Access Type

Open Access Dissertation

Date of Award

January 2017

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Biomedical Engineering

First Advisor

King H. Yang

Abstract

Finite element (FE) model is a useful tool frequently used for investigating the injury mechanisms and designing protection countermeasures. At present, no 10 years old (YO) pedestrian FE model has been developed from appropriate anthropometries and validated against limitedly available impact response data. A 10 YO child FE pelvis and lower extremities (PLEX) model was established to fill the gap of lacking such models in this age group. The baseline model was validated against available pediatric postmortem human subjects (PMHS) test data and additional scaled adult data, then the PLEX model was integrated to build a whole-body FE model representing a 10 YO pedestrian.

Additional investigations revealed that the immature tissues, growth plates (GPs), should be explicitly modeled because they have different mechanical properties than the surrounding bones. Epidemiological data revealed that GP accounted for a large portion of pediatric fractures. To investigate the GP’s material property for further advancement of the baseline PLEX FE model for simulating impact mechanical responses, a series of tensile and shearing experiments on porcine bone-GP-bone units were carried out. The GPs from the femoral head, distal femur, and proximal tibia of 20-weeks-old piglets were tested, under different strain rates. Randomized block ANOVA was conducted to determine the effects of anatomic region and strain rate on the material properties of GPs. By comparing the porcine experimental data to the limited data obtained from tests on human subjects reported in the literature, an optimal conversion factor was derived to correlate the material properties of 20-week-old piglet GPs and 10 YO child GPs.

A transversely isotropic hyperelastic material model (MAT_92 available in LS-DYNA) with added viscosity was adopted to mimic the GP tissues. After a series of optimization procedures, the material parameter sets needed for MAT_92 were determined to represent the GPs of a 10 YO child. To further explore the GP modeling techniques, a sub-model representing the proximal femur was extracted from the PLEX model. The femoral head GP in the sub-model was modeled using the geometry from CT scans and the material properties from early optimizations. FE simulations of femoral head shearing were conducted on the sub-model to determine other GP modeling settings. In the following technical application, similar GP modeling techniques were implemented to model the GPs at the hip and knee regions to update the baseline PLEX model, and further the whole-body model. An SUV-to-pedestrian impact scenario was simulated using the updated whole-body model, the remarkable influences of the GPs on the stress distributions in the PLEX were quantitatively assessed.

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