DMMCTE - Artículos de revistas

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Implant Treatment in Atrophic Maxilla by Titanium Hybrid-Plates: A Finite Element Study to Evaluate the Biomechanical Behavior of Plates
(MDPI, 2018-07-02) Prados Privado, Maria; Diederich, Henri; Prados Frutos, Juan Carlos
A severely atrophied maxilla presents serious limitations for rehabilitation with osseointegrated implants. This study evaluated the biomechanical and long-term behavior of titanium hybrid-plates in atrophic maxilla rehabilitation with finite elements and probabilistic methodology. A three-dimensional finite element model based on a real clinical case was built to simulate an entirely edentulous maxilla with four plates. Each plate was deformed to become accustomed to the maxilla's curvature. An axial force of 100 N was applied in the area where the prosthesis was adjusted in each plate. The von Mises stresses were obtained on the plates and principal stresses on maxilla. The difference in stress between the right and left HENGG-1 plates was 3%, while between the two HENGG-2 plates it was 2%, where HENGG means Highly Efficient No Graft Gear. A mean maximum value of 80 MPa in the plates' region was obtained, which is a lower value than bone resorption stress. A probability cumulative function was computed. Mean fatigue life was 1,819,235 cycles. According to the results of this study, it was possible to conclude that this technique based on titanium hybrid-plates can be considered a viable alternative for atrophic maxilla rehabilitation, although more studies are necessary to corroborate the clinical results.
The effect of initial texture on multiple necking formation in polycrystalline thin rings subjected to dynamic expansion
(Elsevier, 2023-06-01) N Souglo, Komi Espoir; Kowalczyk Gajewska, Katarzyna; Marvi Mashhadi, Mohammad; Rodríguez Martínez, Guillermo; European Commission
In this paper, we have investigated, using finite element calculations, the effect of initial texture on the formation of multiple necking patterns in ductile metallic rings subjected to rapid radial expansion. The mechanical behavior of the material has been modeled with the elasto-viscoplastic single crystal constitutive model developed by Marin (2006). The polycrystalline microstructure of the ring has been generated using random Voronoi seeds. Both 5000 grain and 15000 grain aggregates have been investigated, and for each polycrystalline aggregate three different spatial distributions of grains have been considered. The calculations have been performed within a wide range of strain rates varying from to , and the rings have been modeled with four different initial textures: isotropic texture, Goss texture, R Goss texture and Z fiber texture. The finite element results show that: (i) the spatial distribution of grains affects the location of the necks, (ii) the decrease of the grain size delays the formation of the necking pattern and increases the number of necks, (iii) the initial texture affects the number of necks, the location of the necks, and the necking time, (iv) the development of the necks is accompanied by a local increase of the slip activity. This work provides new insights into the effect of crystallographic microstructure on dynamic plastic localization and guidelines to tailor the initial texture in order to delay dynamic necking formation and, thus, to improve the energy absorption capacity of ductile metallic materials at high strain rates.
Evaluation of Fatigue Behavior in Dental Implants from In Vitro Clinical Tests: A Systematic Review
(MDPI, 2018-05-03) Rojo López, Rosa; Prados Privado, Maria; Reinoso, Antonio J.; Prados Frutos, Juan Carlos
In the area of dentistry, there is a wide variety of designs of dental implant and materials, especially titanium, which aims to avoid failures and increase their clinical durability. The purpose of this review was to evaluate fatigue behavior in different connections and implant materials, as well as their loading conditions and response to failure. In vitro tests under normal and dynamic loading conditions evaluating fatigue at implant and abutment connection were included. A search was conducted in PubMed, Scopus, and Science Direct. Data extraction was performed independently by two reviewers. The quality of selected studies was assessed using the Cochrane Handbook proposed by the tool for clinical trials. Nineteen studies were included. Fourteen studies had an unclear risk and five had high risk of bias. Due to the heterogeneity of the data and the evaluation of the quality of the studies, meta-analysis could not be performed. Evidence from this study suggests that both internal and morse taper connections presented a better behavior to failure. However, it is necessary to unify criteria in the methodological design of in vitro studies, following methodological guidelines and establishing conditions that allow the homogenization of designs in ISO (International Organization for Standardization) standards.
Remote monitoring of vibrational information in spider webs
(2018-05-22) Mortimer, B; Soler Presas, Ana; Siviour, Cr; Vollrath, F
Vibration, Spider, Orb web, FEA model, Vibrometry, Communicated by: Sven Thatje Spiders are fascinating model species to study information-acquisition strategies, with the web acting as an extension of the animal"s body. Here, we compare the strategies of two orb-weaving spiders that acquire information through vibrations transmitted and filtered in the web. Whereas Araneus diadematus monitors web vibration directly on the web, Zygiella x-notata uses a signal thread to remotely monitor web vibration from a retreat, which gives added protection. We assess the implications of these two information-acquisition strategies on the quality of vibration information transfer, using laser Doppler vibrometry to measure vibrations of real webs and finite element analysis in computer models of webs. We observed that the signal thread imposed no biologically relevant time penalty for vibration propagation. However, loss of energy (attenuation) was a cost associated with remote monitoring via a signal thread. The findings have implications for the biological use of vibrations by spiders, including the mechanisms to locate and discriminate between vibration sources. We show that orb-weaver spiders are fascinating examples of organisms that modify their physical environment to shape their information-acquisition strategy.
Biomechanical and histological analysis of titanium (machined and treated surface) versus zirconia implant materials: An in vivo animal study
(MDPI, 2019-03-02) Alexandre Gehrke, Sergio; Prados-Frutos, Juan Carlos; Prados-Privado, María; Calvo-Guirado, José Luis; Aramburu Junior, Jaime; Pérez-Diaz, Leticia; Mazón, Patricia; Aragoneses, Juan Manuel; De Aza, Piedad N.
Objectives: The aim of this study was to perform an in vivo histological comparative evaluation of bone formation around titanium (machined and treated surface) and zirconia implants. For the present study were used 50 commercially pure titanium implants grade IV, being that 25 implants with a machined surface (TiM group), 25 implants with a treated surface (TiT group) and, 25 implants were manufactured in pure zirconia (Zr group). The implants (n = 20 per group) were installed in the tibia of 10 rabbits. The implants distribution was randomized (n = 3 implants per tibia). Five implants of each group were analyzed by scanning electron microscopy and an optical laser profilometer for surface roughness characterization. Six weeks after the implantation, 10 implants for each group were removed in counter-torque for analysis of maximum torque value. The remaining samples were processed, included in historesin and cut to obtain non-decalcified slides for histomorphological analyses and histomorphometric measurement of the percentage of bone-implant contact (BIC%). Comparisons were made between the groups using a 5% level of significance (p < 0.05) to assess statistical differences. The results of removal torque values (mean +/- standard deviation) showed for the TiM group 15.9 +/- 4.18 N cm, for TiT group 27.9 +/- 5.15 N cm and for Zr group 11.5 +/- 2.92 N cm, with significant statistical difference between the groups (p < 0.0001). However, the BIC% presented similar values for all groups (35.4 +/- 4.54 for TiM group, 37.8 +/- 4.84 for TiT group and 34.0 +/- 6.82 for Zr group), with no statistical differences (p = 0.2171). Within the limitations of the present study, the findings suggest that the quality of the new bone tissue formed around the titanium implants present a superior density (maturation) in comparison to the zirconia implants.
Influence of bone definition and finite element parameters in bone and dental implants stress: A literature review
(MDPI, 2020-08) Prados-Privado, María; Martínez-Martínez, Carlos; Gehrke, Sergio A.; Prados-Frutos, Juan Carlos
Bone plays an important role in dental implant treatment success. The goal of this literature review is to analyze the influence of bone definition and finite element parameters on stress in dental implants and bone in numerical studies. A search was conducted of Pubmed, Science Direct and LILACS, and two independent reviewers performed the data extraction. The quality of the selected studies was assessed using the Cochrane Handbook tool for clinical trials. Seventeen studies were included. Titanium was the most commonly-used material in dental implants. The magnitude of the applied loads varied from 15 to 300 N with a mean of 182 N. Complete osseointegration was the most common boundary condition. Evidence from this review suggests that bone is commonly defined as an isotropic material, despite being an anisotropic tissue, and that it is analyzed as a ductile material, instead of as a fragile material. In addition, and in view of the data analyzed in this review, it can be concluded that there is no standardization for conducting finite element studies in the field of dentistry. Convergence criteria are only detailed in two of the studies included in this review, although they are a key factor in obtaining accurate results in numerical studies. It is therefore necessary to implement a methodology that indicates which parameters a numerical simulation must include, as well as how the results should be analyzed.
Special-purpose elements to impose Periodic Boundary Conditions for multiscale computational homogenization of composite materials with the explicit Finite Element Method
(Elsevier, 2019-01-15) Sádaba, S.; Naya Montans, Fernando; Herráez, M.; González, G.; Llorca, J.; Lopes, C. S.; European Commission; Ministerio de Economía y Competitividad (España)
A novel methodology is presented to introduce Periodic Boundary Conditions (PBC) on periodic Representative Volume Elements (RVE) in Finite Element (FE) solvers based on dynamic explicit time integration. This implementation aims at overcoming the difficulties of the explicit FE method in dealing with standard PBC. The proposed approach is based on the implementation of a user-defined element, named a Periodic Boundary Condition Element (PBCE), that enforces the periodicity between periodic nodes through a spring-mass-dashpot system. The methodology is demonstrated in the multiscale simulation of composite materials. Two showcases are presented: one at the scale of computational micromechanics, and another one at the level of computational mesomechanics. The first case demonstrates that the proposed PBCE allows the homogenization of composite ply properties through the explicit FE method with increased efficiency and similar reliability with respect to the equivalent implicit simulations with traditional PBC. The second case demonstrates that the PBCE coupled with Periodic Laminate Elements (PLE) can effectively be applied to the computational homogenization of elastic and strength properties of entire laminates taking into account highly nonlinear effects. Both cases motivate the application of the methodology in multiscale virtual testing in support of the building-block certification of composite materials.
Transverse cracking of cross-ply laminates: A computational micromechanics perspective
(Elsevier, 2015-04-06) Herráez, Miguel; Mora, Diego; Naya Montans, Fernando; Lopes, Claudio S.; González, Carlo; Llorca, Javier; Ministerio de Economía y Competitividad (España)
Transverse cracking in cross-ply carbon/epoxy and glass/epoxy laminates in tension is analyzed by means of computational micromechanics. Longitudinal plies were modeled as homogenized, anisotropic elastic solids while the actual fiber distribution was included in the transverse plies. The mechanical response was obtained by the finite element analysis of a long representative volume element of the laminate. Damage in the transverse plies was triggered by interface decohesion and matrix cracking. The simulation strategy was applied to study the influence of ply thickness on the critical stress for the cracking of the transverse plies and on the evolution of crack density in 02=90n=2 s laminates, with n = 1, 2, 4 and 8. It was found that the transverse ply strength corresponding to the initiation and propagation of a through-thickness crack was independent of the ply thickness and that the transverse strength of carbon/epoxy laminates was 35% higher than that of the glass fiber counterparts. In addition, the mechanisms of crack initiation and propagation through the thickness as well as of multiple matrix cracking were ascertained and the stiffness reduction in the 90 ply as a function of crack density was computed as a function of the ply thickness.
Micromechanical study on the origin of fiber bridging under interlaminar and intralaminar mode I failure
(Elsevier, 2019-02-15) Naya Montans, Fernando; Pappas, G.; Botsis, J.
Fiber reinforced polymers (FRPs) subjected to mode I fracture show important toughening due to the development of large scale bridging (LSB). Experimental studies of this phenomenon in unidirectional carbon/epoxy laminates using double cantilever beam specimens, demonstrate important differences in R-curve response for inter- and intralaminar fracture. Post fracture observation of composite’s cross-section pointed out dissimilar fiber bundle size and shape, as the main origin of their differences. In the present paper, representative volume elements with the composite’s constituents, based on the actual material microstructure, and homogenized 2D finite element models were developed to study the effects of microstructure on the first stage of damage leading to LSB development in carbon/epoxy composites under mode I fracture. The differences between inter- and intralaminar fracture were investigated along with the influence of fiber dispersion and the presence of interply and intraply resin-rich zones. The numerical simulations captured different microcrack morphologies for inter- and intralaminar fracture, supporting the experimental observations, while parametric studies showed the influence of the microstructure in the formation of LSB. In particular, fiber dispersion within a ply and resin rich zone between plies play significant roles in mode I fracture and can be used to control toughening mechanisms in FRPs.
Multiscale modelling of thermoplastic woven fabric composites: From micromechanics to mesomechanics
(Elsevier, 2019-11-15) Múgica, J. I.; Lopes, Claudio S.; Naya Montans, Fernando; Herráez, M.; Martínez, V.; González, C.; Ministerio de Economía y Competitividad (España)
The mechanical properties of woven composites can be predicted by using a multiscale modelling approach. The starting point to its application is the microscale (the level of fibres, matrix and interfaces), that allows the computation of the homogenised behaviour of the yarn. The aim of this work was to predict the yarn-level behaviour of a thermoplastic-based woven composite in order to allow the formulation of a representative constitutive model that can be used to predict ply properties at the mesoscale. To accomplish this purpose, an in situ characterisation of the microconstituents was carried out. This served to generate inputs for three different representative volume element (RVE) models that allowed predicting the yarn longitudinal, transverse and shear responses. These mechanical characteristics allowed the determination of homogenised yarn constitutive behaviour which was found to be characterised by significant non-linearity until failure, specially in transverse and shear directions.
Computational micromechanics of the transverse and shear behavior of unidirectional fiber reinforced polymers including environmental effects
(Elsevier, 2017-01) Naya Montans, Fernando; González, C.; Lopes, Claudio S.; Van Der Veen, S.; Pons, F.
Qualification of Fiber Reinforced Polymer materials (FRP’s) for manufacturing of structural components in the aerospace industry is usually associated with extensive and costly experimental campaigns. The burden of testing is immense and materials should be characterized under different loading states (tension, compression, shear) and environmental conditions (temperature, humidity) to probe their structural integrity during service life. Recent developments in multiscale simulation, together with increased computational power and improvements in modeling tools, can be used to alleviate this scenario. In this work, high-fidelity simulations of the material behavior at the micro level are used to predict ply properties and ascertain the effect of ply constituents and microstructure on the homogenized ply behavior. This approach relies on the numerical analysis of representative volume elements equipped with physical models of the ply constituents. Its main feature is the ability to provide fast predictions of ply stiffness and strength properties for different environmental conditions of temperature and humidity, in agreement with the experimental results, showing the potential to reduce the time and costs required for material screening and characterization.
Interface characterization in fiber-reinforced polymer-matrix composites
(Springer, 2017-01) Naya Montans, Fernando; Molina-Aldareguía, J. M.; Lopes, Claudio S.; González, C.; Llorca, J.; Comunidad de Madrid; Ministerio de Ciencia e Innovación (España)
A novel methodology is presented and applied to measure the shear interface strength of fiber-reinforced polymers. The strategy is based in fiber push-in tests carried out on the central fiber of highly-packed fiber clusters with hexagonal symmetry, and it is supported by a detailed finite element analysis of the push-in test to account for the influence of hygrothermal residual stresses, fiber constraint and fiber anisotropy on the interface strength. Examples of application are presented to determine the shear interface strength in carbon and glass fiber composites reinforced with either thermoset or thermoplastic matrices. In addition, the influence of the environment (either dry or wet conditions) on the interface strength in C/epoxy composites is demonstrated.
Multiscale characterization of nano-engineered fiber-reinforced composites: Effect of carbon nanotubes on the out-of-plane mechanical behavior
(Hindawi, 2017-04-30) Medina, Carlos; Fernandez, Eduardo; Salas, Alexis; Naya Montans, Fernando; Molina-Aldereguía, Jon; Melendrez, Manuel F.; Flores, Paulo
The mechanical properties of the matrix and the fiber/matrix interface have a relevant influence over the mechanical properties of a composite. In this work, a glass fiber-reinforced composite is manufactured using a carbon nanotubes (CNTs) doped epoxy matrix. The influence of the CNTs on the material mechanical behavior is evaluated on the resin, on the fiber/matrix interface, and on the composite. On resin, the incorporation of CNTs increased the hardness by 6% and decreased the fracture toughness by 17%. On the fiber/matrix interface, the interfacial shear strength (IFSS) increased by 22% for the nanoengineered composite (nFRC). The influence of the CNTs on the composite behavior was evaluated by through-thickness compression, short beam flexural, and intraply fracture tests. The compressive strength increased by 6% for the nFRC, attributed to the rise of the matrix hardness and the fiber/matrix IFSS. In contrast, the interlaminar shear strength (ILSS) obtained from the short beam tests was reduced by 8% for the nFRC; this is attributed to the detriment of the matrix fracture toughness. The intraply fracture test showed no significant influence of the CNTs on the fracture energy; however, the failure mode changed from brittle to ductile in the presence of the CNTs.
Computational micromechanics of fiber kinking in unidirectional FRP under different environmental conditions
(Elsevier, 2017-05-26) Naya Montans, Fernando; Herráez, M.; Lopes, Claudio S.; González, C.; Van Der Veen, S.; Pons, F.; Ministerio de Economía y Competitividad (España)
The determination of ply properties of Fiber Reinforced Polymers (FRP) for particular operational environmental conditions in aeronautical applications is mandatory in order to fulfill current industry stringent certification requirements. However, the traditional experimental approach requires massive investments of resources and time. From the behaviour obtained experimentally, constitutive equations including failure criteria are then devised to be used in the design of FRP structures. The ply longitudinal behaviour under compression is generally the most difficult to measure and characterize. In this work, an alternative coupled experimental-computational micromechanics approach is proposed to determine the longitudinal compression properties of unidirectional FRP plies under different environmental conditions. This methodology includes experimental characterization of matrix and fiber/matrix interface, combined with numerical simulations of realistic microstructures. The interface decohesion is simulated using cohesive-frictional interactions. A pressure dependent, elasto-plastic model that includes tensile damage is employed to capture the matrix nonlinear behaviour. The numerical predictions match the experimentally-obtained ply properties available in the literature in a remarkable way and suggest that virtual ply property characterization is a mature and reliable approach to conduct screening of materials.
The Effect on Bone Stress in Oral Prosthetic Rehabilitation Supported by Different Number of Dental Implants: A Numerical Analysis
(MDPI, 2019-11-02) Prados Privado, María; Gehrke, Sergio A.; Tozaki, Lúcia Kurokawa; Silveira Zanatta, Luiz Carlos; Cruz, Paulo; Mazon, Patricia; De Aza, Piedad N.; Prados Frutos, Juan Carlos
The aim of this study was to compare the mechanical behavior of two types of prosthesis as well as the stress distribution on the prostheses’ components and the bone. Two groups were analyzed: in the first group (M1), the prothesis was composed of two implants placed at a distance of 14 mm; in the second group (M2), the prothesis was composed of three implants installed at a distance of 9.7 mm from each other. An axial load of 100 N distributed on the cantilever throughout the region from the distal implant and a 30 N axial load on the implants in the inter-foramen region, were applied in both model 1 and model 2. In both models, the stress was concentrated in the region near the neck of the implant, resulting in a maximum value of 143 MPa in M1 and of 131MPa in M2. In M1, the stress along the bone varied from of −4.7 MPa to 13.57 MPa, whereas in M2, it varied from −10 to 12 MPa. According to the results obtained, the model corresponding to six implants presented a better distribution of bone stress around the implants.
A Finite Element Analysis of the Fatigue Behavior and Risk of Failure of Immediate Provisional Implants
(MDPI, 2019-05-08) 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.

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