Quantitative computed tomography-based finite element analysis (QCT/FEA) is a promising tool to predict femoral properties. One of the modeling parameters required as input for QCT/FEA is the elastic modulus, which varies with the location-dependent bone mineral density (ash density). The aim of this study was to develop optimized equations for the femoral elastic modulus. An inverse QCT/FEA method was employed, using an optimization process to minimize the error between the predicted femoral stiffness values and experimental values. We determined optimal coefficients of an elastic modulus equation that was a function of ash density only, and also optimal coefficients for several other equations that included along with ash density combinations of the variables sex and age. All of the optimized models were found to be more accurate than models from the literature. It was found that the addition of the variables sex and age to ash density made very minor improvements in stiffness predictions compared to the model with ash density alone. Even though the addition of age did not remarkably improve the statistical metrics, the effect of age was reflected in the elastic modulus equations as a decline of about 9% over a 60year interval.
In this study, a novel, bio-based polyol was used in the formulation of a polyurethane (PU) matrix for a composite material where fl ax fi ber was used as the reinforcement. The viscoelastic properties of the matrix and fl ax fi ber were determined by a linear viscoelastic model through experimentation and the results were used as input for the material properties in the computational model. A fi nite element micromechanical model of a representative volume element (RVE) in terms of repeating unit cells (RUC) was developed to predict the mechanical properties of composites. Six loading conditions were applied on the RUC to predict and defi ne the viscoelastic behavior of the composite unit cell. The time-history of averaged response was determined in terms of stress and strains. The results of this study suggest that applying the overall rate-dependent behavior of fl ax fi ber to the micromechanical model leads to a good agreement between the micromechanical modeling and experimental results. The modeling approach is effi cient and accurate as long as the periodicity in the composite rules. This modeling approach can be used as a powerful algorithm in determining linear and nonlinear properties in material mechanics analysis and characterization.
We fractured 100 cadaveric femora with different areal bone mineral density (aBMD) (normal, osteopenic, and osteoporotic) in a fall on the hip loading configuration using a mechanical testing system. Two single-axis and one multi-axis load cells measured the forces and moments in the femoral head, shaft, and the greater trochanter. Two high-speed video cameras recorded the events leading to fracture from the anterior and posterior directions.Force-displacement curve of a typical experiment showed a linear elastic region followed by post-yielding associated with sinking of the superior neck region into greater trochanter (73 of the tested femora). Fatal crack initiated in tension on the inferior region of the neck or medial shaft. Femoral strength (peak trochanteric force) exhibited strong correlation with aBMD. One-way analysis of variance showed significantly lower values for means of fracture forces and moments of osteoporotic femora compared to those of osteopenic and normal femora. Fracture forces showed very weak correlation with the femoral geometric parameters measured from CT scans. Using post-fracture CT scans and with the help of an orthopedist, the femoral fractures were classified into subcapital, transcervical, intertrochanteric and pertrochanteric. Oneway analysis of variance indicated that femora with intertrocanteric fracture had significantly lower neck aBMD than femora with pertrochanteric and transcervical fractures.
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