ABSTRACT

This thesis involves the simulation and practical experiment of the hard material to calculate the elasticity and phase velocity of the material without harming or effecting the materials usefulness which is a Non-destructive technique (NDT). The research studies the surface acoustic wave (SAW) is applied to investigate the elastic properties of the hard material models such Aluminium, Steel, Plastic, Steel with Plastic and Steel with defect.

The aim is achieved through the simulation which is processed by a finite element analysis software, ANSYS. ANSYS tool is very powerful and capable to solve some tough problems which covers the area of stress and displacement. In this simulation, the SAW is generated by a Laser Ultrasonic and through the Laser Vibrometer the data of the waves in the material is detected and treated as an Input. Signal processing is applied to the SAW results to obtain the phase velocity with the frequency obtain by using a MATLAB software. By studying the variation of phase velocity, the change of the hard material properties can be determined. These results represent the improvement of the SAW study which can be applied into industrial field.

This thesis not only calculate the elasticity of the material through the simulation but also carry out the practical experiment to cross-validate the results. The results achieved from the simulation of ANSYS and the practical experiment were successfully achieved with the tolerance of human error.

CHAPTER 1 – INTRODUCTION

1.1  MOTIVATION AND RESEARCH OBJECTIVES

In many industries it is tremendously difficult to fabricate items that will be absolutely insusceptible to cracking and softening up, quality check, and amid utilize, basic. Cracks can happen in various materials, for example, metals, composites, plastics and minerals, and may fail in industries including car, aviation, building, designing and assembling [106].

Today acoustic has a wide field of activities in logical and mechanical examinations and administrations, for example, pharmaceutical, medico assessment equipment, and so forth. Albeit static and dynamic destructive tests, for example, bending test, tensile quality, pressure test and impact testing etc. [102.5] are widely used to quantify flexible properties of hard materials, they also contain issues; for instance, system is irreversible in light of the fact that the specimen is demolished, accomplishment of anticipated example geometry as indicated by the standard is difficult, progressive equipments and long methods time is required [105].

Conversely, non-destructive technique (NDT) methods which have no harm and undesirable impacts on the specimen, could gauge hard material properties with high precision in a short sample of time [105]. NDT is an instrument utilized by specialists to recognize absconds in materials and structures, either amid assembling or while in administration [100]. As an engineering field, Non-Destructive Testing offers a critical part in consistent schedule, such as, things utilized as a part of our everyday life as it is key to ensure the security and dependability. For example, NDT testing can be utilized in an engine vehicle, air ship, pipelines, trains, building, extensions, refineries and oil stages [1].

By 2022, NDT market is anticipated to reach $24.23 Billion contrasted with $15.06 Billion in 2016, at a CAGR of 8.24% from 2016 to 2022. The expanding interest for non-damaging testing in the business is due to the fact NDT guarantees safety and efficiency in the manufacturing procedure of geometrically complex material components [101].

The initial noted uses of NDT were in 1868, where Englishman S.H. Saxby depended on the magnetic characteristics of a compass to discover cracks in gun barrels. Then, the initial NDT method to come into modern application was the X-Ray system in 1895 [102].

NDT techniques offer not just the benefits of discovering potential or real issues in the manufacturing programme without harming or effecting the material usefulness but also certain feedback as to how to revise the issue at the earliest conceivable point [103].

To evaluate the quality and reliability of the components by NDT, there are many methods which can be implied such as [104]: Magnetic particle testing (MT), Radiographic testing (RT), Visual Testing (VT), and Electromagnetic testing (ET), Liquid Penetrant testing (PT) and Ultrasonic Testing (UT).

The surface acoustic wave (SAW) innovation has been utilized as a part of mechanical applications, for example, examining surface structures, composition geometry, roughness and elastic properties of metallic samples. SAW technique is primarily used to assess the mechanical properties of materials since it has preferred standpoint to quantitatively evaluate Young’s modulus.

The values of phase velocity are connected with the Young’s modulus, then, the quantitative elasticity data of material layer, the propagation of the SAW can be calculated. The SAW can be found through the most widely recognised method by utilizing the ultrasound transducer [21] which involves the physical contact of the sample. This necessity prompts various disadvantages: the detecting range is restricted by the transducer, leakage of wave energy happens at the material-transducer boundary, wave alteration will be produced due to the weight of the transducer on the sample etc. To overcome these problems, a suitable method is utilizing a non-contact and non-damaging way to detect the SAW, which is a Laser Ultrasonic. Laser Ultrasonic strategy has been generally utilized on the grounds that it is non-contact and remote, thus no surface loading.

Laser Ultrasound detects the SAW and through the Finite element method (FEM) using ANSYS able to calculate the values of the material which represents the waves inside the material from where elasticity of the material can be obtained. ANSYS is a finite element analysis tool for structural examination, including linear, nonlinear and dynamic studies. It approaches to simulate all the complexities of the problem, such as varying shape, boundary and loading conditions on a structure and regulate the structures response to the conditions.

ANSYS is also beneficial for the practical experiments to cross-validate with the simulation results. As the accuracy of the ANSYS is very reasonable thus it is currently the demanding tool as it able to simulate and give accurate results which saves time and cost of materials rather than testing again and again until the practical experiment gets the accurate results.

The aim of the project in this thesis is to develop finite element models to simulate SAW elastography in different properties of hard materials in single, double layers and defect layers by a non-destructive technique. The SAW elastography and behaviour in the hard materials will be investigated through the NDT which is chosen to be Laser Ultrasonic. In Laser Ultrasonic, lasers are used to generate and then measure, ultrasonic waves in a material. The waves produced in a material is Surface Acoustic waves (SAW). Through the waves, the data can be collected by using laser Vibrometer. Laser Vibrometer works by aiming light at the vibrating subject and study the returned beam and transferred the information into ANSYS where it able to visualise the waves. The experiment will be carried out on six various materials such as Steel, Aluminium, Plastic, Plastic with Steel, Steel defect layer and finally 5% of Agar before coming to the conclusion.

The objective in this project is as follows:

• Use the software ANSYS to simulate the thermal and structural analysis of the different hard materials
• Use the software MATLAB to convert the raw data of ANSYS into phase velocity and plot the graphs of waveform of the Surface Acoustic Wave.
• Cross-validation of the simulation result with the experimental data.

1.2 OUTLINE OF THESIS

Chapter 2 of this thesis is the literature review, which includes several methods of Non-Destructive testing (NDT) and by comparing between it, the best and suitable method was chosen; Ultrasonic testing. Next topic focus on different types of waves such as Primary, Shear and Surface acoustic waves and explain why SAW is the best option out of all and how it can be used to generate and detect the SAW by giving various option to pick suitable generator and detector for the SAW.

Chapter 3 introduces to the Finite element analysis in ANSYS. The Finite Element Analysis (FEA) is an approach to simulate all the complexities of the problem, such as varying shape, boundary and loading conditions on a structure and regulate the structures response to the conditions. This chapter demonstrate the general knowledge of using ANSYS and the theory provide a convincing basis all through the thesis.

Chapter 4 introduces the process of simulation using Finite Element Analysis. This chapter will cover the method FEA simulation of the laser generated SAW in different material models. A preliminary FEA simulation results from ANSYS.

Chapter 5 presents the signal processing of SAW which includes the frequency analysis, de-nosing of the signal. Also the phase velocity will be investigated. Varity of the de-nosing method will be introduced in this chapter. The inversion producers of SAW signals to elasticity information will be introduced, which will monitor the mechanical changes of the different hard materials including defect materials.

Chapter 6 validate the simulation results with the first-hand experiment.

Chapter 7 presents the conclusion of this work along with some suggestion for further study