1,721,174 research outputs found
A hyperelastic and almost incompressible material model as an approach to intervertebral disc analysis
No full textThe literature contains many references to intervertebral disc analysis using experimental techniques which represent a basis for analytical and numerical approaches. The scatter of experimental results may be one reason for difficulties in interpretation. Apart from analytical approaches, which often seem inadequate to deal with the peculiar complexities of the problem, numerical techniques are reliable and can lead to significant results. In this work, a formulation based on the finite element method is described, adopting a nonlinear model with hyperelastic material configuration. Particular attention is paid to modelling the material constituting the nucleus, involving incompressibility characteristics and avoiding simulation techniques. This approach allows the mechanical behaviour of the real configuration of the disc to be investigated and also provides a reliable analysis of disc degeneration phenomena. The theoretical and operational aspects of the formulation are reported. The results obtained are compared with responses from various numerical and experimental data
Nonlinear interaction phenomena between bone and pin
No full textInteraction phenomena between bone and pin are investigated according to a contact surface strategy and assuming that bone material properties range in an elasto-plastic field. The analysis is performed by adopting a numerical model that considers coupled geometric and material nonlinearities. Particular attention is paid to the theoretical formulation of the contact problem and of the material constitutive law. Results are reported in terms of stress fields in bone material andbone-pin interface and of detachment displacements
A comparative analysis based on different strength criteria for evaluation of risk factor for dental implants
No full textA numerical analysis is developed to study the interaction phenomena between endousseus titanium
dental implants and surrounding jawbone tissue. The interest is focused on the most appropriate
evaluation of the stress state arising in the tissue because of the implant under physiological loading.
The problem is considered with regard to linear elastic response of the one and to short time effect.
Different configurations of bone–implant system are described, using axial–symmetrical and threedimensional
models, by means of finite and geometric element method. The investigation attains to the
stress states induced in bone that lead to a limit condition near the effective failure surface. The
parameter commonly adopted in literature, such as the Von Mises stress, represents an excessive
simplification of problem formulation, leading to an incorrect evaluation of the real failure risk for the
implant, due to the assumption of the isotropic and deviatoric nature of the adopted stress measure.
More suitable criterion can be assumed, such as the Tsai–Wu criterion, to take into account the
anisotropy that characterises the response of bone, as well as the influence of a hydrostatic stress state.
The analysis developed offers a comparison of results by using different criteria, leading to an
evaluation of reliability of the procedure to be followed and addressing also to an evaluation of a risk
factor for the implant investigated
Nonlinear analysis of intervertebral disk under dynamic load.
No full textThis study pertains to the response of intervertebral joint under dynamic axial load. The numerical model represents two vertebral bodies with an interposed disk and uses three-dimensional elements. A transversely isotropic material law is adopted for cortical bone and an isotropic law for cancellous bone. Annulus collagen fibers are modelled using truss elements with no compressive resistance. The disk material is assumed hyperelastic, using a mixed finite element approach, allowing a representation of the disk involving the incompressibility characteristics for the material. The analysis considers finite displacement and strain fields under dynamic load. Intensity, trend and distribution of loads on the vertebral body are deduced from the literature. The problem is investigated with reference to different compressibility levels of disk material related to disk degenerationn phenomena
Ultrasound velocity and attenuation in cancellous bone samples from lumbar vertebra and calcaneus
No full textWe report a study of ultrasound velocity and
broadband ultrasound attenuation (BUA) in human
cancellous bone samples. The influence of density and
microarchitecture on ultrasound propagation in cancellous
bone was examined. A total of 20 samples from
vertebra L1 and 21 from calcanei were studied. The
direction of ultrasound propagation was anteroposterior
in the vertebra and lateromedial in the calcaneus. The
relationships between ultrasonic parameters and density
of bone samples, apparent ash density, trabecular bone
volume (BV/TV) and trabecular thickness (Tb.Th) were
analyzed using a simple linear model and a multiple
regression model. Velocity of ultrasound and BUA were
positively correlated with density and morphometric
parameters, in both vertebra and calcaneus. The best
correlation was found between velocity and bone sample
density in vertebra (r = 0.961, p < 0.0001) and the worst
between velocity and trabecular thickness in calcaneus
(r = 0.632, p = 0.002). The best correlation for BUA was
with BV/TV in vertebra (r = 0.960, p < 0.0001). Using
the stepwise regression procedure, BV/TV only was
selected as significant for BUA and apparent ash density
with Tb.Th for velocity, in both vertebra and in
calcaneus. The possible influence of trabecular configuration
on ultrasonic parameters is discussed, emphasizing
the different slopes of regression lines obtained for
vertebra and calcaneus, sites with different architecture
of trabecular bone
Numerical formulation of intevertebral joint with regard to ageing problems of hard and soft tissue
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