Howie Fang

An object-oriented framework for finite element pavement analysis

In this study, we developed an object-oriented (OO) framework with interactive graphics to assist pavement studies using finite element analysis (FEA). FEA has been proven to be effective in studying various pavement failure problems; however, it is time consuming and error prone to manually generate the load sequences where non-regular tire footprints, non-uniform tire-pavement contact stresses, and transverse wheel wander distributions are used. After FEA, extracting the deformations for failure analysis is necessary but tedious. The OO framework developed in this study handles the preprocessing and postprocessing tasks for the FEA of pavements. It has a graphical user interface and is platform independent. It was successfully used in developing a new criterion for characterizing pavement failures that involved approximately four hundred different FEA simulations.

Crash analysis and evaluation of cable median barriers on sloped medians using an efficient finite element model

Abstract Perpetual high traffic volumes on U.S. highways have raised more public concern than ever about transportation safety. Over the years, various traffic barrier systems, including cable median barriers (CMBs), have been developed to reduce the number and severity of vehicle crashes. Despite their general effectiveness, there remains room for improvement, especially when CMBs are installed on unlevelled terrains such as sloped medians. The destructive nature of crashes imposes significant challenges to barrier design using full-scale physical testing; numerical simulations thus become a viable means to support crash analysis, performance evaluation, and barrier designs. In this study, validated vehicle and CMB models were used to perform full-scale simulations of vehicle-CMB impacts. Several CMB designs, including the currently used one, were evaluated under vehicular impacts at different velocities and angles. To address the challenge of modeling slender members such as cables and hook-bolts in contact analyses, an efficient beam-element contact model was employed in the analysis. Different design options of cable height and spacing under various impact velocities and angles were investigated in this study.

A numerical study of occupant responses and injuries in vehicular crashes into roadside barriers based on finite element simulations

Occupant responses and injuries are important considerations in the design and assessment of roadside safety devices such as barriers. Although incorporating occupant responses and injuries into the design of safety devices is highly recommended by the current safety regulations, there are limited studies that directly consider occupant responses and injuries. Crash test dummies are seldom equipped in the state-of-the-art crash testing of roadside barriers and thus occupant responses and injury risks are evaluated primarily based on vehicle responses. In the present work, occupant responses and injuries in automotive crash events were investigated by incorporating crash test dummies into the vehicle model that was used in the finite element (FE) simulations of roadside crashes. The FE models of a Ford F250 pickup truck and a Hybrid III 50th percentile crash test dummy were employed and a passive restraint system was developed in the FE model. The FE model was validated using existing experiments including a sled test and a full-frontal impact test. Simulations of the Ford F250 impacting a concrete barrier and a W-beam guardrail were conducted and the occupant responses were analyzed. Furthermore, occupant injuries were quantitatively estimated using occupant injury criteria based directly on dummy responses and compared to those based solely on vehicle responses. The correlations between vehicle responses and occupant injuries were studied. An FE model incorporated with a hybrid-III dummy was developed for roadside vehicular crash simulations.Occupant injury risks were evaluated for vehicular crashes into two roadside barrier systems.Barrier performance was assessed using occupant injury criteria based on vehicle responses and occupant responses.Correlations between injury criteria based on vehicle and occupant responses were studied.