Rasoul Moradi

Evaluation of the kinematics and injury potential to different sizes of pedestrians impacted by a utility vehicle with a frontal guard

A review of accident data reveals that in most pedestrian accidents, the head and lower extremity injuries are the predominant areas of injury to the pedestrian. The vehicle front geometry profile and stiffness, as well as impact speed are important factors governing pedestrian kinematics. Accident data show that the fatality rate for pedestrian/utility vehicle impact is greater than that for pedestrian/passenger car impact. The addition of a front guard on light trucks and sports utility vehicles to mitigate damage during off-road activity, or to provide mounting points for extra lights, makes the pedestrian more vulnerable to the impact. In this study, a computational technique is utilised to quantify the influence of the added front guard on the impacted pedestrian. A computer-aided design model of a typical commercial frontal guard is developed, and the finite element analysis, along with impact test, is conducted to obtain the stiffness properties of the guard. Different sizes of pedestrian models in the MADYMO code are utilised, and the validated facet-surface model of a pickup truck is used to generate a vehicle front surface. The entire model is validated by comparing the pedestrian kinematics and injury parameters with the published data. This study demonstrates that for all sizes of pedestrians, the mid-body region is more vulnerable when a guard is added to the vehicle. The results from this study can be utilised in the designing of front guards, the frontal crash zone of utility vehicles and installation of these aftermarket guards in order to protect vulnerable road users.

Lumbar load attenuation for rotorcraft occupants using a design methodology for the seat impact energy-absorbing system

Aircraft occupant crash-safety considerations require a minimum cushion thickness to limit the relative vertical motion of the seat-pelvis during high vertical impact loadings in crash landings or accidents. In military aircraft and helicopter seat design, due to the potential for high vertical accelerations in crash scenarios, the seat system must be provided with an energy absorber to attenuate the acceleration level sustained by the occupants. Because of the limited stroke available for the seat structure, the design of the energy absorber becomes a trade-off problem between minimizing the stroke and maximizing the energy absorption. The available stroke must be used to prevent bottoming out of the seat as well as to absorb maximum impact energy to protect the occupant. In this study, the energy-absorbing system in a rotorcraft seat design is investigated using a mathematical model of the occupant/seat system. Impact theories between interconnected bodies in multibody mechanical systems are utilized to study the impact between the seat pan and the occupant. Experimental responses of the seat system and the occupant are utilized to validate the results from this study for civil and military helicopters according to FAR 23 and 25 and MIL-S-58095 requirements. A model for the load limiter is proposed to minimize the lumbar load for the occupant by minimizing the relative velocity between the seat pan and the occupant’s pelvis. The modified energy absorber/load limiter is then implemented for the seat structure so that it absorbs the energy of impact in an effective manner and below the tolerable limit for the occupant in a minimum stroke. Results show that for a designed stroke, the level of occupant lumbar spine injury would be significantly attenuated using this modified energy-absorber system.

Kinematic analysis of a motorcyclist impact on concrete barriers under different road conditions

In many countries, motorcycle crashes constitutes a significant proportion of road crash injuries. Several roadside guard systems such as concrete barriers, wire road barriers and steel guard rails are used to protect cars or heavy trucks occupants, yet motorcycle riders are vulnerable to these barriers and guard systems, resulting in major injuries. The road and climatic conditions also have a major impact on motorcyclists’ accidents. The safety measures can be successful only if more attention is devoted to this issue. The aim of this study is to understand the most influential factors causing motorcycle accidents. For this, a multi-body motorcycle model with a Hybrid III 50th percentile male dummy rider is developed under normal road condition in the MADYMO 6.3. The motorcycle model as well as the motorcycle and rider model has been validated using full scale crash test of a motorcycle with a rider available in a literature. Motorcycle kinematics, rider kinematics and the rider injury criteria are validated with the test results. The simulations results are found to be in a reasonable agreement with the experimental data. A parametric study is then conducted to investigate the nature of crash injuries for various impact speeds, different impact angles and for normal and icy road conditions to assess rider kinematics and potential injuries. The results from this study can help in designing road barriers and guard systems in order to protect the occupants of cars and motorcycles. The results from the parametric study indicate a significant difference on the motorcycle and rider kinematics when compared the icy road conditions to normal road conditions. It is also observed that the head injury risk is the major mode of injury in motorcycle accident.Copyright

Biodynamic Modeling of a Pedestrian Impact With a Rigid Frontal Guard of a Utility Vehicle

Accident data reveals that in most pedestrian accidents, the pedestrian head and lower extremity are vulnerable to serious injuries. The vehicle front geometry profile as well as the impact speed are important factors affecting the pedestrian kinematics and injury potential. In the US, accident data also shows that the fatality rate for pedestrian/light trucks and vans (LTV) impact is greater than that for the pedestrian/passenger-car impact. Addition of a front guard on light trucks and sports utility vehicles to mitigate damage during off-road activity or to provide mounting points for extra lights, makes the pedestrian more vulnerable to the impact. In this paper, a computational technique is utilized to study the influence of the added front guard on the impacted pedestrian. A CAD model of a typical commercial frontal guard is developed and converted into a rigid facet model, and attached to the vehicle front. The validated standing dummy model in the MADYMO code is used to simulate a pedestrian, and the rigid facet-surface model of a pickup truck is used to generate a vehicle front surface. This computational model is validated by comparing the pedestrian kinematics with the published data. This study demonstrates that the pedestrian mid body region is more vulnerable with the addition of guard on the vehicle. The result from this study facilitates a better understanding of a guard design and its geometry profile as required to protect vulnerable road users.Copyright

Energy Absorption Characteristics of a Thin-Walled Tube Filled With Carbon Nano Polyurethane Foam and Application in Car Bumper

Over the past few decades, much research work has been conducted on the development of advance crashworthy structures to increase the energy absorption of mechanical systems. Thin-walled tubes are primarily used as structural reinforcements and as energy absorbing components. The high-energy absorption characteristics of cellular foams have attracted great attention to further enhance this superior capability. In particular, nanotechnology has been utilized in the development of advanced cellular materials for the automotive and aerospace industry. The primary objective of this study is to conduct a parametric study using experimental and finite element methods to examine and quantify the performances of thin-walled tube when filled with carbon nano particulates. To accomplish this study, compression tests are carried out to obtain the load-deflection curves of the nano-foams when subjected to different weight percentages of carbon nano fibers. Next, the specific energy absorbed and the collapse mechanism of nano foam filled thin-walled tubes are analyzed and compared with the empty ones. Finally, an illustrative study on the use of nano foams for vehicular applications is presented by using a vehicle bumper numerical model. The carbon nano foam is installed into the cavity of the bumper model and a full-frontal crash simulation is performed. Overall, this study has shown that the energy absorption capacity of thin-walled structures can be significantly enhanced with the use of carbon nano foams.Copyright

A response surface methodology in predicting injuries to out-of-position occupants from frontal airbags

Out-of-position (OOP) occupants, especially smaller females and children, are quite vulnerable to injuries caused by deploying airbags. This study is aimed at investigating the effects of various design parameters of a frontal airbag on OOP occupants’ resulting injury levels. The study also investigates the predictive capability of the occupant’s injury potential using a regression model developed from the response surface methodology. For this, the OOP occupant is represented using a MADYMO 3-year old child dummy. The objective measurements identified as the main injury causation parameters include the fabric permeability, friction coefficient between the occupant and the airbag, and the occupant’s initial position. Due to the complexity of the airbag model, small iterations are performed until the numerical model is found to be in reasonable agreement with another study available in the literature. The first part of the work is focused on analyzing the effect of a single parameter on the injury responses of the 3-year old child. The second part of the work covers the development of a set of regression model to predict the combined effects of various parameters on the injury responses of the occupant. It is shown that the regression model is fairly accurate and sufficient in predicting various injury levels to OOP occupants from a deploying airbag.Copyright

Vehicle Mass Optimization for Frontal Structure Using I-Sight and Study of Weld Parameterization for Mass Improvement

In order to meet the Federal Motor Vehicle Safety Standards (FMVSS) requirement, the frontal structure of the vehicle needs to be design to maximize energy absorption in the presence powertrain design layout constraint. This needs the basis for structural optimization using a pragmatic approach. With regards to passive safety of a vehicle, there is a constant increase of the requirements to the BIW (Body in White) stiffness in ever greater extent, without a significant increase in vehicle weight. The primary objective of this study is to demonstrate mass optimization in a virtual tryout chain and generate optimized analytical model that can be leveraged in future assessment of a car. For this, a parameter investigation concerning variation of input data is done using I-sight. Simplified model of the bumper subsystem is developed for the offset crash test to serve as a base for the creation of designs by changing design variables. The optimization is carried out using I-sight to explore design space for this subsystem. Finally the effectiveness of optimized bumper subsystem is examined using full vehicle impact test. The focus of the work is further promoting the trend for light weight construction by weld optimization. Overall, this virtual tryout leads in sustainability by lighter transport on road, thus saving fuel and reducing emission.Copyright

A numerical analysis of pre-deployment effect of side-impact airbags in reducing occupant injuries

Side impact collisions represent the second greatest cause of fatality in motor vehicle accidents. Side-impact airbags (SABs), though not mandated by NHTSA, have been installed in recent model year vehicle due to its effectiveness in reducing passengers’ injuries and fatality rates. However, the increase in number of frontal and side airbags installed in modern vehicles has concomitantly led to the rise of airbag related injuries. A typical side-impact mechanical or electronic sensor require much higher sensitivity due to the limited crush zones making SABs deployment more lethal to out-of-position passengers and children. Appropriate pre-crash sensing needs to be utilized in order to properly restraint passengers and reduce passengers’ injuries in a vehicle collision. A typical passenger vehicle utilizes sensors to activate airbag deployment when certain crush displacement, velocity and or acceleration threshold are met. In this study, it is assumed that an ideal pre-crash sensing system such as a combination of proximity and velocity and acceleration sensors is used to govern the SAB pre-deployment algorithm. The main focus of this paper is to provide a numerical analysis of the benefit of pre-deploying SAB in lateral crashes in reducing occupant injuries. The effectiveness of SABs at low and high speed side-impact collisions are examined using numerical Anthropomorphic Test Dummy (ATD) model. Finite Element Analysis (FEA) is primarily used to evaluate this concept. Velocities ranging from 33.5mph to 50mph are used in the FEA simulations. The ATD used in this test is the ES-2re 50th percentile side-impact dummy (SID). Crucial injury criteria such as Head Injury Criteria (HIC), Thoracic Trauma Index (TTI), and thorax deflection are computed for the ATD and compared against those from a typical airbag system without pre-crash sensing. It is shown that the pre-deployment of SABs has the potential of reducing airbag parameters such as deployment velocity and rise rate that will directly contribute to reducing airbag related injuries.© 2013 ASME

Crash Energy Management of Rotorcraft Seat Based on Limit Load Curves and Corresponding Occupant Pelvic Load

In military aircraft and helicopter seat design, the seat system must be provided with an energy absorber (EA) to attenuate the acceleration level sustained by the occupants. Because of the limited stroke available for the seat structure, the design of the energy absorber becomes a trade-off problem between the seat stroke and the impact energy absorption. The available stroke must be used to prevent bottoming out of the seat, and also to absorb as much impact energy as possible to protect the occupant. In this study, the energy absorbing systems in civil and military aircraft seat design are evaluated and improved using a mathematical model of the occupant/seat system. Three load-limit design curves, namely, simple EA, two-stage EA, and two-stage EA with initial spike, are modeled, examined, and compared. A model of the load limiter is recommended to minimize the load sustained by the occupant by limiting the relative velocity between the seat pan and the occupant pelvis. Experimental responses of seat system and occupant from literature are utilized to validate the results from this study for civil and military helicopters. A modified energy-absorber/load-limiter is then implemented for the seat structure so that it absorbs the impact energy in an effective manner below the tolerable limit for the occupant and within a minimum stroke. Results from this study indicate that for a designed stroke, the occupant pelvic/lumbar spine injury level is significantly attenuated using the modified energy-absorber system.Copyright

FEA Robustness Verification in the Modeling of 1-D Stress Wave Propagation for a Split Hopkinson Bar (SHB) Test

Impact loading on mechanical structures and components produces stress conditions that are large in magnitude and fluctuate with time which are difficult for the engineer to assess for design. The Stress Wave Propagation (SWP) is a classical methodology to account for these large stress levels. Due to the highly mathematical approach of stress wave theory along with consideration of boundary conditions interactions in the struck solid, the stress wave propagation method generates closed solutions to impact problems that are only 1-D in nature [1, 2]. In engineering practice, most mechanical problems are more complex than 1-D and thus numerical methods need to be applied to provide engineering solutions. The Finite Element Method (FEM) is a numerical technique that is commonly used in static and dynamic loading conditions to provide engineering solution to complex geometry and loading. In this paper, the FEM is examined to determine if this methodology is robust enough to accurately represent Stress Wave Propagation in solid mediums by the capturing wave propagation velocities, boundary reflections and transmissions along with large transient stress magnitudes using simple 2-D axisymmetrical elements. The most complex 1-D problem and perhaps the most practical solved problem by the Stress Wave Propagation is the Split Hopkinson Bar (SHB) test. The purpose of this test is to determine the dynamic strength of materials. A finite element (FE) model of an as-built SHB test apparatus was developed. In the same function as the strain gages, two nodes were used to extract the strain time histories from the FE model of the apparatus bars. It was found that the pseudo-strain gages of the FEA compared well to the SWP theory. The pulse magnitudes of strains, strain rates and stress were found extremely similar and exhibited magnitudes within 4% between SWP and direct examination.This model replicating a dynamic impact event demonstrated that the FEA can be used to solve complex impact problems involving stress wave propagation with the use of simple 2-D axisymmetric elements reducing computation time.Copyright