This article presents a probabilistic framework to characterize the dynamic and stability parameters of composite laminates with spatially varying micro and macro-mechanical system properties. A novel approach of stochastic representative volume element (SRVE) is developed in the context of two dimensional plate-like structures for accounting the correlated spatially varying properties. The physically relevant random field based uncertainty modelling approach with spatial correlation is adopted in this paper on the basis of Karhunen-Loeve expansion. An efficient coupled HDMR and DMORPH based stochastic algorithm is developed for composite laminates to quantify the probabilistic characteristics in global responses. Convergence of the algorithm for probabilistic dynamics and stability analysis of the structure is verified and validated with respect to direct Monte Carlo simulation (MCS) based on finite element method. The significance of considering higher buckling modes in a stochastic analysis is highlighted. Sensitivity analysis is performed to ascertain the relative importance of different macromechanical and micromechanical properties. The importance of incorporating source-uncertainty in spatially varying micromechanical material properties is demonstrated numerically. The results reveal that stochasticity (/system irregularity) in material and structural attributes influences the system performance significantly depending on the type of analysis and the adopted uncertainty modelling approach, affirming the necessity to consider different forms of source-uncertainties during the analysis to ensure adequate safety, sustainability and robustness of the structure.

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Probabilistic micromechanical spatial variability quantification in laminated composites

Uncertainty quantification of aeroelastic stability of composite plate wings using lamination parameters

Composite materials are heterogeneous in nature and suffer from complex non-linear modes of failure, such as delamination, matrix crack, fiber-breakage, and voids, among others. The early detection of damage in composite structures, such as airplanes, is imperative to avoid catastrophic failure and tragic consequences. This paper reports on the use of machine learning techniques for the damage assessment (i.e., detection, quantification, and localization) of smart composite structures. The success of the machine learning paradigm for damage assessment depends on the representational capability of the discriminative features for the problems of interest. However, from a practical standpoint, it is not possible to define a global or superset of discriminative features that could discriminate between damaged and undamaged states of the structures, and simultaneously make a distinction between various modes of failures. In addition, one machine learning algorithm may show optimum performance for the discriminative features of a particular problem but fails for others. This article focuses on a review of discriminative features and the corresponding machine learning algorithms (both supervised and unsupervised), for various types of damage in smart composite structures.

Damage assessment of smart composite structures via machine learning: a review

This paper addresses the interaction between the health monitoring and control functions of a smart structure. A finite element model is developed for a composite plate with surface mounted piezoceramic actuators and matrix cracks by integrating a classical laminate plate theory approach with a matrix crack model. The effect of matrix cracks in a cantilevered smart composite plate with different electrical and mechanical loadings is studied for several different laminate types and ply angles. It is observed that matrix crack saturation depends on the loading conditions, applied voltage, laminate type, and ply angles. It is found that the static and dynamic behavior of the plate changes significantly due to matrix cracking. Changes in deflection caused by loss of stiffness due to matrix cracks can be compensated by applied voltage. A negative velocity feedback control algorithm is used for active control of damping, and it is found that there is a change in the decay rate of the response due to matrix cracks and that this change can be compensated by increasing the control gain of the active damping algorithm. Different applied voltages and control gains can be used to interrogate the structure at varying loading conditions, which creates more data for structural damage detection. The model developed in this work is useful for structural health monitoring applications.

https://iopscience.iop.org/article/10.1088/0964-1726/18/2/025002/pdf

Shape and vibration control of a smart composite plate with matrix cracks

Spatially varying fuzzy multi-scale uncertainty propagation in unidirectional fibre reinforced composites

This work explores a feasibility of using vibratory hub loads and support vector machine (SVM) to predict damage and hence the life consumption of the composite helicopter rotor blade. Generally, the initial part of the composite's life is dominated by matrix cracking; the intermediate part by debonding/delamination and the final failure due to fiber breakage. The simulated hub loads under various damage levels are obtained using a comprehensive aeroelastic analysis of the composite rotor blade with physics based damage modes and are then linked with the life consumption of the blade using a phenomenological model. The SVM is used for classification of the useful life of the blade into three classes which are useful to decide the prognostic action. The performance of the blade damage detection system is demonstrated using simulated hub loads obtained using a two-cell airfoil section representing the stiff-inplane blade. The model based hub load variations are contaminated with noise to simulate the real data. It is observed that the SVM based damage detection system is more robust, reliable and easy to implement than the rotating frame measurement based methods.

Support Vector Machine based Online Composite Helicopter Rotor Blade Damage Detection System

Purpose – The purpose of this paper is to develop an analytical approach to evaluate the influence of material uncertainties on cross‐sectional stiffness properties of thin walled composite beams.Design/methodology/approach – Fuzzy arithmetic operators are used to modify the thin‐walled beam formulation, which was based on a mixed force and displacement method, and to obtain the uncertainty properties of the beam. The resulting model includes material uncertainties along with the effects of elastic couplings, shell wall thickness, torsion warping and constrained warping. The membership functions of material properties are introduced to model the uncertainties of material properties of composites and are determined based on the stochastic behaviors obtained from experimental studies.Findings – It is observed from the numerical studies that the fuzzy membership function approach results in reliable representation of uncertainty quantification of thin walled composite beams. The propagation of uncertainties ...

Fuzzy approach for uncertainty analysis of thin walled composite beams

In this work, an active vibration reduction of hingeless composite rotor blades with dissimilarity is investigated using the active twist concept and the optimal control theory The induced shear strain on the actuation mechanism by the piezoelectric constant d15 from the PZN?8% PT-based single-crystal material is used to achieve more active twisting to suppress the extra vibrations The optimal control algorithm is based on the minimization of an objective function comprised of quadratic functions of vibratory hub loads and voltage control harmonics The blade-to-blade dissimilarity is modeled using the stiffness degradation of composite blades The optimal controller is applied to various possible dissimilarities arising from different damage patterns of composite blades The governing equations of motion are derived using Hamilton's principle The effects of composite materials and smart actuators are incorporated into the comprehensive aeroelastic analysis system Numerical results showing the impact of addressing the blade dissimilarities on hub vibrations and voltage inputs required to suppress the vibrations are demonstrated It is observed that all vibratory shear forces are reduced considerably and the major harmonics of moments are reduced significantly However, the controller needs further improvement to suppress 1/rev moment loads A mechanism to achieve vibration reduction for the dissimilar rotor system has also been identified

https://iopscience.iop.org/article/10.1088/0964-1726/18/3/035013/pdf

Active twist control methodology for vibration reduction of a helicopter with dissimilar rotor system

Purpose – This study aims to investigate the effects of mass and stiffness imbalance in a tail rotor induced by damage in forward flight.
Design/methodology/approach – An aeroelastic analysis based on finite element in space and time and capable of modeling dissimilar blades is carried out to study the effect of damage occurring in one, two, and three blades in a four-bladed tail rotor system in forward flight. The effect of damage growth on vibratory hub loads and blade responses is studied using a comprehensive aeroelastic code.
Findings – The diagnostic chart which is the summary of damage analysis of tail rotor shows that the root hub vibration spectrum gives enough indication to predict damage growth in the tail rotor blade. Hence, this can be useful towards development of health monitoring system for tail rotor blades.
Originality/value – The proposed analysis helps in understanding the basic physics behind the damaged tail rotor and also gives qualitative assessment of damaged tail rotor where obtaining the flight test data with damaged tail rotor is difficult.

On the effect of mass and stiffness unbalance on helicopter tail rotor system behavior

In this study, an assessment is made for the helicopter vibration reduction of composite rotor blades using an active twist control concept. Special focus is given to the feasibility of implementing the benefits of the shear actuation mechanism along with elastic couplings of composite blades for achieving maximum vibration reduction. The governing equations of motion for composite rotor blades with surface bonded piezoceramic actuators are obtained using Hamilton's principle. The equations are then solved for dynamic response using finite element discretization in the spatial and time domains. A time domain unsteady aerodynamic theory with free wake model is used to obtain the airloads. A newly developed single-crystal piezoceramic material is introduced as an actuator material to exploit its superior shear actuation authority. Seven rotor blades with different elastic couplings representing stiffness properties similar to stiff-in-plane rotor blades are used to investigate the hub vibration characteristics. The rotor blades are modeled as a box beam with actuator layers bonded on the outer surface of the top and bottom of the box section. Numerical results show that a notable vibration reduction can be achieved for all the combinations of composite rotor blades. This investigation also brings out the effect of different elastic couplings on various vibration-reduction-related parameters which could be useful for the optimal design of composite helicopter blades.

https://iopscience.iop.org/article/10.1088/0964-1726/17/6/065009/pdf

Sung Nam Jung

Papers

Support Vector Machine based Online Composite Helicopter Rotor Blade Damage Detection System

Fuzzy approach for uncertainty analysis of thin walled composite beams

Active twist control methodology for vibration reduction of a helicopter with dissimilar rotor system

On the effect of mass and stiffness unbalance on helicopter tail rotor system behavior

Single-crystal-material-based induced-shear actuation for vibration reduction of helicopters with composite rotor system