Finite element (FE) models of long bones constructed from computed-tomography (CT) data are emerging as an invaluable tool in the field of bone biomechanics. However, the performance of such FE models is highly dependent on the accurate capture of geometry and appropriate assignment of material properties. In this study, a combined numerical-experimental study is performed comparing FE-predicted surface strains with strain-gauge measurements. Thirty-six major, cadaveric, long bones (humerus, radius, femur and tibia), which cover a wide range of bone sizes, were tested under three-point bending and torsion. The FE models were constructed from trans-axial volumetric CT scans, and the segmented bone images were corrected for partial-volume effects. The material properties (Young's modulus for cortex, density-modulus relationship for trabecular bone and Poisson's ratio) were calibrated by minimizing the error between experiments and simulations among all bones. The R(2) values of the measured strains versus load under three-point bending and torsion were 0.96-0.99 and 0.61-0.99, respectively, for all bones in our dataset. The errors of the calculated FE strains in comparison to those measured using strain gauges in the mechanical tests ranged from -6% to 7% under bending and from -37% to 19% under torsion. The observation of comparatively low errors and high correlations between the FE-predicted strains and the experimental strains, across the various types of bones and loading conditions (bending and torsion), validates our approach to bone segmentation and our choice of material properties.

Revolutionary developments in the way aircraft are managed and maintained while in service are needed to enable the U.S. Air Force to reduce its maintenance burden and increase aircraft availability while still ensuring airworthiness and safety. The Airframe Digital Twin (ADT) is envisioned to be an ultra-realistic, cradle-to-grave computer model of an aircraft structure that is used to assess the aircraft's ability to meet mission requirements. The ADT will virtually fly each flight that the physical aircraft flies in order to determine loading and subsequent damage. This paper presents results of a study to assess the current state of the art of performing such a virtual flight. A simplistic ADT was "flown" through a Touch-and-Go practice using the flight parameters recorded during the flight. Technical gaps preventing the full realization of the ADT vision were identified along with alternative approaches that are possible with current technology. Nomenclatureg's g = gravitational acceleration constant, ft/sec 2 p = roll rate, rad/sec q = pitch rate, rad/sec r = yaw rate, rad/sec u = velocity in the x-direction, ft/sec v = velocity in the y-direction, ft/sec w = velocity in the z-direction, ft/sec φ = roll Euler angle θ = pitch Euler angle ψ = yaw Euler angle ω i = angular velocity about the i-axis, rad/sec ̇ = derivative of x with respect to time

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