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Structural Geometry (structural + geometry)
Selected AbstractsEffects of Current and Discontinued Estrogen Replacement Therapy on Hip Structural Geometry: The Study of Osteoporotic Fractures,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 11 2001Thomas J. Beck Abstract It is assumed that estrogen influences bone strength and risk of fractures by affecting bone mineral density (BMD). However, estrogen may influence the mechanical strength of bones by altering the structural geometry in ways that may not be apparent in the density. Repeated dual energy X-ray absorptiometry (DXA) hip scan data were analyzed for bone density and structural geometry in elderly women participating in the Study of Osteoporotic Fractures (SOF). Scans were studied with a hip structural analysis program for the effects of estrogen replacement therapy (ERT) on BMD and structural geometry. Of the 3964 women with ERT-use data, 588 used ERT at both the start and end of the ,3.5-year study, 1203 had past use which was discontinued by clinic visit 4, and 2163 women had never used ERT. All groups lost BMD at the femoral neck, but the reduced BMD among users of ERT was entirely due to subperiosteal expansion and not bone loss, whereas both bone loss and expansion occurred in past or nonusers. BMD increased 0.8%/year at the femoral shaft among ERT users but decreased 0.8%/year among nonusers. Section moduli increased at both the neck and shaft among ERT users but remained unchanged in past and nonusers. Current, but not past, use of estrogen therapy in elderly women seems to increase mechanical strength of the proximal femur by improving its geometric properties. These effects are not evident from changes in femoral neck BMD. [source] Discrete-element modelling of detachment foldingBASIN RESEARCH, Issue 4 2005Stuart Hardy ABSTRACT A two-dimensional, discrete-element modelling technique is used to investigate the initiation and growth of detachment folds in sedimentary rocks above a weak décollement level. The model depicts the sedimentary rocks as an assemblage of spheres that obey Newton's equations of motion and that interact with elastic forces under the influence of gravity. Faulting or fracturing between neighbouring elements is represented by a transition from repulsive,attractive forces to solely repulsive forces. The sedimentary sequence is mechanically heterogeneous, consisting of intercalated layers of markedly different strengths and thicknesses. The interlayering of weak and strong layers within the sedimentary rocks promotes the localization of flexural flow deformation within the weak layers. Even with simple displacement boundary conditions, and straightforward interlayering of weak and strong layers, the structural geometries that develop are complex, with a combination of box, lift-off and disharmonic detachment fold styles forming above the décollement. In detail, it is found that the modelled folds grow by both limb rotation and limb lengthening. The combination of these two mechanisms results in uplift patterns above the folds that are difficult, or misleading, to interpret in terms of simple kinematic models. Comparison of modelling results with natural examples and with kinematic models highlights the complexities of structural interpretation in such settings. [source] Effects of non-proportional loading paths on the orientation of fatigue crack pathFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2005L. REIS ABSTRACT Fatigue crack path prediction and crack arrest are very important for structural safety. In real engineering structures, there are many factors influencing the fatigue crack paths, such as the material type (microstructure), structural geometry and loading path, etc. In this paper, both experimental and numerical methods are applied to study the effects of loading path on crack orientations. Experiments were conducted on a biaxial testing machine, using specimens made of two steels: 42CrMo4 and CK45 (equivalent to AISI 1045), with six different biaxial loading paths. Fractographical analyses of the plane of the stage I crack propagation were carried out and the crack orientations were measured using optical microscopy. The multiaxial fatigue models, such as the critical plane models and also the energy-based critical plane models, were applied for predicting the orientation of the critical plane. Comparisons of the predicted orientation of the damage plane with the experimental observations show that the shear-based multiaxial fatigue models provide good predictions for stage I crack growth for the ductile materials studied in this paper. [source] Plastic Dissipation Mechanisms in Periodic Microframe-Structured PolymersADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Lifeng Wang Abstract Novel lightweight micro- and nanostructured materials are being used as constituents in hierarchically structured composites for providing high stiffness, high strength, and energy absorbing capability at low weight. Three dimensional SU-8 periodic microframe materials with submicrometer elements exhibit unusual large plastic deformations. Here, the plastic dissipation and mechanical response of polymeric microframe structures is investigated using micromechanical modeling of large deformations. Finite element analysis shows that multiple deformation domains initiate, stabilize, and then spread plasticity through the structure; simulated deformation mechanisms and deformation progression are found to be in excellent agreement with experimental observation. Furthermore, the geometry can be used to tailor aspects of 3D behavior such as effective lateral contraction ratios (elastic and plastic) during tensile loading as well as negative normal stress during simple shear deformation. The effects of structural geometry on mechanical response are also studied to tailor and optimize mechanical performance at a given density. These quantitative investigations enable simulation-based design of optimal lightweight material microstructures for dissipating energy. [source] Effects of Current and Discontinued Estrogen Replacement Therapy on Hip Structural Geometry: The Study of Osteoporotic Fractures,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 11 2001Thomas J. Beck Abstract It is assumed that estrogen influences bone strength and risk of fractures by affecting bone mineral density (BMD). However, estrogen may influence the mechanical strength of bones by altering the structural geometry in ways that may not be apparent in the density. Repeated dual energy X-ray absorptiometry (DXA) hip scan data were analyzed for bone density and structural geometry in elderly women participating in the Study of Osteoporotic Fractures (SOF). Scans were studied with a hip structural analysis program for the effects of estrogen replacement therapy (ERT) on BMD and structural geometry. Of the 3964 women with ERT-use data, 588 used ERT at both the start and end of the ,3.5-year study, 1203 had past use which was discontinued by clinic visit 4, and 2163 women had never used ERT. All groups lost BMD at the femoral neck, but the reduced BMD among users of ERT was entirely due to subperiosteal expansion and not bone loss, whereas both bone loss and expansion occurred in past or nonusers. BMD increased 0.8%/year at the femoral shaft among ERT users but decreased 0.8%/year among nonusers. Section moduli increased at both the neck and shaft among ERT users but remained unchanged in past and nonusers. Current, but not past, use of estrogen therapy in elderly women seems to increase mechanical strength of the proximal femur by improving its geometric properties. These effects are not evident from changes in femoral neck BMD. [source] | ||||||||||