Jason Stammen

MADYMO modeling of the IHRA head-form impactor

The International Harmonization Research Activities Pedestrian Safety Working Group (IHRA PSWG) has proposed design requirements for two head-forms for vehicle hood (bonnet) impact testing. This paper discusses the development of MADYMO models representing the IHRA adult and child head-forms, validation of the models against laboratory drop tests, and assessment of the effect of IHRA geometric and mass constraints on the model response by conducting a parameter sensitivity analysis. The models consist of a multibody rigid sphere covered with a finite element modeled vinyl skin. The most important part in developing the MADYMO head-form models was to experimentally determine the material properties of the energy-absorbing portion of the head-form (vinyl skin) and incorporate these properties into MADYMO using a suitable material model. Three material models (linear isotropic, viscoelastic, hyperelastic) were examined. It was determined that the vinyl material behaved as a hyperelastic material when comparing MADYMO simulation results with laboratory certification test results. The MADYMO model of the IHRA adult head-form was validated with laboratory head-form drop tests from four different heights. Parameter sensitivity analysis was conducted by varying the head-form parameters within their respective IHRA tolerances. Because of physical limitations of locating accelerometers near the head-form center of gravity, this analysis was much more easily accomplished using a MADYMO model. It was found that the peak acceleration was well within the IHRA-specified range for both the adult and child head-forms when the mass and geometric parameters were varied within the IHRA tolerances.

Assessment of the Simulated Injury Monitor (SIMon) in Analyzing Head Injuries in Pedestrian Crashes

Objectives Examination of head injuries in the Pedestrian Crash Data Study (PCDS) indicates that many pedestrian head injuries are induced by a combination of head translation and rotation. The Simulated Injury Monitor (SIMon) is a computer algorithm that calculates both translational and rotational motion parameters relatable head injury. The objective of this study is to examine how effectively HIC and three SIMon correlates predict the presence of either their associated head injury or any serious head injury in pedestrian collisions. Methods Ten reconstructions of actual pedestrian crashes documented by the PCDS were conducted using a combination of MADYMO simulations and experimental headform impacts. Linear accelerations of the head corresponding to a nine-accelerometer array were calculated within the MADYMO models head simulation. Injury risk calculated by SIMon (relative motion damage measure RMDM, cumulative strain damage measure CSDM, dilatation damage measure DDM) and HIC were compared to the presence or absence of either their associated injury or any serious head injury in each case using receiver operating characteristic (ROC) analysis. Results HIC (AUC = 0.91) and CSDM (AUC = 0.89) were both very effective at predicting their associated injury types (AIS 3+ skull fracture and DAI, respectively). DDM (AUC = 0.68) and RMDM (AUC = 0.56) were not as effective in predicting their respective injury types (contusion and acute subdural hematoma, respectively). However, HIC (AUC = 0.67) and CSDM (AUC = 0.62) were less effective than RMDM and DDM (AUC = 0.86 for both) for predicting any AIS 3+ head injury type. Conclusions For the ten cases evaluated in this study, each correlate was strong at predicting either its associated injury or any head injury. However, there was no single injury correlate that performed effectively in predicting both its associated injury and any AIS 3+ head injury. Because pedestrian head injuries are often associated with a combination of linear and rotational loading, supplementing HIC with correlates that capture other loading patterns could lead to more robust head injury assessment. Language: en

Development of a fluid-filled catheter system for dynamic pressure measurement in soft-tissue trauma

Abstract In victims of motor vehicle crashes, rapid increases in internal fluid pressure may play a role in causing injury to solid abdominal organs such as the liver. The objective of this study was to develop a practical and cost-effective technique to measure impact-induced pressure changes within physiologically pressurised porcine liver specimens. This technique employs instrumentation that is remote from the impacted organ and could be applied to fluid-filled abdominal components of crash-test dummies. A fluid-filled catheter (FFC) pressure-measurement device was modelled as an under-damped second-order linear system. A transfer function was defined to correct the characteristic distortion of pressure waveforms in the FFC pressure-measurement system. Linear regression analysis was employed to evaluate the accuracy of transfer function-corrected pressure measurements in impact tests of a simplified model system and of physiologically pressurised ex vivo porcine livers. Results demonstrated a very high correlation between transfer function-corrected FFC pressure measurements and reference pressures in model system impacts (R = 0.95–0.97) and in ex vivo porcine liver impacts (R = 0.91–0.96). A near one-to-one relationship between the magnitudes of the corrected FFC pressures and the reference pressures was demonstrated by calculating the slopes of the regression equations (0.821 ± 0.016 to 1.085 ± 0.005, p < 0.05). The FFC technique has the potential to be a valuable tool in future studies requiring dynamic measurements of extremely high intravascular pressures associated with impact loading of soft tissues such as the liver. Information about the relationship between pressure and injury in solid abdominal organs could be applied to improve the design of crash-test dummies.