Rasoul Moradi - Academia.edu (original) (raw)
Papers by Rasoul Moradi
ABSTRACT The surface roughness influences the mechanical properties of materials, such as elastic... more ABSTRACT The surface roughness influences the mechanical properties of materials, such as elastic modulus, hardness, tensile and yield strengths and ductility. Previous studies have shown the behavior of hardness changes by surface roughness of the material using spherical indenters on the spherical surfaces. The effect of the elastic modulus changes with the roughness, but this has not been truly investigated. The main purpose of this study is to develop a computational methodology to estimate the behavior of elastic modulus and hardness of the material on different surfaces. The models used in this study are developed using the Msc Patran and simulated by a finite element analysis code LS-DYNA. In this study, four models have been developed with different surfaces to estimate the behavior of elastic modulus and hardness by nano-indentation using a sharp tip conical indenter. The change in modulus and roughness are estimated by nano-indentation using the Oliver and Pharr’s theory. The penetration depths are normalized as the change in roughness scale on the material and also as the change in radius of the indenter. The study shows that as the roughness of a surface increases, the hardness increases from the actual hardness at various depths, and it carries on a first order model of roughness with a fractal surface material by nano-indentation method. Not only the roughness influences the material properties but also when the material has damage, it also influences the material properties. For this, the models are developed by placing some voids in the material, and the behavior of elastic modulus and hardness of material with and without damage are estimated. Finally, the penetration depth estimated from nano-indentation is compared using the classical macro-scale Hertzian theory, and interestingly found that this theory can also be used for nano-indentation of metals and solids. The results from this research can be utilized to estimate roughness and modulus degradation caused by nano-indentation.
Agricultural and construction equipment are commonly implemented with rectangular tubing in their... more Agricultural and construction equipment are commonly implemented with rectangular tubing in their structural frame designs. A typical joining method to fabricate these frames is by welding and the use of ancillary structural plating at the connections. This aids two continuous members to pass through an intersection point of the frame with some degree of connectivity, but the connections are highly unbalanced as the tubing centroids exhibit asymmetry. Due to the practice of welded continuous member frame intersections in current agricultural equipment designs, a conviction may exist that welded continuous member frames are superior in structural strength over that of structural frame intersections implementing welded non-continuous members where the tubing centroids lie within two planes of symmetry, a connection design that would likely fabricating a more fatigue resistant structural frame. Three types of welded continuous tubing frame intersections currently observed in the designs of agricultural equipment were compared to two non-continuous frame intersection designs. Each design was subjected to the same loading condition and then examined for stress levels using the Finite Element Method to predict fatigue life. Results demonstrated that a lighter weight, non-continuous member frame intersection design was two magnitudes superior in fatigue resistance than some current implemented frame designs when using Stress-Life fatigue prediction methods and empirical fatigue strengths for fillet welds. Stress-Life predictions were also made using theoretical fatigue strength calculations for the fatigue strength at the welds for comparison to the empirical derived weld fatigue strength.
ABSTRACT In military aircraft and helicopter seat design, the seat system must be provided with a... more ABSTRACT 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.
To estimate the aggressivity of vehicles in frontal crashes, national highway traffic safety admi... more To estimate the aggressivity of vehicles in frontal crashes, national highway traffic safety administration (NHTSA) has introduced the driver fatality ratio, DFR, for different vehicle-to-vehicle categories. The DFR proposed by NHTSA is based on the actual crash statistical data, which makes it difficult to evaluate for other vehicle categories newly introduced to the market, as they do not have sufficient crash statistics. A finite element (FE) methodology is proposed in this study based on computational reconstruction of crashes and some objective measures to predict the relative risk of DFR associated with any vehicle-to-vehicle crash. The suggested objective measures include the ratios of maximum intrusion in the passenger compartments of the vehicles in crash, and the transmitted peak deceleration of the vehicles’ center of gravity, which are identified as the main influencing parameters on occupant injury. The suitability of the proposed method is established for a range of bullet light truck and van (LTV) categories against a small target passenger car with published data by NHTSA. A mathematical relation between the objective measures and DFR is then developed. The methodology is then extended to predict the relative risk of DFR for a crossover category vehicle, a light pick-up truck, and a mid-size car in crash against a small size passenger car. It is observed that the ratio of intrusions produces a reasonable estimate for the DFR, and that it can be utilized in predicting the relative risk of fatality ratios in head-on collisions. The FE methodology proposed in this study can be utilized in design process of a vehicle to reduce the aggressivity of the vehicle and to increase the on-road fleet compatibility in order to reduce the occupant injury out- come.
ABSTRACT Accident data reveals that in most pedestrian accidents, the pedestrian head and lower e... more ABSTRACT 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.
Volume 12: Vibration, Acoustics and Wave Propagation, 2012
ABSTRACT Impact loading on mechanical structures and components produces stress conditions that a... more ABSTRACT 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.
Volume 1: Advances in Aerospace Technology, 2012
ABSTRACT Dynamic aircraft seat regulations are identified in the Code of Federal Regulations (CFR... more ABSTRACT Dynamic aircraft seat regulations are identified in the Code of Federal Regulations (CFR), 14 CFR Parts § XX.562 for crashworthy evaluation of a seat in dynamic crash environment. The regulations specify full-scale dynamic testing on production seats. The dynamic tests are designed to demonstrate the structural integrity of the seat to withstand an emergency landing event and occupant safety. These tests are carried out on a 50th percentile Hybrid II Anthropomorphic Test Device (ATD) representing average 50 percent of human population. In this study, the dynamic performance of seats are evaluated for larger passenger population for both transport and general aviation seats. For this, Finite Element Analysis (FEA) of an aircraft seat model is analyzed by utilizing a 50th percentile e-ATD and validated with a 50th percentile ATD sled test results. Then the effect of a 95th percentile standard ATD in an aircraft passenger seat is investigated using FEA. Comparison of the 50th percentile and the 95th percentile electronic ATD models (e-ATDs) is carried out on the test parameters. This includes the restraint loads, the floor reactions and the head paths. Based on the comparison it is concluded that the seat loads go up in the range of 20 to 30% if designed for larger passenger population.
Central European Journal of Engineering, 2012
Aircraft occupant crash-safety considerations require a minimum cushion thickness to limit the re... more 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.
Volume 13: Transportation Systems, 2013
ABSTRACT Side impact collisions represent the second greatest cause of fatality in motor vehicle ... more ABSTRACT 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.
ABSTRACT Roadside guard systems such as concrete and wire barriers and steel guard rails are main... more ABSTRACT Roadside guard systems such as concrete and wire barriers and steel guard rails are mainly developed to protect occupants of the errant cars or trucks. Yet motorcycle riders are vulnerable to these barriers and guard systems, and impact on these barriers may result in major injuries. The objective of this study is to examine the major factors causing injuries in motorcycle-barriers accidents. A mathematical multi-body motorcycle model with a motorcycle anthropometric test device, MATD, is developed in the MADYMO 7.2 for this purpose. The motorcycle model as well as the motorcycle and rider model are validated using full-scale crash test data available in the literature. The simulations results are found to be in a reasonable agreement with the experimental data. A parametric study using the design of experiment (DOE) is then conducted to investigate the nature of crash injuries for various impact speeds, impact angles, different bike and rider positions to assess the rider kinematics and potential injuries. The results from this study can help in designing road barriers and guard systems in order to protect the motorcycle riders.
This paper examines the effectiveness of analyzing impact events in mechanical systems for design... more This paper examines the effectiveness of analyzing impact events in mechanical systems for design purposes using simple or low ordered finite elements. Traditional impact dynamics analyses of mechanical systems namely stereomechanics, energy method, stress-wave propagation and contact mechanics approaches are limited to very simplified geometries and provide basic analyses in making predictions and understanding the dominant features of the impact in a mechanical system. In engineering practice, impacted systems present a complexity of geometry, stiffness, mass distributions, contact areas and impact angles that are impossible to analyze and design with the traditional impact dynamics methods. In real cases, the effective tool is the finite element (FE) method. The high-end FEA codes though may be not available for typical engineer/designer. This paper provides information on whether impact events of mechanical systems can be successfully modeled using simple or low-order finite elements. FEA models using simple elements are benchmarked against theoretical impact problems and published experimental impact results. As a case study, an FE model using simple plastic beam elements is further tested to predict stresses and deflections in an experimental structural impact.
In an impact condition of a mechanical system, traditional static solid mechanics approaches are ... more In an impact condition of a mechanical system, traditional static solid mechanics approaches are invalid as they do not account for the dynamic response of the system. Methodologies that account for the dynamic stress/strain effects are namely stereomechanics, energy method, contact mechanics, and stress wave propagation. This chapter presents the fundamental governing equations for mechanical stress wave propagation within engineering solids due to an impact or sudden loading event.
ABSTRACT In many countries, motorcycle crashes constitutes a significant proportion of road crash... more ABSTRACT 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.
7th Annual Symposium on Graduate …, 2011
In car/truck collisions, the size, weight, and stiffness mismatch results in much larger structur... more In car/truck collisions, the size, weight, and stiffness mismatch results in much larger structural deformation of the car compare to the truck. This is further aggravated when the passenger vehicle trends beneath the rear or side of the taller truck. Truck under-ride increases the probability of death or serious injury for smaller vehicle occupants due to intrusion of parts of both small car and the truck into the smaller car passenger compartment. A computational technique is utilized in this study to quantify the influence of a side guard attached to a large truck in reducing the intrusion to the car and thus reducing the injury sustained by the occupants of a car in side impact scenarios. A parametric study is utilized to identify the critical guard height resulting in optimum cabin deceleration and compartment intrusion of the small car.
The driver fatality ratio (DFR) proposed by the National Highway Traffic Safety Administration (N... more The driver fatality ratio (DFR) proposed by the National Highway Traffic Safety Administration (NHTSA) demonstrates the relative fatality risks of occupants in various vehicle-to-vehicle (VtV) crashes. The readily available DFR is based on statistical crash data; hence, estimating the DFR of occupants for newer fleet of vehicles can be quite difficult. Three systematic methods such as the intrusion, decel- eration and stiffness ratios of two colliding vehicles in side-impact accidents are proposed to estimate the DFR. A fleet of light trucks and vans (LTVs) striking a sedan car is reconstructed using the non-linear explicit code, LS-DYNA. The simulation results have shown that the intrusion and acceleration ratios-based approaches are in good agreement with the statistical DFR, whereas the DFR estimated using the stiffness-ratio based approach yielded poor agreement. The intrusion and acceleration ratios-based approaches are then utilized to formulate a combined DFR estimation model. In the second part of the study, the proposed methodology is carried further to estimate the DFR of occupants for a fleet of LTVs impacting a newer passenger car. The proposed methodology can be a viable tool for estimating the DFR for newer road vehicles and to improve its crash compatibility with collision partners.
ABSTRACT The surface roughness influences the mechanical properties of materials, such as elastic... more ABSTRACT The surface roughness influences the mechanical properties of materials, such as elastic modulus, hardness, tensile and yield strengths and ductility. Previous studies have shown the behavior of hardness changes by surface roughness of the material using spherical indenters on the spherical surfaces. The effect of the elastic modulus changes with the roughness, but this has not been truly investigated. The main purpose of this study is to develop a computational methodology to estimate the behavior of elastic modulus and hardness of the material on different surfaces. The models used in this study are developed using the Msc Patran and simulated by a finite element analysis code LS-DYNA. In this study, four models have been developed with different surfaces to estimate the behavior of elastic modulus and hardness by nano-indentation using a sharp tip conical indenter. The change in modulus and roughness are estimated by nano-indentation using the Oliver and Pharr’s theory. The penetration depths are normalized as the change in roughness scale on the material and also as the change in radius of the indenter. The study shows that as the roughness of a surface increases, the hardness increases from the actual hardness at various depths, and it carries on a first order model of roughness with a fractal surface material by nano-indentation method. Not only the roughness influences the material properties but also when the material has damage, it also influences the material properties. For this, the models are developed by placing some voids in the material, and the behavior of elastic modulus and hardness of material with and without damage are estimated. Finally, the penetration depth estimated from nano-indentation is compared using the classical macro-scale Hertzian theory, and interestingly found that this theory can also be used for nano-indentation of metals and solids. The results from this research can be utilized to estimate roughness and modulus degradation caused by nano-indentation.
Agricultural and construction equipment are commonly implemented with rectangular tubing in their... more Agricultural and construction equipment are commonly implemented with rectangular tubing in their structural frame designs. A typical joining method to fabricate these frames is by welding and the use of ancillary structural plating at the connections. This aids two continuous members to pass through an intersection point of the frame with some degree of connectivity, but the connections are highly unbalanced as the tubing centroids exhibit asymmetry. Due to the practice of welded continuous member frame intersections in current agricultural equipment designs, a conviction may exist that welded continuous member frames are superior in structural strength over that of structural frame intersections implementing welded non-continuous members where the tubing centroids lie within two planes of symmetry, a connection design that would likely fabricating a more fatigue resistant structural frame. Three types of welded continuous tubing frame intersections currently observed in the designs of agricultural equipment were compared to two non-continuous frame intersection designs. Each design was subjected to the same loading condition and then examined for stress levels using the Finite Element Method to predict fatigue life. Results demonstrated that a lighter weight, non-continuous member frame intersection design was two magnitudes superior in fatigue resistance than some current implemented frame designs when using Stress-Life fatigue prediction methods and empirical fatigue strengths for fillet welds. Stress-Life predictions were also made using theoretical fatigue strength calculations for the fatigue strength at the welds for comparison to the empirical derived weld fatigue strength.
ABSTRACT In military aircraft and helicopter seat design, the seat system must be provided with a... more ABSTRACT 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.
To estimate the aggressivity of vehicles in frontal crashes, national highway traffic safety admi... more To estimate the aggressivity of vehicles in frontal crashes, national highway traffic safety administration (NHTSA) has introduced the driver fatality ratio, DFR, for different vehicle-to-vehicle categories. The DFR proposed by NHTSA is based on the actual crash statistical data, which makes it difficult to evaluate for other vehicle categories newly introduced to the market, as they do not have sufficient crash statistics. A finite element (FE) methodology is proposed in this study based on computational reconstruction of crashes and some objective measures to predict the relative risk of DFR associated with any vehicle-to-vehicle crash. The suggested objective measures include the ratios of maximum intrusion in the passenger compartments of the vehicles in crash, and the transmitted peak deceleration of the vehicles’ center of gravity, which are identified as the main influencing parameters on occupant injury. The suitability of the proposed method is established for a range of bullet light truck and van (LTV) categories against a small target passenger car with published data by NHTSA. A mathematical relation between the objective measures and DFR is then developed. The methodology is then extended to predict the relative risk of DFR for a crossover category vehicle, a light pick-up truck, and a mid-size car in crash against a small size passenger car. It is observed that the ratio of intrusions produces a reasonable estimate for the DFR, and that it can be utilized in predicting the relative risk of fatality ratios in head-on collisions. The FE methodology proposed in this study can be utilized in design process of a vehicle to reduce the aggressivity of the vehicle and to increase the on-road fleet compatibility in order to reduce the occupant injury out- come.
ABSTRACT Accident data reveals that in most pedestrian accidents, the pedestrian head and lower e... more ABSTRACT 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.
Volume 12: Vibration, Acoustics and Wave Propagation, 2012
ABSTRACT Impact loading on mechanical structures and components produces stress conditions that a... more ABSTRACT 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.
Volume 1: Advances in Aerospace Technology, 2012
ABSTRACT Dynamic aircraft seat regulations are identified in the Code of Federal Regulations (CFR... more ABSTRACT Dynamic aircraft seat regulations are identified in the Code of Federal Regulations (CFR), 14 CFR Parts § XX.562 for crashworthy evaluation of a seat in dynamic crash environment. The regulations specify full-scale dynamic testing on production seats. The dynamic tests are designed to demonstrate the structural integrity of the seat to withstand an emergency landing event and occupant safety. These tests are carried out on a 50th percentile Hybrid II Anthropomorphic Test Device (ATD) representing average 50 percent of human population. In this study, the dynamic performance of seats are evaluated for larger passenger population for both transport and general aviation seats. For this, Finite Element Analysis (FEA) of an aircraft seat model is analyzed by utilizing a 50th percentile e-ATD and validated with a 50th percentile ATD sled test results. Then the effect of a 95th percentile standard ATD in an aircraft passenger seat is investigated using FEA. Comparison of the 50th percentile and the 95th percentile electronic ATD models (e-ATDs) is carried out on the test parameters. This includes the restraint loads, the floor reactions and the head paths. Based on the comparison it is concluded that the seat loads go up in the range of 20 to 30% if designed for larger passenger population.
Central European Journal of Engineering, 2012
Aircraft occupant crash-safety considerations require a minimum cushion thickness to limit the re... more 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.
Volume 13: Transportation Systems, 2013
ABSTRACT Side impact collisions represent the second greatest cause of fatality in motor vehicle ... more ABSTRACT 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.
ABSTRACT Roadside guard systems such as concrete and wire barriers and steel guard rails are main... more ABSTRACT Roadside guard systems such as concrete and wire barriers and steel guard rails are mainly developed to protect occupants of the errant cars or trucks. Yet motorcycle riders are vulnerable to these barriers and guard systems, and impact on these barriers may result in major injuries. The objective of this study is to examine the major factors causing injuries in motorcycle-barriers accidents. A mathematical multi-body motorcycle model with a motorcycle anthropometric test device, MATD, is developed in the MADYMO 7.2 for this purpose. The motorcycle model as well as the motorcycle and rider model are validated using full-scale crash test data available in the literature. The simulations results are found to be in a reasonable agreement with the experimental data. A parametric study using the design of experiment (DOE) is then conducted to investigate the nature of crash injuries for various impact speeds, impact angles, different bike and rider positions to assess the rider kinematics and potential injuries. The results from this study can help in designing road barriers and guard systems in order to protect the motorcycle riders.
This paper examines the effectiveness of analyzing impact events in mechanical systems for design... more This paper examines the effectiveness of analyzing impact events in mechanical systems for design purposes using simple or low ordered finite elements. Traditional impact dynamics analyses of mechanical systems namely stereomechanics, energy method, stress-wave propagation and contact mechanics approaches are limited to very simplified geometries and provide basic analyses in making predictions and understanding the dominant features of the impact in a mechanical system. In engineering practice, impacted systems present a complexity of geometry, stiffness, mass distributions, contact areas and impact angles that are impossible to analyze and design with the traditional impact dynamics methods. In real cases, the effective tool is the finite element (FE) method. The high-end FEA codes though may be not available for typical engineer/designer. This paper provides information on whether impact events of mechanical systems can be successfully modeled using simple or low-order finite elements. FEA models using simple elements are benchmarked against theoretical impact problems and published experimental impact results. As a case study, an FE model using simple plastic beam elements is further tested to predict stresses and deflections in an experimental structural impact.
In an impact condition of a mechanical system, traditional static solid mechanics approaches are ... more In an impact condition of a mechanical system, traditional static solid mechanics approaches are invalid as they do not account for the dynamic response of the system. Methodologies that account for the dynamic stress/strain effects are namely stereomechanics, energy method, contact mechanics, and stress wave propagation. This chapter presents the fundamental governing equations for mechanical stress wave propagation within engineering solids due to an impact or sudden loading event.
ABSTRACT In many countries, motorcycle crashes constitutes a significant proportion of road crash... more ABSTRACT 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.
7th Annual Symposium on Graduate …, 2011
In car/truck collisions, the size, weight, and stiffness mismatch results in much larger structur... more In car/truck collisions, the size, weight, and stiffness mismatch results in much larger structural deformation of the car compare to the truck. This is further aggravated when the passenger vehicle trends beneath the rear or side of the taller truck. Truck under-ride increases the probability of death or serious injury for smaller vehicle occupants due to intrusion of parts of both small car and the truck into the smaller car passenger compartment. A computational technique is utilized in this study to quantify the influence of a side guard attached to a large truck in reducing the intrusion to the car and thus reducing the injury sustained by the occupants of a car in side impact scenarios. A parametric study is utilized to identify the critical guard height resulting in optimum cabin deceleration and compartment intrusion of the small car.
The driver fatality ratio (DFR) proposed by the National Highway Traffic Safety Administration (N... more The driver fatality ratio (DFR) proposed by the National Highway Traffic Safety Administration (NHTSA) demonstrates the relative fatality risks of occupants in various vehicle-to-vehicle (VtV) crashes. The readily available DFR is based on statistical crash data; hence, estimating the DFR of occupants for newer fleet of vehicles can be quite difficult. Three systematic methods such as the intrusion, decel- eration and stiffness ratios of two colliding vehicles in side-impact accidents are proposed to estimate the DFR. A fleet of light trucks and vans (LTVs) striking a sedan car is reconstructed using the non-linear explicit code, LS-DYNA. The simulation results have shown that the intrusion and acceleration ratios-based approaches are in good agreement with the statistical DFR, whereas the DFR estimated using the stiffness-ratio based approach yielded poor agreement. The intrusion and acceleration ratios-based approaches are then utilized to formulate a combined DFR estimation model. In the second part of the study, the proposed methodology is carried further to estimate the DFR of occupants for a fleet of LTVs impacting a newer passenger car. The proposed methodology can be a viable tool for estimating the DFR for newer road vehicles and to improve its crash compatibility with collision partners.