stringent safety regulations (FMVSS, ECE, AIS) and consumer tests (US-NCAP, Euro-NCAP, C-NCAP) is a priority for manufacturers to improve safety ratings while reducing weight, cost, and design cycle times. This research is motivated by the real-world challenges experienced by engineers in the design of crashworthy structures for automotive vehicles. The methods used in this project leverage the fundamental properties of structures to solve complex problems encountered during the product design. 1) Macro Element Method (MEM) with simplified Super Beam Element (SBE) for exploring design concepts quickly, 2) Multi material combination of Ultra High Strength Steels (UHSS) and Auxetic materials for maximizing energy absorption in thin-walled box structures, and 3) Target Setting for Optimal Design Parameters to Enhance Automotive Frontal Crash Safety 4) Equivalent Energy Absorption (EEA) for quick crash performance vs weight trade-off studies.
1) Application Of Macro Element Method (MEM) for Faster Automotive Crash Safety Design During Concept Stage:
This study explores the application of the Macro Element Method (MEM) using a simplified Super Beam Element (SBE) for rapid crash analysis during the early concept stage of vehicle design. MEM has the potential to accelerate the product development process, with analysis run times of a few seconds. A calibration study validates MEM against Finite Element Method (FEM) and experimental results for a metallic thin-walled square frusta under axial compression. Results show over 97% correlation between MEM, FEM, and experimental data. MEM is further evaluated for full vehicle simulations, including full width frontal crash and side pole crash analyses, demonstrating its robustness for product development applications.
2) Maximizing the Energy Absorption Capacity of Thin Walled Box Structures using Auxetics & Ultra High Strength Steels (UHSS) at Sensitive Zones:
This study proposes a novel methodology for maximizing the energy absorption capacity of thin-walled front-end box structures by utilizing optimal combinations of auxetic and ultrahigh strength materials at critical locations. Through Finite Element Analysis (FEA), a crush box made of mild steel is initially analyzed, followed by combinations of mild steel and high strength steels at sensitive areas to enhance energy absorption. Results show that the specific energy absorption (SEA) capacity can increase by over 90% with the optimal combination of shape and materials. Additionally, incorporating auxetic materials yields a further increase, up to 140% SEA. Full vehicle crash simulations demonstrate reduced structural intrusions and improved crash safety performance.
3) Target Setting for Optimal Design Parameters to Enhance Automotive Frontal Crash Safety
This study proposes a methodology to enhance crashworthiness in early vehicle design by determining optimal parameters such as front crush length, crash pulse severity, restraint properties and occupant packaging space to minimize peak occupant acceleration. The occupant responses are predicted using Lumped Mass Spring (LMS) models and Finite Element Models (FEM) achieving a close degree of correlation with the test values. Target values are derived for average vehicle acceleration, restraint stiffness, ride-down efficiency, and occupant packaging space parameters, aimed at reducing peak occupant acceleration. Using the targeted vehicle acceleration, a methodology is devised to determine the optimal frontend crush length necessary to satisfy the structural criteria for frontal impacts through fundamental analytical calculations. To validate the method, a full vehicle finite element crash simulation is conducted, resulting in a strong correlation with analytically predicted values. The findings highlight the usefulness of this methodology in establishing architectural targets for crash performance during the conceptual stage of vehicle development.
4) Equivalent Energy Absorption (EEA) - A Methodology for Improved Automotive Crash Safety Design: UHSS are crucial for meeting safety targets by absorbing impact energy and withstanding higher loads during collisions. Safety simulations are complex and time-consuming, hindering quick evaluation of performance using different material grades. This research proposes a new methodology, Equivalent Energy Absorption (EEA), for faster trade-off studies on performance and weight. A relationship is established between component gauge, grade, and equivalent safety performance, enabling quick decision-making with minimal simulations. A case study demonstrates significant evaluation time reduction of over 80% using this methodology, highlighting its efficiency for evaluating vehicle safety performance.
It has been demonstrated that all the four methods described above contribute to the two primary targets of automotive industry, which is reducing cost, and improving time-to-market, while ensuring good or enhanced product quality. The utilization of Target Setting and MEM methods facilitates early-stage quick concept and pre-concept simulation-driven development, while the combination of Multi Material and EEA methods aids in achieving lightweighting goals. Collectively, these innovative approaches and techniques lead to reduced development & manufacturing costs and increases flexibility in the product development.