Within the last few years, Finite Element Analysis (FEA), generally referred to as "Computer Simulations", provided advanced engineering support for many accident-related cases. FEA can provide a very thorough analysis and deep understanding of the overall accident as well as the performance of each component involved in the accident. For any collision, FEA can precisely calculate and/or predict crucial engineering information in two areas:
FEA will provide major compelling engineering evidence to unfold the mystery of any crash-related case. It will provide a better understanding of the accident overall as well as which factors contributed most to the severity of the accident. FEA/Computer simulations can provide substantial engineering support to almost all accident-related cases. The significant contributions of FEA to common areas in the accident-related field are highlighted below.
FEA/Computer simulations have already provided excellent engineering support to accident analyses in this area. Within the last twenty years, the research centers at several major universities funded by the Department of Transportation (DOT), and all automotive OEMs have developed many accurate and reliable Finite Element (FE) vehicle models for several classes of vehicles (passenger cars and SUVs, vans, trucks, etc.). Millions of computing hours and tens of thousands of full vehicle and subcomponent crash tests have resulted in the validation and refinement of this technique, leading to a reliable and widely accepted design and analysis tool. A few vehicle impact simulations are shown in Figure 1. A detailed FE vehicle model for a 2001 Ford Taurus is shown in Figure 2-a. The model has about one million elements and can be used for all types of crashes (frontal, rear, side, and roll-over). The detailed model includes not only the main vehicle's structure but also the vehicle's interior as shown in Figure 2-b. In Figure 3, the FEA accurately predicted the standard test for the W-beam guardrail (NCHRP-350, Test Level-3). As shown, the FEA predicted behavior of the guardrail and the pick-up truck is virtually identical to the behavior during the actual test. In Figure 4, the FEA results compared very well to the actual test of a pick-up truck impacting a portable concrete barrier. In this area, the FEA can accurately calculate and predict the kinematics of the impact (i.e. motion of the vehicle and barrier) and mutual forces between the vehicle and the rail/barrier. It can also provide an accurate and detailed structural analysis for every part involved in the impact (deformation, stress, strain, failure, etc.).
In this case, the FEA can accurately predict the vehicle's motion, deformation and reaction forces during the collision. The structural analysis for each part of the vehicle is calculated and provided by FEA. Dummy models are also used to represent the driver and/or passengers. FE models for airbags and seatbelts can also be combined with the vehicle model. The impact forces applied on the driver, either through the restraining system or during the impact with the vehicle's interior can be accurately calculated. In Figure 5, the FEA results of a 1996 Neon impacting an offset rigid wall correlated very well with the actual test results.
In Figure 6, the FEA accurately predicted the behavior of a steel mailbox when impacted by a vehicle. The FEA accurately calculated the vehicle damage and the behavior of the windshield when impacted by the flying mailbox. It is also clear that the FEA was able to predict the exact deformation of the mailbox post as a result of the collision with the vehicle's bumper.
Accurate and reliable FE models for seatbelts and airbags (frontal, side and head) are developed and combined with the dummy and vehicle models to study the behavior and effect of such protecting devices. In Figure 7, dummy models are placed inside the vehicle model, together with the proper restraining systems.
Several FE dummy models and detailed human models were developed and used for crash/injury evaluations. The FEA can accurately calculate the impact force applied on each part of the human model. Using certain measures, it is feasible to calculate the level of injury severity the human body encounters during a certain impact. Several human models are shown in Figure 8.
Detailed FE vehicle models, together with dummy and human models were be used to conduct advanced roll over analysis as shown in Figure 9.
Advanced features are constantly added in FE codes that enable the modeling of more complex problems, such as fluid/structure interaction. Such advances allow the complex analysis of fuel behavior inside tanks and pipelines. This made it feasible to calculate accurately the deformation and stresses in the fuel tank structure taking into consideration the fuel/structure interaction. The advanced FEA conducted in this field provided excellent results that correlated very well with the test results and allowed a thorough understanding to the fuel tank behavior during the impact. A reliable FEA of Grand Voyager fuel tank is shown in Figure 10.
Detailed FEA were used to simulate engine blade bird strike as shown in Figure 11. FEA were also successfully used to calculate and predict the survivability of occupants in non-catastrophic impacts as shown in Figure 12.
Blast effects could also be accurately calculated using FEA. Head Injury Criteria (HIC), resultant head, pelvis and chest accelerations are predicted for a 50th percentile Hybrid-III dummy sitting on the driver's side as shown in Figure 15. FEA were successfully used to predict the IED/mine blast effect on a pick-up truck as shown in Figure 16.
For more than three decades, FEA have been used extensively for military and defense applications. Several Ballistic applications using our FEA expertise are shown in Figures 17 below.
The cost of conducting a thorough FEA to analyze any accident is far below any other traditional engineering technique. Considering the common case of vehicle impacting a guardrail in a highway accident, the cost of conducting the FEA for such a case is generally under $10,000. This is almost 20% of the cost of a single full scale crash test. Unlike the actual test that is destructive in nature and the parts can only be used once and thrown away thereafter, the FEA provides accurate and reliable computer models that can be used whenever needed to analyze any impact scenario under investigation. These developed computer models accurately represent the actual parts involved in the accident in terms of geometry, material properties, connections, and functions. In this sense, it is important to point out clearly that these computer models (Finite Element Models) provide an accurate physical representation for the actual parts not a computer-graphic representation. Another advantage of the FEA is that it provides an unlimited amount of data at any particular part of the structure while testing output is limited to the sensors or testing device. Today, FEA is extremely cost-effective and accurate, and its usage for most crash-related cases is justified in terms of both time and cost.
There is a plethora of court cases where FEA tools were used as supporting evidence. Failures of weldments, bolted joints, and other types of connections have been analyzed with FEA and used in court cases for years. Modern FEA modeling not only provides accurate physics-based analyses but also convinces the jury by means of realistic and sophisticated animations of the crash. ART experts have been successful in making full scale vehicle crash modeling and simulation accepted in court cases. In a recent accident investigation case in Orlando, FL involving the crash of a midsize sedan into a highway guardrail (resulting in a fatality and severe injury), the FEA, conducted by ART experts, provided the major compelling engineering evidence in the case. The opponent lawyer filed a motion to block the FEA from being presented in the trial. After a 90 minute hearing in which the ART expert witness provided his scientific testimony to questions posed by both parties, the court denied the motion and allowed the FEA to be presented in the case as "scientific evidence". The court also indicated that it became very clear from the evidence and answers provided in the hearing that FEA is a scientific technique that has been well recognized by the engineering and scientific community as an advanced, powerful and effective analytical tool and, therefore, the court will allow it; just like any other scientific evidence. The Orlando case is among many that provide sufficient precedence and will undoubtedly motivate other courts nationwide to do the same. It is well known that courts always allow and welcome new scientific tools to be presented in order to provide better analysis and supporting evidence. As far as we know, no court has ever denied FEA from being used and presented in accident investigation cases.