OUTLINE OF THE THESIS INTRODUCTION

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1.3 OUTLINE OF THE THESIS

A brief summary of the thesis is presented in this section. The research work undertaken consists of two major parts. Firstly, finite element modeling is used to establish excitation frequencies for nonlinear acoustics. Secondly, analyze result to perform and to investigate Modulus Intensity R value for nonlinear acoustic modulations in the presence of the stiffness. Damage detection by using nonlinear acoustic effects are reviewed in a chapter 2. This chapter indicates the explanation of crack detection method and analytical modeling method. Finite Element Analysis FEA is described in chapter 3. Finite Element Analysis focused to the uncrack and crack of the aluminum plate. Analysis of structure used the ABAQUS software. Next chapter discussed the modal analysis of the aluminum plate that conducted to know the mode shape of the structure. This chapter consists of the result uncrack and cracked plate structure of the mode shape and frequency response function. Result analysis can to get after modal analysis is being described. Relation between material stiffness against modulation intensity R Value can to look. Last chapter is a conclusion and recommendation of the thesis. Scope of this study is only limited the analytical analysis using Finite Element Method with use of ABAQUS software. 1.4 PROBLEM STATEMENT The mechanism of the nonlinear acoustic effect is not quite established R.B Jenal 2010 had assumed that one of the mechanisms is due to the behavior of the fatigue crack surfaces interaction. From the above hypothesis this study is aimed to relate the relation of the material stiffness surfaces interaction with the high frequency vibration. 5 CHAPTER 2 DAMAGE DETECTION BY USING NONLINEAR ACOUSTIC EFFECT

2.1 INTRODUCTION

There are many ways that we can use to analyze whether the product can be safely used or whether it is in good condition or not. Non-destructive testing is the best method. This is because, it not only saves cost but also the products used for the analysis can also be used again. An examples of the ways that we commonly as magnetic particle, dye penetration, eddy current, radiography, ultrasound and others against summarized by Staszewski et. al. 2004 and Gdoutus. However, the overall methodology used to test the different deformities. Magnetic particle is a method of using the principle that a flaw in magnetic material produces distortion in an induced magnetic field. The method is easy, fast and economical to apply, but similarly to the dye penetration method it can only be used to detect cracks or damage near the applied surface. Dye penetration is a method of applying colour or fluorescent dye onto the cleaned surface of a component to detect any surface flaws. After applying the dye onto any surface and applying a post-penetrant material such as chalk, flaws will appear as coloured lines. It is a fast method for damage detection and can detect small cracks, but it is only capable of detecting surface flaws. Eddy-current is a method of using the change of impedance in a coil caused by the eddy current from a tested conductor surface. A coil with alternating current is 6 placed near the conductor surface to induce an eddy current. The sensitivity of the method to the defect is dependent on the penetration depth of the eddy current into the conductor and is influenced by the frequency of the alternating current, the magnetic permeability and electrical conductivity of the conductor, and the geometry of the coil and conductor. Therefore the method is highly sensitive for defects near the conductor surface but it is difficult to relate the defect size to the impedance change and the impedance change is also affected by others factors. Radiography is the oldest NDT method and uses X- or γ-ray to detect a defect. The X-ray is transmitted to a tested material and the emerging radiation is measured. If the material contains defects or variations in its thickness or density, the emerged radiation intensity will not be uniform. This method is suitable for detecting volumetric defects. However it is important to know the orientation of the defect beforehand to get the best effect. Ultrasound is a method of transmitting ultrasonic waves into a test material. Any defects and boundaries in the specimen will reflect a pulse wave and the reflection waves are measured. By using the reflection wave data, the defect size and location can be estimated. It is a very effective method for detecting defects in most positions, gives a quick response, is economical, is applicable to thick material, and is highly portable in-situ. However, it is very difficult to distinguish between cracks and other types of defect and it has limited application to certain specimen geometry. We can see an example as follows: Figure 2-1 : specimen with impact damage area 2 7 The above diagram figure 2-1 shows an example of the damage that we can analyze occurred in a surface structure. Damage occurred in the middle. It may be due to various factors.

2.2 CRACK DETECTION METHOD