Sled Tests Research Articles

US rail equipment crashworthiness standards

In 1999 the US Department of Transportation's Federal Railroad Administration (FRA) issued new regulations and the American Public Transportation Association (APTA) issued new standards for rail passenger equipment crashworthiness. These new regulations and standards include conventional strength-based requirements for equipment used below 200km/h (125 mile/h), crashenergy management for equipment used above 200km/h (125 mile/h) and dynamic sled testing of occupant seats.

Comparative evaluation of the THOR advanced frontal crash test dummy

Ten 48 km/h frontal sled tests were conducted to evaluate the biofidelity of the THOR dummy. Three replicate tests were conducted with THOR, three with a 50 th percentile male Hybrid III dummy, and four with post-mortem human surrogates (PMHS). The tests, conducted in a buck representing a mid-size US sedan, included a force-limited three-point belt system with buckle-side pretensioner and a driver side airbag. Following the tests, select parameters were used to compare THOR's responses with those of the Hybrid III dummy and the PMHS. The tesults were mass scaled in order to account for size differences between the subjects. Based on cadaveric response corridors, the sled test results provided evidence that THOR is more biofidelic than the Hybrid III dummy. THOR lap belt loads, head acceleration, and movement of the anterior chest wall were more similar to those of the PMHS than were those of the Hybrid III. However, THOR recorded less head forward movement and pelvic acceleration than did the PMHS.

Comparison and evaluation of contemporary restraint systems in the driver and front-passenger environments

Restrained driver and passenger kinematics and injury outcome in frontal collisions are compared using US fatality field data and post-mortem human surrogate sled tests. The fatality data indicate that a frontal airbag may provide greater benefit for a passenger than for a driver. The thoracic injuries sustained by passenger-side surrogates restrained by a force-limited, pre-tensioned belt and airbag are evaluated, and kinematics are compared with driver-side subjects exposed to a similar impact. Driver and passenger kinematic differences are identified and the implications are discussed with respect to the injury-predictive ability of existing thoracic injury criteria. The chest acceleration of the passenger-side subjects exhibited a bimodal profile with an initial (and global) maximum before the subject loaded the airbag. A second acceleration peak occurred as the subject loaded both the belt and the airbag. A similarly restrained driver-side subject loaded the belt and airbag concurrently at the time of peak chest acceleration and therefore did not exhibit this biomodal chest acceleration. While the injury-causing or injury-mitigating significance of this bimodal response is not known, its significance with respect to thoracic injury prediction is discussed.

Crash analyses and design of a belt integrated seat for occupant safety

The performance of a belt integrated seat (BIS) is evaluated by using a sled test and occupant analysis software. The seat belt is attached to the seat back in the BIS to improve occupant safety. A simulation model of a BIS is established by using an occupant analysis program, SAFE. The model is constructed on the basis of data obtained from the structural investigation and a frontal sled test of a BIS. The numerical result from the simulation model is validated for consistency by comparison with high speed photographs taken during the sled test. Characteristics of both the conventional seat and the BIS are discussed. It is shown that occupant safety can be improved considerably with the BIS. A parametric study is conducted for various seat belts and a recommendation for an appropriate one is proposed. Structural analysis and optimization of the BIS are performed to establish the preliminary design trend considering occupant safety. A finite element model of the BIS is created, and the structure is optimized by the structural analysis and optimization program GENESIS. The seat components are reinforced on the basis of the shape of the existing BIS product. The results are discussed and a design recommendation for a BIS is made.

A Study of Standards for Child Restraint System Sled Tests

A method is developed for finding the best and worst possible responses of a child dummy in a child seat sled test where the sled deceleration pulse must follow a prescribed corridor. Constrained optimization techniques are applied to a two-degree-of-freedom lumped mass model of the sled test to determine the best and worst sled deceleration pulses, within the prescribed corridor, that produce the minimum and maximum child chest decelerations. A three-dimensional multi-body model is used to predict the values of the peak child chest g's in sled tests with the best and worst sled deceleration pulses. The results are useful as a measure of the variability of child dummy response that can be expected for a prescribed sled deceleration corridor. The standards for child seat safety testing can be evaluated and compared quantitatively using this sensitivity information. Results indicate that some prescribed sled deceleration corridors are too wide, allowing extreme variations in occupant responses, and some are too narrow, or perhaps unnecessarily complex.

Occupant behaviour simulation using DADS and design of seat belt for occupant safety

The occupant and seat belt restraint system were modelled mathematically using multi-body dynamics. The interactions between belt and dummy such as belt slip and energy dissipation were considered in three dimensional mathematical models of 50th percentile Hybrid111 dummy and 3-point seat belt system. In this study, the commercial software DADS (Dynamic Analysis and Design System) was used for dynamic simulation of occupant impact response in sled tests and barrier crash tests. Results from the sled test simulations were compared with those available in the literature in order to validate the mathematical model for occupant behaviour analysis. In order to simulate the occupant behaviour in barrier crash tests, simple models of car interior system and energy-absorbing steering system were also established. And the effect of seat belt systems on occupant protection was evaluated through the occupant behaviour simulation in barrier crash tests. Several factors, which were thought to be closely related to the performance of seat belt systems for occupant protection, were considered. Orthogonal array table was used for a systematic procedure to lay out the factors and conditions in the barrier crash test simulation. The various injury values were investigated in response to the change of seat belt variables such as shoulder belt slackness, lap belt slackness, belt stiffness, retractor performance, and outer D-ring position. The contribution of seat belt variables to occupant protection was analysed by ANOVA (analysis of variance). From this analysis, it was found that seat belt slackness had the most dominant effect on occupant injuries, and seat belt pretension can increase the occupant safety. Through the systematic applications of orthogonal array table and ANOVA to seat belt design, the modified combination of seat belt variables was obtained, and the initial occupant injury values could be decreased.

A system for simulating structural intrusion in automobile full-frontal and frontal-offset crashes in the laboratory sled test environment

A sled system capable of producing structural intrusion in the footwell region of an automobile has been developed. The system couples the hydraulic decelerator of the sled to actuator pistons attached to the toepan and floorpan structure of the buck. Characterization of the footwell intrusion event is based on developing a toepan pulse analogous to the acceleration pulse used to characterize sled and vehicle decelerations. Sled tests with the system indicate that it is capable of accurately and repeatably simulating toepan/floorpan intrusion into the occupant footwell. Test results, including a comparison of lower extremity response between intrusion sled tests and no intrusion sled tests, indicate that this system is capable of repeatable, controlled structural intrusion during a sled test impact. Test results also suggest that lower extremity forcing during footwell intrusion is significantly larger than such forcing with no intrusion, and that response and risk of injury for occupants in frontal or frontal-offset crashes are more severe.

A parametric study of a side airbag system to meet deflection based criteria.

A side airbag system comprising of 12 liter bag to cover the BioSid chest and the abdomen down to the arm rest level, and 75 mm of padding to cover the pelvic/thigh area was evaluated by a series of sled tests at two different velocities, 10 m/s and 12 m/s. The initial bag (over) pressure was varied from 0 to 80 kPa and the bag ventilation area was varied from zero to 1500 mm2. Compressed air was used to fill the bag. It was found that the ventilation of the bag reduced the maximum chest deflection by 30 percent and the maximum viscous criterion, VC, by 50 percent (comparison was made with the same bag without ventilation). A suitable initial bag (over) pressure was found to be about 50 kPa, when the loading of the abdomen was also taken into consideration. The results indicate that the chest deflection is proportioned to the door average velocity (during the first 20 ms of deflection) to the power of about 2 and that the VC is proportional to the same velocity to the power of about 4. It was also found that a 12 liter ventilated side airbag resulted in 30-40 percent lower chest deflection and about 60 percent lower VC than 50 mm of chest padding (Ethafoam 220).

Thoracic response and injury with belt, driver side airbag, and force limited belt restraint systems

Abstract The performance of belt, airbag, and force limited belt restraint systems for the driver were compared using frontal sled tests. Nine human cadaver and six dummy sled tests were conducted at 56 km/h using a test buck representing a mid-size vehicle. Subject instrumentation included upper and lower chestbands to measure local thoracic deformations and sternal and spinal accelerometers to record torso deceleration. Following the sled tests, radiographs and autopsy results were used to correlate cadaver injury with measured engineering parameters and dummy response. Chest compression, acceleration, change in curvature and Viscous Criteria were evaluated for all occupants. Occupant kinematics were determined from analysis of high speed film. Local differences in the chest loading behavior among the restraint systems were identified using the chestband contours. The results of the research indicate that improvements in thoracic occupant protection may be achieved with the use of force limited belt and pretensioner systems.

Impact on planar kinematic chain of rigid bodies: Application to movements of anthropomorphic dummy in a crash

Numerical simulation of crash phenomena in rigid multi-body approach brings up problems when the various bodies constituting the mechanical system come into contact. The planar modeling of contact requires bodies' geometry to be taken into account. The method used permits the simultaneous management of constraints due to their contact and to kinematic joints, by introduction of holonomic constraints. We validate this method on Biomechanical applications. The results arising from a numerical model, and from a sled test, where we recreated the dummy seating conditions, are compared.

Evaluation of four processing methods of the VCM ankle joint model

Despite improvements in vehicle design and safety technologies, frontal automotive collisions continue to result in a substantial number of injuries and fatalities each year. Although a considerable amount of research has been performed on PMHSs and ATDs, matched dynamic whole-body frontal testing with PMHSs and the current ATD aimed at quantifying both kinetic and kinematic data in a single controlled study is lacking in the literature. Therefore, a total of 4 dynamic matched frontal sled tests were performed with three male PMHSs and a Hybrid III 50th percentile male ATD (28.6 g, Δv = 40 kph). Each subject was restrained using a 4 kN load limiting, driver-side, 3-point seatbelt. Belt force was measured for the lap belt and shoulder belt. Reaction forces were measured at the seat pan, seat back, independent foot plates, and steering column. Linear head acceleration, angular head acceleration, and pelvic acceleration were measured for all subjects. Acceleration of C7, T7, T12, both femurs, and both tibias were also measured for the PMHSs. A Vicon motion analysis system, consisting of 12 MX-T20 2 megapixel cameras, was used to quantify subject 3D motion (±1 mm) at a rate of 1 kHz. Excursions of select anatomical regions were normalized to their respective initial positions and compared by test condition and between subject types. Notable discrepancies were observed in the responses of the PMHSs and the ATD. The reaction forces and belt loading for the ATD, particularly foot plate, seat back, steering column, and lap belt forces, were not in agreement with those of the PMHSs. The forward excursions of the ATD were consistently within those of the PMHSs with the exception of the left upper extremity. This could potentially be due to the known limitations of the Hybrid III ATD shoulder and chest. The results presented herein demonstrate that there are some limitations to the current Hybrid III ATD under the loading conditions evaluated in the current study. Overall, this study presents a comprehensive data set of belt forces, reaction forces, accelerations, and bilateral displacement data that can be used to evaluate the performance of ATDs and validate computational models.

A mathematical model of the BIOSID dummy

A two-dimensional lumped-mass model of the BIOSID dummy was developed to be used as a complement to mechanical simulations. The software used was the crash victim simulation program MADYM02D. The mathematical BIOSID dummy consisted of eleven body parts; head, neck, arm, shoulder rib, thoracic ribs, abdominal ribs, spine, and pelvis. The spine and ribs were connected by a number of non linear springs and dampers. The model was used to evaluate the protective effects of side-airbags and interior padding in automobile side impacts. To validate the mathematical model, the mechanical BIOSID dummy was impacted by a pendulum at various impact speeds. In addition, tests were conducted with padding and pre-inflated airbags on the pendulum. Sled tests at impact velocities of 9 m/s and 6 m/s were also used to validate the model. The tested padding in the mechanical sled tests consisted of 50 mm of compliant padding at the thorax level, and 75 mm of the same padding at the pelvis level. The airbag used was an 8 1 bag at the thorax level with an internal pressure of approximately 1 bar. At the pelvis level it was used with the 75 mm padding. It was found that predictions of the model were in good agreement with the results from the mechanical sled tests. The lumped-mass model of the BIOSID dummy is a good tool for evaluating the protective effect of padding or airbags in the side door. Language: en

A side airbag system to meet chest injury measures: evaluation by mathematical simulations

Abstract A mathematical sled model that included a BIOSID dummy was used to evaluate the potential injury reducing benefits of padding or airbags in side impacts. The side impact simulations were carried out using the crash victim simulation software MADYMO2D. The model has been validated against mechanical sled tests at two impact velocities: with padding, or with airbags mounted to the door. The airbags were filled with compressed air and had varying initial (over) pressures and ventilation areas. The protective system resulting in the lowest injury measures for the dummy was thus determined. The lowest TTI was obtained with the airbag with 0 kPa initial over pressure and 1500 mm2 ventilation area, while the lowest chest deflection and chest VC were obtained with an airbag with 40 kPa initial over pressure and 2000 mm2 ventilation area. The risk of the head impacting the side window was significantly reduced with the addition of an airbag. It was found that the airbag has to be at least 120 mm thick when fully inflated in order to significantly reduce injury measures. The arm and shoulder of the occupant have to be engaged in the impact. The model of the BIOSID dummy was found to be a very valid and valuable tool for evaluating the protective effect of padding and airbags in the side door.

Crash pulse recorder—validation in full scale crash tests

Estimation of the accident severity is a fundamental requirement in accident reconstruction and analysis. Accident severity can be measured in many different ways, but in frontal collisions change of velocity, energy equivalent speed or equivalent barrier speed are frequently used parameters. These parameters are most often estimated from vehicle deformation. It is known, however, that the quality of these estimates is limited if compared with these obtained in laboratory test conditions. To be able to achieve almost the same measurements and measurement accuracy in real-life accidents as in the laboratory, where the acceleration time history is measured, an on-board measurement technique is required. This presentation gives results of tests of a low cost device for measuring the crash pulse for a car involved in an accident, concerning systematic and random error. The device, called the Crash Pulse Recorder (CPR), has been tested previously in several sled tests. The CPR is based on measurment of the movement of the mass in a spring mass system in a collision. A brief description of its construction is also included. The CPR is an integral part of a large accident data collection system including interior and exterior deformation measurements and evaluation of injury outcome. This report presents the results of several full-scale crash tests, undertaken to evaluate the accuracy and precision of the CPR in cars in different impact modes. The tests comprised both offset and angled collisions. Most of the tests were car to car collisions, but barrier tests were also performed. The random error of the CPR was found to be 2.2 km/hr for the ΔV measurements and 0.6 g for mean acceleration.

Computer Simulations of Contact Forces for Airbags with Different Folding Patterns During Deployment Phase

An explicit finite element method was used to study the neck load and the contact force between an occupant and an airbag during an out-of-position frontal automobile crash. Two different folding patterns and two different mounting angles of the airbag were simulated. For the four cases simulated, the occupant’s neck axial force ranged from 156 to 376% of the data obtained from in-position sled tests using the Hybrid III dummy. The neck shear force ranged from 87 to 229% and the neck flexion moment ranged from 68 to 127% of in-position experimental results. In both 300 mounting angle simulations, the neck axial forces were higher than that of the two simulations with 00 mounting angles, but the trend for the neck shear force was the opposite. Although the kinematics of the model appear reasonable, the numbers generated by the model must be reviewed with great caution because the model has not been fully validated.

Computer Simulations of Contact Forces for Airbags with Different Folding Patterns During Deployment Phase

An explicit finite element method was used to study the neck load and the contact force between an occupant and an airbag during an out-of-position frontal automobile crash. Two different folding patterns and two different mounting angles of the airbag were simulated. For the four cases simulated, the occupant’s neck axial force ranged from 156 to 376% of the data obtained from in-position sled tests using the Hybrid III dummy. The neck shear force ranged from 87 to 229% and the neck flexion moment ranged from 68 to 127% of in-position experimental results. In both 300 mounting angle simulations, the neck axial forces were higher than that of the two simulations with 00 mounting angles, but the trend for the neck shear force was the opposite. Although the kinematics of the model appear reasonable, the numbers generated by the model must be reviewed with great caution because the model has not been fully validated.

Reverse Velocity Rocket Sled Test Bed for Inertial Guidance Systems

The High Speed Rocket Sled Test Track at Holloman AFB, New Mexico is a precision, highly-instrumented facility which has found extensive use in the quantitative error evaluation of state-of-the-art guidance systems. The sleds, containing the guidance system tested and extensive monitoring instrumentation, are subjected to a positive and negative acceleration profile tailored to both simulate missile environment and maximize separability of test system errors. While thrust is provided by rocket engines, deceleration has traditionally been accomplished by water brake: a sledborne scoop which disperses water from a channel between the two rails. With the evolution of high speed flight computers has come a trend toward real time guidance system error compensation. This has resulted in enhanced visibility of errors such as high order nonlinearities and effects due to erroneous compensation. The isolation of system errors is so strongly a function of the sled acceleration profile which drives those errors that the success of a specific profile to aid error separation can be simulated prior to actual testing. This was shown for the case of an anticipated sled test project which was to involve high (>50 g) accelerations and was expected to propagate unusually highly-correlated errors: the result was that no level of water brake deceleration provided the velocity change necessary for error separation. Thus the reverse velocity sled concept was proposed and analyzed in 1979. This technique uses a reverse thruster to provide a sled brake of desired magnitude and time duration, the optimal retro thrust resulting in a considerable reverse sled velocity. This sled is presently under design and construction and is to be thoroughly tested in calendar year 1982. The aerodynamics of the reverse velocity sled being built are such that the sled will return to the launch point. This factor leads to new dimensions in this test concept. Firstly, start and stop points can be measured to extreme accuracy, because of their proximity, permitting excellent determination of non-cancelling errors such as asymmetries and even-powered nonlinearities. Secondly, traversal of the Test Track in two directions decouples Track survey errors from test guidance system errors. Thus, if the test system performance conforms to a deterministic model, then the test system can be used to help identify, and then remove, many errors in the Track reference itself. This paper reviews the efforts accomplished to date, including an analysis of the above-mentioned benefits of sled return to the launch point.

A comparison of nonfatal motor vehicle occupant injuries in crash versus noncrash events

The description of cervical spine motion and the risk to sustain a cervical spine injury is mainly based on cadaver studies. As the active influence of soft tissue is neglected in cadaver studies, our understanding of the kinematic model for whiplash is limited. Therefore the objective of this study was, to describe the in vivo cervical spine motion and acceleration during rear-end sled collisions to identify sequences of motion in which the risk of injury to the cervical spine is increased.A rear-end collision with a speed change (ΔV) of 6.3 km/h was simulated in a sled test with eight female subjects with no history of prior injury or pain of the cervical spine. A high-speed camera was used to document motion data. Acceleration data were recorded using accelerometers. Acceleration input to the cervical spine was assessed by the simultaneous analysis of the head angle and angular head acceleration as well as the simultaneous analysis of the relative motion and the relative acceleration between the head and T1 to define intervals of increased risk of cervical spine injuries during rear-end collision.The motion sequence is characterized by the same phases that have already been described for male volunteers. Increasing angular head acceleration can explain facet joint injuries during the extension movement (100–120 ms) and hence occur about 50 ms later than shown in cadaver models. In the late rebound the combination of maximal ventral head acceleration and head movement is underestimated and can be responsible for soft tissue injuries.The study shows that during the extension phase and the late rebound phase, acceleration and movement pattern occur that could lead to cervical spine injuries.

Simulating Rain Impact Damage to Supersonic Missile Radomes

Abstract A test simulating the rain impact damage to two ceramic missile radomes traveling at supersonic speeds is described. A water-jet gun has been developed which fires a short burst of water at speeds up to 5000 ft/s (1524 m/s). This gun was used to simulate the impact of raindrops on the radomes. Equations are given relating the crater volume and area of a single jet impact to the energy of the jet. Then equations are given which express the cumulative damage as a function of impact angle, drop size distribution, velocity, and rain field length and intensity. A computer code has been written to solve these equations. The computer code gave results that agreed well with an actual rocket sled test. The code was used to predict the damage for a new set of conditions, and the water-jet gun was used on full-scale radomes to simulate the predicted rain impact damage.

Recording Effects of Rain Erosion with High Speed Photographic Techniques

Although controlled rain erosion testing is one of many types of captive dynamic testing that is carried out for missile and space vehicle systems at the Holloman High Speed Track, it is unique in that the photographic recording of this artificial rain and its effects offer unusual problems not encountered in ordinary sled testing. The 6,000 foot rain test section normally used produces an artificial rain with a mean drop diameter of 1.5mm, and has controllable rain drop concentration outputs plus special nozzles and tanks for isolated rain simulations. Sleds traveling at speeds up to Mach 5.5 have carried various test items through this environment so that scientists can study the effects of the rain on test items at various stations along the sled path as well as the total erosion effects after the vehicles are recovered. Detailed photographs of the test object while in the environment are best recorded by synchroballistic techniques. By sampling at intervals along the path, progressive deterioration can be recorded with space-time correlations as the test item passes through the rain field. Aerodynamic characteristics are recorded using photographic shadowgraph techniques. Engineering and general surveillance data is provided by high speed cameras and various lighting techniques.