Drone-Based StereoDIC: System Development,Experimental Validation and Infrastructure Application

Background

Digital Image Correlation (DIC) is widely used for remote and non-destructive structural health evaluation of infrastructure. Current DIC applications are limited to relatively small areas of structures and require the use of stationary stereo vision camera systems that are not easy to transfer and deploy in remote areas.

Objective

The enclosed work describes the development and validation of an Unmanned Aircraft System (UAS, commonly known as drone) with an onboard stereo-vision system capable of acquiring, storing and transmitting images for analysis to obtain full-field, three-dimensional displacement and strain measurements.

Methods

The UAS equipped with a StereoDIC system has been developed and tested in the lab. The drone system, named DroneDIC, autonomously hovers in front of a prestressed railroad tie under pressure and DIC data are collected. A stationary DIC system is used in parallel to collect data for the railroad tie. We compare the data to validate the readings from the DroneDIC system.

Results

We present the analysis of the results obtained by both systems. Our study shows that the results we obtain from the DroneDIC system are similar to the ones gathered from the stationary DIC system.

Conclusions

This work serves as a proof of concept for the successful integration of DIC and drone technologies into the DroneDIC system. DroneDIC combines the high accuracy inspection capabilities of traditional stationary DIC systems with the mobility offered by drone platforms. This is a major step towards autonomous DIC inspection in portions of a structure where access is difficult via conventional methods.

     

Optimal Synthesis of Frameworks under Elastic and Plastic Performance Constraints Using Discrete Sections *, †

ABSTRACT

A computer-based method is presented for minimum-weight design of planar frameworks under service and ultimate performance conditions using discrete member sections. Service-load conditions ensure acceptable elastic stresses and displacements, and ultimate-load conditions ensure adequate safety against plastic collapse. The sizes of the discrete sections, which can be of any type; e.g., WF, HSS, etc., may be constrained to satisfy fabrication requirements related to member continuity and structure symmetry. The design method is iterative in nature and remarkably efficient. The number of iterations is generally small and almost totally independent of the complexity of the structure. Several comparative designs for simple truss and frame structures are presented to illustrate features of the method.     

The Explicit Expression of Internal Forces in Prismatic Membered Structures*

ABSTRACT

Analytic expressions for member forces in linear elastic redundant trusses have recently been given by the author. It was shown that the internal forces in a truss are the ratios of two multilinear homogeneous polynomials in the longitudinal stiffnesses of the elements of the structure. The order of the polynomials is equal to the number of nodal degrees of freedom of the structure. The number of terms of each polynomial is equal to the number of statically determinate stable substructures that can be derived from the original structure. It was shown that coefficients of the polynomials can be computed through the equilibrium equations and by enforcing global compatibility of deformations. This paper generalizes these results to the case of linear elastic structures, composed of uniform prismatic elements that have extensional, flexural, and torsional stiffness. This is done by replacing each bi-modal bending element with a unimodal moment element and a unimodal shear element. This allows the representation of deformation of the elements by six uncoupled basic deformation patterns in the case of structures in space, thus paving the way for truss-type analysis for general structures that are composed of uniform prismatic elements. As a result, multilinear polynomials that appear in expressions for stress resultants are the products of axial, bending, and torsional stiffnesses of subsets of the original structure. The number of terms appearing in the polynomials renders the exact analytic expressions intractable for practical engineering structures. However, the construct of the analytic equations may constitute a basis for writing approximate expressions for member forces in frames, explicitly in terms of rigidities of components of the structure. This paper describes such an approximate expression, with a reduced number of terms in the polynomials. The theory is illustrated with numerical examples of analysis of planar structures     

Deflection Stability of Work-Hardening Structures

ABSTRACT

This paper considers the adaptation problem of structures of elastic-strain-hardening material. In particular, the modes of inadaptation of such structures are investigated, and the deflection response obtained. It is shown that recognition of the way in which the structure violates the shakedown limit can drastically reduce the amount of computational work involved in the evaluation of that limit. Finally, three possible failure modes of ductile structures are described.     

Complicated deformation simulating on temperature-driven 4D printed bilayer structures based on reduced bilayer plate model

The four-dimensional (4D) printing technology, as a combination of additive manufacturing and smart materials, has attracted increasing research interest in recent years. The bilayer structures printed with smart materials using this technology can realize complicated deformation under some special stimuli due to the material properties. The deformation prediction of bilayer structures can make the design process more rapid and thus is of great importance. However, the previous works on deformation prediction of bilayer structures rarely study the complicated deformations or the influence of the printing process on deformation. Thus, this paper proposes a new method to predict the complicated deformations of temperature-sensitive 4D printed bilayer structures, in particular to the bilayer structures based on temperature-driven shape-memory polymers (SMPs) and fabricated using the fused deposition modeling (FDM) technology. The programming process to the material during printing is revealed and considered in the simulation model. Simulation results are compared with experiments to verify the validity of the method. The advantages of this method are stable convergence and high efficiency, as the three-dimensional (3D) problem is converted to a two-dimensional (2D) problem. The simulation parameters in the model can be further associated with the printing parameters, which shows good application prospect in 4D printed bilayer structure design.

     

Shakedown and Inadaptation Mechanisms of Bellows Subject to Constant Pressure and Cyclic Axial Force

Abstract

In the design of pipelines, a thermal expansion of the pipes is usually compensated for by a thin-walled, flexible shell of revolution, called a bellows. The process of cyclic loading of the structure may result in the formation of a sequence of plastic strain fields in the shell, which often leads to the collapse of the structure. Therefore, the question of whether the structure shakes down or collapses under the combined, cyclic loading is of particular importance to engineers

The Reissner-type equations for the perfectly elastoplastic model of the shell are formulated on the basis of the geometrically nonlinear third-order theory. Various mechanisms of plastic collapse (e.g., maximal load or formation of plastic hinge) are discussed for the quasistatically loaded S-type bellows, as well as for the bellows subjected to cyclic, complex loadings. The analogy between these cases, as far as the failure modes are concerned, is explained. The adaptation (shakedown) and inadaptation (nonsymmetric alternating plasticity, incremental collapse) domains for the particular case of the S-type bellows (C-type geometry) acted upon by internal pressure and variable repeated axial force are presented.     

Postbuckling Analysis of Nonconservative Elastic Systems

Abstract

Previous work on the postbuckling and imperfection-sensitivity of elastic structures has concentrated on conservative systems. The results of Koiterand others have led to a general theory of nonlinear stability behavior for these systems. The theory must be modified when nonconservative forces are present, and this is the aim of the present paper.

Discrete, nonconservative, elastic systems which exhibit static (divergence) instability are considered. The nonlinear behavior in the neighborhood of a critical point is analyzed by means of a perturbation procedure. When the critical point is simple, the results are similar to those for conservative systems. When a coincident critical point exists, however, different types of behavior occur. In many cases there is no bifurcation at all, with only the fundamental (trivial) equilibrium path passing through the critical point. Imperfection-sensitivity is more severe than for the typical bifurcation points and can even occur when the perfect system has no bifurcation. The results are illustrated with the use of a nonlinear double pendulum model subjected to a partial follower load.     

On the Design of Structure and Controls for Optimal Performance of Actively Controlled Flexible Structures

ABSTRACT

The simultaneous design of scruccure and active controls is considered for structures equipped with force controllers. Both requirements for mission control (prescribed terminal conditions) and for the control of structural response (control damping) are reflected in developments for the design of

distributed parameter and large scale structures. As an example of problems with simple modal control, the optimal design is predicted for a cantilevered beam and for the feedback gains and actuator positions of its discrete controllers. Also the additional criterion to limit control spillover is incorporated into the formulation for modal control with a prescribed number of controlled modes. Computational results indicate that in some cases the use of a fully coupled model for the design of structure and its control devices leads to a considerable improvement in performance.     

Videometrics Measurement for Dynamic Topography of Large Flexible Cable Net Based on Tiny Light Spot Markers

Background:

Traditional videometric method can not be used in the measurement of large flexible cable-net structure for its large overall size and small partial size.

Objective

A videometrics technique was proposed in this work to measure the topography and deformation of a large cable net structure.

Methods

Tiny spots with high brightness (and large gray gradient) are used to mark the cable net nodes. By arranging the imaging light path properly, the light spot markers can be enlarged and accurately identified in the captured images.

Results

The relationship between the imaging parameters and the gray distribution of the light spot markers were derived and verified. And a topographical measurement experiment of a cable net structure was carried out with the proposed videometrics technique.

Conclusions

The topography/deformation of the cable net can be measured with tiny-light spot markers, and the effectiveness and robustness of the technique on topography and deformation measurement of large cable-net structures are demonstrated.

     

Magnetically driven foldable shell type swimmers at Stokes flow

This paper focuses on the interaction of low Reynolds number (Re) flows and thin shell type deformable structures in the context of flexible body locomotion and addresses the coupled field problem through a numerical solution framework. The thin structure is discretized by enhanced three-node finite elements and coupled with boundary element based treatment of Stokes flow in a monolithic manner. The locomotion is triggered and driven by an external magnetic field that generates displacement dependent body couples over the magnetically sensitive parts of the flexible structure. A particular novelty of the paper is the use of internal hinges through which very large rotations and structural deformations can be combined in an efficient way. Using this concept; new, on the fly locomotion direction reversal mechanisms can be generated as demonstrated by the foldable bi-directional swimmer.

     

Analytical Treatment of Some Extended Problems in Structural Optimization,Part II

ABSTRACT

The Prager-Shield theory of optimal plastic design is applied to systems of preassigned topography (configuration) subject to either a single or several alternate load conditions. For the particular case of pin-jointed frames and a single load system, the criteria derived are shown to reduce to a condition obtained recently by Prager. The method is extended to cover joints of nonzero cost and it is illustrated with examples of trusses and grillages.

Finally, the optimization of discrete grillages having movable beams in preassigned directions is considered.     

Neighborhood Relationships of Widely Distributed and Irregularly Shaped Particles in Partially Dewatered Filter Cakes

A more thorough understanding of the properties of bulk material structures in solid–liquid separation processes is essential to understand better and optimize industrially established processes, such as cake filtration, whose process outcome is mainly dependent on the properties of the bulk material structure. Here, changes of bulk properties like porosity and permeability can originate from local variations in particle size, especially for non-spherical particles. In this study, we mix self-similar fractions of crushed, irregularly shaped Al₂O₃ particles (20 to 90 µm and 55 to 300 µm) to bimodal distributions. These mixtures vary in volume fraction of fines (0, 20, 30, 40, 50, 60 and 100 vol.%). The self-similarity of both systems serves the improved parameter correlation in the case of multimodal distributed particle systems. We use nondestructive 3D X-ray microscopy to capture the filter cake microstructure directly after mechanical dewatering, whereby we give particular attention to packing structure and particle–particle relationships (porosity, coordination number, particle size and corresponding hydraulic isolated liquid areas). Our results reveal widely varying distributions of local porosity and particle contact points. An average coordination number (here 5.84 to 6.04) is no longer a sufficient measure to describe the significant bulk porosity variation (in our case, 40 and 49%). Therefore, the explanation of the correlation is provided on a discrete particle level. While individual particles?<?90 µm had only two or three contacts, others?>?100 µm took up to 25. Due to this higher local coordination number, the liquid load of corresponding particles (liquid volume/particle volume) after mechanical dewatering increases from 0.48 to 1.47.

     

Elastic Buckling with Infinitely Many Local Modes

ABSTRACT

ABSTRACT In some cases, asymptotic methods present an appealing alternative to full nonlinear analyses. In other cases, the value of an asymptotic analysis may merely be that, in a qualitative way, it can characterize the behavior of a structure. Whether an asymptotic method is applied for one or the other purpose it is of interest to attempt an estimation of its range of validity. The present paper addresses this question for an asymptotic method to predict imperfection sensitivity of elastic structures with mode interaction. The particular structure that is investigated possesses an infinity of nearly simultaneous local buckling modes. It is found that very few of these modes need to be taken into account.     

Buckling Models for Higher Catastrophes∗

Abstract

An illustrative study of higher order catastrophes (elliptic umbilic and two kinds of double cusp) is presented on a simple elastic structure using polar co-ordinates. The bifurcation paths are analyzed for both perfect and imperfect structures.     

Displacement Bounding Principles in the Dynamics of Elastoplastic Continua

Abstract

General bounds on the total displacements of structures subjected to any dynamic loading process are developed for an elastic perfectly plastic material. These bounds are subsequently extended to linear kinematic hardening materials. Previously developed bounds for the dynamics of impulsively loaded structures are recognized to be particular cases of the present formulation. A simple example indicates that the proposed technique is relatively easy to apply for numerical computations     

Path dependency in hybrid structures with simultaneous ductile and brittle connections and materials

This article considers a steel–stud–concrete hybrid structure with a Fibre Reinforced Polymer plate adhesively-bonded to the steel member. Owing to the combination of ductile and brittle materials and connections present, the failure behavior of such a structure can be influenced by residual stresses, which in turn depend on the plasticity-inducing load paths previously experienced by the structure. Plasticity of only the stud connections generates a different residual stress pattern from plasticity of only the steel member, and an understanding of the mechanics of residual stress generation in each case is fundamental to the development of a framework of ideas on path dependency in such structures. Measurements of deformation do not necessarily permit faithful reconstruction of residual stress profiles, as these measurements typically give total (elastic plus plastic) deformations from the times that the measurements start, while the residual stresses are related to the elastic components of deformation from the times that the structural components were manufactured. Numerical work is thus needed to determine residual stresses. To that end, a verified finite element program is here used to investigate residual stress patterns in the above hybrid structure due to plasticity of either the studs or the steel member. For yield of the steel, the effects on the residual stresses of initial self-equilibrating stresses in the steel member are investigated. Crucial to the success of the analyses are curvilinear or multi-linear loading/unloading constitutive relationships not only for the materials, but also for the connections. The residual stress profiles from the steel yield and stud yield analyses are examined and compared, and ideas for extension of the work are suggested.     

Controllability Properties and Invariance Pressure for Linear Discrete-Time Systems

For linear control systems in discrete time controllability properties are characterized. In particular, a unique control set with nonvoid interior exists and it is bounded in the hyperbolic case. Then a formula for the invariance pressure of this control set is proved.

     

How to compute invariant manifolds and their reduced dynamics in high-dimensional finite element models

Invariant manifolds are important constructs for the quantitative and qualitative understanding of nonlinear phenomena in dynamical systems. In nonlinear damped mechanical systems, for instance, spectral submanifolds have emerged as useful tools for the computation of forced response curves, backbone curves, detached resonance curves (isolas) via exact reduced-order models. For conservative nonlinear mechanical systems, Lyapunov subcenter manifolds and their reduced dynamics provide a way to identify nonlinear amplitude–frequency relationships in the form of conservative backbone curves. Despite these powerful predictions offered by invariant manifolds, their use has largely been limited to low-dimensional academic examples. This is because several challenges render their computation unfeasible for realistic engineering structures described by finite element models. In this work, we address these computational challenges and develop methods for computing invariant manifolds and their reduced dynamics in very high-dimensional nonlinear systems arising from spatial discretization of the governing partial differential equations. We illustrate our computational algorithms on finite element models of mechanical structures that range from a simple beam containing tens of degrees of freedom to an aircraft wing containing more than a hundred–thousand degrees of freedom.

     

Coupled thermoviscoelasticity: A way to the stress-strain analysis of polymeric industrial components?

Summary The general relations between stress-strain fields and temperature change field are reported for elastic and viscoelastic bodies, and the energy equation is derived for the Zener's solid. Simple experimental thermographie analyses allow the coupled thermoviscoelasticity theory to be evaluated when applied to the structural analysis of machine components made of dissipative materials.

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Sommario Si presentano le relazioni generali tra i campi tensionali e deformabili ed il campo di variazione della temperatura nel caso di corpi elastici e viscoelastici, ricavando l'equazione dell'energia nel caso del Solido di Zenner. Semplici prove termografiche permettono di valutare l'applicabilità della teoria della termoviscoelasitcità accoppiata all'analisi strutturale di componenti di macchine realizzati con materiali dissipativi.

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In conclusions, the author thinks that the introduced thermomechanical approach could be used satisfactorily in the structural analysis of viscoelastic units, on explicit condition that critical parameters could be controlled. In particular, an attempt to limit the environment influences and to improve the optical resolution of infrared systems (by means of a thermostatic chamber and of a microscope) is being planned. The aim is to start studying the temperature change field at the tip of a crack in a stressed continuum.     

Piezo-ElectroMechanical (PEM) structures: passive vibration control using distributed piezoelectric transducersStructures Piézo-ÉlectroMécaniques (PEM) : contrôle passif de vibrations en utilisant des transducteurs piézo-électriques distribués

A piezo-electromechanical structural member is composed of a host member, a uniformly distributed array of piezoelectric transducers and a passive electric circuit (acting as a controller) interconnecting their electric terminals. Such a circuit has to be designed to assure the most efficient transduction of mechanical into electrical energy. The needed circuits are synthesized for bars, beams and plates and the performances of the corresponding PEM structures are determined. Once suitable dissipative elements are included in the controller, it is proven that, in PEM structures, mechanical vibrations are the most efficiently damped. To cite this article: F. dell'Isola et al., C. R. Mecanique 331 (2003).