Crashworthiness simulation of roadside safety structures with development of material model and three-dimensional fracture procedure

Impact simulation utilizing nonlinear FE analysis is rapidly becoming an effective tool in designing and evaluating roadside safety structures. The subject of this investigation is crashworthiness simulation of a highway guardrail system and implementation of a FE crash simulation code. In this study, a FE model is developed to accurately simulate a truck impacting a G4(1S) strong-post w-beam guardrail system, the most common system in the USA. A roadmap for simulation of highway safety structures is proposed and three major issues, which involve the use of springs to simulate component crashworthiness behavior, are investigated: rail to blockout bolt connection, soil-post-dynamic interaction, and effect of ends of guardrail. Both qualitative and quantitative validations of the crash simulation are presented and discussed. A systematic parametric study is consequently carried out to understand the effects of some parameters of the G4(1S) guardrail system for improvement of the system. Appropriate reduction of the embedment depth of the posts is anticipated to be a favorable approach for minimizing the risk of rollover of vehicles impacting the G4(1S) guardrail system. Since few attempts are described in the FE literature for modeling of 3-D nonlinear wood material and 3-D fracture processes, much effort in this dissertation is also focused on the implementation of a 3-D nonlinear wood material model and automated 3-D fracture procedure which are often needed in crash simulation of roadside safety structures. The DYNA3D explicit FE code is utilized in this study for implementation. The implemented 3-D wood model uses incremental-loading and curve-fitting techniques to trace the nonlinear behavior. User-defined nonlinear parameters are introduced to control the stiffness change based on the stiffness of previous iteration or initial stiffness. A modified Johnson rate dependent model is employed to account for the influence of strain rate. The model efficiently captured the nonlinear characteristics of wood, and therefore provides a new 3-D material modeling approach for wood materials. The implemented 3-D Fracture models have the capabilities of simulating automatic crack propagation without user intervention. An element deletion-and-replacement remeshing procedure is proposed for updating the explicit geometric description of evolving cracks. Fracture parameters such as stress intensity factors, energy release rates and crack tip opening angle are evaluated. The maximum circumferential stress criterion is utilized to predict the direction of crack advancement. Seven crack problems are presented to verify the effectiveness of the methodology. The simulated results are compared well with the element-free Galerkin (EFG) method. Mesh sensitivity and loading rate effects are studied in the validation of the presented procedure.