Evaluating the Reliability of Underrun Protection System in Heavy Vehicles Using FEA

Evaluating the Reliability of Underrun Protection System in Heavy Vehicles Using FEA

Underrun protection systems, often known as underride guards, are utilized in trucks and buses to prevent intrusion of small passenger cars during the event of collision. Research figures reveal that trucks with a gross weight of more than 3.5 tonnes are involved in 20% of the road accidents; from which, 60% are car to truck accidents. It is obvious that the injuries are far more fatal for small vehicles during such collisions. Most common accidents however are front and rear collisions, resulting into fatal injuries for car passengers. This is manly because the bottom rear and front of the trucks nearly level with that of the head of an adult passenger seated in a car. In such instances, the only protection the car passenger has is a windshield. Due to the difference in height of a car bumper and the trailer platform, the crumple zones do not get involved and there’s a direct impact on the windshield without activating air bags, resulting into fatalities.

To protect car passenger during such collisions, many safety regulation authorities across different countries have made it mandatory for trucks to have front and rear underride guards. These guards act as a rigid assembly hanging down from the bottom front and rear of the truck or trailer, providing a means of protection to the small passenger vehicles during collisions. Authorities like NHTSA recommends including side underrun guards apart from front and rear ones for increased safety.


Looking these underride guards from a design perspective, they are subjected to sudden impacts, which can lead to excessive deformation and breaking forces. As such it has to withstand heavy short-duration loadings without much deformation. Its design should ensure that the crumple zones of a colliding car absorb all the energy while preventing the shock from transmitting to the cabin portion. In total, the underride guard should possess excellent structural strength, allow the car crumple zone to absorb the impact energy and must not break or get detached during collisions.

While physical tests are a must to evaluate these guards, they are often costly when it comes to testing alternative design concepts. FEA remains a handy tool in such cases, which can be utilized to develop a virtual model representing actual crash scenario. Modern solver capabilities allow capturing the physics during sudden or short-lived yet large impact loadings on structures through explicit dynamics. Finite element through explicit approach allows fast simulations for large deformation dynamics. With elements in the model having suitable degree of freedom to capture non linear deformation, the design of the underride guards can be evaluated cost-effectively.

Utilizing finite element analysis will allow better understanding the load distribution across the guard geometry and predict the possible deformation regions requiring more strength. Any possible alternative design can be put to test using the loading conditions, and its strength and reliability can be examined subsequently. However, this does not essentially mean that physical tests can be eliminated from the design process. The benefit of using FEA is to reduce the number of physical crash experiments which are often very costly and time-consuming. The results obtained from FEA can be validated against physical test to ensure its reliability.

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