Browsing by Subject "Finite Element Modeling"

Now showing 1 - 3 of 3
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    The Mechanical Environment of the Supraspinatus During Arm Elevation: A Three-Dimensional Finite Element Analysis
    (2019-05) Spracklin, Anna
    Rotator cuff pathology is extremely common, and can significantly reduce one’s function in activities of daily living. The mechanisms of rotator cuff pathology are not well understood. This study aims to understand how supraspinatus stress and strain vary across a range of scapular plane elevation. Secondarily, to understand how imposing humeral head translations in the superior and inferior directions (±2 and ±5 mm) affect tendon mechanics. It was found that both stress and strain increased across the range of arm elevation. The posterior portion of the tendon underwent the greatest amount of strain, while the anterior portion near the footprint experienced the greatest levels of stress. With superior humeral head translation, the maximum stress and strain decreased, while inferior translation caused stress and strain increased. Further study is required to validate the finite element model. Alterations to the model may be done in order to address more clinical questions, such as how varying anatomy and subject specific kinematics affect rotator cuff mechanics.
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    Modeling and monitoring the long-term behavior of post-tensioned concrete bridges
    (2014-06) Hedegaard, Brock Daniel
    The time-dependent and temperature-dependent behavior of post-tensioned concrete bridges were investigated through a case study of the St. Anthony Falls Bridge, consisting of laboratory testing of concrete time-dependent behaviors (i.e., creep and shrinkage), examination of data from the in situ instrumented bridge, and time-dependent finite element models. Laboratory results for creep and shrinkage were measured for 3.5 years after casting, and the data were best predicted by the 1978 CEB/FIP Model Code provisions. To compare the in situ readings to constant-temperature finite element models, the time-dependent behavior was extracted from the measurements using linear regression. The creep and shrinkage rates of the in situ bridge were found to depend on temperature. An adjusted age using the Arrhenius equation was used to account for the interactions between temperature and time-dependent behavior in the measured data. Results from the time-dependent finite element models incorporating the full construction sequence revealed that the 1990 CEB/FIP Model Code and ACI-209 models best predicted the in situ behavior. Finite element analysis also revealed that problems associated with excessive deflections or development of tension over the lifetime of the bridge would be unlikely. The interactions between temperature and time-dependent behavior were further investigated using a simplified finite element model, which indicated that vertical deflections and stresses can be affected by the cyclic application of thermal gradients. The findings from this study were used to develop an anomaly detection routine for the linear potentiometer data, which was successfully used to identify short-term and long-term perturbations in the data.
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    On the representative volume element of asphalt concrete with applications to low temperature.
    (2009-07) Velasquez, Raul Andres
    The representative volume element (RVE) of asphalt concrete with applications to low temperatures is investigated based on statistical analysis and modeling of an extensive set of experiments. The experimental part consisted of three-point bending creep tests performed on beams of different sizes: 6.25 × 12.5 × 100 mm (1x), 12.5 × 25 × 200 mm (2x), and 18.75 × 37.5 × 300 mm (3x). The creep stiffness of ten asphalt mixtures was determined at three low pavement service temperature levels. The experimental results showed that a representative creep stiffness of asphalt concrete can be obtained from testing at least three replicates of the thin (1x) mixture beams, even though the mixtures contained aggregate sizes that are larger than the smallest dimension of the beam. In the theoretical part, asphalt concrete specimens of different sizes were analyzed based on digital image analysis, micromechanics, and finite element modeling. The volumetric fractions and particle size distributions of the different specimen sizes were estimated from their binary images after digital processing. The volumetric fraction and the average size distribution of aggregates for the 3x, 2x, and 1x specimens were found to be very similar and based on these mixture properties, RVE sizes were proposed. Detailed information on the internal structure of asphalt concrete was investigated by estimating the spatial correlation functions of specimens of different sizes. No large differences were observed between the correlation functions of the specimens of different sizes. Micromechanical models were used to investigate the influence of the specimen size on the relaxation modulus of asphalt concrete. The empirical model predicted fairly well the relaxation modulus. However, the higher order models were poor predictors of this parameter due to the high stiffness contrast of the phases. Finally, the results from two-dimensional finite element simulations of tension tests were used to suggest minimum sizes for the RVE of asphalt concrete for low temperature applications.