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Papers by Aitziber Lopez-Arancibia

Research paper thumbnail of Additively manufactured lattice structures with controlled transverse isotropy for orthopedic porous implants

Computers in Biology and Medicine

Research paper thumbnail of Analytical model of the elastic behavior of a modified face-centered cubic lattice structure

Journal of the Mechanical Behavior of Biomedical Materials, 2019

As result of the advances made in additive manufacturing in recent years, the design of porous ma... more 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. Finally, the elastic response was further analyzed by introducing variability in the aspect ratio in order to enable the design of unit cells with controlled anisotropy.

Research paper thumbnail of Bolted joints for single-layer structures: numerical analysis of the bending behaviour

Structural Engineering and Mechanics, 2015

This paper deals with a new designed joint system for single-layer spatial structures. As the sta... more This paper deals with a new designed joint system for single-layer spatial structures. As the stability of these structures is greatly influenced by the joint behaviour, the aim of this paper is the characterization of the joint response in bending through Finite Element Method (FEM) analysis using ABAQUS. The behaviour of the joints studied here was influenced by many geometrical factors, such as bolts and plate sizes, distance between bolts and end-plate thickness. The study comprised five models of joints with different values of those parameters. The numerical results were compared to the results of previous experimental tests and the agreement was good enough. The differences between the numerical and experimental initial stiffness are attributed to the simplifications introduced when modelling the bolt threads as well as the presence of residual stresses in the test specimens.

Research paper thumbnail of Influence of geometrical and structural parameters on the behaviour of squared plan-form single-layer structures

Journal of Constructional Steel Research, 2012

Although there is a great deal of papers on single-layer latticed structures, practically the tot... more Although there is a great deal of papers on single-layer latticed structures, practically the totality of them is devoted to domes. Therefore, the authors have chosen to analyse squared plan-form single-layer structures studying the influence of joint-rigidity, mesh-density, rise-to-span ratio and load combination in their behaviour, through a Design of Experiments analysis. After identifying the most influential parameters, more FEM analyses were run resulting in interesting conclusions which included economic considerations. The influence of initial imperfections was also investigated.

Research paper thumbnail of Finite element models of a joint for single-layer reticulated structures

The IES Journal Part A: Civil & Structural Engineering, 2012

The necessity to offer differentiated solutions for architectural projects is fostering the devel... more The necessity to offer differentiated solutions for architectural projects is fostering the development of single-layer spatial structures. As the stability of these structures largely depends on the stiffness of the joints, new joint designs have to be sought. The authors performed various experimental tests on a new kind of joint for tubular members of single-layer structures in order to evaluate the joint stiffness. The aim of the study is to find a finite element model to reproduce the experimental responses, so that the behaviour of the joint can be predicted without the need for further experimentation. The proposed models mainly differed in the way the bolt connection was simulated, as bolts were the most complex elements. The paper presents the comparison between experimental results and numerical results obtained from the different finite element models developed for the joints. One of the three models provided good results even though it was simple.

Research paper thumbnail of Practical approach to plastic collapse of conical shells under axial compression

Thin-Walled Structures, 2021

Steel cylindrical shell structures such as silos and tanks are very sensitive to geometric imperf... more 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 semivertex 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. endshortening 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.

Research paper thumbnail of Additively manufactured lattice structures with controlled transverse isotropy for orthopedic porous implants

Computers in Biology and Medicine

Research paper thumbnail of Analytical model of the elastic behavior of a modified face-centered cubic lattice structure

Journal of the Mechanical Behavior of Biomedical Materials, 2019

As result of the advances made in additive manufacturing in recent years, the design of porous ma... more 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. Finally, the elastic response was further analyzed by introducing variability in the aspect ratio in order to enable the design of unit cells with controlled anisotropy.

Research paper thumbnail of Bolted joints for single-layer structures: numerical analysis of the bending behaviour

Structural Engineering and Mechanics, 2015

This paper deals with a new designed joint system for single-layer spatial structures. As the sta... more This paper deals with a new designed joint system for single-layer spatial structures. As the stability of these structures is greatly influenced by the joint behaviour, the aim of this paper is the characterization of the joint response in bending through Finite Element Method (FEM) analysis using ABAQUS. The behaviour of the joints studied here was influenced by many geometrical factors, such as bolts and plate sizes, distance between bolts and end-plate thickness. The study comprised five models of joints with different values of those parameters. The numerical results were compared to the results of previous experimental tests and the agreement was good enough. The differences between the numerical and experimental initial stiffness are attributed to the simplifications introduced when modelling the bolt threads as well as the presence of residual stresses in the test specimens.

Research paper thumbnail of Influence of geometrical and structural parameters on the behaviour of squared plan-form single-layer structures

Journal of Constructional Steel Research, 2012

Although there is a great deal of papers on single-layer latticed structures, practically the tot... more Although there is a great deal of papers on single-layer latticed structures, practically the totality of them is devoted to domes. Therefore, the authors have chosen to analyse squared plan-form single-layer structures studying the influence of joint-rigidity, mesh-density, rise-to-span ratio and load combination in their behaviour, through a Design of Experiments analysis. After identifying the most influential parameters, more FEM analyses were run resulting in interesting conclusions which included economic considerations. The influence of initial imperfections was also investigated.

Research paper thumbnail of Finite element models of a joint for single-layer reticulated structures

The IES Journal Part A: Civil & Structural Engineering, 2012

The necessity to offer differentiated solutions for architectural projects is fostering the devel... more The necessity to offer differentiated solutions for architectural projects is fostering the development of single-layer spatial structures. As the stability of these structures largely depends on the stiffness of the joints, new joint designs have to be sought. The authors performed various experimental tests on a new kind of joint for tubular members of single-layer structures in order to evaluate the joint stiffness. The aim of the study is to find a finite element model to reproduce the experimental responses, so that the behaviour of the joint can be predicted without the need for further experimentation. The proposed models mainly differed in the way the bolt connection was simulated, as bolts were the most complex elements. The paper presents the comparison between experimental results and numerical results obtained from the different finite element models developed for the joints. One of the three models provided good results even though it was simple.

Research paper thumbnail of Practical approach to plastic collapse of conical shells under axial compression

Thin-Walled Structures, 2021

Steel cylindrical shell structures such as silos and tanks are very sensitive to geometric imperf... more 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 semivertex 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. endshortening 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.