Prashant M. Pawar

Matrix Crack Detection in Thin-walled Composite Beam using Genetic Fuzzy System

Since thin-walled composite structures are widely used in structural engineering, damage in such structures is an important issue of research. Matrix cracking is a principal cause of failure in composites. In the present study, a composite matrix cracking model is implemented in a thin-walled hollow circular cantilever beam using an effective stiffness approach. Such structures are used to model connecting shafts and helicopter tail boom, for example, because of their high stiffness-to-weight ratios and excellent crashworthiness characteristics. The effect of variation in crack density on the fundamental frequency, for various combinations of 1/2 m =90n s composite is studied. Using these change in frequencies due to matrix cracking, a genetic fuzzy system for crack density and crack location detection is generated. The genetic fuzzy system combines the uncertainty representation characteristics of fuzzy logic with the learning ability of genetic algorithm. It is observed that the success rate of the genetic fuzzy system in the presence of noise is dependent on crack density (level of damage), number of 90 plies, angle of constraining layer (), and noise level. It is found that the genetic fuzzy system shows excellent damage detection and isolation performance, and is robust to presence of noise in data.

Helicopter rotor health monitoring - a review

Abstract A review of the literature on helicopter rotor system health monitoring is conducted in this paper. An introduction is provided to the work on rotor track and balance and commercial health and usage monitoring systems. Research on the modelling of typical rotor system faults using aeroelastic analysis is discussed and the use of damage detection algorithms based on neural network, fuzzy logic, and system identification is pointed out. The use of non-destructive testing (NDT) approaches, such as modal methods, acoustic emission, and wave-based approaches for rotor health monitoring is discussed. Finally, work on the health monitoring of composite helicopter rotors is discussed and inverse problem solution and life prediction issues are addressed. Future research needs in the area are pointed out.

Damage detection in beams using spatial Fourier analysis and neural networks

This study investigates the effect of damage on beams with fixed boundary conditions using Fourier analysis of mode shapes in the spatial domain. A finite element model is used to obtain the mode shapes of a damaged fixed—fixed beam, and the damaged mode shapes are expanded using a spatial Fourier series and the effect of damage on the harmonics is investigated. This approach contrasts with the typical time domain application of Fourier analysis for vibration problems. It is found that damage causes considerable change in the Fourier coefficients of the mode shapes, which are found to be sensitive to both damage size and location. Therefore, a damage index in the form of a vector of Fourier coefficients is formulated. A neural network is trained to detect the damage location and size using Fourier coefficients as input. Numerical studies show that damage detection using Fourier coefficients and neural networks has the capability to detect the location and damage size accurately. Finally, the performance of the method in the presence of noise is studied and it is found that the method performs satisfactorily in the presence of some noise in the data.

Fuzzy-Logic-Based Health Monitoring and Residual-Life Prediction for Composite Helicopter Rotor

A health-monitoring and life-estimation strategy for composite rotor blades is developed in this work. The cross-sectional stiffness reduction obtained by physics-based models is expressed as a function of the life of the structure using a recent phenomenological damage model. This stiffness reduction is further used to study the behavior of measurable system parameters such as blade deflections, loads, and strains of a composite rotor blade in static analysis and forward flight. The simulated measurements are obtained using an aeroelastic analysis of the composite rotor blade based on the finite element in space and time with physics-based damage modes that are then linked to the life consumption of the blade. The model-based measurements are contaminated with noise to simulate real data. Genetic fuzzy systems are developed for global online prediction of physical damage and life consumption using displacement- and force-based measurement deviations between damaged and undamaged conditions. Furthermore, local online prediction of physical damage and life consumption is done using strains measured along the blade length. It is observed that the life consumption in the matrix-cracking zone is about 12-15% and life consumption in debonding/delamination zone is about 45-55% of the total life of the blade. It is also observed that the success rate of the genetic fuzzy systems depends upon the number of measurements, type of measurements and training, and the testing noise level. The genetic fuzzy systems work quite well with noisy data and are recommended for online structural health monitoring of composite helicopter rotor blades.

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

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 composites 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.

Modeling Multi-Layer Matrix Cracking in Thin Walled Composite Rotor Blades

Helicopter rotor blades are made of fiber-reinforced composite materials that are prone to matrix cracking. Matrix cracking precedes more serious damage mechanisms such as delamination and fiber breakage and is therefore a useful indicator of structural health. In the present study, the effect of matrix cracking on composite blade stiffness and deflections is investigated. A stiff inplane rotor blade with a rectangular box and two-cell airfoil section with [0/ +/-45/90], family of laminates is considered. It is observed that the stiffness decreases rapidly in initial phase of matrix cracking and then becomes saturated. Study of the behavior of composite rotor blade from matrix cracking in single, two and complete lamina group show a bending stiffness loss of 6-12 percent and a torsion stiffness loss of 25-30 percent at the point where matrix cracking saturates, and more severe forms of damage such as debonding/delamination and fiber breakage begin.

Structural health monitoring using genetic fuzzy systems

Introduction.- Genetic Fuzzy Systems.- SHM of Beams.- SHM of Composite Beams.- SHM of Helicopter Rotors.

Fuzzy approach for uncertainty analysis of thin walled composite beams

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 ...

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

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 Hamiltons 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.

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

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.