In the past decades, automotive structure design has sought to minimize its mass while maintainin... more In the past decades, automotive structure design has sought to minimize its mass while maintaining or improving structural performance. As such, topology optimization (TO) has become an increasingly popular tool during the conceptual design stage. While the designs produced by TO methods provide significant performance-to-mass ratio improvements, they require considerable computational resources when solving large-scale problems. An alternative for large-scale problems is to decompose the design domain into multiple scales that are coupled with homogenization. The problem can then be solved with hierarchical multiscale topology optimization (MSTO). The resulting optimal, homogenized macroscales are de-homogenized to obtain a high-fidelity, physically-realizable design. Even so MSTO methods are still computationally expensive due to the combined costs of solving nested optimization problems and performing de-homogenization. To address these issues, this paper presents an efficient de...
A common scenario in engineering design is the availability of several black-box functions that d... more A common scenario in engineering design is the availability of several black-box functions that describe an event with different levels of accuracy and evaluation cost. Solely employing the highest fidelity, often the most expensive, black-box function leads to lengthy and costly design cycles. Multi-fidelity modeling improves the efficiency of the design cycle by combining information from a small set of observations of the high-fidelity function and large sets of observations of the low-fidelity, fast-to-evaluate functions. In the context of Bayesian optimization, the most popular multi-fidelity model is the auto-regressive (AR) model, also known as the co-kriging surrogate. The main building block of the AR model is a weighted sum of two Gaussian processes (GPs). Therefore, the AR model is well suited to exploit information generated by sources that present strong linear correlations. Recently, the non-linear auto-regressive Gaussian process (NARGP) model has appeared as an alter...
RESUMEN El proceso de optimización de un proyecto multidisciplinario en ingeniería involucra la d... more RESUMEN El proceso de optimización de un proyecto multidisciplinario en ingeniería involucra la descomposición de un sistema en distintas disciplinas y la posterior asociación de sus contribuciones. El objetivo de este trabajo es presentar los esquemas de desagregación y asociación más utilizados actualmente en procesos de diseño óptimo multidisciplinario-Multidisciplinary Design Optimization (MDO). Entre los esquemas de desagregación se presentan la descomposición jerárquica y no jerárquica, así como los métodos computacionales más comunes. Los esquemas de asociación incluyen: formulación de un solo nivel (e.g., optimización integrada y análisis y diseño simultáneos), formulación de múltiples niveles (e.g., optimización en espacios concurrentes y optimización colaborativa) y diseño robusto. El trabajo presenta también un ejemplo de aplicación resuelto numéricamente. Palabras clave: Palabras clave: diseño óptimo multidisciplinario, descomposición de un sistema, optimización colaborativa.
Experimental_reference_AFS.xlsx: Results of three experimental, compression tests on reference AF... more Experimental_reference_AFS.xlsx: Results of three experimental, compression tests on reference AFS. Results include displacement, force, strain, and stress. FEA_results.xlsx: Results of all numerical experiments including parametric studies on pin number (layout), radius (size), and material. Z-pinned.xlsx: Results of experimental tests on Z-pinned samples (single and quad). Energy absorption efficiency data and plots.
Advances in Structural and Multidisciplinary Optimization, 2017
This work introduces a metamodel-based global optimization method for crashworthiness with the ab... more This work introduces a metamodel-based global optimization method for crashworthiness with the ability to synthesize continuum structures with an optimal distribution of material phases or gauges. The proposed optimization method makes use of fully nonlinear, dynamic crash simulations and consists of three main elements: (1) the generation of a conceptual design from the structures crash response, (2) the optimal clustering of the conceptual design to define the location of the material phases or gauges, (3) the metamodel-based global optimization, which aims to find the optimal settings for each cluster. The conceptual design can be generated from extracting finite element analysis information or by using structural optimization. The conceptual design is then clustered using clustering analysis to reduce the dimension of the design space. The global optimization problem aims to find the optimal material distribution on the reduced design space using metamodels. The metamodels are built using sampling and cross-validation, and sequentially updated using an expected improvement function until convergence. The proposed methodology is demonstrated using examples from multi-objective crashworthiness design examples.
Lattice Heat Transfer (LHT) structures provide superior structural support while improving the he... more Lattice Heat Transfer (LHT) structures provide superior structural support while improving the heat transfer coefficient through their high surface-to-volume ratios. By using current Additive Manufacturing (AM) technologies, LHT with highly complex structures is possible. In this study, the design concept of LHT is further improved by implementing a thermomechanical topology optimization method. With utilization of design-dependent heat source, the method can be applied to generate stiffer LHT structures under mechanical and thermomechanical loads, without decreasing their thermal performance; relative to a design made of a uniform LHT having the same mass fraction. Two numerical examples are presented to illustrate how to use the proposed approach to design LHT sections. The results show that the mechanical performance can be improved more than 50% compared to a uniform LHT with the same mass fraction, without decreasing the thermal performance. The method does not require a fluid ...
This work presents innovative origami optimization methods for the design of unit cells for compl... more This work presents innovative origami optimization methods for the design of unit cells for complex origami tessellations that can be utilized for the design of deployable structures. The design method used to create origami tiles utilizes the principles of discrete topology optimization for ground structures applied to origami crease patterns. The initial design space shows all possible creases and is given the desired input and output forces. Taking into account foldability constraints derived from Maekawa’s and Kawasaki’s theorems, the algorithm designates creases as active or passive. Geometric constraints are defined from the target 3D object. The periodic reproduction of this unit cell allows us to create tessellations that are used in the creation of deployable shelters. Design requirements for structurally sound tessellations are discussed and used to evaluate the effectiveness of our results. Future work includes the applications of unit cells and tessellation design for or...
Additive manufacturing allows the fabrication parts and tools of high complexity. This capability... more Additive manufacturing allows the fabrication parts and tools of high complexity. This capability challenges traditional guidelines in the design of conformal cooling systems in heat exchangers, injection molds, and other parts and tools. Innovative design methods, such as network-based approaches, lattice structures, and structural topology optimization have been used to generate complex and highly efficient cooling systems; however, methods that incorporate coupled thermal and fluid analysis remain scarce. This paper introduces a coupled thermal-fluid topology optimization algorithm for the design of conformal cooling channels. With this method, the channel position problem is replaced to a material distribution problem. The material distribution directly depends on the effect of flow resistance, heat conduction, as well as forced and natural convection. The problem is formulated based on a coupling of Navier-Stokes equations and convection-diffusion equation. The problem is solve...
Attitudes towards peace and war have been taken as two poles of a single plane from the classical... more Attitudes towards peace and war have been taken as two poles of a single plane from the classical positions. Sirlopu & Leon (2016) propose a scale where there are more than two attitudes. From this model, we wanted to understand the attitudes toward peace and war in a Colombian population. For this, the answers and the factors found were analyzed in relation to the demographic variables age, sex, gender, socioeconomic level and involvement of some form of violence associated with the armed conflict. In this regard, only age is reported as an influential element in attitudes towards peace and war. Where older people tend to have more pacifist attitudes than young people. The role of national identity, nationalism and orientation to social dominance as modulators of attitudes towards peace and war was also analyzed. From it, relationships were found as modulating variables with national identity and nationalism. Then, it is proposed that national identity plays a very important role a...
Volume 2B: 43rd Design Automation Conference, Aug 6, 2017
This work introduces the design of a lattice array of multimaterial compliant mechanisms (LCM) th... more This work introduces the design of a lattice array of multimaterial compliant mechanisms (LCM) that diverts the impact radial force into tangential forces through the action of elastic hinges and connecting springs. When used as the helmet liner, the LCM liner design has the potential to reduce the risk of head injury through improved impact energy attenuation. The compliant mechanism array in the liner is optimized using a multi-material topology optimization algorithm. The performance of the LCM liner design is compared with the one obtained by expanded polypropylene (EPP) foam, which is traditionally used in sport helmets. An impact test is carried out using explicit, dynamic, nonlinear finite element analysis. The parameters under consideration include the internal energy, the peak linear force, as well as von Mises stress and effective plastic strain distributions. Although there is a small increase in stress and strain values, the simulations show that the maximum internal of the LCM liner design is four times the one of the foam design while the peak linear force is reduced to about half. While the use of the LCM liner design is intended for sports helmets, this design may find application in other energy absorbing structures such as crashworthy vehicle components, blast mitigating structures, and protective gear.
This work introduces a cluster-based structural optimization (CBSO) method for the design of cate... more This work introduces a cluster-based structural optimization (CBSO) method for the design of categorical multimaterial structures subjected to crushing, dynamic loading. The proposed method consists of three steps: conceptual design generation, design clustering, and Bayesian optimization. In the first step, a conceptual design is generated using the hybrid cellular automaton (HCA) algorithm. In the second step, threshold-based cluster analysis yields a lower-dimensional design. Here, a cluster validity index for structural optimization is introduced in order to qualitatively evaluate the clustered design. In the third step, the optimal design is obtained through Bayesian optimization, minimizing a constrained expected improvement function. This function allows to impose soft constraints by properly redefining the expected improvement based on the maximum constraint violation. The Bayesian optimization algorithm implemented in this work has the ability to search over (i) a real desi...
Under the concept of "Industry 4.0", production processes will be pushed to be increasingly inter... more Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization goes beyond the traditional aim of capacity maximization, contributing also for organization's profitability and value. Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization's value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity optimization might hide operational inefficiency.
Sandwich structures with honeycomb core are widely used in the lightweight design and impact ener... more Sandwich structures with honeycomb core are widely used in the lightweight design and impact energy absorption applications in automotive, sporting, and aerospace industries. Recently, the auxetic honeycombs with negative Poisson's ratio attract a substantial attention for different engineering products. In this study, we implement Additive Manufacturing technology, experimental testing, and Finite Element Analysis (FEA) to design and investigate the mechanical behavior of a novel unit cell for sandwich structure core. The new core model contains the conventional and auxetic honeycomb cells beside each other to create a Hybrid Honeycomb (HHC) for the sandwich structure. The different designs of unit cells with the same volume fraction of 15% are 3D-printed using Fused Deposition Modeling technique, and the comparative study on the mechanical behavior of conventional honeycomb, auxetic honeycomb, and HHC structures is conducted. The quasi-static uniaxial compression tests are performed on the printed samples to investigate the mechanical behavior of the printed structures. The deformation and failure modes of the different designs are studied at the cell level utilizing FEA of the compression test and experimental observation. The compressive strength of the different design is measured using three experimental tests. The new HHC unit cell design shows significantly higher mechanical properties than the auxetic and the conventional designs. Modifying the design variables of hybrid cellular core structure allows us to tailor the mechanical properties and deformation pattern in macro level to achieve the desired mechanical properties in sandwich structures.
Broncas r esonancias de las campanas de la ig•lesia de La Candelaria, en el Bogotá que fu e. Son ... more Broncas r esonancias de las campanas de la ig•lesia de La Candelaria, en el Bogotá que fu e. Son las ocho de la noche y llueve a porfía. En los canalones, el agua fluye musicalmente y un niño se refugia en el amplio y pulcro lecho materno. Trae en sus brazos un libro, hermosamente empastado en España. E s uno de los volúmenes de las Ob ras cotnpletas de Julio V crne, en versión ca stellana publicada por la histórica edito rial madrileña de "Gaspar y Roig, Impresores".
This work introduces a new design algorithm to optimize progressively folding thin-walled structu... more This work introduces a new design algorithm to optimize progressively folding thin-walled structures and in order to improve automotive crashworthiness. The proposed design algorithm is composed of three stages: conceptual thickness distribution, design parameterization, and multi-objective design optimization. The conceptual thickness distribution stage generates an innovative design using a novel one-iteration compliant mechanism approach that triggers progressive folding even on irregular structures under oblique impact. The design parameterization stage optimally segments the conceptual design into a reduced number of clusters using a machine learning K-means algorithm. Finally, the multiobjective design optimization stage finds non-dominated designs of maximum specific energy absorption and minimum peak crushing force. The proposed optimization problem is addressed by a multiobjective genetic algorithm on sequentially updated surrogate models, which are optimally selected from a set of 24 surrogates. The effectiveness of the design algorithm is demonstrated on an S-rail thin-walled structure. The best compromised Pareto design increases specific energy absorption and decreases peak crushing force in the order of 8% and 12%, respectively. Recently, our research group has proposed the use of HCA topometry (thickness distribution) methods for compliant, plastically deformable structures to support the generation of conceptual design for progressively folding thin-walled components including S-rails [28]. This method follows the design principles of compliant mechanisms and their ability to transfer force and displacement from a given input
52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 2011
The field of topology design of compliant mechanisms has developed from infancy to well grown sta... more The field of topology design of compliant mechanisms has developed from infancy to well grown state in last 15 years. Born from the need of hingeless mechanisms in MicroElec-troMechanical Systems (MEMS), compliant mechanims are finding their use in wide range of applications like snap-through mechanisms, piezoelectric actuators and wing flapping mechanisms among many others. Most of the work developed so far, consider linear elastic material behavior and small displacment theory to design compliant mechanisms. In order to account for the effect of large displacements in mechanism design, geometric nonlinearity is considered by many researchers, however, nonlinearities arising from plasticity and contact are seldomly studied. One of the major challenges in the design of mechanisms considering nonlinearities is sensitivity analysis. Analytical expressions for sensitivities of objective function with respect to design variables can not be expressed in closed form when nonlinear finite element methods are used. Moreover, commercial finite element softwares which use implicit/explict solvers can not be used for such sensitivity calculations as they do not store stiffness matrices. In this work, optimal design for compliant mechanisms using control based material update scheme (HCA) is developed for linear case and the idea is extended to obtain concept topologies for nonlinear cases. Since this method does not involve sensitivity calculations when nonlinearities are considered, commercial FEA packages can be used which help in handling complex design problems in 2D and 3D. Although the final designs for nonlinear cases can not be claimed 'optimal', this method gives designer, a candidate designs which perform satisfactorily well under nonlinear conditions. This method is developed particularly for potential applications of compliant mechanisms in crashworthy designs where considering nonlinearity becomes essential. The applicability of the proposed method is shown by considering 2 examples.
In the past decades, automotive structure design has sought to minimize its mass while maintainin... more In the past decades, automotive structure design has sought to minimize its mass while maintaining or improving structural performance. As such, topology optimization (TO) has become an increasingly popular tool during the conceptual design stage. While the designs produced by TO methods provide significant performance-to-mass ratio improvements, they require considerable computational resources when solving large-scale problems. An alternative for large-scale problems is to decompose the design domain into multiple scales that are coupled with homogenization. The problem can then be solved with hierarchical multiscale topology optimization (MSTO). The resulting optimal, homogenized macroscales are de-homogenized to obtain a high-fidelity, physically-realizable design. Even so MSTO methods are still computationally expensive due to the combined costs of solving nested optimization problems and performing de-homogenization. To address these issues, this paper presents an efficient de...
A common scenario in engineering design is the availability of several black-box functions that d... more A common scenario in engineering design is the availability of several black-box functions that describe an event with different levels of accuracy and evaluation cost. Solely employing the highest fidelity, often the most expensive, black-box function leads to lengthy and costly design cycles. Multi-fidelity modeling improves the efficiency of the design cycle by combining information from a small set of observations of the high-fidelity function and large sets of observations of the low-fidelity, fast-to-evaluate functions. In the context of Bayesian optimization, the most popular multi-fidelity model is the auto-regressive (AR) model, also known as the co-kriging surrogate. The main building block of the AR model is a weighted sum of two Gaussian processes (GPs). Therefore, the AR model is well suited to exploit information generated by sources that present strong linear correlations. Recently, the non-linear auto-regressive Gaussian process (NARGP) model has appeared as an alter...
RESUMEN El proceso de optimización de un proyecto multidisciplinario en ingeniería involucra la d... more RESUMEN El proceso de optimización de un proyecto multidisciplinario en ingeniería involucra la descomposición de un sistema en distintas disciplinas y la posterior asociación de sus contribuciones. El objetivo de este trabajo es presentar los esquemas de desagregación y asociación más utilizados actualmente en procesos de diseño óptimo multidisciplinario-Multidisciplinary Design Optimization (MDO). Entre los esquemas de desagregación se presentan la descomposición jerárquica y no jerárquica, así como los métodos computacionales más comunes. Los esquemas de asociación incluyen: formulación de un solo nivel (e.g., optimización integrada y análisis y diseño simultáneos), formulación de múltiples niveles (e.g., optimización en espacios concurrentes y optimización colaborativa) y diseño robusto. El trabajo presenta también un ejemplo de aplicación resuelto numéricamente. Palabras clave: Palabras clave: diseño óptimo multidisciplinario, descomposición de un sistema, optimización colaborativa.
Experimental_reference_AFS.xlsx: Results of three experimental, compression tests on reference AF... more Experimental_reference_AFS.xlsx: Results of three experimental, compression tests on reference AFS. Results include displacement, force, strain, and stress. FEA_results.xlsx: Results of all numerical experiments including parametric studies on pin number (layout), radius (size), and material. Z-pinned.xlsx: Results of experimental tests on Z-pinned samples (single and quad). Energy absorption efficiency data and plots.
Advances in Structural and Multidisciplinary Optimization, 2017
This work introduces a metamodel-based global optimization method for crashworthiness with the ab... more This work introduces a metamodel-based global optimization method for crashworthiness with the ability to synthesize continuum structures with an optimal distribution of material phases or gauges. The proposed optimization method makes use of fully nonlinear, dynamic crash simulations and consists of three main elements: (1) the generation of a conceptual design from the structures crash response, (2) the optimal clustering of the conceptual design to define the location of the material phases or gauges, (3) the metamodel-based global optimization, which aims to find the optimal settings for each cluster. The conceptual design can be generated from extracting finite element analysis information or by using structural optimization. The conceptual design is then clustered using clustering analysis to reduce the dimension of the design space. The global optimization problem aims to find the optimal material distribution on the reduced design space using metamodels. The metamodels are built using sampling and cross-validation, and sequentially updated using an expected improvement function until convergence. The proposed methodology is demonstrated using examples from multi-objective crashworthiness design examples.
Lattice Heat Transfer (LHT) structures provide superior structural support while improving the he... more Lattice Heat Transfer (LHT) structures provide superior structural support while improving the heat transfer coefficient through their high surface-to-volume ratios. By using current Additive Manufacturing (AM) technologies, LHT with highly complex structures is possible. In this study, the design concept of LHT is further improved by implementing a thermomechanical topology optimization method. With utilization of design-dependent heat source, the method can be applied to generate stiffer LHT structures under mechanical and thermomechanical loads, without decreasing their thermal performance; relative to a design made of a uniform LHT having the same mass fraction. Two numerical examples are presented to illustrate how to use the proposed approach to design LHT sections. The results show that the mechanical performance can be improved more than 50% compared to a uniform LHT with the same mass fraction, without decreasing the thermal performance. The method does not require a fluid ...
This work presents innovative origami optimization methods for the design of unit cells for compl... more This work presents innovative origami optimization methods for the design of unit cells for complex origami tessellations that can be utilized for the design of deployable structures. The design method used to create origami tiles utilizes the principles of discrete topology optimization for ground structures applied to origami crease patterns. The initial design space shows all possible creases and is given the desired input and output forces. Taking into account foldability constraints derived from Maekawa’s and Kawasaki’s theorems, the algorithm designates creases as active or passive. Geometric constraints are defined from the target 3D object. The periodic reproduction of this unit cell allows us to create tessellations that are used in the creation of deployable shelters. Design requirements for structurally sound tessellations are discussed and used to evaluate the effectiveness of our results. Future work includes the applications of unit cells and tessellation design for or...
Additive manufacturing allows the fabrication parts and tools of high complexity. This capability... more Additive manufacturing allows the fabrication parts and tools of high complexity. This capability challenges traditional guidelines in the design of conformal cooling systems in heat exchangers, injection molds, and other parts and tools. Innovative design methods, such as network-based approaches, lattice structures, and structural topology optimization have been used to generate complex and highly efficient cooling systems; however, methods that incorporate coupled thermal and fluid analysis remain scarce. This paper introduces a coupled thermal-fluid topology optimization algorithm for the design of conformal cooling channels. With this method, the channel position problem is replaced to a material distribution problem. The material distribution directly depends on the effect of flow resistance, heat conduction, as well as forced and natural convection. The problem is formulated based on a coupling of Navier-Stokes equations and convection-diffusion equation. The problem is solve...
Attitudes towards peace and war have been taken as two poles of a single plane from the classical... more Attitudes towards peace and war have been taken as two poles of a single plane from the classical positions. Sirlopu & Leon (2016) propose a scale where there are more than two attitudes. From this model, we wanted to understand the attitudes toward peace and war in a Colombian population. For this, the answers and the factors found were analyzed in relation to the demographic variables age, sex, gender, socioeconomic level and involvement of some form of violence associated with the armed conflict. In this regard, only age is reported as an influential element in attitudes towards peace and war. Where older people tend to have more pacifist attitudes than young people. The role of national identity, nationalism and orientation to social dominance as modulators of attitudes towards peace and war was also analyzed. From it, relationships were found as modulating variables with national identity and nationalism. Then, it is proposed that national identity plays a very important role a...
Volume 2B: 43rd Design Automation Conference, Aug 6, 2017
This work introduces the design of a lattice array of multimaterial compliant mechanisms (LCM) th... more This work introduces the design of a lattice array of multimaterial compliant mechanisms (LCM) that diverts the impact radial force into tangential forces through the action of elastic hinges and connecting springs. When used as the helmet liner, the LCM liner design has the potential to reduce the risk of head injury through improved impact energy attenuation. The compliant mechanism array in the liner is optimized using a multi-material topology optimization algorithm. The performance of the LCM liner design is compared with the one obtained by expanded polypropylene (EPP) foam, which is traditionally used in sport helmets. An impact test is carried out using explicit, dynamic, nonlinear finite element analysis. The parameters under consideration include the internal energy, the peak linear force, as well as von Mises stress and effective plastic strain distributions. Although there is a small increase in stress and strain values, the simulations show that the maximum internal of the LCM liner design is four times the one of the foam design while the peak linear force is reduced to about half. While the use of the LCM liner design is intended for sports helmets, this design may find application in other energy absorbing structures such as crashworthy vehicle components, blast mitigating structures, and protective gear.
This work introduces a cluster-based structural optimization (CBSO) method for the design of cate... more This work introduces a cluster-based structural optimization (CBSO) method for the design of categorical multimaterial structures subjected to crushing, dynamic loading. The proposed method consists of three steps: conceptual design generation, design clustering, and Bayesian optimization. In the first step, a conceptual design is generated using the hybrid cellular automaton (HCA) algorithm. In the second step, threshold-based cluster analysis yields a lower-dimensional design. Here, a cluster validity index for structural optimization is introduced in order to qualitatively evaluate the clustered design. In the third step, the optimal design is obtained through Bayesian optimization, minimizing a constrained expected improvement function. This function allows to impose soft constraints by properly redefining the expected improvement based on the maximum constraint violation. The Bayesian optimization algorithm implemented in this work has the ability to search over (i) a real desi...
Under the concept of "Industry 4.0", production processes will be pushed to be increasingly inter... more Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization goes beyond the traditional aim of capacity maximization, contributing also for organization's profitability and value. Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization's value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity optimization might hide operational inefficiency.
Sandwich structures with honeycomb core are widely used in the lightweight design and impact ener... more Sandwich structures with honeycomb core are widely used in the lightweight design and impact energy absorption applications in automotive, sporting, and aerospace industries. Recently, the auxetic honeycombs with negative Poisson's ratio attract a substantial attention for different engineering products. In this study, we implement Additive Manufacturing technology, experimental testing, and Finite Element Analysis (FEA) to design and investigate the mechanical behavior of a novel unit cell for sandwich structure core. The new core model contains the conventional and auxetic honeycomb cells beside each other to create a Hybrid Honeycomb (HHC) for the sandwich structure. The different designs of unit cells with the same volume fraction of 15% are 3D-printed using Fused Deposition Modeling technique, and the comparative study on the mechanical behavior of conventional honeycomb, auxetic honeycomb, and HHC structures is conducted. The quasi-static uniaxial compression tests are performed on the printed samples to investigate the mechanical behavior of the printed structures. The deformation and failure modes of the different designs are studied at the cell level utilizing FEA of the compression test and experimental observation. The compressive strength of the different design is measured using three experimental tests. The new HHC unit cell design shows significantly higher mechanical properties than the auxetic and the conventional designs. Modifying the design variables of hybrid cellular core structure allows us to tailor the mechanical properties and deformation pattern in macro level to achieve the desired mechanical properties in sandwich structures.
Broncas r esonancias de las campanas de la ig•lesia de La Candelaria, en el Bogotá que fu e. Son ... more Broncas r esonancias de las campanas de la ig•lesia de La Candelaria, en el Bogotá que fu e. Son las ocho de la noche y llueve a porfía. En los canalones, el agua fluye musicalmente y un niño se refugia en el amplio y pulcro lecho materno. Trae en sus brazos un libro, hermosamente empastado en España. E s uno de los volúmenes de las Ob ras cotnpletas de Julio V crne, en versión ca stellana publicada por la histórica edito rial madrileña de "Gaspar y Roig, Impresores".
This work introduces a new design algorithm to optimize progressively folding thin-walled structu... more This work introduces a new design algorithm to optimize progressively folding thin-walled structures and in order to improve automotive crashworthiness. The proposed design algorithm is composed of three stages: conceptual thickness distribution, design parameterization, and multi-objective design optimization. The conceptual thickness distribution stage generates an innovative design using a novel one-iteration compliant mechanism approach that triggers progressive folding even on irregular structures under oblique impact. The design parameterization stage optimally segments the conceptual design into a reduced number of clusters using a machine learning K-means algorithm. Finally, the multiobjective design optimization stage finds non-dominated designs of maximum specific energy absorption and minimum peak crushing force. The proposed optimization problem is addressed by a multiobjective genetic algorithm on sequentially updated surrogate models, which are optimally selected from a set of 24 surrogates. The effectiveness of the design algorithm is demonstrated on an S-rail thin-walled structure. The best compromised Pareto design increases specific energy absorption and decreases peak crushing force in the order of 8% and 12%, respectively. Recently, our research group has proposed the use of HCA topometry (thickness distribution) methods for compliant, plastically deformable structures to support the generation of conceptual design for progressively folding thin-walled components including S-rails [28]. This method follows the design principles of compliant mechanisms and their ability to transfer force and displacement from a given input
52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 2011
The field of topology design of compliant mechanisms has developed from infancy to well grown sta... more The field of topology design of compliant mechanisms has developed from infancy to well grown state in last 15 years. Born from the need of hingeless mechanisms in MicroElec-troMechanical Systems (MEMS), compliant mechanims are finding their use in wide range of applications like snap-through mechanisms, piezoelectric actuators and wing flapping mechanisms among many others. Most of the work developed so far, consider linear elastic material behavior and small displacment theory to design compliant mechanisms. In order to account for the effect of large displacements in mechanism design, geometric nonlinearity is considered by many researchers, however, nonlinearities arising from plasticity and contact are seldomly studied. One of the major challenges in the design of mechanisms considering nonlinearities is sensitivity analysis. Analytical expressions for sensitivities of objective function with respect to design variables can not be expressed in closed form when nonlinear finite element methods are used. Moreover, commercial finite element softwares which use implicit/explict solvers can not be used for such sensitivity calculations as they do not store stiffness matrices. In this work, optimal design for compliant mechanisms using control based material update scheme (HCA) is developed for linear case and the idea is extended to obtain concept topologies for nonlinear cases. Since this method does not involve sensitivity calculations when nonlinearities are considered, commercial FEA packages can be used which help in handling complex design problems in 2D and 3D. Although the final designs for nonlinear cases can not be claimed 'optimal', this method gives designer, a candidate designs which perform satisfactorily well under nonlinear conditions. This method is developed particularly for potential applications of compliant mechanisms in crashworthy designs where considering nonlinearity becomes essential. The applicability of the proposed method is shown by considering 2 examples.
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Papers by Andres Tovar