Papers by Author: Arkadiusz Zak

Abstract: According to the latest research results presented in the literature changes in propagating waves are one of the most promising parameters for damage identification algorithms. Numerous publications describe methods of damage identification based on the analysis of signals reflected from damage. They also include complicated signal processing techniques. Such methods work well for damage localisation, but it is rather difficult to use them in order to estimate the size of damage. It is natural that propagating wave reflects from any structural discontinuity. The bigger the disturbance the bigger part of a propagating wave reflects from it. The amount of energy reflected and transmitted through any discontinuity can expressed as reflection and transmission coefficients. In the literature different application for these coefficients may be found – the most often cited application is connected with localising changes in the geometry of structures. Changes in the coefficients due to cross section variations in rods and beams or due to existence of stiffeners in plates are well documented. However there are no application of using the reflection and transmission coefficients for damage size identification. For this reason the analysis presented in this paper has been carried out. The article presents a method of damage identification in 1D elements based on the wave propagation phenomenon and changes in reflection and transmission coefficients. The changes in transmission and reflection coefficients for waves propagating in isotropic rods with different types of damage have been analysed. The rods have been modelled with the elementary, two and three mode theories or rods. For numerical modelling the Spectral Finite Element Method has been used. Several examples are given in the paper.

Abstract: The aim of this paper is development of an algorithm for damage localisation in composite plates based on wave propagation signals registered by sensors. It is proposed to distribute the sensors uniformly over the area of a plate-like structure performing triangulation. Next the registered signals are processed and a damage influence map is created in each triangle separately in order to avoid problems connected with reflections from boundaries of the structure. The proposed procedure has been verified on numerical signals as well as experimental signals.

Abstract: This work is focused on two major applications of multi–functional materials. In the first one the use of piezoelectric transducers have been studied in order to monitor the health of composite plate–like structures. These transducers can act as signal sources and sensors for guided elastic waves in inspected structures. The excited waves propagating in the material can reflect from various discontinuities such like: boundaries, notches, cracks and delamination. In the next step the time responses registered by the sensors, as inputs for a signal processing algorithm, may be processed to correlate the measured arriving waves with the discontinuities in the structures enabling one to indicate the location of the discontinuities. In the second application the use of shape memory alloy (SMA) components integrated with composite structural elements are investigated. SMA elements in the forms of wires, strips, ribbons, beams, tubes, etc. can be bonded to, or integrated within, various structural elements in order to control their mechanical properties, static as well as dynamic behaviour. This can be obtained thanks to unique effects associated with thermal activation of SMAs leading to significant changes in SMA material properties, which next can also be applied for control purposes. The use of such controllable properties of SMA components in active control of static (deflection) and dynamic (natural frequencies, modes of vibrations, amplitudes of forced vibrations) characteristics of laminated composite beams–like structures have been demonstrated.

Abstract: In this paper the authors present a new one-dimensional phenomenological model of the magnetic shape memory effect (MSME) observed in magnetic shape memory alloys (MSMAs). The model takes into account elementary processes associated with the magnetisation of MSMAs. Its correctness has been checked against selected models known from the literature. The model developed by the authors has been verified in the case of a rod element made out of a MSMA by the use of the finite element method (FEM). A study on the influence of activation of MSMA beam actuators in the case of forced vibration of a composite beam has been performed. The authors have also carried out investigation connected with the influence of a transverse and open crack on the effectiveness of vibration reduction in the case of a composite beam by the use of MSM actuators.

Abstract: The aim of this paper is to investigate the influence of temperature fields on wave propagation in composite plates (A0 mode of the Lamb wave has been used). This phenomenon is modelled by the Spectral Element Method. For this purpose a spectral composite plate element, which enables one to take into account thermal effects, has been developed. Different temperature fields have been considered. Results of numerical simulations have been used as input data for a special damage location algorithm. The proposed damage location algorithm utilises signals registered by a clock-like sensor array. In the next step the results from crack location for different temperature fields have been compared.

Abstract: This study investigates a possibility for representing, interpreting and visualising the vibration response of aircraft panels using time domain measurements. The aircraft panels are modelled as thin orthotropic plates and their vibration response is simulated using FE modelling. The vibration response of a thin aluminium panel is simulated using FE modelling. The first ten resonant frequencies are estimated for the FE model and for the dynamically tested panel. They were found to show somewhat low sensitivity to damage. Then the simulated vibration response of the panel is transformed and expanded in a new phase space. This presents an alternative way to study and analyse the dynamics of a structure. A two dimensional phase space is used in this investigation. Thus instead of studying the single dimension measured vibration characteristics one is faced with expanded two dimensional variables which can be visualised and this facilitates the comparison between the damaged and the non-damage states.