Andres Tovar | Indiana University Indianapolis (original) (raw)

Papers by Andres Tovar

Electrochem

This work presents a contribution to the study of a new Ni-rich spinel cathode material, LiNiMnO4... more This work presents a contribution to the study of a new Ni-rich spinel cathode material, LiNiMnO4, for Li-ion batteries operating in the 5-V region. The LiNiMnO4 compound was synthesized by a sol-gel method assisted by ethylene diamine tetra-acetic acid (EDTA) as a chelator. Structural analyses carried out by Rietveld refinements and Raman spectroscopy, selected area electron diffraction (SAED) and X-ray photoelectron (XPS) spectroscopy reveal that the product is a composite (LNM@NMO), including non-stoichiometric LiNiMnO4-δ spinel and a secondary Ni6MnO8 cubic phase. Cyclic voltammetry and galvanostatic charge-discharge profiles show similar features to those of LiNi0.5Mn1.5O4 bare. A comparison of the electrochemical performances of 4-V spinel LiMn2O4 and 5-V spinel LiNi0.5Mn1.5O4 with those of LNM@NMO composite demonstrates the long-term cycling stability of this new Ni-rich spinel cathode. Due to the presence of the secondary phase, the LNM@NMO electrode exhibits an initial spec...

Mechanics of Additive and Advanced Manufacturing, Volume 9

Laser-based metal additive manufacturing technologies such as Selective Laser Sintering (SLS) and... more Laser-based metal additive manufacturing technologies such as Selective Laser Sintering (SLS) and Selective Laser Melting (SLM) allow the fabrication of complex parts by selectively sintering or melting metallic powders layer by layer. Although elaborate features can be produced by these technologies, heat accumulation in overhangs leads to heat stress and warping, affecting the dimensional and geometrical accuracy of the part. This work introduces an approach to mitigate heat stress by minimizing the temperature gradient between the heat-accumulated zone in overhangs and the layers beneath. This is achieved by generating complex support structures that maintain the mechanical stability of the overhang and increase the heat conduction between these areas. The architecture of the complex support structures is obtained by maximizing heat conduction as an objective function to optimize the topology of support structure. This work examines the effect of various geometries on the objective function in order to select a suitable one to consume less material with almost same conduction. Ongoing work is the development of an experimental testbed for verification.

Nanomaterials

This work aimed at synthesizing MoO3 and MoO2 by a facile and cost-effective method using extract... more This work aimed at synthesizing MoO3 and MoO2 by a facile and cost-effective method using extract of orange peel as a biological chelating and reducing agent for ammonium molybdate. Calcination of the precursor in air at 450 °C yielded the stochiometric MoO3 phase, while calcination in vacuum produced the reduced form MoO2 as evidenced by X-ray powder diffraction, Raman scattering spectroscopy, and X-ray photoelectron spectroscopy results. Scanning and transmission electron microscopy images showed different morphologies and sizes of MoOx particles. MoO3 formed platelet particles that were larger than those observed for MoO2. MoO3 showed stable thermal behavior until approximately 800 °C, whereas MoO2 showed weight gain at approximately 400 °C due to the fact of re-oxidation and oxygen uptake and, hence, conversion to stoichiometric MoO3. Electrochemically, traditional performance was observed for MoO3, which exhibited a high initial capacity with steady and continuous capacity fadi...

Advances in Structural and Multidisciplinary Optimization

During the injection molding cycle, molten material is injected at high pressure inside the mold ... more During the injection molding cycle, molten material is injected at high pressure inside the mold and cooled down to form a solid part. This creates thermomechanical stresses that are alleviated by the correct design of a cooling system. In conventional molds, the cooling system consists of straight-line cooling channels, which can be manufactured using machining processes; however, they are thermally inefficient and unable to cool the injected part uniformly. The emergence of metal-based additive manufacturing techniques such as direct metal laser sintering (DMLS) allows the fabrication of molds with conformal cooling channels. Conformal cooling molds cool down the part faster and more uniformly; however, they face limitations. First, their fabrication cost is 10 to 20 times higher than the one of a conventional mold. Second, the DMLS process, which is the most popular fabrication method of conformal cooling molds, produces internal thermal stresses that distort the mold. The development of structural optimization methods such as multiscale topology optimization offers the potential to create novel and complex cellular structures that alleviate these current limitations. The objective of this research is to establish a multiscale topology optimization method for the optimal design of non-periodic cellular structures subjected to thermomechanical loads. The result is a hierarchically complex design that is thermally efficient, mechanically stable, and suitable for additive manufacturing. The proposed method seeks to minimize the mold mass at the macroscale, while satisfying the thermomechanical constraints at the mesoscale. The thermomechanical properties of the mesoscale cellular unit cells are estimated using homogenization theory. A gradient-based optimization algorithm is used for which macroscale and mesoscale sensitivity coefficients are derived. The design and evaluation of a porous injection mold is presented to demonstrate the proposed optimization method.

Advances in Structural and Multidisciplinary Optimization

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.

Revista Internacional De Metodos Numericos Para Calculo Y Diseno En Ingenieria, 2005

Summary The hybrid cellular automaton (HCA) algorithm is a methodology developed to simulate the ... more Summary The hybrid cellular automaton (HCA) algorithm is a methodology developed to simulate the process of structural adaptation in bones. This methodology combines elements of the cellular automaton paradigm with finite element analysis. With some modifications, the HCA algorithm has proved to be computationally efficient to solve structural optimization problems. The objective of this investigation is to demonstrate the use of the HCA algorithm in topology optimization to obtain light structures with maximum rigidity.

: Shape structural optimization for blast mitigation seeks to counteract the damaging effects of ... more : Shape structural optimization for blast mitigation seeks to counteract the damaging effects of an impulsive threat on occupants and critical components. The purpose of a vehicle energy-deflecting hull is to mitigate blast energies by channeling blast products and high-pressure fluids away from the target structure. Designs of pyramid‐shaped protective structures have been proposed in existing and concept vehicle's platforms. These structures are more effective than the traditional flat-plate designs in terms of cabin penetration and weight. Studies on other blast concept design remain scarce. This investigation addresses the design of blast‐protective structures from the design optimization perspective. The design problem is stated as to finding the optimum shape of the protective shell of minimum mass satisfying a deformation and envelops constraints. Performance improvements are observed as the envelope constraint is relaxed and the optimization problem includes a larger num...

The hybrid cellular automaton (HCA) method is a biologically inspired algorithm capable of topolo... more The hybrid cellular automaton (HCA) method is a biologically inspired algorithm capable of topology synthesis that was developed to simulate the behavior of the bone functional adaptation process. In this algorithm, the design domain is divided into cells with some communication property among neighbors. Local evolutionary rules, obtained from classical control theory, iteratively establish the value of the design variables in order to minimize the local error between a field variable and a corresponding target value. Karush-Kuhn-Tucker (KKT) optimality conditions have been derived to determine the expression for the field variable and its target. While averaging techniques mimicking intercellular communication have been used to mitigate numerical instabilities such as checkerboard patterns and mesh dependency, some questions have been raised whether KKT conditions are fully satisfied in the final topologies. Furthermore, the averaging procedure might result in cancellation or attenuati...

Volume 2B: 44th Design Automation Conference

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...

Plastic injection molding industry uses traditionally machined tools and dies to manufacture vari... more Plastic injection molding industry uses traditionally machined tools and dies to manufacture various sizes and shapes of plastic products. With the advent of advanced manufacturing technology and expanding global competition in business, it is necessary to provide innovative solutions to the injection molding industry to sustain their business. Typically, the cooling time comprises more than half of the overall injection molding cycle time. The application of additive manufacturing technique can provide a solution to reduce the cooling time in injection molding process. The potential of 3D printing technology to produce any size and shape of products using metal powders provides an opportunity to design and produce innovative injection molding tools, which is unattainable by traditional machining process. Though the conformal cooling channels are capable of reducing the cooling time significantly, the cost of manufacturing the injection molds by 3D printing is quite high and hence a...

Structural optimization efforts for blast mitigation seek to counteract the damaging effects of a... more Structural optimization efforts for blast mitigation seek to counteract the damaging effects of an impulsive threat on critical components of vehicles and to protect the lives of the crew and occupants. The objective of this investigation is to develop a novel optimization tool that simultaneously accounts for both energy dissipating properties of a shaped hull and the assembly constraints of such a component to the vehicle system. The resulting hull design is shown to reduce the blast loading imparted on the vehicle structure. Component attachment locations are shown to influence the major deformation modes of the target and the final hull design. INTRODUCTION Gross vehicle acceleration, often measured in peak and sustained g's, is of interest in the vehicle level blast mitigation problem. Unlike frontal crash events, the acceleration of the vehicle achieved during a blast event translates to vertical loads exerted on the pelvis and compression of the spinal cord, resulting in ...

A major challenge in the design of structural components subject to dynamic loading is the optimu... more A major challenge in the design of structural components subject to dynamic loading is the optimum design of the optimum transient response of the structure. The reduction in size of lightweight, fuel-efficient vehicles has promoted the use of new engineering materials in sophisticated designs of structural components that may act as energy absorbers in a collision. That makes the use of material optimization for crashworthiness attractive and increasing in popularity among automotive companies. This investigation incorporates optimization approach with modeling of viscoelastic structures to minimize the maximum nodal acceleration of the structure as well as minimize the maximum nodal displacement. Uni-dimensional models demonstrate the complexity of the analytical solution. For the theoretical approximation, the dynamic response of structural members is obtained employing Kelvin-Voigt (solid) viscoelastic models. The design variables correspond to the stiffness and damping coeffici...

This is a framework for optimizing additive manufacturing of plastic injection molds. The propose... more This is a framework for optimizing additive manufacturing of plastic injection molds. The proposed system consists of three modules, namely process and material modeling, multi-scale topology optimization, and experimental testing, calibration and validation. Advanced numerical simulation is implemented for a typical die with conformal cooling channels to predict cycle time, part quality and tooling life. A thermo-mechanical topology optimization algorithm is being developed to minimize the die weight and enhance its thermal performance. The technique is implemented for simple shapes for validation before it is applied to dies with conformal cooling in future work. A method for designing a die with porous material which can be produced in additive manufacturing is developed. Also a comprehensive set of systemic design rules are developed and to be integrated with CAD modeling to automate the process of obtaining viable plastic injection dies with conformal cooling channels. Finally,...

Journal of Medical Devices

This paper presents the mechatronic (mechanical and control system) design of a functional protot... more This paper presents the mechatronic (mechanical and control system) design of a functional prototype of a portable mechanical ventilator to treat patients with a compromised respiratory function. The portable ventilator ensures adequate oxygenation and carbon dioxide clearance while avoiding ventilator-induced lung injury (VILI). Oxygen is delivered through the compression of a bag valve (Ambu bag) using a moving strap. Carbon dioxide is cleared through the control of a pinch valve actuated by a low-torque servomotor. The positive end-expiratory pressure (PEEP) is controlled by an adjustable mechanical valve of the system. An Arduino Mega microcontroller board is used in this prototype to control the respiratory variables. All mechanical components as well as sensors, actuators, and control hardware are of common use in robotics and are very inexpensive. The total cost of the prototype built in this work is about $425 U.S. dollars. The design is meant to be replicated and utilized i...

Structural and Multidisciplinary Optimization

This work introduces an optimization procedure derived from the targeting force-displacement resp... more This work introduces an optimization procedure derived from the targeting force-displacement response (TFDR) method to improve the crashworthiness of full-size vehicle structures. The proposed method aims at targeting the vehicle’s acceleration-time response (ATR) under a crash event using topometry (thickness) optimization. In contrast to the original TFDR method, the proposed targeting method uses a moving coordinate system (MCS) that allows addressing fully dynamic crash models with initial velocity. By setting a proper target ATR curve, the proposed method can improve several crashworthiness indicators including specific energy absorption, maximum deceleration, dynamic penetration, and crash load efficiency. The result of the topometry optimization could be a guideline for the further design. In the proposed method, the nonlinear optimization problem is discretized into a series of analytical subproblems using equivalent dynamic load (EDL). In each iteration, the dynamic response from an explicit dynamic finite element (FE) analysis is utilized to define and solve a subproblem. To demonstrate the proposed iterative method, the baseline FE model of a Dodge Grand Caravan vehicle, obtained from the US National Highway Traffic Safety Administration (NHTSA) website, is optimized. The results show the effectiveness of the algorithm finding the element thickness distribution to make the acceleration-time response of the vehicle’s center of gravity (VCG) gradually approach a target curve. The proposed EDL algorithm finds a converged solution using less than 15 crash simulations. This makes it possible to solve problems involving full-size vehicle FE models.

Additive Manufacturing for the Aerospace Industry

Abstract Additive manufacturing (AM) is transforming all segments of the aerospace industry, incl... more Abstract Additive manufacturing (AM) is transforming all segments of the aerospace industry, including commercial and military aircraft, space applications, as well as missiles systems. Such transformation is due to the unique ability of AM to produce parts with complex designs, reduce manufacturing costs (material waste, assembly due to part consolidation, and the need for tools and fixtures), and fabricate parts with premium materials with small production runs and short turnaround times. AM allows the realization of advanced part designs that provide additional space, multifunctional parts, multimaterial parts, part consolidation, and parts that are difficult to machine. The capability of AM to fabricate freeform designs makes it very suitable for the aerospace industry. To date, aerospace companies, such as Boeing, have installed tens of thousands AM parts (including 200 unique nonmetallic part references) on 16 commercial and military aircraft. It has also started the production of titanium AM parts that will allow savings of up to three million USD per aircraft in the near future. GE Aviation is using metal AM to manufacture thousands of fuel nozzles annually for its new LEAP engine. Similarly, Airbus is utilizing metal AM brackets and bleed pipes on its aircraft. It is currently collaborating with Arconic on the production of large-scale AM airframe components and expects to produce 30 t of AM metal parts by December 2018. The main applications of AM in the aerospace industry are rapid prototyping, rapid tooling, and repair, as well as direct digital manufacturing (DDM) of parts made of metal, plastic, ceramic, and composite materials. Currently, the fastest growing application is DDM (final part manufacturing). For metal parts, the main AM technologies in aerospace applications are directed energy deposition and powder bed fusion. For nonmetallic parts, the dominant AM technologies are vat photopolymerization, material jetting, and material extrusion. This chapter reviews the applications, benefits, and opportunities of AM for the aerospace industry, describes the relevant AM technologies, and discusses the current challenges and potential applications.

Advances in Structural and Multidisciplinary Optimization, Dec 6, 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.

Electrochem

This work presents a contribution to the study of a new Ni-rich spinel cathode material, LiNiMnO4... more This work presents a contribution to the study of a new Ni-rich spinel cathode material, LiNiMnO4, for Li-ion batteries operating in the 5-V region. The LiNiMnO4 compound was synthesized by a sol-gel method assisted by ethylene diamine tetra-acetic acid (EDTA) as a chelator. Structural analyses carried out by Rietveld refinements and Raman spectroscopy, selected area electron diffraction (SAED) and X-ray photoelectron (XPS) spectroscopy reveal that the product is a composite (LNM@NMO), including non-stoichiometric LiNiMnO4-δ spinel and a secondary Ni6MnO8 cubic phase. Cyclic voltammetry and galvanostatic charge-discharge profiles show similar features to those of LiNi0.5Mn1.5O4 bare. A comparison of the electrochemical performances of 4-V spinel LiMn2O4 and 5-V spinel LiNi0.5Mn1.5O4 with those of LNM@NMO composite demonstrates the long-term cycling stability of this new Ni-rich spinel cathode. Due to the presence of the secondary phase, the LNM@NMO electrode exhibits an initial spec...

Mechanics of Additive and Advanced Manufacturing, Volume 9

Laser-based metal additive manufacturing technologies such as Selective Laser Sintering (SLS) and... more Laser-based metal additive manufacturing technologies such as Selective Laser Sintering (SLS) and Selective Laser Melting (SLM) allow the fabrication of complex parts by selectively sintering or melting metallic powders layer by layer. Although elaborate features can be produced by these technologies, heat accumulation in overhangs leads to heat stress and warping, affecting the dimensional and geometrical accuracy of the part. This work introduces an approach to mitigate heat stress by minimizing the temperature gradient between the heat-accumulated zone in overhangs and the layers beneath. This is achieved by generating complex support structures that maintain the mechanical stability of the overhang and increase the heat conduction between these areas. The architecture of the complex support structures is obtained by maximizing heat conduction as an objective function to optimize the topology of support structure. This work examines the effect of various geometries on the objective function in order to select a suitable one to consume less material with almost same conduction. Ongoing work is the development of an experimental testbed for verification.

Nanomaterials

This work aimed at synthesizing MoO3 and MoO2 by a facile and cost-effective method using extract... more This work aimed at synthesizing MoO3 and MoO2 by a facile and cost-effective method using extract of orange peel as a biological chelating and reducing agent for ammonium molybdate. Calcination of the precursor in air at 450 °C yielded the stochiometric MoO3 phase, while calcination in vacuum produced the reduced form MoO2 as evidenced by X-ray powder diffraction, Raman scattering spectroscopy, and X-ray photoelectron spectroscopy results. Scanning and transmission electron microscopy images showed different morphologies and sizes of MoOx particles. MoO3 formed platelet particles that were larger than those observed for MoO2. MoO3 showed stable thermal behavior until approximately 800 °C, whereas MoO2 showed weight gain at approximately 400 °C due to the fact of re-oxidation and oxygen uptake and, hence, conversion to stoichiometric MoO3. Electrochemically, traditional performance was observed for MoO3, which exhibited a high initial capacity with steady and continuous capacity fadi...

Advances in Structural and Multidisciplinary Optimization

During the injection molding cycle, molten material is injected at high pressure inside the mold ... more During the injection molding cycle, molten material is injected at high pressure inside the mold and cooled down to form a solid part. This creates thermomechanical stresses that are alleviated by the correct design of a cooling system. In conventional molds, the cooling system consists of straight-line cooling channels, which can be manufactured using machining processes; however, they are thermally inefficient and unable to cool the injected part uniformly. The emergence of metal-based additive manufacturing techniques such as direct metal laser sintering (DMLS) allows the fabrication of molds with conformal cooling channels. Conformal cooling molds cool down the part faster and more uniformly; however, they face limitations. First, their fabrication cost is 10 to 20 times higher than the one of a conventional mold. Second, the DMLS process, which is the most popular fabrication method of conformal cooling molds, produces internal thermal stresses that distort the mold. The development of structural optimization methods such as multiscale topology optimization offers the potential to create novel and complex cellular structures that alleviate these current limitations. The objective of this research is to establish a multiscale topology optimization method for the optimal design of non-periodic cellular structures subjected to thermomechanical loads. The result is a hierarchically complex design that is thermally efficient, mechanically stable, and suitable for additive manufacturing. The proposed method seeks to minimize the mold mass at the macroscale, while satisfying the thermomechanical constraints at the mesoscale. The thermomechanical properties of the mesoscale cellular unit cells are estimated using homogenization theory. A gradient-based optimization algorithm is used for which macroscale and mesoscale sensitivity coefficients are derived. The design and evaluation of a porous injection mold is presented to demonstrate the proposed optimization method.

Advances in Structural and Multidisciplinary Optimization

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.

Revista Internacional De Metodos Numericos Para Calculo Y Diseno En Ingenieria, 2005

Summary The hybrid cellular automaton (HCA) algorithm is a methodology developed to simulate the ... more Summary The hybrid cellular automaton (HCA) algorithm is a methodology developed to simulate the process of structural adaptation in bones. This methodology combines elements of the cellular automaton paradigm with finite element analysis. With some modifications, the HCA algorithm has proved to be computationally efficient to solve structural optimization problems. The objective of this investigation is to demonstrate the use of the HCA algorithm in topology optimization to obtain light structures with maximum rigidity.

: Shape structural optimization for blast mitigation seeks to counteract the damaging effects of ... more : Shape structural optimization for blast mitigation seeks to counteract the damaging effects of an impulsive threat on occupants and critical components. The purpose of a vehicle energy-deflecting hull is to mitigate blast energies by channeling blast products and high-pressure fluids away from the target structure. Designs of pyramid‐shaped protective structures have been proposed in existing and concept vehicle's platforms. These structures are more effective than the traditional flat-plate designs in terms of cabin penetration and weight. Studies on other blast concept design remain scarce. This investigation addresses the design of blast‐protective structures from the design optimization perspective. The design problem is stated as to finding the optimum shape of the protective shell of minimum mass satisfying a deformation and envelops constraints. Performance improvements are observed as the envelope constraint is relaxed and the optimization problem includes a larger num...

The hybrid cellular automaton (HCA) method is a biologically inspired algorithm capable of topolo... more The hybrid cellular automaton (HCA) method is a biologically inspired algorithm capable of topology synthesis that was developed to simulate the behavior of the bone functional adaptation process. In this algorithm, the design domain is divided into cells with some communication property among neighbors. Local evolutionary rules, obtained from classical control theory, iteratively establish the value of the design variables in order to minimize the local error between a field variable and a corresponding target value. Karush-Kuhn-Tucker (KKT) optimality conditions have been derived to determine the expression for the field variable and its target. While averaging techniques mimicking intercellular communication have been used to mitigate numerical instabilities such as checkerboard patterns and mesh dependency, some questions have been raised whether KKT conditions are fully satisfied in the final topologies. Furthermore, the averaging procedure might result in cancellation or attenuati...

Volume 2B: 44th Design Automation Conference

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...

Plastic injection molding industry uses traditionally machined tools and dies to manufacture vari... more Plastic injection molding industry uses traditionally machined tools and dies to manufacture various sizes and shapes of plastic products. With the advent of advanced manufacturing technology and expanding global competition in business, it is necessary to provide innovative solutions to the injection molding industry to sustain their business. Typically, the cooling time comprises more than half of the overall injection molding cycle time. The application of additive manufacturing technique can provide a solution to reduce the cooling time in injection molding process. The potential of 3D printing technology to produce any size and shape of products using metal powders provides an opportunity to design and produce innovative injection molding tools, which is unattainable by traditional machining process. Though the conformal cooling channels are capable of reducing the cooling time significantly, the cost of manufacturing the injection molds by 3D printing is quite high and hence a...

Structural optimization efforts for blast mitigation seek to counteract the damaging effects of a... more Structural optimization efforts for blast mitigation seek to counteract the damaging effects of an impulsive threat on critical components of vehicles and to protect the lives of the crew and occupants. The objective of this investigation is to develop a novel optimization tool that simultaneously accounts for both energy dissipating properties of a shaped hull and the assembly constraints of such a component to the vehicle system. The resulting hull design is shown to reduce the blast loading imparted on the vehicle structure. Component attachment locations are shown to influence the major deformation modes of the target and the final hull design. INTRODUCTION Gross vehicle acceleration, often measured in peak and sustained g's, is of interest in the vehicle level blast mitigation problem. Unlike frontal crash events, the acceleration of the vehicle achieved during a blast event translates to vertical loads exerted on the pelvis and compression of the spinal cord, resulting in ...

A major challenge in the design of structural components subject to dynamic loading is the optimu... more A major challenge in the design of structural components subject to dynamic loading is the optimum design of the optimum transient response of the structure. The reduction in size of lightweight, fuel-efficient vehicles has promoted the use of new engineering materials in sophisticated designs of structural components that may act as energy absorbers in a collision. That makes the use of material optimization for crashworthiness attractive and increasing in popularity among automotive companies. This investigation incorporates optimization approach with modeling of viscoelastic structures to minimize the maximum nodal acceleration of the structure as well as minimize the maximum nodal displacement. Uni-dimensional models demonstrate the complexity of the analytical solution. For the theoretical approximation, the dynamic response of structural members is obtained employing Kelvin-Voigt (solid) viscoelastic models. The design variables correspond to the stiffness and damping coeffici...

This is a framework for optimizing additive manufacturing of plastic injection molds. The propose... more This is a framework for optimizing additive manufacturing of plastic injection molds. The proposed system consists of three modules, namely process and material modeling, multi-scale topology optimization, and experimental testing, calibration and validation. Advanced numerical simulation is implemented for a typical die with conformal cooling channels to predict cycle time, part quality and tooling life. A thermo-mechanical topology optimization algorithm is being developed to minimize the die weight and enhance its thermal performance. The technique is implemented for simple shapes for validation before it is applied to dies with conformal cooling in future work. A method for designing a die with porous material which can be produced in additive manufacturing is developed. Also a comprehensive set of systemic design rules are developed and to be integrated with CAD modeling to automate the process of obtaining viable plastic injection dies with conformal cooling channels. Finally,...

Journal of Medical Devices

This paper presents the mechatronic (mechanical and control system) design of a functional protot... more This paper presents the mechatronic (mechanical and control system) design of a functional prototype of a portable mechanical ventilator to treat patients with a compromised respiratory function. The portable ventilator ensures adequate oxygenation and carbon dioxide clearance while avoiding ventilator-induced lung injury (VILI). Oxygen is delivered through the compression of a bag valve (Ambu bag) using a moving strap. Carbon dioxide is cleared through the control of a pinch valve actuated by a low-torque servomotor. The positive end-expiratory pressure (PEEP) is controlled by an adjustable mechanical valve of the system. An Arduino Mega microcontroller board is used in this prototype to control the respiratory variables. All mechanical components as well as sensors, actuators, and control hardware are of common use in robotics and are very inexpensive. The total cost of the prototype built in this work is about $425 U.S. dollars. The design is meant to be replicated and utilized i...

Structural and Multidisciplinary Optimization

This work introduces an optimization procedure derived from the targeting force-displacement resp... more This work introduces an optimization procedure derived from the targeting force-displacement response (TFDR) method to improve the crashworthiness of full-size vehicle structures. The proposed method aims at targeting the vehicle’s acceleration-time response (ATR) under a crash event using topometry (thickness) optimization. In contrast to the original TFDR method, the proposed targeting method uses a moving coordinate system (MCS) that allows addressing fully dynamic crash models with initial velocity. By setting a proper target ATR curve, the proposed method can improve several crashworthiness indicators including specific energy absorption, maximum deceleration, dynamic penetration, and crash load efficiency. The result of the topometry optimization could be a guideline for the further design. In the proposed method, the nonlinear optimization problem is discretized into a series of analytical subproblems using equivalent dynamic load (EDL). In each iteration, the dynamic response from an explicit dynamic finite element (FE) analysis is utilized to define and solve a subproblem. To demonstrate the proposed iterative method, the baseline FE model of a Dodge Grand Caravan vehicle, obtained from the US National Highway Traffic Safety Administration (NHTSA) website, is optimized. The results show the effectiveness of the algorithm finding the element thickness distribution to make the acceleration-time response of the vehicle’s center of gravity (VCG) gradually approach a target curve. The proposed EDL algorithm finds a converged solution using less than 15 crash simulations. This makes it possible to solve problems involving full-size vehicle FE models.

Additive Manufacturing for the Aerospace Industry

Abstract Additive manufacturing (AM) is transforming all segments of the aerospace industry, incl... more Abstract Additive manufacturing (AM) is transforming all segments of the aerospace industry, including commercial and military aircraft, space applications, as well as missiles systems. Such transformation is due to the unique ability of AM to produce parts with complex designs, reduce manufacturing costs (material waste, assembly due to part consolidation, and the need for tools and fixtures), and fabricate parts with premium materials with small production runs and short turnaround times. AM allows the realization of advanced part designs that provide additional space, multifunctional parts, multimaterial parts, part consolidation, and parts that are difficult to machine. The capability of AM to fabricate freeform designs makes it very suitable for the aerospace industry. To date, aerospace companies, such as Boeing, have installed tens of thousands AM parts (including 200 unique nonmetallic part references) on 16 commercial and military aircraft. It has also started the production of titanium AM parts that will allow savings of up to three million USD per aircraft in the near future. GE Aviation is using metal AM to manufacture thousands of fuel nozzles annually for its new LEAP engine. Similarly, Airbus is utilizing metal AM brackets and bleed pipes on its aircraft. It is currently collaborating with Arconic on the production of large-scale AM airframe components and expects to produce 30 t of AM metal parts by December 2018. The main applications of AM in the aerospace industry are rapid prototyping, rapid tooling, and repair, as well as direct digital manufacturing (DDM) of parts made of metal, plastic, ceramic, and composite materials. Currently, the fastest growing application is DDM (final part manufacturing). For metal parts, the main AM technologies in aerospace applications are directed energy deposition and powder bed fusion. For nonmetallic parts, the dominant AM technologies are vat photopolymerization, material jetting, and material extrusion. This chapter reviews the applications, benefits, and opportunities of AM for the aerospace industry, describes the relevant AM technologies, and discusses the current challenges and potential applications.

Advances in Structural and Multidisciplinary Optimization, Dec 6, 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.