In order of published date
[9]
Investigation of Dynamic Impact Behavior of Bighorn Sheep Horn
International Journal of Solids and Structures
Volume 307, 2025, 113133, ISSN 0020-7683
Emre Palta, Howie Fang, Qian Wang, Zheng Li
Abstract: The horn of the bighorn sheep is composed of keratin-based biological material that has a tubule-lamella structure, which gives it anisotropic hardening properties under impact loading. This paper aims to investigate the energy dissipation mechanisms inherent in bighorn sheep horns by developing a numerical material model that accounts for the horn’s anisotropic features and strain-rate effects. To this end, a transversely isotropic constitutive model, which includes both anisotropic hardening and strain-rate effects, was formulated to accurately predict the mechanical behavior of bighorn sheep horns. Material characterization was conducted through uniaxial compression tests that were conducted under quasi-static and dynamic conditions. The developed constitutive model was implemented into LS-Dyna via a user-defined material subroutine and was validated against empirical data. The validated numerical model was used to investigate the horn’s mechanical responses under dynamic loading conditions. The paper focused on impact energy dissipation mechanisms, including energy absorption and transition, stress distribution, and displacement wave propagation. The insights gained from this paper are expected to significantly contribute to the development of novel artificial materials with enhanced energy absorption and impact mitigation properties.
Keywords: Bighorn sheep; Keratin; Impact; Dynamic analysis; Numerical modeling; Finite element (FE); Material modeling
[8]
Constitutive Modeling and Dynamic Impact Analysis of Bighorn Sheep Horn
The University of North Carolina at Charlotte ProQuest Dissertations & Theses
29069156, 2022
Zheng Li
Abstract: Bighorn sheep (Ovis canadensis) is known for its giant spiral horns that can sustain impact loading at a speed up to 5.5 m/s during ramming without causing severe damage or head concussion. The bighorn sheep horn is composed of a keratin-based biological material with a tubule-lamella structure. This special structure produces the anisotropic hardening characteristics of the horn material under impact loading. Investigating the mechanisms of energy dissipation of bighorn sheep horn can inspire the design and development of artificial materials with high capacity of energy dissipation and/or impact mitigation. In this study, a transversely isotropic constitutive model with anisotropic hardening and strain-rate effects was developed for predicting the mechanical responses of the horn under impact loading. The characterization of material properties was conducted using test data from uniaxial compression tests of the horns under both quasi-static and dynamic loadings. The constitutive model was later implemented into the commercial finite element code, LS-Dyna, as user-defined material subroutine and was successfully validated against test results. Finite element simulations were conducted on the dynamic impact against the bighorn sheep horn, and the user-defined constitutive model was used to study the mechanical responses of the horn material subjected to large impact loads without causing severe damage. The mechanism of energy dissipation was also investigated from energy absorption and conversion, stress distributions, and propagation of displacement waves.
[7]
Evaluation of Four Bridge Rail Systems for Compliance with the 2016 Edition of Manual for Assessing Safety Hardware (MASH)
North Carolina Department of Transportation, Research and Analysis Group
United States Department of Transportation, Federal Highway Administration
FHWA/NC/2019-23, 2022
Howie Fang, Zheng Li, Joshua Fatoki, Cody S. Stolle
Abstract: In this project, the NC Two-bar Metal Rail (2BMR) was evaluated for compliance with the 2016 edition of Manual for Assessing Safety Hardware (MASH) under Test Level 3 (TL-3) conditions. Two full-scale crash tests, MASH Tests 3-10 and 3-11, were performed on a 90-ft section of the 2BMR and successfully passed all MASH evaluation criteria. A finite element (FE) model of the test section was created and used in simulations to determine the critical impact points and to predict the 2BMR performance under MASH TL- 3 conditions. The simulation results were shown to agree well with test data and all the performance metrics met the MASH requirements. An application was submitted to FHWA to obtain a letter of eligibility for federal-aid reimbursement and the application was approved in August 2021. In addition to the work on 2BMR, the FE models of three additional bridge rails were created: the Oregon Rail, the Three-bar Metal Rail, and the Classic Rail. Finite element simulations were performed to evaluate their performance under different MASH test conditions: the Oregon Rail under MASH TL-4 conditions, the Three-bar Metal Rail under MASH TL-2 and TL-3 conditions, and the Classic Rail under MASH TL-2 and TL-3 conditions. The simulation results demonstrated the performance trends of these three bridge rails as well as indicated some potential issues or safety concerns. Finite element modeling and simulation were shown to be a powerful tool for assisting roadside safety research. The FE models of the vehicles and bridge rails from this project are readily available for use in other investigations.
[6]
A Numerical Study of Strong-post Double-faced W-beam and Thrie-beam Guardrails under Impacts of Vehicles of Multiple Size Classes
Accident Analysis & Prevention
Volume 159, 2021, 106286, ISSN 0001-4575
Zheng Li, Howie Fang, Joshua Fatoki, Matthew Gutowski, Qian Wang
Abstract: Median barrier systems are safety features between opposite travel lanes to redirect or prevent errant vehicles from intruding into oncoming traffic lanes. Different barriers systems have been developed and used for decades. In this study, finite element (FE) modeling and simulations were adopted to study the performance of double-faced W-beam and Thrie-beam guardrails at 29- and 31-inch installation heights. The in-service guardrail performance was evaluated under impacts of multiple sized vehicles at Test Level 4 and Test Level 5 conditions specified in Manual for Assessing Safety Hardware (MASH). The effectiveness of the guardrails was assessed using guardrail dynamic deflections, vehicle responses, and vehicle redirection characteristics. The MASH exit box criterion, MASH evaluation criterion F (roll and pitch angle limit), and MASH evaluation criterion N (vehicle trajectory) were adopted in the evaluations. Additionally, occupant safety and injury risk were determined using occupant impact velocities (OIVs), occupant ridedown accelerations (ORAs), and acceleration severity indices (ASIs). The crash simulation results showed that both W-beam and Thrie-beam guardrails could retain all test vehicles and prevent them from getting into oncoming travel lanes. All the guardrails were considered generally effective in terms of occupant risk factors and vehicle impact responses. It was also observed that in certain cases, the installation height and the type of guardrail blockout could affect the impact severity for small-sized vehicles.
Keywords: Median barrier; Vehicular impact; Finite element; W-beam guardrail; Thrie-beam guardrail; Highway safety
[5]
Crash Safety Evaluation of Three-bar Metal Bridge Rail Using Finite Element
Analysis
16th U.S. National Congress on Computational Mechanics
2021, Chicago, IL
Zheng Li, Howie Fang, Qian Wang
Abstracts: Crash safety involving bridge rails is one of the major concerns in highway safety due to the severe consequence of a failed system under vehicular impacts. With the adoption of the new highway safety standard, Manual for Assessing Safety Hardware (MASH), it is necessary to evaluate existing bridge rails to ensure they meet the MASH safety requirements. The objective of this study was to evaluate the impact performance of an NCDOT three-bar metal bridge rail under MASH Test Level 2 (TL-2) conditions, i.e., under impacts by a small passenger car and a pickup truck at 70 km/h and a 25-degree angle. Finite element modeling and simulations were employed as the major tool of investigation in this study. The effectiveness of the three-bar metal bridge rail was evaluated using the MASH exit box criterion, vehicle row and pitch angles, dynamic barrier deflections, and occupant safety in terms of occupant impact velocity (OIV), occupant ridedown acceleration (ORA). Following a successful evaluation at Test Level 2, the bridge rail was further evaluated under Test Level 3 conditions along with a parametric study on the effect of the stiffness of reinforcement bars on occupant risk factors (i.e., OIV and ORA). This research provided insights on the performance of the three-bar metal bridge rail as well as guidance on improving the current bridge rail design for safety enhancement.
[4]
Risk Assessment of Roadside Utility Structures Under Vehicular Impacts
North Carolina Department of Transportation, Research and Analysis Group
United States Department of Transportation, Federal Highway Administration
NCDOT 2018-24, 2020
Howie Fang, Zheng Li, Oyeboade Fatoki, Emre Palta
Abstracts: Roadside structures such as bus shelters and cluster mailboxes are increasingly used in urban areas. These structures raise safety concerns due to the likelihood of being struck by errand vehicles. The main objective of this research was to evaluate a bus shelter and two types of cluster mailboxes under impacts of MASH compliant vehicles. Finite element modeling and simulations were employed as the major tool of the investigation. The simulation results showed that there was no potential occupant injury in vehicular crashes into both single- and dual-unit Type I and Type IV mailboxes under MASH TL-1 conditions. In vehicular crashes into the bus shelter under MASH TL-2 conditions, the simulation results indicated no potential occupant injury; however, there was a high likelihood of injury to adjacent pedestrians caused by the falling roof and windscreen debris. Furthermore, pedestrians inside the bus shelter were highly likely to get severe injury by the striking vehicles.
[3]
Vehicular Impact Analysis and Safety Evaluation of Clustered Mailboxes
15th U.S. National Congress on Computational Mechanics
2019, Austin, TX
Zheng Li, Emre Palta, Joshua Fatoki, Howie Fang
Abstracts: Roadside utilities structures such as clustered mailboxes and bus shelters are increasingly used with the rapid development and urbanization of large cities. Vehicular impacts into these utilities structures could results in severe injuries to the occupants and adjacent pedestrians in addition to damages to the striking vehicles and economic loss. In this study, vehicular impacts on clustered mailboxes are conducted using finite element (FE) modeling and simulation. The test vehicles used in this study, i.e., a small passenger car and a pickup truck, are in compliance with the Manual for Assessing Safety Hardware (MASH). Different impact speeds and impact angles are considered for both test vehicles. A Hybrid III crash test dummy is also used in the FE models to directly obtain occupant
responses. The results of this research could provide insights into vehicular responses and potential occupant risk in the impacts of clustered mailboxes. The results could also shed light on transportation safety enhancement and future guideline developments regarding the design or installation of roadside utilities structures.
[2]
Performance Evaluation of a Two-Bar Bridge Rail Using Finite Element Analysis
15th U.S. National Congress on Computational Mechanics
2019, Austin, TX
Joshua Fatoki, Howie Fang, Emre Palta, Zheng Li
Abstracts: Roadside barriers are important safety devices installed on highways to mitigate the severity of serious crashes by errant vehicles. Safety features such as longitudinal barriers are commonly used to contain and redirect errant vehicles. The two-bar metal bridge rail is a frequently used longitudinal barrier in North Carolina and is recognized for its performance and aesthetics. Currently, all safety devices used on U.S. highways must be tested to meet the safety criteria specified by the Manual for Assessing Safety Hardware (MASH) issued by the American Association of State Highway and Transportation Officials (AASHTO). While full-scale crash testing is a valid means to evaluate the safety performance of bridge rails, physical crash testing is very expensive, time-consuming, and difficult to perform. With the rapid development of computing hardware and commercial software for high performance computing, computer simulations have been increasingly used to assess the performance of roadside safety systems. In this study, the FE model of a two-bar bridge rail was developed and used in the evaluation of its compliance with MASH Test Level 3 (TL-3) requirements. The test vehicles used for MASH TL-3 tests include a small passenger car (a 2016 Toyota Yaris) and a pickup truck (a 2016 Chevy Silverado). The bridge rail was evaluated at an impact speed of 62 mph and at an angle of 25 degree. Post-impact performance and structural adequacy of the Two-bar bridge rail were accessed and evaluated.
[1]
Performance Evaluation of Cable Barriers on a 6:1 Sloped Median under MASH TL-3 Conditions
North Carolina Department of Transportation, Research and Analysis Group
United States Department of Transportation, Federal Highway Administration
NCDOT 2017-13, 2019
Howie Fang, Emre Palta, Zheng Li, Oyeboade Fatoki
Abstracts: In this study, non-linear finite element simulations were conducted to evaluate the performance of the current North Carolina Department of Transportation (NCDOT) cable median barrier (CMB) and two retrofit CMB designs (named “Sixth Design Retrofit” and “Four-cable Design Retrofit”) placed on a 6H:1V sloped median. The aim of this research was to investigate possibility of replacing the current CMB design with one of the two retrofit designs. All three CMB designs were evaluated under Manual for Assessing Safety Hardware (MASH) Test Level 3 (TL- 3) conditions, i.e., under the impacts of a 1100C passenger car and a 2270P pick-up truck at 100 km/hr (62 mph) and a 25-degree impact angle. The CMBs were impacted from both front-sides and backsides at two different impact locations: (1) on a post in the CMB mid-span, and (2) at the midpoint between two adjacent posts in the mid-span. The CMB performance was evaluated using vehicular responses specified in MASH, i.e., the exit-box criterion, MASH evaluation criteria A, D and F, exit angle, yaw, pitch and roll angles, and transverse velocities. The simulation results demonstrated the effectiveness of each of the three CMB designs on a 6H:1V sloped median under vehicular impacts. The simulation results showed that cable heights and the number of cables played an important role in the effectiveness of CMBs when placed on sloped medians. The finite element modeling and simulation works were shown to be both effective and efficient and can be used to study crash scenarios that are difficult and/or extremely expensive to conduct with physical crash testing.
Keywords: Cable systems; Median barriers; Roadside structures; Highway safety; Retrofitting; Finite element method
Zheng Li 