Per Lövsund

A Human-Body 3D Mathematical Model for Simulation of Car-Pedestrian Impacts

A 3D mathematical model of the human body was developed to simulate responses of pedestrians in car impacts. The model consists of fifteen body segments connected by fourteen joints, including two human-like knee joints and two breakable-leg segments. The anthro pometrical data for the model were generated by the GEBOD program, and characteristics of the body segments and the joints were defined based on available biomechanical data. The validity of the model was evaluated against full-scale impact tests with pedestrian substitutes and an experimental car in terms of the kinematics of the pedestrian substitute, bumper impact forces, accelerations of the body segments, and failure description from anatomical investigations of the pedestrian substitutes. The sensitivity of the model to input variables was studied at impact speeds of 15 and 40 km/h with the following car-front parameters: bumper height, bumper stiffness, bumper lead distance, height of hood edge, and hood-edge stiffness. The validated model demonstrated its capability in simulations of car-pedestrian impacts for the assessment of responses of pedestrians, prediction of risks of pedestrian injuries and for the development of safety countermeasures.

Neck injuries in car collisions — a review covering a possible injury mechanism and the development of a new rear-impact dummy

A review of a few Swedish research projects on soft tissue neck injuries in car collisions is presented together with some new results. Efforts to determine neck injury mechanisms was based on a hypothesis stating that injuries to the nerve root region in the cervical spine are a result of transient pressure gradients in the spinal canal during rapid neck bending. In experimental neck trauma research on animals, pressure gradients were observed and indications of nerve cell membrane dysfunction were found in the cervical spinal ganglia. The experiments covered neck extension, flexion and lateral bending. A theoretical model in which fluid flow was predicted to cause the transient pressure gradients was developed and a neck injury criterion based on Navier-Stokes Equations was applied on the flow model. The theory behind the Neck Injury Criterion indicates that the neck injury occurs early on in the rearward motion of the head relative to the torso in a rear-end collision. Thus the relative horizontal acceleration and velocity between the head and the torso should be restricted during the early head-neck motion to avoid neck injury. A Bio-fidelic Rear Impact Dummy (BioRID) was developed in several steps and validated against volunteer test results. The new dummy was partly based on the Hybrid III dummy. It had a new articulated spine with curvature and range of motion resembling that of a human being. A new crash dummy and a neck injury criterion will be very important components in a future rear-impact crash test procedure.

Human Volunteer Kinematics in Rear-End Sled Collisions

Validation of new crash test dummies for rear-end collision testing requires human response data from pertinent test situations. Eleven human volunteers were exposed to 23 low-speed rear impacts to determine human response in well-defined test seats, and to quantify repeatability, variability and the effect of seat design on human response. The results showed vertical motion of the volunteers’ H-point caused by ramping up along the seat, and an upward motion of the volunteers’ torso and head. The latter was caused by a combination of ramping up along the seatback and straightening of the thoracic kyphosis. During the first 100 ms, the volunteers flexed their necks. Thereafter, the volunteers extended their necks. These new data have proven to be useful in validation of rear-impact dummies.

Strain relief from the cerebral ventricles during head impact: experimental studies on natural protection of the brain

Physical models of the parasagittal human skull/brain have been tested to investigate whether the cerebral ventricles provide natural protection of the brain by relieving strain during head rotation. A sophisticated model included anatomical structures, and a semicircular model consisted of a cylinder divided into two semicircles. Silicone gel simulated the brain and was detached from the vessel by a layer of liquid paraffin simulating the cerebrospinal fluid. Both models were run with and without an elliptical inclusion filled with liquid paraffin simulating a cerebral ventricle. The 2D models were exposed to angular acceleration by a pendulum impact causing 7600 rad/s2 peak rotational acceleration with 6 ms pulse duration. After rotating 100 degrees, the models were decelerated during 30 ms. The trajectory of grid markers was analyzed from high-speed video (1000 frames/s). Rigid-body displacement, shear strain and principal strain were determined from the displacement of three-point sets inferior and superior to the ventricle. For the subventricular (inferior) region in the sophisticated model, approximately 40% lower peak strain values were obtained in the model with ventricle than in the one without. Subcortical displacement was reduced by 12%. Corresponding strain reduction in the subcortical (superior) region was approximately 40% following the acceleration and 25% following the deceleration. Similar but less pronounced effects were found for the semicircular model. The lateral ventricles play an important role as strain relievers and provide natural protection against brain injury.

Effects on driving performance of visual field defects: A driving simulator study☆

To elucidate the possible traffic safety risks induced by visual field defects, a method was developed based on a driving simulator. The capacity to detect stimuli of different sizes appearing in 24 different positions on the screen in front of the driver was measured. Two groups of normal subjects and a number of subjects with different visual field defects were studied. In the groups of normals, the median reaction times were fairly homogenous. There was a slight difference between central and peripheral stimuli, which was somewhat larger for the older subjects. Among the subjects with field defects, the individual variations were very dominant. Very few of these showed a capacity to compensate for their deficiency. In order to gain insight into possible compensatory mechanisms of these persons, eye movement recordings were made. The results indicate that the visual search pattern may be of importance in this respect. Some comparisons with respect to detection capacity were also made with one-eyed subjects and with optically generated field restrictions (spectacles and spectacle frames).

THE INFLUENCE OF SEAT-BACK AND HEAD-RESTRAINT PROPERTIES ON THE HEAD-NECK MOTION DURING REAR-IMPACT

The influence of different seat properties on the head-neck motion during a low-velocity rear-end impact was tested using a Hybrid III-dummy fitted with a modified neck (RID-neck). The results show that by modifying the properties of the seat-back and head-restraint it is possible to influence the head-neck kinematics to a great extent. It was possible to virtually eliminate the neck extension motion during a rear-impact. This will hopefully result in a significant decrease in neck injury risk in real world rear-impacts.

Car occupant safety in frontal crashes: a parameter study of vehicle mass, impact speed, and inherent vehicle protection

A new mathematical model was developed to estimate average injury and fatality rates in frontal car-to-car crashes for changes in vehicle fleet mass, impact speed distribution, and inherent vehicle protection. The estimates were calculated from injury fatality risk data, delta-V distribution and collision probability of two vehicles, where delta V-depends on impact speed and mass of the colliding vehicles. The impact speed distribution was assumed to be unaffected by a change in fleet mass distribution. The results showed that safety in frontal crashes would improve 27-35% by a 10% increase in fatality risk parameters, which reflected substantial improvement in inherent vehicle protection. A 40% safety improvement was attained by a 10% impact speed reduction. Consequences of vehicle fleet mass were not as strong, but depended on the average mass ratio of the fleet. A reduction in mass range would be the most beneficial, while a uniform mass reduction of 20% would increase the fatality rate by 5.4%. The model estimates trends in traffic safety and may help to identify priorities in active and passive safety.

A Study of Influences of Vehicle Speed and Front Structure on Pedestrian Impact Responses Using Mathematical Models

A validated pedestrian multibody model was used to investigate the influences of impact speed and vehicle front structure on the pedestrian dynamic responses in vehicle collisions. To predict the injury risks of pedestrians at different impact speeds, the injury-related parameters concerning head, chest and lower extremity areas were calculated from mathematical simulations. Four vehicle types including large and compact passenger cars, minivans and light trucks were simulated according to their frequency of involvement in real world accidents. The influences of various vehicle front shape and compliance parameters were analyzed. Based on the results from the parametric study, the possible benefits from speed control in urban area were assessed, and a feasible speed limit was proposed to reduce the risks of pedestrian injuries. Moreover, the possible countermeasures on basis of vehicle front design to mitigate the injury severity of the pedestrians were discussed.

BIOMECHANICS OF BRAIN AND SPINAL-CORD INJURY: ANALYSIS OF NEUROPATHOLOGIC AND NEUROPHYSIOLOGIC EXPERIMENTS

The determination of brain and spinal cord injury mechanisms has perplexed medical and biomechanical scientists for a very long time. This paper analyzes some neural impact tests on brain and spinal cord, by using 46 brain and 48 spinal cord impact experiments. These tests provide a database on brain and spinal cord injury, and the results indicate that strain is not a sufficient parameter of neural injury risk, and that the product of strain rate and strain provides a key biomechanical parameter for brain and spinal cord injury.

Ultimate strength of the lumbar spine in flexion—An in vitro study

The ultimate strength in flexion of 16 lumbar functional spinal units (FSU) was determined. The specimens were exposed to a combined static load of bending and shearing in the sagittal plane until overt rupture occurred (simulated flexion-distraction injuries). The biomechanical response of the FSU was measured with a force and moment platform. Mechanical displacement gauges were used to measure vertical displacements (flexion angulation) of the specimens. Photographs were taken after each loading step for determination of horizontal displacements and the centre of rotation. The lumbar FSU could resist a combination of bending moment and shear force of 156 Nm and 620 N respectively, before complete disruption occurred. The tension force acting on the posterior structures was 2.8 kN. The flexion angulation just before failure was 20 degrees and the anterior horizontal displacement between the upper and lower vertebrae was 9 mm. The centre of rotation was located in the posterior part of the lower vertebral body. The bone mineral content in the vertebrae appeared to be a good predictor of ultimate strength of the lumbar FSU. Knowledge of the biomechanical response of the lumbar spine under different static traumatic loads is a first step to better understand the injury mechanisms of the spine in traffic accidents.