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This paper will address several critical aspects of bumper system performance, including vehicle damage protection and crash-severity sensing considerations, energy-absorption capacity and efficiency, and low-speed impact consistency and sensitivity to temperature changes. The objective is to help engineers and designers establish a realistic perspective of the capability of the various technologies based on actual test performance. The scope of the evaluation will include a comparison of several bumper-beam material constructions when subjected to a 16-km/hr swinging barrier impact over a range of temperatures the bumper could see in service (-30 to 60C).

With the increased focus on fuel economy in the automotive industry today vehicle mass reduction is becoming increasingly important to automotive engineers. A common method to reduce mass for bumper reinforcement beams is to use aluminum extrusion technology. However, the use of aluminum extrusions comes at a higher cost than comparable steel systems. Two hybrid design approaches for bumper reinforcement beams are presented in order to reduce mass while maintaining a lower cost than aluminum bumper systems.

Laboratory testing and computer aided engineering (CAE) techniques have long been employed in the development and optimization of automotive bumper systems. However, as more aggressive automotive styling and performance trends and mass and cost reduction objectives continue to push the limits of known bumper system construction, early optimization techniques will need to improve proportionately. The limitations of today's test and analysis techniques for providing accurate predictions can lead to excessive factors of safety (waste) and/or expensive rework during latter stages of vehicle development. Much work has been done to improve the capability of computer simulations for predicting impact behavior (1). However, some of the development limitations can also be attributed to an inability to achieve repeatable results or to accurately simulate the low speed impact behavior of a vehicle with universal test vehicles (UTV).

Today's interior systems design engineer has been challenged with providing significantly lighter, simpler and more cost-effective instrument panel (IP) design solutions, while simultaneously meeting rigorous occupant protection and quality standards. These issues provided the motivation behind the fully-integrated structural instrument panel design developed for Chrysler's Dodge Dakota Truck Platform. This total system design approach greatly depends on the stiffness and ductility of the engineering thermoplastic substrate and cross-sectional design for managing the energy of unrestrained occupants during frontal collisions. The structural IP consists of a fully integrated, three-piece monocoque thermoplastic structure that replaces the traditional retainer, air delivery ducts, steel beams and reinforcements typically used in IP designs.

A fully-integrated thermoplastic structural instrument panel (IP) system will be implemented on Chrysler's Dodge Dakota Truck Platform. The structural IP consists of a three-piece monocoque thermoplastic injection molded structure that replaces the traditional retainer, air delivery ducts, steel beams and reinforcements typically used in IP designs. Ribbed thermoplastic bolster systems have been incorporated as part of the energy management system. The structural IP provides the required stiffness to satisfy noise, vibration, and harshness (NVH) quality targets and the necessary strength and rigidity to effectively meet FMVSS No. 208 requirements for managing occupant and passenger air bag (PAB) deployment loading during 48 km/h (30 mph) frontal crashes.

The primary purpose of an automotive bumper is to protect the vehicle from damage, which may otherwise result from a low speed impact. Major insurance companies typically conduct low speed crash tests of new vehicles in order to establish appropriate insurance classifications based on the estimated costs to repair the resulting damage. One such test, which is carried out by the Allianz insurance organisation, has become the European standard by which automobile insurance rates are set. Although commonly known as the Allianz test, it may be more specifically referred to as the Danner test, after Max Danner, the originator of the test. This test is conducted at 15 km/h with a 0° oriented rigid barrier overlapping 40% of the vehicle for frontal collisions and a 1000 kg moveable barrier with a 40% overlap for impacts to the rear of the vehicle.

Automotive styling trends point to reduced bumper overhang, greater sweeps, and reduced overall package space for the bumper system. At the same time engineers are charged with improving bumper performance to reduce collision repair costs and enhance occupant safety further. Two key performance parameters for the bumper to meet these conflicting objectives are fast but controlled loading and efficient energy absorption (EA). The majority of today's North American passenger-car bumper systems consist of a reinforcing bar either of steel, aluminum, or composite construction, and an energy absorption media. The most widely used energy-absorber construction is made from an expanded-polypropylene foam (EPP). Honeycomb energy absorbers, which are made from an ethylene vinyl acetate (EVA) copolymer, are also still used on some of today's cars. This paper will address an alternative to the bumper energy absorber systems described above.

An efficient energy absorber (EA) will absorb impact energy through a combination of elastic and plastic deformation. However, the EA is typically coupled with a steel reinforcing beam, which can also elastically and plastically deform during an impact event. In order to design and optimize an EA/Beam system that will meet the specified vehicle impact requirements, the response of the entire assembly must be accurately predicted. This paper will describe a finite element procedure and material model that can be used to predict the impact response of a bumper system composed of an injection molded thermoplastic energy absorber attached to a steel beam. The first step in the process was to identify the critical material, geometric, and boundary condition parameters involved in the EA and Beam individually. Next, the two models were combined to create the system model. Actual test results for 8km/hr.