HORK Enterprises
3221 Quick Road
Holly, MI 48442, USA
 +1 (248) 328-0231
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Frontal Impact Analysis

Occupant and Vehicle Simulation Models are the Key Engineering Tool for Crash Safety Development. Crash analysis differs from strength analysis of bridges and airplanes in that there is a time dimension added to the equation. That makes the analysis dynamic, for which dedicated tools have been developed. Time is discretized into small steps, on the order of nanoseconds to microseconds, and for each step, the equations of motion are solved for the structures and the forces acting upon them. With more and more trucks out on the roads, vehicle bumper height incompatibility becomes an ever greater problem. Cars can easily slide under the bumper of a truck without their crush zone being engaged. Especially for accurate crash severity sensing, an enhanced upper structure rigidity is required to ensure propagation of the pulse to the crash sensor. Using computer analysis many different crash scenarios can be studied, without the need for costly prototypes being consumed in crash testing. The structure can be optimized to have enough rigidity to propagate the impact pulse to the main structure of the vehicle and the crash sensors. From the early days of airbag development, simulation tools have been used to find the optimum parameters, that make them work in combination with seat belt, seat, steering column, and knee-restraints. Initially the models were two-dimensional and the results could only be viewed after a series of images were plotted to paper. The dummy models were based on linked rigid bodies and had limited biofidelity. The belt models were based on non-linear springs and the airbag models on heuristic formula that estimated the volume carved out of the airbag by the occupant. The first production airbags were designed with the help of these tools and lots of laboratory testing. With the introduction of afordable graphical Unix workstations around 1990 the abilities to analyze and view the occupant kinematics vastly improved. The increased compute power allowed for full 3-dimensional models and finite element airbag analysis. Explicit Finite Element Analysis codes such as LS-Dyna, Pam-Safe, and Radioss, as well as the Multi-Body code MADYMO expanded to add specific features necessary for airbag modeling and analysis. MADYMO initially opted for a single integration point, triangular element, leading to the iconic driver airbag mesh that adorned multiple publications. Special element properties, such as orthotropic material properties, and reduced compression stiffness, implemented across the board, allow for a better approximation of airbag fabrics. Dummy models have traditionally been modeled with multi-body techniques. Multi-body techniques can be used when the deformations of the object do not play a significant role or can be represented with a simple force-deflection characteristic. Multi-body techniques have the advantage of relatively fast analysis since they can describe large bodies with a few equations. They also allow accurate modeling of the joints between the body segments. Finite Element techniques allow a detailed description of the geometry and stiffness characteristics of objects. This is important for objects that are subjected to large deformations, such that the initial geometry is no longer representative. The more detailed description comes with a price of additional computation time, but with the ever increasing speed of computers, this is less of a problem today than it was 32 years ago.

Advanced Airbags

By 1996 reports were getting stronger that airbags, designed to restrain an unbelted average adult male in a 30mph rigid barrier crash, could be dangerously powerful. In a number of moderate speed collisions the airbag deployment caused serious injuries to short stature drivers and children that were seated in the front passenger seat. Laboratory testing showed that there was a problem with the force of airbag deployment, but only numerical analysis could quantify the problem and provide guidance towards solutions. The U.S. Government first lowered the protection requirements, so inflators could be made less powerful, to mitigate the injury risk. Then the industry added a second stage to the lower output inflator to gain back the protection levels for higher severity crashes. Computational fluid dynamics analysis, was used to optimize both inflator stages to minimize the injury risk to a short stature driver from a deploying airbag, and maximize the protection for all occupants in high speed crashes. Children being the most vulnerable occupants involved in vehicle crashes, they require their own restraint systems. Child dummies help in evaluating the risks and protection requirements. Dummies representative of 3 year old and 6 year old children, as well as an infant, are part of the Advanced Airbag Rule. They are also featured in certification tests for child safety seats (more formally Child Restraint Systems, or CRS).
In Europe this is governed by the ECE R44 regulation and in the USA by FMVSS 213. Slightly different tests, but both with the main objective to assess the integrity of the CRS under vehicle crash conditions.
Several new car assessment programs, such as EuroNCP and it's derivatives Latin-NCAP and China-NCAP also incorporate a CRS with infant or child dummy in their testing. The star rating of the vehicle is affected by certain performance measures of the child dummy.
The effectiveness of a CRS in protecting a child is significantly affected by how well it is installed in the vehicle and how well the child is restrained within the CRS. Developments such as ISOFIX and LATCH address the former, while the U.S. Department of Transportation, National Highway Traffic Safety Administration, the Department of Motor Vehicles and various consumer organizations address the latter with informational media.