In order to investigate the performance and emissions behavior of a high compression ratio Compression Ignition (CI) engine operating in Partially Premixed Charge Compression Ignition (PPCI) mode, a series of experiments were conducted using a single cylinder naturally aspirated engine with a high-pressure rail fuel injection system. This included a moderately advanced direct injection strategy to attempt PPCI combustion under low load conditions by varying the injection timing between 25° and 35° Before Top Dead Center (BTDC) in steps of 2.5°. Furthermore, during experimentation the fuel injection pressure, engine speed, and engine torque (through variance of the fuel injection quantity) were kept constant. In-cylinder pressure, emissions, and performance parameters were measured and analyzed using a zero-dimensional heat release model. Compared to the baseline conventional 12.5° BTDC injection, in-cylinder pressure and temperature was higher at advanced timings for all load conditions considered. Additionally, NO x , PM, CO, and THC were higher than conventional results at the 0.5 N-m load condition. While PM emissions were lower, and CO and THC emissions were comparable to conventional injection results at the 1.5 N-m load condition between 25° and 30° BTDC, NO x emissions were relatively high. Hence, there was limited success in beating the NO x -PM tradeoff. In addition, since Start of Combustion (SOC) occurred BTDC, the resulting higher peak combustion pressures restricted the operating condition to lower loads to ensure engine safety. As a result, further investigation including Exhaust Gas Recirculation (EGR) and/or variance in fuel Cetane Number (CN) is required to achieve PPCI in a high compression ratio CI engine.

A simplified roll-plane model is proposed to assess the effect of the vertical position of the center of gravity of the body-cargo system, on the rail fatigue life. A set of assumptions are made to simplify the analysis, including neglecting the bogie’s dynamic contribution to the wheel-rail forces. Three performance measures are defined to assess the effect of different dedicated railway cars on the rail fatigue life, including the fourth-power law, the load dispersion, and the rail fatigue. The simulation results suggest that the vertical position of the center of gravity of the body-cargo set, severely affects the fatigue life of the railway material, with the two-stack car being the most aggressive. For example, twice as aggressive as the gondola car.

The complicated steel wheel and rail interaction on curve causes side wear on rail head. Thus, the cost of maintenance for the track on curve is significantly higher than that for track on a tangent. The objective of this research is to develop 3D printing technology for repairing the side wear. In this paper, the study examines induced residual thermal stresses on a rail during the cooling down process after 3D printing procedure using the coupled finite volume and finite element method for thermal and mechanical analysis respectively. The interface of the railhead and additive materials should conserve high stresses to prevent any crack initiation. Otherwise, the additive layer would likely shear off the rail due to crack propagation at the rail/additive interface. In the numerical analysis, a cut of 75-lb ASCE (American Society of Civil Engineers) worn rail is used as a specimen, for which a three-dimensional model is developed. The applied residual stresses, as a result of temperature gradient and thermal expansion coefficient mismatch between additive and rail materials, are investigated. At the beginning, the worn rail is at room temperature while the additive part is at a high initial temperature. Then, additive materials start to flow thermal energy into the worn rail and the ambient. The thermal distribution results from thermal analysis are then employed as thermal loads in the mechanical analysis to determine the von-Mises stress distribution as the decisive component. Then, the effect of preheating on residual stress distribution is studied. In this way, the thermo-mechanical analysis is repeated with an increase in railhead’s initial temperature. In thermal analysis, the temperature contours at different time steps for both the non-preheated and preheated cases indicate that preheating presents remarkably lower temperature gradient between rail and additive part and also represents a more gradual cooling down process to allow enough time for thermal expansion mismatch alignment. In mechanical analysis, the transversal von-Mises stress distribution at rail/additive interface is developed for all cases for comparison purposes. It is shown that preheating is a key factor to significantly reduce residual stresses by about 40% at all points along transversal direction of interface.

The U.S. Department of Transportation (DOT) Federal Railroad Administration (FRA) began promulgating regulations for the structural crashworthiness of passenger rail equipment at 49 Code of Federal Regulations (CFR) Part 238 on May 12, 1999. These Passenger Equipment Safety Standards (PESS) [1] include requirements affecting the designs of sidewall structures on passenger rail equipment. The FRA’s Office of Research, Development and Technology and the DOT’s Volpe National Transportation Systems Center are conducting research to evaluate the side impact strength of Tier I passenger rail equipment designs that have been constructed according to the current side structure regulations in §238.215 and §238.217. Following a fatal 2011 accident in which a highway semitrailer truck impacted the side of a passenger train that was transiting a grade crossing in Miriam, NV, the National Transportation Safety Board (NTSB) recommended that the FRA “develop side impact crashworthiness standards (including performance validation) for passenger railcars that provide a measurable improvement compared to the current regulation for minimizing encroachment to and loss of railcar occupant survival space” [2]. This paper describes the status of the current FRA research related to side structure integrity and describes the planned next stage of the research program which will include analyzing the performance of generalized passenger railcar structures in side impact collision scenarios. A discussion of the technical challenges associated with analyzing side impacts on passenger rail equipment is also presented.

The Hybrid-III Rail Safety (H3-RS) anthropomorphic test device (ATD), also known as a crash test dummy, was developed by the Rail Safety and Standards Board (RSSB), DeltaRail (now Resonate Group Ltd.), and the Transport Research Laboratory (TRL) in the United Kingdom between 2002 and 2005 for passenger rail safety applications [1]. The H3-RS is a modification of the standard Hybrid-III 50th percentile male (H3-50M) ATD with additional features in the chest and abdomen to increase its biofidelity and eight sensors to measure deflection. The H3-RS features bilateral (left and right) deflection sensors in the upper and lower chest and in the upper and lower abdomen; whereas, the standard H3-50M only features a single unilateral (center) deflection sensor in the chest with no deflection sensors located in the abdomen. Additional H3-RS research was performed by the Volpe National Transportation Systems Center (Volpe Center) under the direction of the U.S. Department of Transportation, Federal Railroad Administration (FRA) Office of Research, Development, and Technology. The Volpe Center contracted with TRL to conduct a series of dynamic pendulum impact tests [2]. The goal of testing the abdomen response of the H3-RS ATD was to develop data to refine an abdomen design that produces biofidelic and repeatable results under various impact conditions with respect to impactor geometry, vertical impact height, and velocity. In this study, the abdominal response of the H3-RS finite element (FE) model that TRL developed is validated using the results from pendulum impact tests [2]. Results from the pendulum impact tests and corresponding H3-RS FE simulations are compared using the longitudinal relative deflection measurements from the internal sensors in the chest and abdomen as well as the longitudinal accelerometer readings from the impactor. The abdominal response of the H3-RS FE model correlated well with the physical ATD as the impactor geometry, vertical impact height, and velocity were changed. There were limitations with lumbar positioning of the H3-RS FE model as well as the material definition for the relaxation rate of the foam in the abdomen that can be improved in future work. The main goal of validating the abdominal response of the dummy model is to enable its use in assessing injury potential in dynamic sled testing of crashworthy workstation tables, the results of which are presented in a companion paper [3]. The authors used the model of the H3-RS ATD to study the 8G sled test specified in the American Public Transportation Association (APTA) workstation table safety standard [4]. The 8G sled test is intended to simulate the longitudinal crash accleration in a severe train-to-train collision involving U.S. passenger equipment. Analyses of the dynamic sled test are useful for studying the sensitivity of the sled test to factors such as table height, table force-crush behavior, seat pitch, etc., which help to inform discussions on revisions to the test requirements eventually leading to safer seating environments for passengers.

An optimization framework is developed to minimize structural weight of the front-frame of heavy-duty trucks while satisfying stress constraint. The shape of the frame is defined by a number of design parameters (which define the shape of the side-rail, position and width of the internal brackets, and width of the flanges). In addition, the thickness of the engine-mount, the side-rails, inner-brackets, radiator mount, shock absorber and cab-mount connector are also considered as design variables. Aluminum Alloy, 6013-T6 is chosen as the material and the maximum allowable stress is the yield stress (320 MPa). A quantity known as ‘Violation’ is defined as the ratio of area in the front-end module where stress constraint is violated to the total area of the frame is introduced to implement stress constraints. For optimization, the penalty method is used where the objective is to minimize the total weight while keeping the value of the ‘Violation’ parameter less than 0.1 %. The Particle Swarm Optimization Algorithm is implemented using parallel computation for optimizing the structure. Commercial FEA software MSC.PATRAN is used for creating the geometry and the mesh whereas MSC.NASTRAN is used to perform static analysis. Six design load conditions, each corresponding to a road condition are used for the problem.

Metro-Rail transit systems are large-scale networks in numerous modern urban areas that play prominent direct and supportive roles in providing efficient mobility for sustaining communities and local economies. Any event leading to failure of a metro-rail network could have serious societal consequences, such as dramatic effect on the safety and wellbeing of commuters in addition to direct and indirect costs from its diminished performance that lead to resilience loss. Potential performance losses might exhibit complexity and pose a challenge for measurement and prediction. Hence, measuring the resilience of such a network enables its efficient enhancement in a cost-effective manner. Enhancing resilience highly depends on identifying recovery strategies with special attention not only to restoring connectedness but also on reducing associated failure and recovery costs. An effective recovery strategy must demonstrate rapid optimal restoration of a disrupted system while minimizing the cost of the disruption. The objective of this paper is to identify effective recovery strategies to reduce the performance loss and to minimize the total cost of a network during and after a disruptive event, using Washington D.C. Metro with its 91 stations and 140 links as a case study. Method of measuring performance loss in this paper, illustrates that the best recovery sequence typically reflects the order of components ranked based on their degree of vulnerability in the network. Also, the proposed cost model provides a basis to decision makers to identify an optimal recovery strategy according to both paramount recovery sequence and minimum cost consideration.

Fixed workstation tables in passenger rail coaches can pose a potential injury hazard for passengers seated at them during an accident. Tables designed to absorb impact energy while minimizing contact forces can reduce the risk of serious injury, while helping to compartmentalize occupants during a train collision. The Rail Safety and Standards Board (RSSB) in the U.K. issued safety requirement GM/RT2100, Issue 5 [1] and the American Public Transportation Association (APTA) in the U.S. issued safety standard APTA PR-CS-S-018-13, Rev. 1 [2] with the goals of setting design and performance requirements for energy-absorbing workstation tables. The U.S. Department of Transportation, Federal Railroad Administration (FRA) Office of Research, Development and Technology directed the Volpe National Transportation Systems Center (Volpe Center) to evaluate the performance of the Hybrid-III Rail Safety (H3-RS) anthropomorphic test device (ATD), also known as a test dummy, in the APTA sled test in order to incorporate a reference to the H3-RS in the safety standard. The Volpe Center contracted with the manufacturer of the H3-RS, Transport Research Laboratory (TRL), in the U.K. to conduct a series of sled tests [3] with energy-absorbing tables, donated by various table manufacturers. The tables were either already compliant with the RSSB table standard or were being developed to comply with the APTA table standard. The sled test specified in Option A of the APTA table standard involves the use of two different 50th percentile male frontal impact ATDs. The H3-RS and the standard Hybrid-III (H3-50M) ATDs performed as expected. The H3-RS, which features bilateral deflection sensors in the chest and abdomen, was able to measure abdomen deflections while the H3-50M, which features a single sensor measuring chest compression, was not equipped to measure abdomen deflection. This study attempts to validate a finite element (FE) model of the APTA 8G sled test with respect to the thorax response of the H3-RS and H3-50M. The model uses a simplified rigid body-spring representation of one of the energy absorbing tables tested by TRL. The FE models of the H3-RS ATD and the H3-50M ATD were provided by TRL and LSTC, respectively. Results from the sled tests and FE simulations are compared using data obtained from the chest accelerometer, the chest and abdomen deflection sensors, and the femur load cells. Using video analysis, the gross motion of the dummies and table are also compared. Technical challenges related to model validation of the 8G sled test are also discussed. This study builds on previous analyses conducted to validate the abdomen response of the H3-RS FE model, which are presented in a companion paper [4].

Poles are regularly placed along highways and are used to support signs, lights and electrical lines. The Midwest Guardrail System (MGS) is a standard W-beam guardrail system used throughout the United States to redirect vehicles that leave the roadway away from dangerous roadside obstacles, like ravines, water hazards, and bridge piers. Placing poles near a guardrail may affect its ability to safely contain and redirect vehicles. The compatibility of poles placed in the proximity of the MGS is studied using nonlinear finite element analysis. Computer simulations were conducted with vehicles impacting the MGS with varying lateral pole offsets between the back of the system and the front face of the pole, and varying longitudinal pole location from being placed directly behind a post to directly behind the unsupported rail half-way between posts. Results show that poles placed within 16 inches behind the MGS may cause concern in regard to acceptable crash test performance for guardrail systems. Additional simulations and full-scale crash testing is required before guidelines can be recommended.

Commonly-used sloshing models are either unable to capture changes in the continuous distribution of the fluid free surface, or are not suited for the integration with high fidelity computational multibody system (MBS) algorithms. The objective of this investigation is to address this deficiency by developing a new continuum-based liquid sloshing approach that accounts for the effect of complex fluid and tank geometry and can be systematically integrated with MBS algorithms in order to allow for studying complex motion scenarios. A unified geometry/analysis mesh is used from the outset to examine the effect of liquid sloshing on railroad and highway vehicle dynamics during various maneuvers including braking and curve negotiation [1,2]. Using a non-modal approach, the geometry of the tank and fluid is accurately defined, a continuum-based fluid constitutive model is developed, and a fluid-tank contact algorithm using the penalty approach is employed. In order to examine the effect of liquid sloshing on vehicle dynamics during curve negotiation, a general and precise definition of the outward inertia force is defined, which for flexible bodies does not take the simple form used in rigid body dynamics. During maneuvers, the liquid may experience large displacements and significant changes in shape that can be captured effectively using absolute nodal coordinate formulation (ANCF) finite elements. For rail systems, the liquid sloshing model is integrated with a three-dimensional MBS vehicle algorithm, in which the three-dimensional wheel/rail contact force formulation is used to account for the longitudinal, lateral, and spin creep forces that influence vehicle stability. The effects of fluid sloshing on vehicle dynamics in the case of a tank partially filled with liquid are studied and compared with the equivalent rigid body model in braking and curve negotiation. The results obtained in the study of the rail vehicle model show that liquid sloshing can exacerbate the unbalance effects when the rail vehicle negotiates a curve at a velocity higher than the balance speed, and can significantly increase coupler forces during braking. Analysis of the highway vehicle model shows that the liquid sloshing changes the contact forces between the tires and the ground — increasing the forces on certain wheels and decreasing the forces on other wheels — which in cases of extreme sloshing, can negatively impact the vehicle stability by increasing the possibility of wheel lift and vehicle rollover.

In this paper, a 3-D fluid-structure interaction (FSI) analysis on the performance of the high-pressure fuel pump for diesel engines is presented. The fluid and structure are two-way coupled and several complex factors are taken into accounts in the FSI model. For instance, the fluid model includes not only the high-pressure fuel pump but also the rail and pressure-control valve which are used to maintain a stable delivery pressure of the pump; Gap boundary condition is adopted to simulate the opening and closing of the valve; The flow is assumed to be nonisothermal and the physical properties of the fuel such as dynamic viscosity and density are functions of pressure and temperature. While in the structure model, the spring force on the valve and the contacts between the valve and the valve seat as well as the top block are considered. The calculated volumetric efficiency losses agree well with the experiments, which indicates that the FSI model established in this study could well predict the physical phenomenon taking place in the high-pressure fuel pump. Several new conclusions can be drawn from the discussions on the results such as the suction efficiency loss due to the delay closing of the inlet valve is extremely small while the suction loss due to the expansion of the high-pressure fuel entrapped in the dead volume is very large.

A computer numerically controlled (CNC) milling center is a machine tool for the production of parts with planar, cylindrical and shaped surfaces. The milling center analyzed here includes an open frame — a structure resembling the shape of the letter C. The main cutting motion is performed by a tool clamped in the spindle. Secondary motion can be linear, rotary or a combination of these. Linear movements in three axes are performed by the tool by means of linear motion components (i.e. motion screws and linear guide rails). Rotary motion is performed only when the workpiece is clamped to the rotary table which is mounted on the mounting plate. The basic demands placed on the structure of a milling center include high static and dynamic stiffness during machining processes. This article is primarily aimed at evaluating the response of the frame of the CNC milling machine to the excitation caused by the fluctuation of cutting forces due to step changes in the number of engaged cutting edges. To ensure optimum machining conditions it is important to set suitable cutting conditions for a frame structure with sufficient stiffness. Unsuitable cutting conditions and low stiffness of the machine frame may lead to dimensional inaccuracies of the workpiece, to decreased quality of the machined surfaces or even to the destruction of the tool cutting edges. The aims of the study include the determination of the static deformation, modal analysis to assess the dynamic properties of the frame, and harmonic response analysis, taking into consideration the amplitudes of the loading forces specified in accordance with the recommended operating conditions of the individual tools. Finite element method (FEM) analyses of the frame were performed using MSC.Marc software. Due to the high structural complexity of the computer aided design (CAD) model, the computational model for the FEM analysis had to be simplified. Only the major structural parts and the connecting parts were meshed in detail, combining both structured and unstructured mesh. Geometrically complicated cast parts with large changes of thickness were meshed with linear tetrahedral elements (tetra4) with full integration. Rotationally symmetrical parts, plates and linear guide rails components were meshed with linear brick elements (hex8) with full integration. The overall number of elements was approximately 1,400,000. Tools, including the clamping head and the spindle, are represented by approximate meshes of brick elements. However, a detailed FEM model of the spindle and the tool would be needed for the analysis of the self-excited oscillations during machining, which is the subject of a large number of scientific publications. Increased attention was paid to the incorporation and set-up of the springs between corresponding pairs of nodes of the meshed linear motion components. As a computational model for modal and harmonic response analyses needs to be strictly linear, only linear elastic material properties and linear springs were defined in the analyses presented here.

Research to develop new technologies for increasing the safety of passengers and crew in rail equipment is being directed by the Federal Railroad Administration’s (FRA’s) Office of Research, Development, and Technology. Crash energy management (CEM) components which can be integrated into the end structure of a locomotive have been developed: a push-back coupler and a deformable anti-climber. These components are designed to inhibit override in the event of a collision. The results of vehicle-to-vehicle override, where the strong underframe of one vehicle, typically a locomotive, impacts the weaker superstructure of the other vehicle, can be devastating. These components are designed to improve crashworthiness for equipped locomotives in a wide range of potential collisions, including collisions with conventional locomotives, conventional cab cars, and freight equipment. Concerns have been raised in discussions with industry that push-back couplers may trigger prematurely, and may require replacement due to unintentional activation as a result of service loads. Push-back couplers are designed with trigger loads meant to exceed the expected maximum service loads experienced by conventional couplers. Analytical models are typically used to determine these required trigger loads. Two sets of coupling tests are planned to demonstrate this, one with a conventional locomotive equipped with conventional draft gear and coupler, and another with a conventional locomotive equipped with a push-back coupler. These tests will allow a performance comparison of a conventional locomotive with a CEM-equipped locomotive during coupling. In addition to the two sets of coupling tests, car-to-car compatibility tests of CEM-equipped locomotives, as well as a train-to-train test are also planned. This arrangement of tests allows for evaluation of the CEM-equipped locomotive performance, as well as comparison of measured with simulated locomotive performance in the car-to-car and train-to-train tests. This paper describes the results of the coupling tests of conventional equipment. In this set of tests, a moving locomotive was coupled to a standing cab car. The coupling speed for the first test was 2 mph, the second test 4 mph, and the tests continued with the speed incrementing by 2 mph until the last test was conducted at 12 mph. The damage observed resulting from the coupling tests is described. The lowest coupling speed at which damage occurred was 6 mph. Prior to the tests, a one-dimensional lumped-mass model was developed for predicting the longitudinal forces acting on the equipment and couplers. The model predicted that damage would occur for coupling speeds between 6 and 8 mph. The results of these conventional coupling tests compare favorably with pre-test predictions. Next steps in the research program, including future full-scale dynamic tests, are discussed.

Finite element simulation of composite materials is still challenging as anisotropy of the material brings difficulty in accurately identifying shear properties for modeling. In this study, ±45° tensile tests, Iosipescu shear tests, rail shear tests and Arcan shear tests are conducted to obtain the engineering shear stress-strain curve of woven fiber reinforced polymer. Digital image correlation method is adopted to obtain the strain field of the specimens. It is indicated that Iosipescu shear tests introduce a strain field close to pure shear state while the other three test types introduce relatively large tensile strain or compressive strain. Shear properties obtained from Iosipescu tests are used to calibrate an extensively used composite material model, Matzenmiller-Lubliner-Taylor (MLT) model. The calibrated MLT model is then verified by simulating Arcan tests with different loading angles. The simulations indicate that MLT model gives reliable predictions on Arcan tests with smaller loading angles, while it overestimates the force-displacement responses at larger loading angles.

Following several recent serious rail accidents in North America, changes in regulation and increased public awareness is driving the need to address gaps in rail safety. The industry and regulators have numerous safety initiatives; however prescriptive standards in combination with a performance based approach could be a powerful tool for understanding and mitigating risk in a cost effective way. This paper reviews the principles of safety risk management that can be applied to safe transportation of flammable hydrocarbons by Rail. FRA’s proposed rulemaking on Risk reduction program and its potential impact on the industry are also addressed. The approach proposed in this paper focuses on existing and new proposed safeguards/barriers and how they could be monitored and managed. The paper aims to set the path forward for structured risk based thinking in managing rail safety. The first part of the paper explains the barrier based risk assessment approach using the Lac Megantic accident as an example. A bow-tie is developed to deconstruct the incident timeline and to capture the safeguards that existed at that time and their working status. This diagram cross references Transport Canada’s Investigation findings. The second part of the paper evaluates the new mitigation measures proposed by FRA HM 251 rulemaking ( “Enhanced Tank Car Standards and Operational Controls for High-Hazard Flammable Trains” Final Rulemaking” ) as potential safeguards and their impact on the overall risk of transportation. A baseline risk is first established for transporting crude by rail assuming some common safeguards in place. A simple Quantitative Risk Assessment methodology including likelihood and consequence was then used to estimate the base case risk. Risk mitigation and effect of any additional new measures like Changes in Rail Tank Car design , Oil Conditioning , Enhanced Braking to Mitigate Damage in Derailments , Speed Limit changes , Positive train control , Train manning when loading are assessed.

We have developed a new high strain rate experiment in biaxial tension that allows for constitutive model validation at engineering strain rates from 50/s to over 1000/s. In the experiment, a flat disk of the material is clamped at a fixed radial distance. A rail-guided impact sled with a hemispherical impact head is released from the desired height and impacts the disk at the center, potentially deforming the sample to failure. Drop height and impact mass can be varied to modify peak strain rate and impact energy, and the wide range of test conditions allow for testing to be performed on many classes of materials, including thermoplastics and elastomers. The stress and strain fields are calculated using finite element simulations with the proposed constitutive model, and the constitutive model is validated by matching the force versus displacement data of the impact head recorded during experiment to the simulation. In this paper, we discuss results from the experiment and finite element simulations of the experiment on PA (polyamide, nylon) and PEEK (polyether ether ketone). The new experiment allows for validation and refinement of constitutive models, including failure, at high strain rates and in a multiaxial stress state.

The objective of this study was to define the elements of a rail system capable of achieving a 1000-fold increase in freight throughput, accommodate passenger travel, be capable of a phased implementation, be affordable and have a payback to an adopting railroad of less than seven years. This paper describes a novel New Rail System, “NRS” that achieves the stated objectives. The NRS utilizes existing rail rights-of-way and tracks. It has the capability to accommodate both freight and passenger movement. In its initial implementation it supports speeds of 85 mph. Although no invention is required, three modifications to the railroad infrastructure are required, (1) elimination of at-grade crossings, (2) electrification, and (3) transition from diesel-electric locomotive powered trains to individual electrical powered pallets to allow flexible routing and sorting in the network. The four elements defining NRS are; (1) self-powered 70-foot pallets, (2) freight and passenger payload modules (loadable and unloadable from the pallets), (3) pallet yards, accumulators and transfer stations, and (4) a pallet control system. An initial cost-benefits analysis shows that if BNSF implemented the NRS on its Southern Transcon route between Los Angeles and Chicago a payback of the initial $21.2 billion investment can be achieved in under four-years.

In this paper, a joint simulat ion method based on nonlinear FEM and MBD is proposed. Firstly, the force-deformation character of single vehicle is analysed using nonlinear FEM software Dytran. Then, override simulations of two train units in frontal collision are carried out using multi-body dynamics. Simulation results indicate that the pitching motion of vehicles has great effect to the overriding phenomenon. It also depends on several factors, such as collision mass, pitching frequency, height of the center of mass above the rail level. Besides that, it is shown in this paper the overriding phenomenon is more sensitive to variations in pitching frequency and height of the center of mass, compared to the factor of collision mass.

According to estimates reported in the U.S. Consumer Product Safety Commission’s National Electronic Injury Surveillance System, there were greater than 10,000 stepladder related injuries treated in hospital emergency rooms nationwide per year in the period from 2009 through 2013. Research and experience have sought to correlate specific stepladder damage patterns to the causes of some injuries involving stepladders. Prior studies have associated a specific damage pattern — inward deformation of the stepladder’s front side rails — with impact loading of a user’s body onto the lower portion of a front side rail following a fall from the stepladder. Those prior studies were conducted using stepladders with metal knee braces and with the ladder cap simply supported during impact testing. Currently sold fiberglass stepladders often have plastic rather than metal knee braces. In our study, side rail impact testing was performed in order to evaluate how a design change from metal knee braces to plastic knee braces affects impact damage patterns in fiberglass stepladders. Biomechanics simulations were used to inform the selection of the weights used for impact testing and allowed the test results to be evaluated in the context of potential body contact scenarios that could produce equivalent loading of the side rail. Our study demonstrates that depending on the weight of the impacting body, fiberglass ladders with plastic knee braces show different dynamic responses to impact loading than do their metal counterparts. Additionally, the test methods in this study incorporate realistic dynamics in that the weight impacted the lower portion of the stepladder’s front side rail while the stepladder was actively tipping with only two of its feet in contact with the ground and with the top cap unsupported. The results indicate that ladders with metal knee braces can permanently deform when impacted with loads less than that required to permanently deform the ladders tested with plastic knee braces. The absence of permanent side rail deformation in the plastic knee braced stepladders tested even after undergoing significant elastic deformation during testing gives rise to new questions about the potential for damage that is not observable based on a visual examination.

Composite materials have emerged as promising materials in applications where low weight and high strengths are desired. Aerospace industry has been using composite materials for past several decades exploiting their characteristics of high strength to weight ratio over conventional homogenous materials. To provide a wider selection of materials for design optimization, and to develop lighter and stronger vehicles, automobile industries have been exploring the use of composites for a variety of components, assemblies, and structures. Composite materials offer an attractive alternate to traditional metals as designers have greater flexibility to optimize material and structural shapes according to functional requirements. However, any automotive structure or part constructed from composite materials must meet or exceed crashworthiness standards such as Federal Motor Vehicle Safety Standard (FMVSS) 208. Therefore, for a composite structure designed to support the integrity of the automotive structure and provide impact protection, it is imperative to understand the energy absorption characteristics of the candidate composite structures. In the present study, a detailed finite element analysis is presented to evaluate the energy absorbing characteristics of a carbon fiber reinforced polymer composite lower rail, a critical impact mitigation component in automotive chassis. For purposes of comparison, the analysis is repeated with equivalent aluminum and steel lower rails. The study was conducted using ABAQUS CZone module, finite element analysis software. The rail had a cross-sectional dimension of 62 mm (for each side), length of 457.2 mm, and a wall thickness of 3.016 mm. These values were extracted from automobile chassis manufacturer’s catalog. The rail was impacted by a rigid plate of mass 1 tonne (to mimic a vehicle of 1000 Kg gross weight) with an impact velocity of 35 mph (15646.4 mm/s), which is 5 mph over the FMVSS 208 standard, along its axis. The simulation results show that the composite rail crushes in a continuous manner under impact load (in contrast to a folding collapse deformation mode in aluminum and steel rails) which generates force-displacement curve with invariable crushing reactive force for the most part of the crushing stroke. The energy curves obtained from reactive force-displacement graphs show that the composite rail absorbs 240% and 231% more energy per unit mass as compared to aluminum and steel rails. This shows a significant performance enhancement over equivalent traditional metal (aluminum and steel) structures and suggests that composite materials in conjunction with cellular materials/configurations have a tremendous potential to improve crashworthiness of automobiles while offering opportunities of substantial weight reductions.