Showing papers by "Jason R. Kerrigan published in 2014"

Indentation response of human patella with elastic modulus correlation to localized fractal dimension and bone mineral density.

Abstract: The goal of this study was to determine material properties for the anterior cortex and subcortical regions of human patellae and relate those properties to mineral density and fractal dimension of the bone. Ten human patellae were obtained from eight fresh frozen human cadavers and subjected to anteriorly-directed spherical indentation-relaxation experiments using two different sized indenters to two different indentation depths. Response data were fit to a three-mode viscoelastic model obtained through elastic-viscoelastic correspondence of the Hertzian contact relation for spherical indentation. A location-specific effective bone density measurement that more heavily weighted bone material close to the indentation site (by von Mises stress distribution) was determined from micro-computed tomography (38µm resolution) data captured for each specimen. The same imagery data were used to compute location specific fractal dimension estimates for each indentation site. Individual and averaged patella material models verified the hypothesis that when the larger indenter and greater indentation depth is used to engage the surface and deeper (trabecular) bone, the bone exhibits a more compliant response than when only the surface (cortical) bone was engaged (instantaneous elastic modulus was 325MPa vs. 207MPa, p<0.05). Effective bone mineral density was shown to be a significant predictor of the elastic modulus for both small and large indentation types (p<0.05) despite relatively low correlations. Exponential regressions of fractal dimension on elastic modulus showed significant relationships with high correlation for both the small (R(2)=0.93) and large (R(2)=0.97) indentations.

Occupant Kinematics in Laboratory Rollover Tests: PMHS Response.

Abstract: The objective of the current study was to characterize the whole-body kinematic response of restrained PMHS in controlled laboratory rollover tests. A dynamic rollover test system (DRoTS) and a parametric vehicle buck were used to conduct 36 rollover tests on four adult male PMHS with varied test conditions to study occupant kinematics during the rollover event. The DRoTS was used to drop/catch and rotate the test buck, which replicated the occupant compartment of a typical mid-sized SUV, around its center of gravity without roof-to-ground contact. The studied test conditions included a quasi-static inversion (4 tests), an inverted drop and catch that produced a 3 g vertical deceleration (4 tests), a pure dynamic roll at 360 degrees/second (11 tests), and a roll with a superimposed drop and catch produced vertical deceleration (17 tests). Each PMHS was restrained with a three-point belt and was tested in both leading-side and trailing-side front-row seating positions. Whole-body kinematics were measured using a 3D motion capture system that quantified occupant displacement relative to the vehicle buck for the X-axis (longitudinal), Y-axis (lateral), and Z-axis (vertical) directions. Additionally the spine was divided into five segments to describe intrasegmental kinematics of the spine, including segment rotations as well as spinal extension and compression. The reported data represent the most complete set of kinematic response targets for a restrained occupant in a variety of dynamic rollover conditions, and are immediately useful for efforts to evaluate and improve existing ATDs and computational models for use in the rollover crash environment.

Occupant Kinematics in Laboratory Rollover Tests: ATD Response and Biofidelity

Abstract: Rollover crashes are a serious public health problem in United States, with one third of traffic fatalities occurring in crashes where rollover occurred. While it has been shown that occupant kinematics affect the injury risk in rollover crashes, no anthropomorphic test device (ATD) has yet demonstrated kinematic biofidelity in rollover crashes. Therefore, the primary goal of this study was to assess the kinematic response biofidelity of six ATDs (Hybrid III, Hybrid III Pedestrian, Hybrid III with Pedestrian Pelvis, WorldSID, Polar II and THOR) by comparing them to post mortem human surrogate (PMHS) kinematic response targets published concurrently; and the secondary goal was to evaluate and compare the kinematic response differences among these ATDs. Trajectories (head, T1, T4, T10, L1 and sacrum), spinal segment (head-to-T1, T1-to-T4, T4-T10, T10-L1, and L1-to-sacrum) rotations relative to the rollover buck, and spinal segment extension/compression were calculated from the collected kinematics data from an optical motion tracking system. Response differences among the ATDs were observed mainly due to the different lateral bending stiffness of the spine from their varied architecture, while the additional thoracic joint in Polar II and THOR did not seem to provide more flexion/extension compliance than the other ATDs. In addition, the ATD response data were compared to PMHS response corridors developed from similar tests for assessing ATD biofidelity. All of the ATDs, generally, drifted outboard and upward during the tests similar to the PMHS. However, accompanied with this upward and outward motion, the ATD head and upper torso pitched forward (~10 degrees) while the PMHS' head and upper torso pitching rearward (~10 to ~15 degrees), due to the absence of flexion/extension compliance in the ATD spine. The differences in these pitch motions resulted in a difference of 130 mm to 160 mm in the longitudinal position of the head at 195 degrees of roll angle. Finally, substantially less lateral spinal bending was also observed in the ATDs compared to the PMHS. The results of the current study suggests there is greater upper spine flexion/extension, and lateral bending stiffness in all of the ATDs in comparison to the PMHS, and provided information for improvement of ATD biofidelity in future for rollover crashes.

Pedestrian Protection Overview

Abstract: The World Bank estimates that between 41% and 75% of all road traffic fatalities worldwide are pedestrians and that nearly 35% of all pedestrian fatalities are children. Three factors are important to fully understand a vehicle pedestrian collision. The environment, the vehicle and the pedestrian contribute to accidents and determine their outcome. Further, the accident can be divided into three parts on a time-scale; pre-, in- and post-crash. In each of these time events, the environment, vehicle and road user are more or less influential factors important to consider. Our aim in this chapter is to describe the fundaments of vehicle-pedestrian collisions, covering aspects like influencing factors of the collision, the vehicle structures responsible for pedestrian injuries and active- passive countermeasures from the injury biomechanics point of view. Keywords: pedestrian; traffic; injury; vehicle; accident

Influence of Driving Attributes on the Risk of Rollover and the Touchdown Conditions of a Sedan in Case of Corrective Maneuvers

Abstract: The goal of this study was to assess the sensitivity of (corrective) driving inputs on the risk of rollover of a sedan and the resulting touchdown conditions in case of soil trip rollover crashes. The driving inputs include the initial steer that leads to the departure from the roadway, the corrective steer in an attempt to gain back the control and the initial travel speed of the vehicle. Latin hypercube sampling was used to uniformly sample various combinations of driving inputs and corresponding simulations were run using a multibody model of a sedan validated for aggressive driving maneuvers and quasi‐static suspension tests. Logistic regression model was fit to predict the probability of the binary outcome of rollover with the driving input as predictor variables. The model involving interaction between the predictor variables had a better predictive capability than the main effects model. The initial travel speed and the first steer angle were the most influential in affecting the risk of rollover of the vehicle. The touchdown parameters varied depending on the peak lateral acceleration at trip and the trip location from the road. The peak lateral acceleration and trip location in turn varied depending on the driving inputs. The study established a methodology to estimate the sensitivity of the risk of rollover of a sedan and distribution of corresponding touchdown parameters to driving inputs in case of corrective maneuvers.