Departamento de Mecánica de Medios Continuos y Teoría de Estructuras
http://hdl.handle.net/10016/7174
2019-10-15T09:32:58ZA Finite Element Analysis of the Fatigue Behavior and Risk of Failure of Immediate Provisional Implants
http://hdl.handle.net/10016/28547
A Finite Element Analysis of the Fatigue Behavior and Risk of Failure of Immediate Provisional Implants
Prados Privado, Maria; Ivorra, Carlos; Martínez Martínez, Carlos; Alexandre Gehrke, Sergio; Calvo Guirado, José Luis; Prados Frutos, Juan Carlos
Background: Temporary dental implants are used to support provisional prostheses. The goal of this study was to obtain the stress&-number (S&-N) curves of cycles of five temporary dental implants employing finite element methods. Additionally, a probabilistic analysis was carried out to obtain the failure probability of each dental implant. Methods: To obtain these curves, first the maximum value of the fracture load was obtained by simulation of a compression test. Subsequently, the fatigue life was simulated by varying each of the loads from the maximum value to a minimum value (10% of the maximum value), and the minimum number of cycles that it should support was calculated. Results: The fatigue limit of titanium in these implants was around 200 MPa with the maximum number of cycles between 64,976 and 256,830. The maximum compression load was between 100 and 80 N. Regarding the probability of failure, all implants were expected to behave similarly. Conclusions: This study of finite elements provided the values of maximum load supported by each of the implants, and the relationship between the stress in the implant and the number of cycles that it could support with a probability of failure. An international standard on how to perform fatigue studies in temporary dental implants was deemed necessary.
This article belongs to the Special Issue Titanium in Medical and Dental Applications
2019-05-08T00:00:00ZDynamic spherical cavity expansion in Gurson materials with uniform and non-uniform distributions of porosity
http://hdl.handle.net/10016/28514
Dynamic spherical cavity expansion in Gurson materials with uniform and non-uniform distributions of porosity
Santos, T. dos; N Souglo, Komi Espoir; Rodríguez-Martínez, José A.
This paper investigates both theoretically and using finite elements the elastoplastic field induced by a pressurized spherical cavity expanding dynamically in an infinite medium modelled using the Gurson&-Tvergaard&-Needleman porous plasticity approach. The theoretical model, which assumes that the porosity is uniformly distributed in the material and the cavitation fields are self-similar, incorporates artificial viscous stresses into the original formulation of Cohen and Durban (2013b) to capture the shock waves that emerge at high cavitation velocities. The finite element calculations, performed in ABAQUS/Explicit (2013) using the Arbitrary Lagrangian Eulerian adaptive meshing available in the code, simulate the cavity expansion process in materials with uniform and non-uniform distributions of porosity. The finite element results show that the distribution of porosity has small influence on the cavitation velocity, as well as on the location of the shock wave, which are primarily determined by the cavity pressure and the average material properties. In contrast, it is shown that the intensity of the shock wave, evaluated based on the maximum value of the plastic strain rate within the shock, depends on the local material porosity. The ability of the theoretical model to reproduce the numerical results obtained for the various distributions of porosity used in this work is exposed and discussed.
2019-07-01T00:00:00ZEffects of plastic anisotropy on localization in orthotropic materials: new explicit expressions for the orientation of localization bands in flat specimens subjected to uniaxial tension
http://hdl.handle.net/10016/28512
Effects of plastic anisotropy on localization in orthotropic materials: new explicit expressions for the orientation of localization bands in flat specimens subjected to uniaxial tension
Cazacu, Oana; Rodríguez-Martínez, José A.
This paper presents a theoretical investigation on the inception of plastic localization bands in specimens taken from orthotropic metallic sheets, and subjected to uniaxial tension. For the first time, it is shown that the orientations of the localization bands can be obtained directly from experimental measurements of the uniaxial tensile flow stresses and Lankford coefficients (r-values) of the metallic sheet. In contrast to isotropic materials, it is shown that localization bands equally inclined with respect to the loading axis develop only for the samples of orientations theta* corresponding to the extrema of the uniaxial tensile flow stresses in the plane of the sheet. Moreover, the expression for the bands angle depends solely on the Lankford coefficient r(theta*). For specimen orientations other than theta*, the two localization bands have different inclinations with respect to the loading axis. If for a given specimen orientation experimental values are not available, we show that the orientations of the localization bands can be obtained using the theoretical r-values and uniaxial flow stresses calculated using any orthotropic plastic potential. As an example, explicit expressions for the band angles obtained using Hill (1948) and Cazacu (2018) orthotropic plastic potentials are provided, and further applied to two textured sheets: a 2090-T3 Al alloy, and a 99% Al alloy. The results obtained are compared, and the sensitivity of the orientation of the localization bands to the constitutive model used for description of plastic anisotropy is brought to light.
2019-05-01T00:00:00ZA comparative study of the dynamic fragmentation of non-linear elastic and elasto-plastic rings: the roles of stored elastic energy and plastic dissipation
http://hdl.handle.net/10016/28509
A comparative study of the dynamic fragmentation of non-linear elastic and elasto-plastic rings: the roles of stored elastic energy and plastic dissipation
Vaz-Romero Santero, Álvaro; Mercier, Sebastien; Rodríguez-Martínez, José A.; Molinari, Alain Louis
We develop a comparative analysis of the processes of dynamic necking and fragmentation in elasto-plastic and hyperelastic ductile rings subjected to rapid radial expansion. For that purpose, finite element simulations have been carried out using the commercial code ABAQUS/Explicit. Expanding velocities which range between 25 and 600 m/s have been investigated. The elasto-plastic material and the hyperelastic material are modelled with constitutive equations which provide nearly the same stress-strain response during monotonic uniaxial tensile loading, and fracture is assumed to occur at the same level of deformation energy. The computations have revealed that, while the number of necks nucleated in the elasto-plastic and hyperelastic rings is similar, the mechanisms which control their development are significantly different. In the elasto-plastic rings several necks are arrested due to the stress waves which travel the specimen after the localization process has started, and thus the number of fractures in the ring is significantly lower than the number of incepted necks. On the contrary, these stress waves do not stop the development of any neck in the hyperelastic rings. The elastic energy released from the sections of the ring which are unloading during the localization process fuels the development of the necks. Hence, for the whole range of investigated velocities, the proportion of necks that develop into fracture sites is much greater for the hyperelastic rings than for the elasto-plastic ones. The comparison between the numerical results obtained for both materials brings to light the roles of elastic unloading and plastic dissipation in multiple necking and fragmentation processes.
2019-05-01T00:00:00Z