Arkadiusz Zak

One-dimensional shape memory alloy models for use with reinforced composite structures

In this paper three models of the shape memory alloy behaviour have been presented and re-investigated. The models are attributed to Tanaka, Liang and Rogers, and Brinson, and have been used extensively in the literature for studying the static or dynamic performance of different composite material structures with embedded shape memory alloy components. The major differences and similarities between these models have been emphasised and examined in the paper. A simple experimental rig was designed and manufactured to gain additional insight into the main mechanics governing the shape memory alloy (SMA) mechanical properties. Data obtained from the experimental measurements on Ni-Ti wires have been used in the numerical simulation for validation purposes. It has been found that the three models all agree well in their predictions of the superelastic behaviour at higher temperatures, above the austenite finish temperature when shape memory alloys stay in the fully austenitic phase. However, at low temperatures, when the alloys stay in the fully martensitic phase, some difficulties may be encountered. The model developed by Brinson introduces two new state variables and therefore two different mechanisms for the instigation of stress-induced and temperature-induced martensite. This enables more accurate predictions of the superelastic behaviour. In general, it can be recommended that for investigations of the shape memory and superelastic behaviour of shape memory alloy components the Brinson model, or refinements based on the Brinson model, should be applied.

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.

Dynamics of multilayered composite plates with shape memory alloy wires

In this paper certain aspects of the dynamic behavior of a multilayered, composite plate with shape memory alloys (SMA) wires have been investigated. The influence of parameters such as the orientation and location of SMA wires, the orientation and relative volume fraction of reinforcing fibers, the thickness-to-length and length-to-width ratios, and different boundary conditions, on changes in the critical load, the natural frequencies and the modes of vibrations of the plate have all been studied and discussed in the paper. The use of two different techniques, generally known in the literature as the active property tuning and active strain energy tuning methods, has also been investigated. The results presented in this paper have been obtained by the use of the finite element method and a new finite element formulated for multilayered composite plates has been applied for this purpose.

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.

A sensitivity analysis of the dynamic performance of a composite plate with shape memory alloy wires

In this paper the dynamic performance of a multi-layered composite plate with embedded shape memory alloy (SMA) wires has been investigated in terms of the changes in its relative fundamental natural frequency. A sensitivity analysis has been carried out on the influence of various geometrical parameters and material properties on the plates dynamic performance, as well as the influence of the form of boundary condition. The use of the active property tuning (APT) method and the active strain energy tuning (ASET) method has also been discussed within the paper. The finite element method has been used for the analysis, and a new element has been exploited for modelling multi-layered composite plates. It has been found that the dynamic performance of the multi-layered composite plate with embedded SMA wires strongly depends on the plate geometry and the form of boundary condition, however, the dynamics can be successfully controlled and influenced by an optimal selection of the geometrical parameters and material properties.

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.

An investigation on damage detection in aircrafts panels using nonlinear time series analysis

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.

Influence of Temperature Fields on Wave Propagation in Composite Plates

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.

Propagation of Elastic Waves in Beams – Including Damping Effects

In this work certain results has been presented of an analysis of the influence of material damping on changes in the propagation of elastic waves in beams. A new and original method has been proposed for formulating the dynamic stiffness matrix for a beam spectral finite element. This new approach enables one to enhance the proposed element by including terms previously ignored likes material damping or initial stresses. Numerical examples presented illustrate the influence of damping intensity on the range of propagating waves, as well as the dispersion effects due to the damping.