Marek Krawczuk

Vibration analysis of a cracked beam

Abstract It is well known that the presence of a transverse crack in a beam introduces local flexibility, which changes the dynamic characteristics of a structure. The assumption of an open and closed crack leads to a model with point finite elements. The beam is modeled by triangular disk finite elements. The forced vibrations of the beam and the effects of the crack locations and sizes on the vibrational behavior of the structure are studied. A basis for crack identification is discussed.

Vibration of a Laminated Composite Plate with Closing Delamination

Vibration of a laminated composite plate with a single and closing delamination is analysed in the present paper by using the finite element method. The delamination of layers is modelled by using additional boundary conditions in the delamination front. Contact forces between delaminated layers are also considered in the model by applying a node-to-node contact model. The influence of the delamination length and position on changes in natural frequencies and modes of vibrations of the plate are investigated in the paper. In the present study the plate is excited to vibrate by a harmonic force or by a force impulse and the resulting time series are analysed using FFT. Results of numerical calculations are verified and compared against experimental data obtained for laminated composite plates with delaminations.

Modal analysis of cracked, unidirectional composite beam

In this paper, a model and an algorithm for creation of the characteristic matrices of a composite beam with a single transverse fatigue crack are presented. The element developed has been applied in analysing the influence of the crack parameters (position and relative depth) and the material parameters (relative volume and fibre angle) on changes in the first four transverse natural frequencies of the composite beam made from unidirectional composite material.

Application of fibre Bragg grating sensors for structural health monitoring of an adaptive wing

This paper presents the concept of application of fibre Bragg grating (FBG) sensors for structural health monitoring (SHM) of an adaptive wing. In this concept, the shape of the wing is controlled and altered due to the wing design and the use of integrated shape memory alloy (SMA) actuators. FBG sensors are great tools for controlling the condition of composite structures due to their immunity to electromagnetic fields as well as their small size and weight. They can be mounted onto the surface or embedded into the wing skin without any significant influence on the wing strength. In the first part of the paper a determination of the twisting moments produced by activation of the SMA actuators is presented. As a first step, a numerical analysis using a finite element method (FEM) commercial code ABAQUS® is presented. Then a comparison between strain values measured by FBG sensors and determined numerically is used for determination of the real value of the activation moment of every SMA actuator. Two types of damage scenarios are analysed and discussed in the paper. The first scenario is reduction of the twisting moment values produced by one of the SMA actuators. The second scenario is outer skin damage. In both damage scenarios, a neural network is used for damage detection and localization.

An adaptive wing for a small-aircraft application with a configuration of fibre Bragg grating sensors

In this paper a concept of an adaptive wing for small-aircraft applications with an array of fibre Bragg grating (FBG) sensors has been presented and discussed. In this concept the shape of the wing can be controlled and altered thanks to the wing design and the use of integrated shape memory alloy actuators. The concept has been tested numerically by the use of the finite element method. For numerical calculations the commercial finite element package ABAQUS® has been employed. A finite element model of the wing has been prepared in order to estimate the values of the wing twisting angles and distributions of the twist for various activation scenarios. Based on the results of numerical analysis the locations and numbers of the FBG sensors have also been determined. The results of numerical calculations obtained by the authors confirmed the usefulness of the assumed wing control strategy. Based on them and the concept developed of the adaptive wing, a wing demonstration stand has been designed and built. The stand has been used to verify experimentally the performance of the adaptive wing and the usefulness of the FBG sensors for evaluation of the wing condition.

Natural Frequencies of Multi-Layer Composite Plate with Embedded Shape Memory Alloy Wires

This paper illustrates stress-strain relationships for a single composite lamina with SMA wires and shows their influence upon changes in natural frequencies of a composite multilayered plate. Governing equations based on the finite element method are presented. The plate is modeled by plate finite elements with eight nodes and five degrees of freedom at each node (i.e., three axial displacements and two rotations). For both axial displacements and rotations biquadratic shape functions are used. Results of numerical calculations for different initial strains of SMA wires and their influence on natural frequencies of a composite laminated plate are presented.

Damage Detection of Structures Using Spectral Element Method

In the paper wave propagation in engineering structures is studied on the basis of detection and estimation of the location, as well as the extent, of structural damage.

Detection of Delamination in Multilayer Composite Beams

W pracy przedstawiono model belki kompozytowej z delaminacją. Omowiono czynniki propagacji fali sprezystej w belce i mozliwości wykorzystania zmian w propagującej fali wywolanych delaminacją do jej detekcji.

Spectral Plate Element for Crack Detection with the Use of Propagating Waves

The article presents a new spectral finite plate element with a crack. It is assumed that the crack having an arbitrary length, depth and location is parallel to one side of the plate. Elastic behaviour of the plate at the crack location is considered as a line spring with a varying stiffness along the crack length. Elaborated model is suitable for the analysis of wave propagation in platelike structures and the same for utilizing the differences in propagating waves for structural health monitoring.

Experimental Verification and Comparison of Mode Shape-Based Damage Detection Methods

This paper presents experimental verification and comparison of damage detection methods based on changes in mode shapes such as: mode shape curvature (MSC), modal assurance criterion (MAC), strain energy (SE), modified Laplacian operator (MLO), generalized fractal dimension (GFD) and Wavelets Transform (WT). The object of the investigation is to determine benefits and drawbacks of the aforementioned methods and to develop data preprocessing algorithms for increasing damage assessment effectiveness by using signal processing techniques such as interpolation and extrapolation measured points. Noise reduction algorithms based on moving average, median filter and wavelet decomposition are also tested. The experiments were performed on a 1m long steal cantilever beam. Damage was introduced in form of 10% and 20% deep saw cut, placed in 10%, 30%, 50%, 70% and 90% beam length. Measurements were made using non-contact Scanning Laser Doppler Vibrometer at 125 points equally spaced along beam length.