[show abstract][hide abstract] 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
[show abstract][hide abstract] 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.
[show abstract][hide abstract] 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
[show abstract][hide abstract] 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.
[show abstract][hide abstract] 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.
[show abstract][hide abstract] 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.
[show abstract][hide abstract] ABSTRACT: Free-standing mesoscale (340 mum x 30 mum x 20 mum) bend bars with an aspect ratio over 15:1 and an edge resolution as fine as a single grain diameter ( approximately 400 nm) have been fabricated in large numbers on refractory ceramic substrates by combining a novel powder processing approach with photoresist molds and an innovative lost-mold thermal process. The colloid and interfacial chemistry of the nanoscale zirconia particulates has been modeled and used to prepare highly concentrated suspensions. Engineering solutions to challenges in mold fabrication and casting have yielded free-standing, crack-free parts. Molds are fabricated using high-aspect-ratio photoresist on ceramic substrates. Green parts are formed using a rapid infiltration method that exploits the shear thinning behavior of the highly concentrated ceramic suspension in combination with gelcasting. The mold is thermally decomposed and the parts are sintered in place on the ceramic substrate. Chemically aided attrition milling disperses and concentrates the as-received 3Y-TZP powder to produce a dense, fine-grained sintered microstructure. Initial three-point bend strength data are comparable to that of conventional zirconia; however, geometric irregularities (e.g., trapezoidal cross sections) are present in this first generation and are discussed with respect to the distribution of bend strength.
Journal of the American Ceramic Society 01/2009; 92(Suppl 1):S63-S69. · 2.11 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this work, a two-stage design optimization procedure is developed to explore the effect of optimal actuator placement and position on energy efficiency in morphing wings. Diamond-shaped cells similar to NextGen's Batwing concept are used to examine this procedure. The finite element model considers elastic skin, actuator, and aerodynamic loads. Force displacement and efficiency studies are conducted using one and two unit cells, respectively. The model is then expanded to include multiple unit cells and actuators. A two-stage optimization process using a Genetic Algorithm and gradient-based optimization is also developed. The two-stage optimization is used to optimize actuator position and placement for different constraints and load cases. Results show that placement and position optimization produce small gains in energy efficiency; morphing using a soft isotropic skin is more efficient than stiff isotropic or anisotropic skins. In addition, the GA did not use all of the available actuators to maximize energy efficiency. The total actuator mass is also considered and is dependent on the maximum applied force per actuator and the number of actuators in the mechanism.
Journal of Intelligent Material Systems and Structures 01/2009; 20(7):815-824. · 1.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: Iterative process improvements have been used to eliminate strength-limiting geometric flaws in mesoscale bend bars composed of yttria-tetragonal zirconia polycrystals (Y-TZP). These improvements led to large quantities of high bend strength material. The metrology of Y-TZP mesoscale bend bars produced using a novel lost mold-rapid infiltration-forming process (LM-RIF) is characterized over several process improvements. These improvements eliminate trapezoidal cross sections in the parts, reduce concave upper surfaces in cross section, and minimize warping along the long axis of 332 x 26 x 17 mum mesoscale bend bars. The trapezoidal cross sections of earlier, first-generation parts were due to the absorption of high-energy ultraviolet (UV) light during the photolithographic mold-forming process, which produced nonvertical mold walls that the parts mirrored. The concave upper surfaces in cross section were eliminated by implementing a RIF-buffing process. Warping during sintering was attributed to impurities in the substrate, which creates localized grain growth and warping as the tetragonal phase becomes destabilized. Precision in the part dimensions is demonstrated using optical profilometry on bend bars and a triangular test component. The bend bar dimensions have a 95% confidence interval of < +/-1 mum, and the tip radius of the triangular test component is 3 mum, consistent with the UV-photolithographic process used to form the mold cavities. The average bend strength of the mesoscale Y-TZP bend exceeds 2 GPa with a Weibull modulus equal to 6.3.
Journal of the American Ceramic Society 01/2009; 92(Suppl 1):S70-S78. · 2.11 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this paper we explore the use of bistable mechanisms for rotor morphing, specifically, blade tip twist. The optimal blade twist distributions for hover and high-speed forward flight are very different, and the ability of the rotor to change effective twist is expected to be advantageous. Bistable or "snap-through" mechanisms have multiple stable equilibrium states and are a novel way to achieve large actuation output stroke at relatively modest effort for gross rotor morphing applications. This is because in addition to the large actuation stroke associated with the snap-through (relative to conventional actuator/ amplification systems) coming at relatively low actuation effort, no locking is required in either equilibrium state (since they are both stable). In this work, the performance of a bistable twisting device is evaluated under an aerodynamic lift load. The device is analyzed using finite element analysis to predict the device's load carrying capability and bistable behavior.
[show abstract][hide abstract] ABSTRACT: Sandwich structures consisting of contact-aided compliant mechanisms are presented for morphing aircraft skin. A contact mechanism is used to alleviate stresses and to decrease the out-of-plane deflection. A methodology to design such mechanisms, which takes into account the aerodynamic loads, is presented. The method is applied to a small UAV and results are compared with those of honeycomb structures in terms of structural mass, global strain and maximum stresses. Different material models such as linearly elastic and multi-linear elastic are considered. For linearly elastic materials, contact-induced stress-relief is advantageous and for nonlinear elastic materials, reduction of transverse deflection due to contact is useful. In either case, the structural mass of the contact-aided structures is less than that of the corresponding non-contact structures.
[show abstract][hide abstract] ABSTRACT: Morphing aircraft wings offer great potential benefits of achieving multi mission capability as well as high maneuverability under different flight conditions. However, they present many design challenges in the form of conflicting design requirements. The current research aims to develop design methodologies for the design of a morphing aircraft wing. Focus of this work is on developing an internal mechanism of the wing that can produce the desired wing shape change. This paper presents a design methodology that employs planar unit cells of pre-determined shape and layout as the internal wing structure for achieving the desired wing shape change. This method is particularly useful in cases where the desired morphing is two-dimensional in nature. In such cases, intuitive cell designs such as diamond or hexagonal shaped cells may be used in layouts that achieve desired wing morphing. The shape change depends on the cell shape as well as cell arrangement in the design domain. In this paper, a design based on the TSCh wing (NextGen Aeronautics Inc.) using cellular mechanisms to achieve a two-dimensional wing shape change is discussed. Additionally, a reeling mechanism for achieving cable actuation is presented
[show abstract][hide abstract] ABSTRACT: This article discusses a methodology for designing compliant mechanisms with piezoelectric actuation to obtain maximum deflection and force at the output point. The focus is on design of compliant mechanisms with multiple piezoelectric actuators. The number, size, and position of the actuators within the compliant mechanism are optimized for the maximum output deflection. Predicted results demonstrate that compliant mechanisms with multiple, optimally placed actuators outperform those with a single actuator placed at a predetermined location.
Journal of Intelligent Material Systems and Structures 03/2007; 18(3):209-217. · 1.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: With recent computer advances, visualization techniques are becoming more prevalently used as decision support tools for parametric
design and engineering optimization. Despite the apparent advantages of visualization techniques, we have found little evidence
in the engineering design literature that assesses the impact of fast graphical design interfaces on the efficiency and effectiveness
of engineering design decisions. In this paper, we present experimental results from an I-beam design problem where the importance
of rapid feedback is investigated by incorporating time delays in the software response to “mimic” computationally expensive
design analyses. Design efficiency is measured by recording the completion time for solving the design problem, and design
effectiveness is measured by calculating the error between a submitted design and the known optimum. The impact of graphical
feedback is examined by comparing user performance on three different design interfaces to determine if their functionality
and graphical capabilities mediate the impact of response delays in the software or the amount of training needed. Experimental
results indicate that, on average, error increased by 280% and completion time increased by 33% when a delay of 1.5s was
present, and the perceived workload significantly increased as well. Meanwhile, user performance improved and perceived workload
decreased as the “richness” of the design interface increased. The combination of a rich interface with a fast response time,
therefore, will lead to the “best” interface as one might surmise, but our work provides the first empirical evidence of the
effect of response delay on user performance within a realistic engineering design setting. Implications for interface development
for engineering design are explored within the context of our findings, as are suggestions for future work.
Research in Engineering Design 01/2007; 18(2):49-65. · 1.56 Impact Factor
[show abstract][hide abstract] ABSTRACT: Electro-elastomers are large strain smart materials capable of both sensing and actuation. Typical electro-elastomer setups consist of either a silicone or acrylic membrane sandwiched between two compliant grease electrodes. Silicone electro-elastomers have maximum elastic strains between 200% and 350%. Acrylic electro-elastomers are more widely employed due to larger actuation strains but are softer than silicone and have a lower force output [Goulbourne, N.C., Frecker, M., Mockensturm, E.M., Snyder, A.J., 2003. Modeling of a dielectric elastomer diaphragm for a prosthetic blood pump. In: Proceedings of SPIE, Smart Structures and Materials: EAPAD, San Diego; Goulbourne, N.C., Mockensturm, E.M., Frecker, M., 2005b. Quasi-static and dynamic inflation of a dielectric elastomer membrane. In: Proceedings of SPIE, Smart Structures and Materials: EAPAD, San Diego]. A numerical formulation for the large deformation response of electro-elastomer membranes subject to electromechanical loading is derived in this paper. The approach is based on modifying the elastic membrane theory of Green, Adkins, and Rivlin [Adkins, J.E., Rivlin, R.S., 1952. Large elastic deformations of isotropic materials IX. The deformation of thin shells. Philosophical Transactions of the Royal Society of London. Series A Mathematical and Physical Sciences 244, 505–531; Green, A.E., Adkins, J.E., 1970. Large Elastic Deformations. Oxford University Press, London]. The electro-elastic stress state is defined as the combination of the electrical Maxwell stress and the mechanical stress for hyperelastic materials [Goulbourne, N.C., Mockensturm, E.M., Frecker, M., 2005a. A nonlinear model for dielectric elastomer membranes. ASME Journal of Applied Mechanics 72, (6) 899–906]. This paper augments our previous work by presenting a mathematical solution procedure for simulating the field responsive behavior of silicone electro-elastomers configured for both in-plane and out-of-plane deformation. Thin axisymmetric membranes subject to electromechanical loads are the focus of this investigation. The numerical analysis shows that there is a delicate balance between the electrical and the mechanical portions of the stress, which must be maintained for the overall stress to remain tensile and by extension the electro-elastomer to remain stable. It is shown that at very high voltages the stress can become negative ultimately leading to transducer failure. For sensing applications, the varying capacitive behavior of electro-elastomers is used to extract information about the membrane’s deformed state.
International Journal of Solids and Structures - INT J SOLIDS STRUCT. 01/2007; 44(9):2609-2626.