Revistas
Revista:
COMPUTERS IN BIOLOGY AND MEDICINE
ISSN:
0010-4825
Año:
2022
Vol.:
150
Págs.:
105761
Additively manufactured lattice structures enable the design of tissue scaffolds with tailored mechanical properties, which can be implemented in porous biomaterials. The adaptation of bone to physiological loads results in anisotropic bone tissue properties which are optimized for site-specific loads; therefore, some bone sites are stiffer and stronger along the principal load direction compared to other orientations. In this work, a semi-analytical model was developed for the design of transversely isotropic lattice structures that can mimic the anisotropy characteristics of different types of bone tissue. Several design possibilities were explored, and a particular unit cell, which was best suited for additive manufacturing was further analyzed. The design of the unit cell was parameterized and in-silico analysis was performed via Finite Element Analysis. The structures were manufactured additively in metal and tested under compressive loads in different orientations. Finite element analysis showed good correlation with the semi-analytical model, especially for elastic constants with low relative densities. The anisotropy measured experimentally showed a variable accuracy, highlighting the deviations from designs to additively manufactured parts. Overall, the proposed model enables to exploit the anisotropy of lattice structures to design lighter scaffolds with higher porosity and increased permeability by aligning the scaffold with the principal direction of the load.
Revista:
JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS
ISSN:
1751-6161
Año:
2021
Vol.:
124
Págs.:
104804
Revista:
SCIENTIFIC REPORTS
ISSN:
2045-2322
Año:
2021
Vol.:
11
N°:
19314
Revista:
JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS
ISSN:
1751-6161
Año:
2021
Vol.:
123
Págs.:
104784
Revista:
THIN-WALLED STRUCTURES
ISSN:
0263-8231
Steel cylindrical shell structures such as silos and tanks are very sensitive to geometric imperfections and prone to a plastic instability failure known as elephant's foot (EF) buckling. This type of buckling arises under axial compression. The aim of this paper is to explore the plastic collapse response in conical shells with low semi-vertex angle values under compression. In a first step, the initial geometric imperfection shapes that dictate which plastic mechanisms arise were identified using finite element (FE) models. In a second step, a parametric study reported two plastic collapse mechanisms and showed that the elephant's foot plastic collapse mechanism is the most likely to appear in compressed conical shells with low d/t values, followed by the Yoshimura collapse mechanism, more common with larger d/t values. Finally, a practical model in which the parameters have been adjusted from numerical models has been derived for the elephant's foot plastic mechanism. This model provides the load-deformation behaviour of compressed conical shells at the post-collapse region. The load vs. end-shortening curves provided by the model have been validated through comparison with curves given by the FE models. The good agreement between the results proves the efficiency of the practical model to predict the collapse response of conical shells.
Revista:
MATERIALS & DESIGN
ISSN:
0264-1275
Año:
2020
Vol.:
189
Págs.:
108546
Cellular materials are gaining interest thanks to developments in additive manufacturing. Whilst Finite Element Analysis (FEA) is commonly used to obtain the mechanical behaviour of these structures, different modelling and simulation methodologies are followed in literature. Consequently, there is not a dear procedure to accurately evaluate the mechanical properties of porous structures. This study presents a method to perform FEA of lattice structures with accurate results. All inputs required to simulate compression testing of lattices in FEA were investigated, these included the modelling type, element size, number of unit cells required, boundary conditions and the material model. The effect of these variables on the modulus and yield strength of a lattice structure was studied. Lattices with two unit cell structures, varying unit cell sizes and relative densities were additively manufactured in stainless steel, compression tested and compared to FE simulations. The material model for the FE simulations was obtained from tensile testing individual micro-struts of varying diameters. FE simulation results were in good agreement with the experimental results with an average error for the modulus and yield strength of -10% and 17% respectively. The methodology presented should provide a foundation to accelerate development and adoption of these structures. (C) 2020 The Authors. Published by Elsevier Ltd.
Autores:
Alana, M. (Autor de correspondencia); Cutolo, A. (Autor de correspondencia); Probst, G. ; et al.
Revista:
MATERIALS & DESIGN
ISSN:
0264-1275
Año:
2020
Vol.:
195
Págs.:
108971
Laser powder bed fusion (L-PBF) allows the production of metal lattice cellular structures with tailored mechanical properties. In order to generate the specific structural behavior it is of utmost importance to understand the response of the unit cells when different load conditions are considered. In this article the mechanical response of diamond based cellular structures has been investigated focusing on the impact of geometrical inaccuracy generated by the manufacturing process on the elastic anisotropy of the mentioned unit cell. The ii-CT analysis of the structures shows that the manufacturing deviations occur in certain orientations that depend highly on the building direction and proximity to nodes. The measured imperfection types were implemented in a finite element model in order to predict their single and combined effects in the elastic directional response. The results indicate that the L-PBF process can induce a significant change of elastic anisotropy in the diamond unit cells, including a substantial variation of the optimal orientation for minimal compliance. Methods are presented to calculate this anisotropy such that it can be taken into account when designing and using such lattice structures in real-life applications with multi-axial load conditions. (c) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).
Revista:
JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS
ISSN:
1751-6161
Año:
2019
Vol.:
98
Págs.:
357 - 368
As result of the advances made in additive manufacturing in recent years, the design of porous materials with controlled mechanical properties has gained importance due to their capability to offer case-specific solutions in multiple applications. In terms of biomaterials, the use of lattice structures provides a considerable variety of mechanical and geometric properties that can enhance osseointegration and reduce stress shielding. In this paper, the elastic response of a modified face-centered cubic (FCC) unit cell was studied, and analytical expressions for macroscopic effective Young's moduli, shear moduli and Poisson's ratios were obtained, thus providing the necessary parameters for the homogenization of the unit cell. The analytical expressions of the homogenization parameters open the possibility for implementation in other research fields, such as topology optimization. Timoshenko beam theory was used to model the struts of the modified FCC unit cell and a finite element analysis using shear flexible beam elements was performed to assess the accuracy of the analytical expressions. In addition to modelling the bending of the beams, axial and torsional displacements were also considered for a more detailed analysis. It can be concluded that the expressions obtained represent the elastic behavior of the modified FCC unit cell with high accuracy.
Revista:
JOURNAL OF BIOMECHANICS
ISSN:
0021-9290
Año:
2017
Vol.:
57
Págs.:
161 - 166
An Abdominal Aortic Aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta at least 1.5 times its normal diameter. The criterion of maximum diameter is still used in clinical practice, although numerical studies have demonstrated the importance of biomechanical factors for rupture risk assessment. AAA phantoms could be used for experimental validation of the numerical studies and for pre intervention testing of endovascular grafts. We have applied multi-material 3D printing technology to manufacture idealized AAA phantoms with anisotropic mechanical behavior. Different composites were fabricated and the phantom specimens were characterized by biaxial tensile tests while using a constitutive model to fit the experimental data. One composite was chosen to manufacture the phantom based on having the same mechanical properties as those reported in the literature for human AAA tissue; the strain energy and anisotropic index were compared to make this choice. The materials for the matrix and fibers of the selected composite are, respectively, the digital materials FLX9940 and FLX9960 developed by Stratasys. The fiber proportion for the composite is equal to 0.15. The differences between the composite behavior and the AAA tissue are small, with a small difference in the strain energy (0.4%) and a maximum difference of 12.4% in the peak Green strain ratio. This work represents a step forward in the application of 3D printing technology for the manufacturing of AAA phantoms with anisotropic mechanical behavior. (C) 2017 Elsevier Ltd. All rights reserved.
Revista:
JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME
ISSN:
0148-0731
Año:
2017
Vol.:
139
N°:
1
An abdominal aortic aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta of at least 1.5 times its normal diameter. Although the criterion of maximum diameter is still used in clinical practice to decide on a timely intervention, numerical studies have demonstrated the importance of other geometric factors. However, the major drawback of numerical studies is that they must be validated experimentally before clinical implementation. This work presents a new methodology to verify wall stress predicted from the numerical studies against the experimental testing. To this end, four AAA phantoms were manufactured using vacuum casting. The geometry of each phantom was subject to microcomputed tomography (lCT) scanning at zero and three other intraluminal pressures: 80, 100, and 120 mm Hg. A zero-pressure geometry algorithm was used to calculate the wall stress in the phantom, while the numerical wall stress was calculated with a finite-element analysis (FEA) solver based on the actual zero-pressure geometry subjected to 80, 100, and 120 mm Hg intraluminal pressure loading. Results demonstrate the moderate accuracy of this methodology with small relative differences in the average wall stress (1.14%). Additionally, the contribution of geometric factors to the wall stress distribution was statistically analyzed for the four phantoms. The results showed a significant correlation between wall thickness and mean curvature (MC) with wall stress.
Revista:
JOURNAL OF MECHANICS IN MEDICINE AND BIOLOGY
ISSN:
0219-5194
Revista:
JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME
ISSN:
0148-0731
Año:
2017
Vol.:
139
N°:
8
Págs.:
081006 - 081006-7
The maximum diameter (MD) criterion is the most important factor when predicting risk of rupture of abdominal aortic aneurysms (AAAs). An elevated wall stress has also been linked to a high risk of aneurysm rupture, yet is an uncommon clinical practice to compute AAA wall stress. The purpose of this study is to assess whether other characteristics of the AAA geometry are statistically correlated with wall stress. Using in-house segmentation and meshing algorithms, 30 patient-specific AAA models were generated for finite element analysis (FEA). These models were subsequently used to estimate wall stress and maximum diameter and to evaluate the spatial distributions of wall thickness, cross-sectional diameter, mean curvature, and Gaussian curvature. Data analysis consisted of statistical correlations of the aforementioned geometry metrics with wall stress for the 30 AAA inner and outer wall surfaces. In addition, a linear regression analysis was performed with all the AAA wall surfaces to quantify the relationship of the geometric indices with wall stress. These analyses indicated that while all the geometry metrics have statistically significant correlations with wall stress, the local mean curvature (LMC) exhibits the highest average Pearson's correlation coefficient for both inner and outer wall surfaces. The linear regression analysis revealed coefficients of determination for the outer and inner wall surfaces of 0.712 and 0.516, respectively, with LMC having the largest effect on the linear regression equation with wall stress. This work underscores the importance of evaluating AAA mean wall curvature as a potential surrogate for wall stress.
Revista:
MEDICAL ENGINEERING AND PHYSICS
ISSN:
1350-4533
Año:
2016
Vol.:
38
N°:
12
Págs.:
1505 - 1512
An Abdominal Aortic Aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta at least 1.5 times its normal diameter. The criterion of maximum diameter is still used in clinical practice, although numerical studies have demonstrated the importance of other biomechanical factors. Numerical studies, however, must be validated experimentally before they can be clinically implemented. We have developed a methodology for manufacturing anisotropic AAA replicas with non-uniform wall thickness. Different composites were fabricated and tested, and one was selected in order to manufacture a phantom with the same properties. The composites and the phantom were characterized by biaxial tensile tests and a material model was fit to the experimental data. The experimental results were compared with data from the literature, and similar responses were obtained. The anisotropic AAA replicas with non-uniform wall thickness can be used in benchtop experiments to validate deformations obtained with numerical simulations or for pre-intervention testing of endovascular grafts. This is a significant step forward considering the importance of anisotropy in numerical simulations.
Revista:
JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME
ISSN:
0148-0731
Año:
2013
Vol.:
136
N°:
1
Págs.:
014502 - 014502-5
The goal of this work is to develop a framework for manufacturing nonuniform wall thickness replicas of abdominal aortic aneurysms (AAAs). The methodology was based on the use of computed tomography (CT) images for virtual modeling, additive manufacturing for the initial physical replica, and a vacuum casting process and range of polyurethane resins for the final rubberlike phantom. The average wall thickness of the resulting AAA phantom was compared with the average thickness of the corresponding patient-specific virtual model, obtaining an average dimensional mismatch of 180 lm (11.14%). The material characterization of the artery was determined from uniaxial tensile tests as various combinations of polyurethane resins were chosen due to their similarity with ex vivo AAA mechanical behavior in the physiological stress configuration. The proposed methodology yields AAA phantoms with nonuniform wall thickness using a fast and low-cost process. These replicas may be used in benchtop experiments to validate deformations obtained with numerical simulations using finite element analysis, or to validate optical methods developed to image ex vivo arterial deformations during pressure-inflation testing.
Nacionales y Regionales
Título:
Optimizacion de las estrategias de diseño y de post-procesado de acabado de piezas obtenidas por fabricacion aditiva metalica mediante operaciones de mecanizado
Código de expediente:
2020-CIEN-000021-01
Investigador principal:
Amaia Jiménez Zaratiegui
Financiador:
DIPUTACIÓN FORAL DE GIPUZKOA
Convocatoria:
2020 DFG Programa Red guipuzcoana de Ciencia, Tecnología e Innovación 2020
Fecha de inicio:
01/06/2020
Fecha fin:
30/09/2021
Importe concedido:
67.406,00€
Otros fondos:
-
Título:
Investigacion sobre la influencia de la cavitacion, las fugas y las desviaciones geometricas en la eficiencia de los futuros sistemas de lubricacion d emotores aeronauticos.
Código de expediente:
KK-2019/00098
Investigador principal:
Gorka Sánchez Larraona
Financiador:
GOBIERNO VASCO
Convocatoria:
2019 GV Elkartek 2019 - Fase I. Programa de apoyo a la investigación colaborativa en áreas estratégicas
Fecha de inicio:
01/04/2019
Fecha fin:
30/09/2020
Importe concedido:
109.160,00€
Otros fondos:
-
Título:
Nuevos materiales, recubrimientos y procesos para mejorar la competitividad de la industria vasca en las energias renovables marinas.
Código de expediente:
KK-2021/00059
Investigador principal:
Íñigo Puente Urruzmendi
Financiador:
GOBIERNO VASCO
Convocatoria:
2020 GV Elkartek -Proyectos de apoyo a la investigacion colaborativa en areas estrategicas.Tipo 1.
Fecha de inicio:
01/03/2021
Fecha fin:
31/12/2022
Importe concedido:
96.277,82€
Otros fondos:
-
