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Proceedings Papers
Proc. ASME. SMASIS2019, ASME 2019 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, V001T05A001, September 9–11, 2019
Paper No: SMASIS2019-5506
Abstract
Abstract This paper proposes a probabilistic model for the placement of sensors that considers uncertain factors in the sensing system to find the best arrangement of sensor locations. Traditional procedures for structural health monitoring (SHM) usually rely on simplified behavior and deterministic factors from structure’s response. Incorporating the sources of uncertainty (e.g., loading condition, material properties, and geometrical parameters) in the design of sensor network will enhance the safety and extend the useful life of the complex mechanical systems. The proposed method is defined in a reliability-based design optimization framework to search for the sufficient number of sensors for failure detection using Genetic Algorithm. The optimal arrangement is found as the one that minimizes the number and size of sensor patches and maximizes the expected probability for failure detection. This design concept involves a new failure diagnosis indicator, named detectability, formulated based on the Mahalanobis Distance (MD). MD distribution is used as a measure of the quality of the obtained sensor configuration suitable for many sensing/actuation SHM processes, while considering the uncertainties such as those from structure properties and operation condition. The MD classifier categorizes large sets of testing data by comparing the distances of the mean with the distribution of available training data sets. Statistical evaluation of failure detectability can be obtained by comparing the distribution of MD for different failure modes. Kriging modeling, used for metamodel-based design optimization, is applied for surrogate modeling of the stochastic performance of system to reduce computational cost. The surrogate model is constructed by correlating the sensor output to the vibration pattern of the structure and sensor variable inputs (e.g., size and location). Direct finite element analysis (FEA) evaluates the sensor output with respect to the input variables. Consequently, the constructed kriging model enables the estimation of sensor output for any arbitrary sensor arrays. As a case study, a rectangular panel with a size of 40 cm × 30 cm is considered that is fastened using eight screw joints. The harmonic vibration force is applied to the center of the plate and its varied vibration pattern is used to detect the joint failure. Eight different combinations of join failure are defined as health statuses (failure modes), and different size and layouts of the piezoelectric sensors are considered to detect the health status. The results verify the capabilities of the new method for failure diagnosis of screw joints in a panel with high sensitivity of fault detection.
Proceedings Papers
Proc. ASME. SMASIS2018, Volume 1: Development and Characterization of Multifunctional Materials; Modeling, Simulation, and Control of Adaptive Systems; Integrated System Design and Implementation, V001T04A020, September 10–12, 2018
Paper No: SMASIS2018-8138
Abstract
Future aircraft wing technology is rapidly moving toward flexible and morphing wing concepts capable to enhance aircraft wing performance in off-design conditions and to reduce operative maneuver and gust loads. However, due to the reduced stiffness, increased mass, and increased degree of freedom (DOF), such mechanical systems require advanced aeroelastic assessments since the early design phases; this appears crucial to properly drive the design of the underlying mechanisms since the conceptual phase by mitigating their impact on the whole aircraft aeroelastic stability. Preliminary investigations have shown that the combined use of adaptive flap tabs and morphing winglets significantly improves aircraft aerodynamic performance in climb and cruise conditions by the order of 6%. Additionally, by adapting span-wise lift distributions to reduce gust solicitations and alleviate wing root bending moment at critical flight conditions, significant weight savings can also be achieved. Within the scope of Clean Sky 2 Airgreen 2 project, flutter and divergence characteristics of a morphing wing design integrating adaptive winglets and flap tabs are discussed. Multi-parametric flutter analyses are carried out in compliance with CS-25 airworthiness requirements (paragraph 25.629, parts (a), (b), (c) and (d)) to investigate static and dynamic aeroelastic stability behavior of the aircraft. The proposed kinematic systems are characterized by movable surfaces, each with its own domain authority, sustained by a structural skeleton and completely integrated with EMA-based actuation systems. For that purpose, a sensitivity analysis was performed taking into account variations of the stiffness and inertial properties of the referred architectures. Such layouts were reduced to a stick-equivalent model which properties were evaluated through MSC-NASTRAN-based computations. The proprietary code SANDY 4.0 was used to generate the aero-structural model and to solve the aeroelastic stability equations by means of theoretical modes association in frequency domain. Analyses showed the presence of critical modal coupling mechanisms in nominal operative conditions as well as in case of system malfunctioning or failure. Design solutions to assure clearance from instabilities were then investigated. Trade-off flutter and divergence analyses were finally carried out to assess the robustness of the morphing architectures in terms of movable parts layout, mass balancing and actuators damping.
Proceedings Papers
Preliminary Failure Analysis and Structural Design of a Morphing Winglet for Green Regional Aircraft
Proc. ASME. SMASIS2018, Volume 1: Development and Characterization of Multifunctional Materials; Modeling, Simulation, and Control of Adaptive Systems; Integrated System Design and Implementation, V001T04A024, September 10–12, 2018
Paper No: SMASIS2018-8236
Abstract
Aircraft wing design optimization typically requires the consideration of many competing factors accounting for both aerodynamics and structures. To address this, research on morphing aircraft has shown its potential by providing large benefits on aircraft performance. In particular, by adapting wing lift distribution, morphing winglets are capable to improve aircraft aerodynamic efficiency in off-design conditions and reduce wing loads at critical flight points. For those reasons, it is expected that these devices will be applied to the aircraft of the very next generation. In the study herein presented, a preliminary failure analysis and structural design of a morphing winglet are presented. The research is collocated within the Clean Sky 2 Regional Aircraft IADP, a large European programme targeting the development of novel technologies for the next generation regional aircraft. The safety-driven design of the proposed kinematic system includes a thorough examination of the potential hazards associated with the system faults, by taking into account the overall operating environment and functions. The mechanical system is characterized by movable surfaces sustained by a winglet skeleton and completely integrated with a devoted actuation system. Such a load control device requires sufficient operational reliability to operate on the applicable flight load envelope in order to match the needs of the structural design. One of the most critical failure modes is assessed to get key requirements for the system architecture consistency. Possible impacts of the defined morphing outline on the FHA analysis are investigated. The structural design process is then addressed in compliance with the demanding requirements posed by the implementation on regional airplanes. The layout static robustness is verified by means of linear stress analyses at the most critical conditions, including possible failure scenarios. Results focus on the assessment of the device static and dynamic structural response and the preliminary definition of the morphing system kinematics, including the integrated actuator system.
Proceedings Papers
Proc. ASME. SMASIS2018, Volume 2: Mechanics and Behavior of Active Materials; Structural Health Monitoring; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies, V002T05A001, September 10–12, 2018
Paper No: SMASIS2018-7908
Abstract
The focus of this study was to apply a robust inspection technique for monitoring damage nucleation and propagation in 7075 aluminum alloy specimens exposed to cyclic loading. A previously developed specimen, linearly tapered in width along the length, was subjected to a sinusoidal tension-tension load while conductivity and strain were measured in-situ. Ex-situ measurements of modulus, hardness, surface potential, digital image correlation strain field, and neutron diffraction were made as a function of fatigue cycles. It is hypothesized that varying levels of induced stress along the length due to equal-force but varying area along the length will create a record of damage which can be probed to intuit a temporal history for the specimen. Baseline, intermediate, and failure sensor measurements for several specimens were compared and analyzed as a function of applied stress (varied linearly along the length) and fatigue cycles (constant). Mechanisms of damage nucleation and propagation due to fatigue cycling are discussed with an emphasis on which inspection methods are most promising for improving structural durability and state monitoring.
Proceedings Papers
Proc. ASME. SMASIS2018, Volume 2: Mechanics and Behavior of Active Materials; Structural Health Monitoring; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies, V002T05A011, September 10–12, 2018
Paper No: SMASIS2018-8182
Abstract
In many structural applications the use of composite material systems in both retrofit and new design modes has expanded greatly. The performance benefits from composites such as weight reduction with increased strength, corrosion resistance, and improved thermal and acoustic properties, are balanced by a host of failure modes whose genesis and progression are not yet well understood. As such, structural health monitoring (SHM) plays a key role for in-situ assessment for the purposes of performance/operations optimization, maintenance planning, and overall life cycle cost reduction. In this work, arrays of fiber Bragg grating optical strain sensors are attached to glass-epoxy solid laminate composite specimens that were subsequently subjected to specific levels of fully reversed cyclic loading. The fatigue loading was designed to impose strain levels in the panel that would induce damage to the laminate at varying numbers of cycles. The objectives of this test series were to assess the ability of the fiber Bragg grating sensors to detect fatigue damage (using previously developed SHM algorithms) and to establish a dataset for the development of a prognostic model to be applied to a random magnitude of fully reversed strain loading. The prognostic approach is rooted in the Failure Forecast Method, whereby the periodic feature rate-of-change was regressed against time to arrive at a failure estimate. An uncertainty model for the predictor was built so that a probability density function could be computed around the time-of-failure estimate, from which mean, median, and mode predictors were compared for robustness.
Proceedings Papers
Proc. ASME. SMASIS2018, Volume 2: Mechanics and Behavior of Active Materials; Structural Health Monitoring; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies, V002T05A005, September 10–12, 2018
Paper No: SMASIS2018-7977
Abstract
Engineering systems subject to high-rate extreme environments can often experience a sudden plastic deformation during a dynamic event. Examples of such systems include civil structures exposed to blast or aerial vehicles experiencing impacts. The change in configuration through deformation can rapidly lead to catastrophic failures resulting in intolerable losses in investments or human lives. A solution is to conduct fast system estimation enabling real-time decisions, in the order of microseconds, to mitigate such high-rate changes. To do so, we propose a model-driven observer coupled with a data-driven adaptive wavelet neural network to provide real-time stiffness estimations to continuously update a system’s model. This real-time system identification method offers adaptability of the system’s parameters to unforeseeable changes. The results of the simulations demonstrate accurate stiffness estimations in milliseconds for three different excitation conditions for a one degree-of-freedom spring, mass, and damper system with variable stiffness.
Proceedings Papers
Proc. ASME. SMASIS2018, Volume 2: Mechanics and Behavior of Active Materials; Structural Health Monitoring; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies, V002T05A014, September 10–12, 2018
Paper No: SMASIS2018-8232
Abstract
Scour is one of the most important problems lead to submarine pipeline failure. In this paper, several scour monitoring techniques based on active thermometry method was introduced. Firstly, DS18B20 digital temperature sensor was used to monitor the surface heat change pattern in the heating process in different media like sand and water. The test results validated the feasibility of the active thermometry method. Then, the submarine pipeline scour monitoring system based on Brillouin distributed optical fiber sensing technique was developed. Due to the high cost of monitoring system of distributed Brillouin fiber optical sensing technology. In order to reduce costs, common armed fiber optic cable was used as both heating and sensing unit, and Raman sensing with relatively lower cost was utilized for distributed temperature sensing for scour monitoring. Laboratory test results shown there is good potential of active thermometry method for scour monitoring in practical field.
Proceedings Papers
Proc. ASME. SMASIS2018, Volume 2: Mechanics and Behavior of Active Materials; Structural Health Monitoring; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies, V002T02A014, September 10–12, 2018
Paper No: SMASIS2018-8234
Abstract
This paper presents the development process of an electrically insulating and liquid-impermeable coating for piezoelectric actuators. Against the background of flow investigations of an adaptive airfoil in a water tunnel the adaptive lip including PZT-ceramics for the active lip deformation must be insulated and sealed up against the ingress of moisture. Due to high electric field strength of 2 kV/mm between electrodes of multilayer actuators any ingress of moisture would lead to a reduction of the dielectric strength and may cause a short circuit. In order to prevent failure of the adaptive lip the electrical connections of the actuators have to be insulated by a waterproof coating. A service life of at least 10 7 load cycles at a frequency of 100 Hz is required for the actuators. Therefore the coating should be as ductile as possible otherwise it could crack and water could diffuse into the actuators. That is why the yield strength of the coating has to be higher than of the actuators, which is 0.3 %. For the investigation of the waterproofness several samples are coated with different materials in various processes. First the actuators are moulded in epoxy resin and then a diffusion-resistant PVF-foil is applied. After a screening of different materials, an additional coating with a two-component tar-epoxy resin in combination with a gold coating applied by a PVD process seems to be the most suitable process. Another promising waterproof coating is the atomic layer deposition (ALD). It is a slightly changed chemical vapor deposition (CVD) and referring to the studies of Abdulagatov et al. an ALD of aluminum oxide (Al 2 O 3 ) and titanium dioxide (TiO 2 ) can slow down the corrosion of static copper specimens in water for ∼80 days [1]. Through a redrying procedure during test intermissions an increased underwater service life of the piezoelectric actuators is achieved.
Proceedings Papers
Proc. ASME. SMASIS2018, Volume 2: Mechanics and Behavior of Active Materials; Structural Health Monitoring; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies, V002T08A013, September 10–12, 2018
Paper No: SMASIS2018-8225
Abstract
Knitted Textiles made from Nickel-Titanium (NiTi) shape memory alloy wires are a new structural element with enhanced properties for a variety of applications. Potential advantages of this structural form include enhanced bending flexibility, tailorable in-plane, and through-thickness mechanical performance, and energy absorption and damping. Inspection of the knit pattern reveals a repeating cell structure of interlocking loops. Because of this repeating structure, knits can be evaluated as cellular structures that leverage their loop-based architecture for mechanical robustness and flexibility. The flexibility and robustness of the structure can be further enhanced by manufacturing with superelastic NiTi. The stiffness of superelastic NiTi, however, makes traditional knit manufacturing techniques inadequate, so knit manufacturing in this research is aided by shape setting the superelastic wire to a predefined pattern mimicking the natural curve of a strand within a knit fabric. This predefined shape-set geometry determines the outcome of the knit’s mechanical performance and tunes the mechanical properties. In this research, the impact of the shape setting process on the material itself is explored through axial loading tests to quantify the effect that heat treatment has on a knit sample. A means of continuously shape setting and feeding the wire into traditional knitting machines is described. These processes lend themselves to mass production and build upon previous textile manufacturing technologies. This research also proposes an empirical exploration of superelastic NiTi knit mechanical performance and several new techniques for manufacturing such knits with adjustable knit parameters. Displacement-controlled axial loading tests in the vertical (wale) direction determined the recoverability of each knit sample in the research and were iteratively increased until failure resulted. Knit samples showed recoverable axial strains of 65–140%, which could be moderately altered based on knit pattern and loop parameters. Furthermore, this research demonstrates that improving the density of the knit increases the stiffness of the knit without any loss in recoverable strains. These results highlight the potential of this unique structural architecture that could be used to design fabrics with adjustable mechanical properties, expanding the design space for aerospace structures, medical devices, and consumer products.
Proceedings Papers
Proc. ASME. SMASIS2017, Volume 1: Development and Characterization of Multifunctional Materials; Mechanics and Behavior of Active Materials; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies, V001T06A009, September 18–20, 2017
Paper No: SMASIS2017-3841
Abstract
A recent achievement in the droplet interface bilayer (DIB) technique is the ability to link multiple lipid-encased aqueous droplets in an oil medium to construct a membrane-based network. Highly flexible, efficient and durable compared to other lipid bilayer modeling techniques, these systems establish a framework for the creation of biocompatible and stimuli-responsive smart materials with applications ranging from biosensing to reliable micro-actuation. Incorporating ferrofluids droplets into this platform has proven to accelerate the networks’ building mechanism through remote magnetic-control of the droplets movement and has reduced the likelihood of failure during the pre-network-completion phase. Additionally, ferrofluid drops may be placed in the final network structure as they are macroscopically homogenous and behave as single phased liquids. Due to their paramagnetic characteristics, no residual magnetization is observed in the ferrofluid upon removal of the external magnetic field, allowing for simple control of the magnetically responsive droplets. Aside from the ferrofluids reliability in contact-free manipulation of bilayer networks, this work shows a different feature of having such hybrid ferrofluid-water DIB networks: magnetic-sensibility and actuation. Once pre-structured mixed networks are formed, a magnetic source is used to generate various magnetic fields in the vicinity of the DIB webs; changes in structural responses are then observed and used to induce protein channel gating in DIB networks channeling the functionality of a switch. Tailored architectures are accordingly evaluated and their suitability for the creation of microfluidic-magneto sensors and actuators is assessed.
Proceedings Papers
Proc. ASME. SMASIS2017, Volume 1: Development and Characterization of Multifunctional Materials; Mechanics and Behavior of Active Materials; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies, V001T08A007, September 18–20, 2017
Paper No: SMASIS2017-3829
Abstract
Self-healing materials have emerged as an alternative solution to the repair of damage in fibre-reinforced composites. Recent developments have largely focused on a vascular approach, due to the ability to transport healing agents over long distances and continually replenish from an external source. However fracture of the vascular network is required to enable the healing agents to infiltrate the crack plane, ceasing its primary function in transporting fluid and preventing the repair of any further damage events. Here we present a novel approach to vascular self-healing through the development and integration of 3D printed, porous, thermoplastic networks into a thermoset matrix. This concept exploits the inherently low surface chemistry of thermoplastic materials, which results in adhesive failure between the thermoplastic network and thermoset matrix on arrival of a propagating crack, thus exposing the radial pores of the network and allowing the healing agents to flow into the damage site. We investigate the potential of two additive manufacturing techniques, fused deposition modeling (FDM) and stereolithography, to fabricate free-standing, self-healing networks. Furthermore, we assess the interaction of a crack with branched network structures under static indentation in order to establish the feasibility of additive manufacture for multi-dimensional 3D printed self-healing networks.
Proceedings Papers
Proc. ASME. SMASIS2017, Volume 1: Development and Characterization of Multifunctional Materials; Mechanics and Behavior of Active Materials; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies, V001T02A010, September 18–20, 2017
Paper No: SMASIS2017-3939
Abstract
Self-healing material structures with the inherent capability to mend damage will lead to a paradigm shift in design as fracture may no longer constitute a failure. Generally, there are two techniques of self-healing that operate at different scales, require different approaches and often are dealt with separately; geometric restoration and crack filling/bonding. Geometric restoration uses shape memory materials that can mechanically close fractures after they occur. Crack filling and bonding fills and chemically bonds fractured parts in place. Materials capable of recovering from complete fractures, that have propagated across the entire component, have typically taken a sparse fiber composite form with a structural matrix encapsulating shape memory fibers. This form of self-healing material has demonstrated the ability recover original bulk geometry. However, lacking bonding, the healed structures have not had the ability to resist subsequent externally applied loads without re-opening the crack. A new approach of pre-straining the shape memory fibers before curing them in a matrix in the pre-strained state is presented in this paper with basic theory and experimental results. Pre-straining the shape memory fibers before casting them in the matrix causes them to undergo constrained recovery upon activation. Thus, the samples create closing loads across the crack which are capable of withstanding external loads without re-opening.
Proceedings Papers
Proc. ASME. SMASIS2017, Volume 1: Development and Characterization of Multifunctional Materials; Mechanics and Behavior of Active Materials; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies, V001T02A012, September 18–20, 2017
Paper No: SMASIS2017-3984
Abstract
Strain in solid materials under external loads cannot be visualized until they reach a high value or failure occurs; and the common measuring method of using strain sensors is effective but limited to wiring or power supply. In this study, we introduce a new concept of self-sensing solid materials by designing thin surface circular delamination regions on a material body to sense and predict the elastic global strain through controlled elastic local buckling. Delamination buckling is an undesirable failure occurrence in laminated composites under compression. However, it can translate imperceptible small global strains on the main material body to a visible large deformation in the surface of the delaminated region due to buckling. We analytically studied the buckling and post-buckling response of a clamped circular thin plate with unilateral constraint using an energy method to obtain the critical buckling loads, the buckling configurations, and the center out-of-plane displacement under uniaxial and biaxial loading conditions. The results show that for a given buckling configuration in the local region, the global strain condition of the main material body can be predicted. The study thus explores and proves a feasible way to design self-sensing materials through controlled delamination buckling.
Proceedings Papers
Proc. ASME. SMASIS2017, Volume 1: Development and Characterization of Multifunctional Materials; Mechanics and Behavior of Active Materials; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies, V001T06A015, September 18–20, 2017
Paper No: SMASIS2017-3879
Abstract
Total Knee Replacement (TKR) is a very common procedure in the United States, especially with the aging population. However, despite high numbers of procedures and advancing technology, about 20% of patients with TKR are unsatisfied with the level of discomfort they experience with their replacement. Prevailing theories suggest that this is due to gradual misalignment of the knee. Multiple methods have been attempted to detect the cause of mechanical failure in replacements. One possible method for performing state detection in knees is the embedding of piezoelectric transducers (PZTs) into the bearing component. Preliminary testing of PZT’s embedded in simplified plastic components has shown that this method contains promise. With this said, further testing on realistic knee implant components is still needed to solidify the method’s validity. Commercial knee implant bearings utilize medical grade Ultra-High Molecular Weight Polyethylene (UHMW) and manufacturers utilize proprietary processing technology to develop the final components. This work focuses on the development of surrogate knee implant prototypes that replicate the material and geometric properties of actual knee implants to provide a convenient and economical solution to evaluate the performance of embedded PZTs. In this work, scans of an original knee bearing are taken and used to create a 3D model. From there, a variety of processes including 3D printing and Computer Numerical Controlled (CNC) machining are used to develop surrogate prototypes that are compared for accuracy to a benchmark. This benchmark is taken as a polished CNC machined non-medical grade UHMW prototype. Standards that the prototypes must meet include cost and time effectiveness as well as similarity in geometry and material property to the benchmark. The performance of the prototypes is experimentally compared through mechanical load testing by using pressure sensitive films placed between the femoral and bearing components of the implant as well as measuring piezoelectric output. In addition, the measured voltage output is compared to predictions from an analytical model for validation of the piezoelectric performance. These two experiments help to derive information about the applied load distribution and location, allowing comparisons to be made to the benchmark. This study shows that, while some types of 3D printing, such as fused deposition modeling, provide fast and cheap prototypes, other options such as stereolithography printing produce higher quality and more replicative components. Results of this study can be used in the development of useful surrogates for the advancement of biomedical sensors.
Proceedings Papers
Proc. ASME. SMASIS2017, Volume 2: Modeling, Simulation and Control of Adaptive Systems; Integrated System Design and Implementation; Structural Health Monitoring, V002T03A037, September 18–20, 2017
Paper No: SMASIS2017-3967
Abstract
Postbuckling response, long considered mainly as a failure limit state is gaining increased interest for smart applications, such as energy harvesting, frequency tuning, sensing, actuation, etc. Cylindrical shells have received less attention as structural form to harness elastic instabilities due to their increased modeling complexity and high imperfection sensitivity. Yet, preliminary experimental and computational evidence indicates that the elastic postbuckling response of cylindrical shells can be controlled and potentially managed. Further, cylindrical shells offer desirable features for the design of mechanical devices and adaptive structures that other forms cannot attain without additional external constraints. This paper presents a study on tailoring the elastic postbuckling response of thin-walled cylindrical shells under compression by means of non-uniform wall stiffness distributions. The pattern of stiffness distribution was designed by discretizing the shell surface into cells and thickening selected cells with respect to a baseline uniform wall thickness. Diverse patterns were characterized in the way of how they affect the postbuckling response through numerical simulations using the finite element method. Results show that the elastic postbuckling response can be tailored into three response types: softening, sustaining, and stiffening; and that number, sequence/time and location/space of localized buckling events can be designed. This work provides new knowledge on the means to design the cylindrical shells with controlled elastic postbuckling behavior for applications in smart materials, mechanical devices, and adaptive structures.
Proceedings Papers
Todd C. Henry, Robert A. Haynes, Daniel P. Cole, Mulugeta A. Haile, Michael D. Coatney, Volker Weiss
Proc. ASME. SMASIS2017, Volume 2: Modeling, Simulation and Control of Adaptive Systems; Integrated System Design and Implementation; Structural Health Monitoring, V002T05A001, September 18–20, 2017
Paper No: SMASIS2017-3780
Abstract
Traditionally, most mechanical testing is conducted on specimens of uniform cross-section and stress magnitude, or only a single position along the specimen length is of interest. Investigations of various stress levels therefore requires separate tests with a unique specimen at each stress level of interest. The impetus of the current work was to develop a method for the design and monitoring of a specimen that simultaneously experiences a continuum of stress magnitudes across various positions. A linearly-tapered specimen was developed and subjected to sinusoidal tension-tension fatigue until specimen failure, with the expectation that a record of damage exists along the length of the specimen due to the varying level of induced stress. Baseline and post-failure scans of x-ray diffraction, electrical resistance via four point probe, nano-indentation, eddy current, and geometric changes were compared. Attempts were made to characterize the pre- and post-test property behaviors as a function of the applied stress, which varied linearly along the specimen, and as a function of fatigue cycles, which were the same along the length of the specimen. The mechanisms of specimen damage due to fatigue cycling were investigated and analyzed to improve durability and damage tolerance understanding.
Proceedings Papers
Proc. ASME. SMASIS2017, Volume 2: Modeling, Simulation and Control of Adaptive Systems; Integrated System Design and Implementation; Structural Health Monitoring, V002T05A009, September 18–20, 2017
Paper No: SMASIS2017-3965
Abstract
Mechanically induced light emission, termed mechanoluminescence (ML) has been a potential candidate for stress sensing, stress visualization, damage detection and crack propagation applications. In this work, we demonstrate utilizing ML from elastic loading, termed elastico-mechanoluminescence (EML), for structural health monitoring and failure prediction applications. EML from ZnS:Cu phosphors impregnated in elastomeric matrix is shown to correlate with the structural health of the matrix as well as indicate impending failure of the matrix. Indicators for real-time monitoring to predict impeding failure are also identified. EML based SHM system can be implemented to monitor health of several existing engineering devices that depend on functional elastomeric components for reliable operation.
Proceedings Papers
Proc. ASME. SMASIS2016, Volume 1: Multifunctional Materials; Mechanics and Behavior of Active Materials; Integrated System Design and Implementation; Structural Health Monitoring, V001T05A008, September 28–30, 2016
Paper No: SMASIS2016-9054
Abstract
Light emission induced by mechanical input, termed mechanoluminescence (ML), has been gaining widespread attention recently. Various theories have been put forth over the years identifying sources and mechanisms behind ML. Several applications utilizing ML such as stress sensing, stress visualization, surface crack propagation detection and environmental friendly light source have been put forth. Despite promising results, large scale implementation of ML based sensing and visualization technologies for industrial applications is yet to be achieved. In this conference paper, we demonstrate a structural health monitoring technique utilizing mechanoluminescence emission that is low power, in-situ and easily scalable for industrial applications. Flexible elastomeric composite coupons impregnated with ML crystals subjected to constant cyclical loading up to millions of cycles. ML emission from the coupons is used to track the strain in the coupon over time. Variations in strain are then correlated to variations in stiffness of the coupon over time thereby monitoring its structural health. We also predict the failure of the coupons based on ML intensity. A pseudo-algorithm that tracks ML intensity and predicts failure ahead in time is also put forth facilitating convenient scale-up for industrial applications.
Proceedings Papers
Proc. ASME. SMASIS2016, Volume 1: Multifunctional Materials; Mechanics and Behavior of Active Materials; Integrated System Design and Implementation; Structural Health Monitoring, V001T01A004, September 28–30, 2016
Paper No: SMASIS2016-9090
Abstract
The development of variable-stiffness systems is key to the advance of compact engineering solutions in a number of fields. Rigidizable structures exhibit variable-stiffness based on external stimuli. This function is necessary for deployable structures, such as inflatable space antennas, where the deployed structure is semi-permanent. Rigidization is also useful for a wide range of applications, such as prosthetics and exoskeletons, to help support external loads. In general, variable-stiffness designs suffer from a tradeoff between the magnitude of stiffness change and the ability of the structure to resist mechanical failure at any stiffness state. This paper presents the design, analysis, and fabrication of a rigidizable structure based on inflatable octet-truss cells. An octet-truss is a lattice-like configuration of elements, traditionally beams, arranged in a geometry reminiscent of that of the FCC lattice found in many metals; namely, the truss elements are arranged to form a single interior octahedral cell surrounded by eight tetrahedral cells. The interior octahedral cell is the core of the octet-truss unit cell, and is used as the main structure for examining the mechanics of the unit as a whole. In this work, the elements of the inflatable octet truss are pneumatic air muscles, also called McKibben actuators. Generalized McKibben actuators are a type of tubular pneumatic actuator that possess the ability to either contract or expand axially due to an applied pressure. Their unique kinematics are achieved by using a fiber wrap around an isotropic elastomeric shell. Under normal conditions, pressurizing the isotropic shell causes expansion in all directions, like a balloon. The fiber wrap constrains the ability of the shell to freely expand, due to the fiber stiffness. The wrap geometry thus guides the extensile/contractile motion of the actuator by controlling its kinematics. It is their ability to contract under pressure that makes McKibben actuators unique, and consequently they are of great interest presently to the robotics community due to their similitude to organic muscles. Kinematic analysis from constrained maximization of the shell volume during pressurization is used to obtain relations between the input work due to applied pressure and the resulting shape change due to strain energy. Analytical results are presented to describe the truss stiffness as a function of the McKibben geometry at varying pressures.
Proceedings Papers
Narges Shayesteh Moghaddam, Amirhesam Amerinatanzi, Soheil Saedi, Ali Sadi Turabi, Haluk Karaca, Mohammad Elahinia
Proc. ASME. SMASIS2016, Volume 1: Multifunctional Materials; Mechanics and Behavior of Active Materials; Integrated System Design and Implementation; Structural Health Monitoring, V001T02A014, September 28–30, 2016
Paper No: SMASIS2016-9289
Abstract
NiTi alloys are interesting materials for biomedical implants since they offer unique characteristics such as superelastic behavior, low stiffness (I.e., modulus of elasticity) close to that of the cortical bone, and shock absorption. Thermal treatments are the most common and practical ways to improve the superelasticity of these alloys. In addition to the superelastic behavior of the metallic implants, it is important for the implants to have a stiffness similar to that of cortical bone in order to reduce the risk of failure caused by stress shielding. The cortical bone has a stiffness ranging from 12 to 31 GPa for different patients (e.g., sex, age, mechanical behavior of bone) and various bone locations (e.g., jaw implant, hip implant), while the untreated Ni-rich NiTi has the stiffness equal to 41.37 GPa. One recently used technique to lower the stiffness of NiTi implant is to introduce porosity into the implant. The major problem associated with the imposed porosity is stress concentration on the pore walls and the subsequent implant failure. In this work, the purpose is to tune the stiffness via changing the post-heat treatment conditions, i.e., aging time and aging temperature. In this study, several bulk specimens of Ni-rich NiTi (SLM Ni50.8Ti49.2) were additively manufactured using selective laser melting (SLM) technique. The samples were solution annealed (950 °C, 5.5 h) and subsequently water quenched to provide equilibrium state in the samples. Subsequently, different aging conditions (350 °C and 450 °C for 5 to 18 hours) were applied to the samples. Mechanical testing (compression) was conducted on the samples and the stiffness of each sample was defined to investigate the effect of aging on the stiffness. Our results indicate that the range of 29.9 to 43.7 GPa for stiffness can be achieved through the implant via different time period and temperatures for aging. The modulus of 43.7 GPa is attributed to 10 hours heat treatment under 450 °C and the modulus of 29.9 GPa is attributed to 18 hours heat treatment under 350 °C.