Mary Frecker

Pennsylvania State University, University Park, Maryland, United States

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Publications (98)43.68 Total impact

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    ABSTRACT: Origami engineering – the use of origami principles in engineering applications – provides numerous opportunities to revolutionize the way we design, manufacture, assemble, and package products and devices. By combining origami principles with active materials, we can create reconfigurable products and devices that can fold and unfold on demand. In origami, the folded medium is paper, yet many engineering applications require materials with finite thickness to provide the necessary strength and stiffness to achieve the desired functionality. In such applications, it is important to distinguish between bending and folding so that we understand the differences in material behavior when actuated. In this paper, we propose definitions for bending and folding for materials used in engineering applications. The literature is reviewed in detail to provide context and support for the proposed definitions, and examples from our own research with active materials, specifically, magneto-active elastomers (MAE) and dielectric elastomers (DE), are used to illustrate the subtle, yet important, differences between bending and folding in materials with finite thickness.
    International Design and Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE), Buffalo, New York; 08/2014
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    ABSTRACT: The field of active origami explores the incorporation of active materials into origami-inspired structures in order to serve as a means of actuation. Active origami-inspired structures capable of folding into complex three-dimensional (3D) shapes have the potential to be lightweight and versatile compared to traditional methods of actuation. This paper details the finite element analysis and experimental validation of unimorph actuators. Actuators are fabricated by adhering layers of electroded dielectric elastomer (3M VHB F9473PC) onto a passive substrate layer (3M Magic Scotch Tape). Finite element analysis of the actuators simulates the electromechanical coupling of the dielectric elastomer under an applied voltage by applying pressures to the surfaces of the dielectric elastomer where the compliant electrode (conductive carbon grease) is present. 3D finite element analysis of the bending actuators shows that applying contact boundary conditions to the electroded region of the active and passive layers provides better agreement to experimental data compared to modeling the entire actuator as continuous. To improve the applicability of dielectric elastomer-based actuators for active origami-inspired structures, folding actuators are developed by taking advantage of localized deformation caused by a passive layer with non-uniform thickness. Two-dimensional analysis of the folding actuators shows that agreement to experimental data diminishes as localized deformation increases. Limitations of using pressures to approximate the electromechanical coupling of the dielectric elastomer under an applied electric field and additional modeling considerations are also discussed.
    Smart Materials and Structures 08/2014; 23(9):094002. · 2.02 Impact Factor
  • S Ahmed, Z Ounaies, M Frecker
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    ABSTRACT: Origami engineering aims to combine origami principles with advanced materials to yield active origami shapes, which fold and unfold in response to external stimuli. This paper explores the potential and limitations of dielectric elastomers (DEs) as the enabling material in active origami engineering. DEs are compliant materials in which the coupled electro-mechanical actuation takes advantage of their low modulus and high breakdown strength. Until recently, prestraining of relatively thick DE materials was necessary in order to achieve the high electric fields needed to trigger electrostatic actuation without inducing a dielectric breakdown. Although prestrain improves the breakdown strength of the DE films and reduces the voltage required for actuation, the need for a solid frame to retain the prestrain state is a limitation for the practical implementation of DEs, especially for active origami structures. However, the recent availability of thinner DE materials (50 μm, 130 μm, 260 μm) has made DEs a likely medium for active origami. In this work, the folding and unfolding of DE multilayered structures, along with the realization of origami-inspired 3D shapes, are explored. In addition, an exhaustive study on the fundamentals of DE actuation is done by directly investigating the thickness actuation mechanism and comparing their performance using different electrode types. Finally, changes in dielectric permittivity as a function of strain, electrode type and applied electric field are assessed and analyzed. These fundamental studies are key to obtaining more dramatic folding and to realizing active origami structures using DE materials.
    Smart Materials and Structures 08/2014; 23(9):094003. · 2.02 Impact Factor
  • Smart Materials and Structures 08/2014; 23(9):090201. · 2.02 Impact Factor
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    ABSTRACT: We are investigating the use of dielectric elastomers (DE) to realize origami-inspired folding and unfolding of structures. DEs are compliant materials where the coupled electro-mechanical actuation takes advantage of the low modulus and high breakdown strength of the elastomer. Until recently, pre-straining of relatively thick DE materials was necessary in order to achieve the high electric fields required to trigger electrostatic actuation. However, the current availability of thinner DE materials (ex: VHB 9469PC-130μm, VHB 9473 PC −260 μm) has enabled their actuation at achievable electric fields without the need to pre-strain. In this work, an exhaustive study on the fundamentals of DE actuation is done by exploring thickness actuation mechanism and studying the change in dielectric permittivity; we also take advantage of the thin DEs to build actuators with very large bending angles. In particular, we relate the electrostatically-induced thickness contraction in a DE monomorph to the resulting bending once an inactive substrate is added. Both statically and dynamically induced electromechanical thickness strains are measured, and the experimental data is used as an input to a bender model to predict and optimize bending response; variables such as type of inactive material, number of DE layers, and type of electrodes are examined. We will also experimentally track the changes in the dielectric constant as a function of strain, electrode type, and applied electric field; the measured behavior will be used to model thickness and bending actuation. These fundamental studies are necessary to determine ability and limitation of DE materials in a bender configuration. Finally, bending of the DE actuator is transformed into folding by a novel geometric approach, where different shaped notches are introduced in the inactive substrate. The folding configuration is a step towards realizing active origami structure.
    ASME 2013 Conference on Smart Materials, Adaptive Structures and Intelligent Systems; 09/2013
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    ABSTRACT: The use of origami principles to create 3-dimensional shapes has the potential to revolutionize active material structures and compliant mechanisms. Active origami structures can be applied to a broad range of areas such as reconfigurable aircraft and deployable space structures as well as instruments for minimally invasive surgery. Our current research is focused on dielectric elastomer (DE) and magneto active elastomer (MAE) materials to create multi-field responsive structures. Such multi-field responsive structures will integrate the DE and MAE materials to enable active structures that fold/unfold in different ways in response to electric and/or magnetic field. They can also unfold either as a result of eliminating the applied field or in response to the application of an opposite field. This concept is demonstrated in a folding cube shape and induced locomotion in the MAE material. Two finite element models are developed for both the DE and MAE materials and validated through physical testing of these materials. The models are then integrated to demonstrate multi-field responses of a bi-fold multi-field responsive structure. The bi fold model is designed to fold about one axis in an electric field and a perpendicular axis in a magnetic field. Future modeling efforts and research directions are also discussed based on these preliminary results.
    Proceedings of the ASME 2013 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference IDETC/CIE 2013, Portland, Oregon, USA; 08/2013
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    ABSTRACT: Compliant mechanisms have many advantages over rigid-link mechanisms. However, one of the challenges of compliant mechanisms is the trade-off between a large range of motion and a high out-of-plane stiffness. Furthermore, the out-of-plane stiffness is shown to vary over the range of motion. Especially for large-displacement compliant mechanisms this can be by a significant amount. In this paper the use of curved beam elements in a compliant mechanism is shown to have impact on this trade-off. The influence of curved beam elements on the out-of-plane stiffness over the entire range of motion is presented for simple structures such as a single beam element and double beam elements, as well as a compliant finger. With the use of a genetic algorithm optimization, the difference in performance of a design with only straight beam elements versus one with curved beam elements is highlighted and the effect on the out-of-plane stiffness profile is presented. The optimization with curved beam elements results in solutions with a performance in terms of objective function values that cannot be found by the optimization with only straight beam elements. It is shown that for simple structures the use of curved beam elements has a large influence on the shape of the out-of-plane stiffness profile along the range of motion, while for the compliant finger the influence is mainly in the variables of the out-of-plane stiffness profile.
    ASME 2013 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference; 08/2013
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    ABSTRACT: Contact-aided compliant cellular mechanisms are cellular structures designed with contact mechanisms integrated into each cell to provide stress relief. This article addresses compliant cellular structures having curved walls and internal contact mechanisms. The use of curved walls in cellular structures tends to improve their performance in terms of global strain capability and is beneficial for fabrication. In some cells, the addition of contact mechanisms results in stress relief, allowing the cells to be stretched farther than they could without contact. The cellular structures with curved walls are modeled, and finite element analysis is used to calculate the maximum global strains for comparable noncontact and contact-aided cells. An optimization procedure is performed to find the cell geometries that result in the highest global strains. Strains of up to 32.4% and 19.7% are predicted for the optimized curved noncontact and contact-aided cells, respectively. Additionally, a comparison of curved and noncurved, noncontact and contact-aided cells shows that the addition of curved walls results in a significantly greater improvement in global strains than that gained by adding a contact mechanism. Mesoscale contact-aided compliant cellular mechanism designs are fabricated via the lost mold–rapid infiltration forming process and are tested using a custom-designed test rig.
    Journal of Intelligent Material Systems and Structures 11/2012; 23(16):1773-1785. · 1.52 Impact Factor
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    ABSTRACT: Contact aided compliant mechanisms are a class of compliant mechanisms where parts of the mechanism come into contact with one another during motion. Such mechanisms can have nonlinear stiffness, cause stress-relief, or generate non-smooth paths. New contact aided compliant mechanisms called bend-and-sweep compliant mechanisms are presented in this paper. These bend-and-sweep mechanisms are made up of compliant joints which are alternately located in two orthogonal directions, and they also exhibit nonlinear stiffness in two orthogonal directions. The stiffness properties of these mechanisms, in each direction, can be tailored by varying the geometry of the compliant joints. One application of these mechanisms is in the passive wing morphing of flapping wing UAVs or ornithopters. A design study is conducted to understand the effect of hinge geometry on the deflections and maximum von Mises stress during upstroke and downstroke. It is shown that the bend-and-sweep compliant elements deflect as desired in both the bending and sweep directions.
    ASME 2012 Conference on Smart Materials, Adaptive Structures and Intelligent Systems; 09/2012
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    ABSTRACT: This paper presents the optimization of hexagonal honeycomb structures with internal contact mechanisms for energy absorption applications. While extensive work has been reported in the literature on traditional honeycombs of varying geometries under dynamic and static loading, contact-aided compliant cellular mechanisms under quasi-static crushing or impact have not been previously considered. This paper addresses this void through the optimization of a hexagonal honeycomb unit cell containing a contact mechanism. An optimization problem is formulated that maximizes the strain energy per area of a contact-aided compliant cellular mechanism. Two- and three-variable optimization problems are considered, using variables that define the cell geometry and the initial contact gap. It is found that with the addition of a contact mechanism, more strain energy can be absorbed when compared to the same cell without a contact mechanism.
    ASME 2012 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference; 08/2012
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    ABSTRACT: Few standardized testing procedures exist for instruments intended for Natural Orifice Translumenal Endoscopic Surgery. These testing procedures are critical for evaluating surgical skills and surgical instruments to ensure sufficient quality. This need is widely recognized by endoscopic surgeons as a major hurdle for the advancement of Natural Orifice Translumenal Endoscopic Surgery. Beginning with tasks currently used to evaluate laparoscopic surgeons and instruments, new tasks were designed to evaluate endoscopic surgical forceps instruments. Six tasks have been developed from existing tasks, adapted and modified for use with endoscopic instruments, or newly designed to test additional features of endoscopic forceps. The new tasks include the Fuzzy Ball Task, Cup Drop Task, Ring Around Task, Material Pull Task, Simulated Biopsy Task, and the Force Gauge Task. These tasks were then used to evaluate the performance of a new forceps instrument designed at Pennsylvania State University. The need for testing procedures for the advancement of Natural Orifice Translumenal Endoscopic Surgery has been addressed in this work. The developed tasks form a basis for not only testing new forceps instruments, but also for evaluating individual performance of surgical candidates with endoscopic forceps instruments.
    JSLS: Journal of the Society of Laparoendoscopic Surgeons / Society of Laparoendoscopic Surgeons 01/2012; 16(1):95-104. · 0.81 Impact Factor
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    ABSTRACT: Knowledge discovery in multi-dimensional data is a challenging problem in engineering design. For example, in trade space exploration of large design data sets, designers need to select a subset of data of interest and examine data from different data dimensions and within data clusters at different granularities. This exploration is a process that demands both humans, who can heuristically decide what data to explore and how best to explore it, and computers, which can quickly extract features that may be of interest in the data. Thus, to support this process of knowledge discovery, we need tools that can go beyond traditional computer-oriented optimisation approaches and support advanced designer-centred trade space exploration and data interaction. This paper is an effort to address this need. In particular, we propose the interactive multiscale-nested clustering and aggregation framework to support trade space exploration of multi-dimensional data common to design optimisation. A system prototype of this framework is implemented to allow users to visually examine large design data sets through interactive data clustering, aggregation, and visualisation. The paper also presents an evaluation study involving morphing wing design using this prototype system.
    Journal of Engineering Design. 01/2012; 23(1):23-47.
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    ABSTRACT: Free standing, micron scale, yttria stabilized zirconia parts for surgical instrument applications have been fabricated using a lithography based mold forming technique. Problems and solutions inherent to molding micron scale ceramic parts, such as suspension viscosity, surface spallation, and surface roughness are addressed. Concentrated zirconia suspensions, achieved through a chemically aided attrition milling process, are gelcast into molds via a screen printing method to form parts. After sintering, near theoretical density (99.8%) is achieved with a grain size of 500 nm.
    Characterization and Control of Interfaces for High Quality Advanced Materials II: Ceramic Transactions, Volume 198, 06/2011: pages 179 - 184; , ISBN: 9781118144145
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    ABSTRACT: Contact-Aided Compliant Cellular Mechanisms (C3M) are compliant cellular structures with integrated contact mechanisms. The focus of the paper is on the design, fabrication, and testing of C3M with curved walls for high strain applications. It is shown that global strains were increased by replacing straight walls with curved walls in the traditional honeycomb structure, while the addition of contact mechanisms increased cell performance via stress relief in some cases. Furthermore, curved walls are beneficial for fabrication at the meso-scale. The basic curved honeycomb cell geometry is defined by a set of variables. These variables were optimized using Matlab and finite element analysis to find the best non-contact and contact-aided curved cell geometries as well as the cell geometry that provides the greatest stress relief. Currently, the most effective contact-aided curved honeycomb cell can withstand global strains approximately 160% greater than the most effective contact-aided, non-curved cell. Four different designs were fabricated via the Lost Mold-Rapid Infiltration Forming (LM-RIF) process. An array of the contact-aided optimized curved cell was then mechanically tested using a custom designed test rig, and the results were found to have a higher modulus of elasticity and lower global strain than the predictions. Despite these discrepancies, a high-strength highstrain cellular structure was developed, for potential use in morphing aircraft applications.
    Proc SPIE 03/2011;
  • Milton E. Aguirre, Mary Frecker
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    ABSTRACT: This work is part of a multidisciplinary project developing design and manufacturing methods for narrow-gauge surgical instruments intended for advanced minimally invasive surgery. The instruments are designed specifically for Penn State’s lost mold rapid infiltration forming process, which is capable of fabricating hundreds of freestanding meso-scale parts. In previous work, a 1 mm diameter forceps case study demonstrated the design and fabrication process. The forceps is a monolithic compliant mechanism (CM) that relies on contact to re-distribute maximum stresses to generate larger elastic tip deflections; a phenomenon defined here as contact stress-relief. Prototypes were developed and evaluated in an end user surgical simulator. Feedback from 11 clinicians identified the total jaw opening of the forceps must be increased in the next generation of prototypes. This paper focuses on exploiting the benefits of contact-aided compliant mechanism (CCM) design to obtain larger elastic tip deflections and thus jaw openings. Using the commercially available finite element software package ANSYS to model large deformation and contact, an optimization problem is developed to determine the effects of incorporating additional contact elements in a CCM design on maximizing elastic tip deflection. Results show that designs with multiple contact elements generate larger elastic tip deflections due to a multi-stage contact stress-relief profile.
    ASME 2011 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference; 01/2011
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    ABSTRACT: Flapping wing Unmanned Aerial Vehicles (UAVs) or ornithopters are proliferating in both the civil and military markets. Ornithopters have the potential to combine the agility and maneuverability of rotary wing aircraft with excellent performance in low Reynolds number flight regimes. These traits promise optimized performance over multiple mission scenarios. Nature achieves this broad performance in birds using wing gaits that are optimized for a particular flight regime. The goal of this work is to improve the performance of ornithopters during steady level flight by passively implementing the Continuous Vortex Gait (CVG) found in natural avian flyers. In this paper we present new experimental results for a one degree of freedom (1DOF) compliant spine which was inserted into an experimental test ornithopter leading edge wing spar in order to achieve the desired kinematics. The lift and thrust along with electric power metrics at different flapping frequencies were measured using a six-channel load cell and a current senor, respectively. These metrics were determined for the test ornithopter both with and without the compliant spine insert. Initial results validate the ability of our compliant spine design to withstand the loads seen during flight at flapping frequencies of up to and including 5 Hz. For the ornithopter test platform used in the study, inserting the compliant spines into the wing leading edge spar accurately simulates the CVG increasing the mean lift by 16%, and reducing the power consumed by 45% without incurring any thrust penalties.
    ASME 2011 Conference on Smart Materials, Adaptive Structures and Intelligent Systems; 01/2011
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    ABSTRACT: Ornithopters or flapping wing Unmanned Aerial Vehicles (UAVs) have potential applications in civil and military sectors. Amongst the UAVs, ornithopters have a unique ability to fly in low Reynolds number regions and also have the agility and maneuverability of a rotary wing aircraft. In nature, birds achieve such special characteristics by morphing their wings. The compliant spine (CS) design concept presented here represents a novel method of achieving wing morphing passively. In this paper, an optimal design method is developed that incorporates dynamic finite element analysis. To solve the CS design problem a new multi-objective optimization problem is formulated with three objective functions. The first objective function seeks to minimize the mass of the compliant spine. The second objective function seeks to maximize the deflection of the compliant spine for a particular dynamic loading condition. Finally, the third objective function seeks to minimize the stress in the design observed under the dynamic loading conditions experienced during flight. The deflections and stresses in the CS design are based on measured wing loads and are calculated by applying a sinusoidal forcing function at a prescribed forcing frequency. The optimization, performed via a controlled elitist genetic algorithm which is a variant of NSGA-II, is used to design CSs operating under dynamic conditions. Modal analysis and frequency response of an optimal compliant spine during the upstroke are also shown.
    ASME 2011 Conference on Smart Materials, Adaptive Structures and Intelligent Systems; 01/2011
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    ABSTRACT: The concept proposed in thei work for chord extension is the use of a bistable arch and thin plate system. There are two foci of this paper: (1) Design of the arch and (2)Model validation via experiment. Results show that bistability and symmetric deformation can be achieved when there are flexible hinges at the boundary and input. In addition, the presented finite element model provides good agreement with experimental results.
    Proc SPIE 03/2010;
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    ABSTRACT: The design and fabrication of meso-scale cellular contact-aided compliant mechanisms with micron sized features are presented in this paper. Cellular structures with internal contact mechanisms exhibit a reduction in stress during deformation and, thus, can be stretched further than they could without a contact mechanism. Fabricating such structures at a meso-scale can result in new high-strength, high-strain materials. Manufacturing at a meso-scale restrains the maximum aspect ratio and the initial contact gap of the mechanism. An analytical model is used to resolve the tradeoffs between these manufacturing constraints and to design suitable contact-aided cellular mechanisms. A lost mold rapid infiltration forming process is employed to fabricate meso-scale cellular mechanisms using either 316L stainless steel or a composite 316L stainless steel with nanoparticulate zirconia. A custom rig was developed to test meso-scale cellular mechanisms. The elastic modulus of 316L stainless steel was found to be about 110 ± 40 GPa both from tensile testing of test bars and from model-matching of cellular mechanisms. The cellular mechanisms were observed to exhibit about 1.1% of overall strain before any local permanent deformation. This study validates the efficacy of the design and fabrication methodology for the meso-scale cellular mechanisms.
    ASME 2010 Conference on Smart Materials, Adaptive Structures and Intelligent Systems; 01/2010
  • Milton E. Aguirre, Mary Frecker
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    ABSTRACT: This work describes a design and optimization method for developing hybrid, multi-material, compliant instruments which are expected to be useful in mini-laparoscopy and natural orifice translumenal endoscopic surgery. These two-material devices are designed specifically for Penn State’s lost mold rapid infiltration process, which is capable of fabricating hundreds of freestanding meso-scale parts in parallel. New narrow-gauge surgical procedures impose severe geometric constraints that challenge traditional compliant mechanism design methods. Since narrow-gauge constraints leave geometry optimization ineffective, new design methods are explored to improve the performance of a 1 mm diameter contact-aided compliant forceps. By considering hybrid designs, new design possibilities are enabled through material variation. The hybrid forceps has desired regions of flexibility and stiffness that can be isolated to improve tool performance. For instance, a hybrid forceps can be designed with greater flexibility in some regions to provide larger jaw openings while maintaining high stiffness in other regions to obtain large grasping forces, both vital features in a surgical forceps. Using ANSYS to model large deformation and contact, an optimization problem is formulated to maximize tool performance and to determine optimal segregation of hybrid materials considering a range of modulus ratios. Materials under consideration include nanoparticulate 3 mol% yttria partially stabilized zirconia (3YSZ) and austenitic (300 series) stainless steel. All results are compared to previously optimized homogeneous designs.
    ASME 2010 Conference on Smart Materials, Adaptive Structures and Intelligent Systems; 01/2010