Modeling Tire Blow-out in Roadside Hardware Simulations Using Ls-dyna

Often when vehicles interact with roadside hardware like guardrails, bridge rails and curbs, the interaction between the roadside hardware and the tire causes the tire to lose its air seal and "blow-out". Once the seal between the rim and rubber tire is lost, the tire deflates. The behavior of the deflated tire is much different than the behavior of an inflated tire such that when this behavior is observed in real world crashes or in fullscale crash tests, the vehicle kinematics are strongly coupled to the behavior of the deflated tire. Accounting for this behavior in LS-DYNA models is crucial in many types of roadside hardware simulations since the forces generated by the deflated tire often introduce instability into the vehicle that can cause rollover or spinout. This paper will present a method for accounting for tire deflation during LS-DYNA simulations and will present examples of the use of this type of improved model. INTRODUCTION Finite element models of pneumatic tires have been developed by others to investigate stresses and deformations in order to evaluate the performance of commercial tires [1]. The objective of such analyses has lead, necessarily, to very sophisticated models that take into account ply orientation, ply overlapping and mechanical properties of different layers of the composite structure of the tire. This approach is necessary and practical if the objective of the study is the design and analysis of the tire itself ignoring the many other components of the vehicle. On the other hand, this approach becomes computationally inefficient for analyses involving large-scale overall response of the vehicle during impact with other structures, such as roadside hardware, where the tires are only one aspect of many intricate parts that must be modeled. In most cases, the simulation of vehicle impact into roadside hardware has been approached using relatively simple models, where the particular aspects of the tire structure were not reproduced. Typically, the tire has been modeled with isotropic membrane elements (thin shells) which may be effective when the dynamics of the tire are negligible. A more realistic model is needed when the tire interacts significantly with other elements of the roadside environment, for instance, in those conditions where the tire directly plays an important role in the vehicle kinematics and stability. BASICS OF TIRE MECHANICS A basic understanding of pneumatic tire mechanics is required in order to develop a simplified model that produces realistic behavior of the tire under the types of loading to which the tire will be subjected. The most common tire construction technology in use today is the radial construction, thus our attention will be focused on this type of pneumatic tires. The tire plays an important role in the vehicle’s dynamics since it must absorb road irregularities while providing a vibration-free motion on smooth roads. There are two conflicting requirements: flexibility is needed to absorb road bumps, while the need for a vibration-free ride requires a rigid round wheel. This conflict is further aggravated by the fact that a pneumatic tire is a doubly curved surface, geometrically a non-developable surface that must be deformed to provide a contact area on flat pavement.