i

ISTANBUL TECHNICAL UNIVERSITY FACULTY OF AERONAUTICS AND ASTRONAUTICS

GRADUATION PROJECT

January, 2018

THE NUMERICAL INVESTIGATION OF THE PARTICLE IMPACT ON A

COMPRESSOR BLADE

Thesis Advisor: Prof. Dr. Halit Süleyman TÜRKMEN

Ramazan KORKMAZ

Department of Aeronautical Engineering

Anabilim Dalı : Herhangi Mühendislik, Bilim

Programı : Herhangi Program

ii

January, 2018

ISTANBUL TECHNICAL UNIVERSITY FACULTY OF AERONAUTICS AND ASTRONAUTICS

THE NUMERICAL INVESTIGATION OF THE PARTICLE IMPACT ON A

COMPRESSOR BLADE

GRADUATION PROJECT

Ramazan KORKMAZ

110160543

Department of Aeronautıcal Engineering

Anabilim Dalı : Herhangi Mühendislik, Bilim

Programı : Herhangi Program

Thesis Advisor: Prof. Dr. Halit Süleyman TÜRKMEN

iii

iv

To my family,

v

FOREWORD

This study, in which the finite element analysis of the simulation of metal particle

impact on a compressor blade was performed, with my academic knowledge and

experience, and my thesis advisor, who supported me in all aspects by providing all

the material spiritual opportunities, I would like to thank Prof. Dr. Halit Süleyman

TÜRKMEN. I would like to thank to my dear friends and especially Oğuz

KORKMAZ, who supported me in every subject during my thesis studies, and also

to my friend Mahir DOĞAN, who had experimented on impact part of the

compressor.

I would like to thank my dear family who have always been with me throughout my

education life and never supported me.

January, 2019 Ramazan KORKMAZ

vi

vii

TABLE OF CONTENTS

Page

FOREWORD .................................................................................................v

TABLE OF CONTENTS .......................................................................... vvii ABBREVIATIONS .....................................................................................ixx

LIST OF TABLES ....................................................................................... xx LIST OF FIGURES ..................................................................................... xi

SUMMARY .................................................................................................. xi

ÖZET ..........................................................................................................xiv

1. INTRODUCTION......................................................................................1 1.1 Purpose of Content ................................................................................ 2

2. FOREIGN OBJECT DAMAGE................................................................2 2.1 Metal Object .......................................................................................... 2

2.2 Sandstone .............................................................................................. 3 2.3 Soft Object ............................................................................................ 3

3. PREVENTION OF METAL IMPACT .....................................................4 4. FINITE ELEMENT ANALYSIS ..............................................................5

4.1 Introduction ........................................................................................... 5 4.2 The Logic of Finite Element Analysis.................................................... 5

4.2.1 Identification ...................................................................................6 4.2.2 Mesh Generation .............................................................................6

4.2.3 Analysis ..........................................................................................6 4.2.4 Visual Presentation ..........................................................................6

4.2.5 Optimization ...................................................................................6

4.3 Mesh Types ........................................................................................... 6

4.4 Mesh Quality Parameters ....................................................................... 7 4.4.1 Grow Rate .......................................................................................7

4.4.2 Aspect Ratio ....................................................................................8 4.4.3 Jacobian Ratio .................................................................................8

4.4.4 Skewness.........................................................................................8

5. COMPRESSOR MODEL ..........................................................................9 5.1 Geometry .............................................................................................. 9 5.2 Material Properties ...............................................................................10

5.2.1 Aluminum 7039 Material Properties .............................................. 10 5.2.1 Steel Material Properties................................................................ 10

6. ANALYSIS RESULTS AND COMPARISON ....................................... 12 6.1 Analysis Results ...................................................................................12

6.1.1 Total Displacement........................................................................ 13

6.1.2 Displacement in z Direction .......................................................... 14 6.1.3 Equivalent Von Misses Stress ........................................................ 15

6.1.4 Maximum Principal Stress ............................................................. 16

viii

6.1.5 Shear Stress .................................................................................. 17

6.1.6 Equivalent Elastic Strain ............................................................... 18 6.1.7 Max. Principal Elastic Strain ......................................................... 19

6.1.8 Shear Elastic Strain ....................................................................... 20

6.2 Comparison Analysis Results and Experiment ..................................... 21

7. OPTIMIZATIONS .................................................................................. 22 7.1 Mesh Optimizations ............................................................................. 22

7.2 Different Velocities .............................................................................. 23

8. COMMENTS ........................................................................................... 24

REFERENCES ............................................................................................ 25

ix

ABBREVIATIONS

ALE : Arbitrary Lagrangian Eulerian

EASA : European Aviation Safety Agency

Ek : Kinetic Energy

FAA : Federal Aviation Administration

FOD : Foreign Object Damage

ICAO : International Civil Aviation Organization

SPH : Smoothed Particle Hydrodynamics

x

LIST OF TABLES

Table 1: Aluminum Material Properties ................................................................ 10

Table 2: Mass Components of Aluminum ............................................................. 10

Table 3: Steel Material Properties ......................................................................... 10

Table 4: Mass Components of Steel ...................................................................... 11

Table 5: Effect of Mesh Density on Analysis Result ............................................. 22

Table 6: Analysis in Different Velocities .............................................................. 23

xi

LIST OF FIGURES

Figure 1: Concorde crash in 2000 ............................................................................1

Figure 2: A screw in runway ...................................................................................2

Figure 3: Compressor damaged by copper parts ......................................................2

Figure 4: Blade damaged by sandstone ....................................................................3

Figure 5: Blade attacked by birds ............................................................................3

Figure 6: Birds attack at departure ...........................................................................3

Figure 7: 1D,2D and 3D Mesh Types ......................................................................6

Figure 8: Ansys Mechanical Outline .......................................................................7

Figure 9: 3D Modelling Compressor in CATIA ......................................................9

Figure 10: Prototype Compressor ............................................................................9

Figure 11: Ball and Blade ..................................................................................... 12

Figure 12: Total deformation of the blade after impact .......................................... 13

Figure 13: Total deformation curve depending on time ......................................... 13

Figure 14: Directional deformation of the blade after impact ................................. 14

Figure 15: Directional deformation curve depending on time ................................ 14

Figure 16: Von Misses stress shape ....................................................................... 15

Figure 17: Von Misses stress curve depending on time ......................................... 15

Figure 18: Maximum Principal Stress ................................................................... 16

Figure 19: Max. principal stress curve depending on time ..................................... 16

Figure 20: Shear stress .......................................................................................... 17

Figure 21: Shear stress curve depending on time ................................................... 17

Figure 22: Equivalent Elastic Strain ...................................................................... 18

Figure 23: Equivalent stress curve depending on time ........................................... 18

Figure 24: Maximum Principal Strain ................................................................... 19

Figure 25: Max. principal strain curve depending on time ..................................... 19

Figure 26: Shear elastic strain ............................................................................... 20

Figure 27: Shear elastic strain curve depending on time ........................................ 20

Figure 28: Physical testing of the blade image ...................................................... 21

Figure 29: Image of blade at the end of analysis (0,0004 sec.) ............................... 21

xii

xiii

THE NUMERICAL INVESTIGATION OF THE PARTICLE IMPACT ON A

COMPRESSOR BLADE

SUMMARY

Thanks to aircraft’s gas turbine engines, they provide thrust. Engines that

allow aircraft to travel in the air are the energy center of the aircraft. Engines take a

large amount of air into the compressor, shoot out at high speeds. There are large

compressor blades at the inlet, and small size compressor blades continuing down

towards the back. When the air enters the engine, blades may be exposed to damage

foreign object in the air. We can classify these parts as metal parts sandstones and

soft materials. These damages may cause the blades to break, failure of the engine

and even loss of life. This type of damage in the aviation sector is seriously

economical damaging to the airline companies. To minimize these losses, impact

tests are performed to the finished parts and the damages are examined this method is

expensive when considered repetitive, or we can do analysis with modeling the

problem in computer environment, defining the real experimental conditions, so we

can review again and again at less cost

The aim of this study is to analyze the metal ball impact of compressor

blade with mathematical modeling and computer analysis. In order to get results that

are closest to reality in this work done in computer environment, it is necessary to

determine the most appropriate analysis method for the problem. When the articles

and previous studies are examined, it is seen that the finite elimination method’s

Lagrange method is the most appropriate method for our problem. Lagrangian

method is used in solid body analysis. In addition, eulerian method is used in the

flow analysis; The ALE method is used in fluid-rigid body analysis and the SPH

method is generally used in bird impact analysis.

In this study examining the damage caused by metal ball impact on

compressor blade. The prototype produced aluminum 7039 compressor part was

taken from KALE R&D company. The results of the same part will be compared

with the experimental results.

Solid modeling required for analysis was performed using CATIA V5 software.

After determining the boundary conditions for analysis, ANSYS software is used to

obtain impact results with Autodyn and Explicit Dynamic modules. As a result of the

analysis, the stresses and their displacements occurring in the compressor blade are

shown together with pictures. In the analysis made under the experimental

conditions, it was seen that the material was under plastic deformation.

xiv

KOMPRESÖR PALİ ÜZERİNE PARÇA ÇARPMASININ SAYISAL

OLARAK İNCELENMESİ

ÖZET

Hava araçları sahip oldukları gaz türbinli motorlar sayesinde itki sağlarlar.

Uçakların ilerlemesini sağlayan motorlar, uçakların enerji merkezleridir. Büyük

miktarlarda havayı içine alıp sıkıştırarak yüksek hızlarda dışarı atmaktadır. Giriş

kısmında büyük kompresör bıçakları ve arkasına doğru küçülerek devam eden

bıçakları vardır. Havanın yutulmasıyla beraber kompresör palleri havanın içerisinde

bulunan yabancı maddelerin hasarlarına maruz kalırlar. Bu yabancı maddeleri; metal

parçalar, kumtaşları ve yumuşak malzemeler olarak sınıflandırabiliriz. Bu hasarlar

pallerin kırılmasına, motorun arızasına ve hatta can kayıplarına neden olabilir.

Havacılık sektöründeki bu tür hasarlar havayolu şirketlerine ciddi şekilde zarar

vermektedir. Bu kayıpları en aza indirgemek için, üretimi tamamlanmış parçalara

çarpma testleri yapılır ki bu yöntem tekrarı düşünüldüğünde pahalıdır. Problemi

bilgisayar ortamında modelleyerek, gerçek deney şartlarında analiz edip daha az

maliyetle tekrar tekrar inceleyebiliriz.

Bu çalışmanın amacı, kompresör paline metal bilye çarpmasının etkisini

görmek için matematik modelleme ve bilgisayar ortamında analiz etmektir.

Bilgisayar ortamında yapılan bu çalışmada gerçekliğe en yakın olan sonuçların elde

edilebilmesi için problem için en uygun analiz yönteminin belirlenmesi

gerekmektedir. Makaleler ve önceki çalışmalar incelendiğinde, sonlu eleme

yönteminin Lagrange metodu problemimiz için en uygun yöntem olduğu

görülmektedir. Lagrange metodu katı cisim analizlerinde kullanılır. Buna ek olarak

akış analizinde euler metodu kullanılır; Akışkan-katı analizinde ALE yöntemi

kullanılır ve SPH yöntemi genellikle kuş çarpması analizinde kullanılır.

Kompresör bıçağı üzerindeki metal bilye darbesinin neden olduğu hasarı

incelemek. Üretilen prototip alüminyum 7039 kompresör parçası KALE Ar-Ge

şirketinden alındı. Aynı parçanın deneyi yapılmış olup deney sonuçları ile

karşılaştırma yapılacaktır. Analiz için gerekli olan katı modelleme, CATIA V5

yazılımı kullanılarak yapıldı. Analiz için sınır koşullarını belirledikten sonra,

AutoDyn ve Explicit Dynamic modülleriyle çarpma sonuçları elde etmek için

ANSYS yazılımı kullanılmıştır. Analiz sonucunda, kompresör palinde oluşan

gerilmeler ve yer değiştirmeler resimlerle birlikte gösterilmektedir. Deney koşulları

altında yapılan analizde, malzemenin plastik deformasyon altında olduğu

görülmüştür.

1

1. INTRODUCTION

In general, the impact is the damage a foreign substance gives to the aircraft. These

substances can be, metal parts bird etc. Aircraft companies lose 12 billion dollars annually

due to foreign object damage (FOD). 4 billion dollars are worth of direct damages parts and

delays, changes in labor, pilot and passenger costs are around 8 billion dollars. [1] For

example; In July 2000, during the departure of the Concorde plane passing through the metal

track on the runway, the metal part caused the tire to break down and the tire parts broke the

fuel tank and caused an accident. 113 people died in the accident and a piece of metal made $

46 million aircraft unusable. [1]

Figure 1: Concorde crash in 2000 [2]

2

1.1 Purpose and Content

Within the scope of this thesis, the changes in the compressor blade related to the

metal ball impact event, the interpretation of the graphs as a result of the analysis and force

energy formulas related to the subject are described. Metal ball is defined as steel and

compressor is defined as alumium7039. Impact tests are performed at different speeds and the

relationship between stress-strain and analysis results has been established.

2. FOREIGN OBJECT DAMAGE

2.1 Metal Object

Foreign metal parts give serious damage to aircraft engines. they cause the knives to

become deformed and the motor does not operate properly. These metal parts are usually

made of bolts, metal balls, stone parts, etc., located on or near the runway during aircraft

landing and take-off. solid objects. [2] Especially in order to achieve maximum thrust during

the departure of the aircraft, foreign engines damage is more likely to occur because the

engines rotate at high speed.

Figure 2: A screw in runway [3] Figure 3: Compressor damaged by copper

parts [2]

3

2.2 Sandstone

The fine and light sandstones can be easily drawn by the engines. The amount of

damage to the blades is quite small. The surfaces that are caused by sand are quite hard and

have no cutting marks. If the size of the sand is greater than 5 millimeters, there may be

rupture of the front blades. [2]

Figure 4: Blade damaged by sandstone [2]

2.3 Soft Object

Soft object damage often refers to bird strikes. Bird aviation is very important in

aviation. They cause serious damage. Unlike a metal stroke, the bird does not behave hard.

Serious damages occur in the input of the engines. [2]

Figure 5: Blade attacked by birds [2] Figure 6: Birds attack at departure [4]

4

3. PREVENTION OF METAL IMPACT

The damage caused by the metal objects, which are the subject of the thesis, to the

aircraft engine and the damages caused by the other foreign substances are an important issue

for the aviation industry both in terms of material and passenger safety. FAA, ICAO and

EASA are the supervisory agencies in the aviation industry. These institutions receive daily

reports of foreign substance inspections by the airline personnel on the track. [5] In addition,

these institutions are responsible for organizing and publishing all kinds of information about

accidents. Airline personnel are on a daily basis on the track and taxi. The ongoing

constructions around the airport should be inspected more frequently. [5] These constructions

should not cause foreign material damage. Staff can be assigned to check this. Since the

aircraft is often subjected to foreign material attack at the time of take-off and landing,

controls on the track are extremely important. The engines are the most exposed to FOD

during the take-off. Because; Since a low pressure field is formed in the front of the motors,

they want to suck in air and foreign matter will move towards the engine. According to this

information, manufacturers can design the structural elements of these regions by making

necessary improvements.

5

4. FINITE ELEMENT ANALYSIS

4.1. Introduction

In the early 1940s, the German mathematician Richard Courant developed a method

used to analyze the behavior and working conditions of the physical systems, which were

shaped by the Ritz method used in the buckling problems of complex structures, and after

which the physical systems were exposed to external influences. There are two important

functions of this method; [6]

Improving product or system design

Quality and control of design

The importance of analysis in a design is indisputable. Finite element analysis is seen

in large sectors such as aircraft and automotive. The reason for this is the difficulty of design

control in mass production in these sectors. In the first period of quality control

systematically, the product was prototyped and tested. This classic method is quite successful

and can be used in structures with less complexity and risk since it gives clear results.

However, in the case of a passenger plane, the cost and reliability of analysis and control are

of high importance.

4.2. The Logic of Finite Element Analysis

As the name suggests, we are talking about the design of the object to be produced

with finite points. We accept that every substance in nature consists of an infinite point.

Therefore, the objects to be designed must be subjected to a limitation and the prototype must

be removed. At this point, the finite element analysis takes place and makes the object

composed of the infinite point finite with the desired limitations. In the first periods of the

analysis, 10 to 100 elements were used because of the hand made of all the processes and the

number of computers increased to 10 million. [6] There are two concepts to know here; node

and element. The nodes represent the points we are reducing from the infinite point by using

the method. The elements are the design parts which are composed of these points. The object

to be designed in summary is divided and analyzed by the elements connected to each other

by nodes. The more the object is divided, the more realism of the results increases.

6

The software used creates linear equations by using the parameters entered in the

nodes of the elements. Equations work well in the case where the virtual drawing of the

design, material properties and boundary values are known. These equations are solved by

linear algebra or numerical methods according to the complexity of the design. Based on the

solution, the virtual test facility is created with the animations drawn by the software. In

summary we can collect on 5 items. [6]

4.2.1. Identification: Drawing of virtual model, entering material properties,

determination of external influences and boundaries.

4.2.2. Mesh Generation: Reduction to the finite point by entering the limit

values in the design.

4.2.3. Analysis: Solving the resulting millions of equations by the appropriate

method.

4.2.4. Visual Presentation: Presentations and graphs of the results of

analysis.

4.2.5. Optimization: By first changing the parameters entered, different

results are obtained and compared with the previous ones and the best

result is found.

4.3. Mesh Types

The solution zone is disaggregated to the sub-regions called finite elements. This

process is called mesh. The first step in solving the finite element problem is determining the

element type. The geometric structure of the solution area should be determined and the most

suitable element should be selected. In the ratio of representing the solution region of the

selected element, the results obtained will be close to the actual solution.

Figure 7: 1D,2D and 3D Mesh Types [7]

7

The three-dimensional mesh generally used are tetragonal and hexagonal mesh. While

the academic world prefers more quadrangular meshes, market engineers may also use

triangular triangles. [8] The tetragonal mesh has 4 surfaces and 4 nodes. The hexagonal mesh

has 6 nodes 8 nodes. Besides, in an analysis, there are some parameters of the quality of the

selected elements in order to obtain the closest results to the real solution.

4.4. Mesh Quality Parameters

In Ansys Mechanical you click on the mesh and the window below the statistics

section. The important point is to keep the values written here with the mesh we keep. Thus,

we can see if the mesh we are throwing is suitable for correct or real results.

Figure 8: Ansys Mechanical Outline [8]

The definitions and limit values of the parameters in the mesh metric section are as follows.

4.4.1. Grow Rate: Refers to the gradual growth of the mesh. The more we can

keep this ratio close to 1, mesh will be better. [8]

8

4.4.2. Aspect Ratio: It is the smallest edge of the mesh with the smallest edge

ratio.

AR = 1 --------> Perfect Mesh

1 <AR <3 -----> Good Mesh

3 <AR <10 ----> Acceptable Mesh

Values greater than 10 will give us false results. [8]

4.4.3. Jacobian Ratio: It relates to the curvature of the elements. Jakobian

points are used for quality elements in the sense of dif. [8]

Jakobian Ratio = 1 ---------> Excellent Element

1 <Jakobian Ratio <40 ----> Acceptable

40 <Jakobian Ratio ---------> Inadmissible

Jakobian Ratio <1 -----------> Never acceptable.

4.4.4. Skewness: A graph showing the ratio between the current mesh structure

and the optimal mesh structure. This method can only be applied to

triangular elements. Skewness takes values between 0 and 1. The closer

our value is to zero, the higher our mesh quality. [8]

0 <Skewness <0.25 ---------> The best mesh

These were our most important mesh parameters. If we can keep three of these

parameters in the healthy intervals we say, the mesh we take is a healthy mesh. In addition,

the mesh command has a relevance command. This command also takes values between -100

and +100, and as it approaches -100, the sensitivity starts to decrease. [8]

9

5. COMPRESSOR MODEL

5.1. Geometry

The prototype compressor we used in our analysis was acquired from Kale

R&D Company. The solid model was obtained using CATIA V5 software. In our

model, there are 14 compressor blades. Blades are 20 mm length and 1.6 mm

thickness. The body diameter is 66 mm and it is 20 mm width. In the analysis, one of

them was used in order not to prolong our solution period. The crash particle is

designed in the form of a ball with a diameter of 10mm.

Figure 9: 3D Modelling Compressor in CATIA

Figure 10: Prototype Compressor

10

5.2. Material Properties

In the study, aluminum 7039 for the compressor and steel for the ball were

selected. The properties of these materials for analysis are given in the tables

below.

5.2.1. Aluminum 7039 Material Properties

Density 2740 kg/

Elastic Modulus 69.4 GPa

Poisson’s ratio 0.33

Yield Strength 380 MPa

Tensile Strength 450 MPa Table 1: Aluminum Material Properties [9]

Component Weight %

Al 90.65-93.95

Cr 0.15-0.25

Cu Max 0.1

Fe Max 0.4

Mg 2.3-3.3

Mn 0.1-0.4

Si Max 0.3

Ti Max 0.1

Zn 3.5-4.5

Table 2: Mass Components of Aluminum [9]

5.2.2. Steel Material Properties

Density 8129 kg/

Elastic Modulus 210 GPa

Poisson’s ratio 0.3

Yield Strength 1750 MPa

Tensile Strength 1830 MPa Table 3: Steel Material Properties [10]

11

Component Weight %

Al 0.05-0.15

C Max 0.03

Mo 2.75-3.25

Fe 75

S Max 0.01

Mn Max 0.01

Si Max 0.01

Ti 1.3-1.45

P Max 0.01

Ni 18-22

Table 4: Mass Components of Steel [10]

The mass was calculated by using the density and volume of the ball.

8129 kg/

V= = =5,23*

m=0.00425 kg

Since the velocity of the ball is 115 m / s, we calculate the kinetic energy it has.

= = =28,14 J

12

6. ANALYSIS RESULTS AND COMPARISON

6.1. Analysis Results

In the analysis, the distance between the ball and the blade will not affect the result.

Therefore, the distance between the two is defined as 1 mm. The part that is important for

us in the analysis is the compressor blade. This is why the blade is important. In order not

to increase the number of mesh, only 1 compressor blade was taken and the root of the

blade was accepted as rigid and fixed support was given. The speed of the ball was

calculated as 115 m / s by using real experiment data. Then analyzed at different speeds.

Figure 11: Ball and Blade

There are 14027 nodes and 15098 elements. There are 9920 hexahedral

elements on the 3D blade model and 5178 tetrahedral elements on the ball. Mesh has

1.4689 aspect ratio, Jacobian ratio is 1.0071, so it is quality mesh.

13

In this analysis, the analysis time was set to 0.4 msec. It was observed that the max

deformation was in this second after the solution was taken in different seconds. The resulting

graphs and figures are shown by reference to the moment when the total deformation is

maximum.

6.1.1. Total Displacement

Figure 12: Total deformation of the blade after impact

It was observed that the metal ball was hit by 115 m / s and the blade was deformed

due to time and a total deformation of 21,584 mm was realized.

Figure 13: Total deformation curve depending on time

14

6.1.2. Displacement in z direction

Figure 14: Directional deformation of the blade after impact

The directional deformation in the Z-axis is as shown in the figure. The maximum

deformation is 10.617 mm in negative direction.

Figure 15: Directional deformation curve depending on time

15

6.1.3. Equivalent Von Misses Stress

Figure 16: Von Misses stress shape

When the ball hit the knife, we see a sudden increase in stress and the maximum von

misses stress is 522.69 MPa. Since the yield strength of the aluminum blade is 380 MPa, this

means that our blade has a plastic shape change.

Figure 17: Von Misses stress curve depending on time

16

6.1.4. Maximum Principal Stress

Figure 18: Maximum Principal Stress

It states that, the failure of a material or component will take place when the maximum

value of stress exceeds the limiting value of stress. It related to tensile or compressive. Max.

principal stress is 590,78 MPa and it is greater than the yield stress and max. tensile strength

of material.

Figure 19: Max. principal stress curve depending on time

17

6.1.5. Shear Stress

Figure 20: Shear Stress (XZ plane)

It states that, the failure or yielding of a component occurs when the working stress

value reaches the limiting shear stress value in a material. The limiting shear stress value is

half of the yielding stress so it is 190 MPa, on the xz plane shear stress is greater than limit

value so failure was occurred.

Figure 21: Shear stress curve depending on time

18

6.1.6. Equivalent Elastic Strain

Figure 22: Equivalent Elastic Strain

Equivalent strain refers to strain caused by all stresses. As we expected, the maximum

equivalent strain occurred in the root of the blade and backside of the point where the ball

strikes.

Figure 23: Equivalent strain curve depending on time

19

6.1.7. Max. Principal Elastic Strain

Figure 24: Maximum Principal Strain

Shape change caused by shear stress is not considered in Principal strain. The

maximum principal strain has already occurred at the root of the blade and backside of the

point where the ball strikes has maximum principal strain. we expect it to be.

Figure 25: Max. principal strain curve depending on time

20

6.1.8. Shear Elastic Strain

Figure 26: Shear elastic strain (XZ plane)

Because of the shear stress impact of the ball on the XZ plane, the material has an

angular distortion in shape. The ratio of inter-plane displacement to the distance between

planes is at most root.

Figure 27: Shear elastic strain curve depending on time

21

6.2. Comparison Analysis Results and Experiment

The analyzes with Ansys lasted for 5 min and 5 seconds with the Monster Abra a5

V.11.1 laptop computer with an i7 2,80 GHz and 8 GB RAM. The results are similar

to the experimental results.

Figure 28: Physical testing of the blade image

Figure 28 shows the physically tested blade, the test was carried out at the Aerospace

Engineering lab at Istanbul Technical University and we saw damage caused by a 10 mm

diameter metal ball effected at 115 m / s.

Figure 29: Image of blade at the end of analysis (0,0004 sec.)

22

Figure 29 shows the analysis result of the knife designed under the same conditions as

the experiment. The analysis period was 0.4 milliseconds. It has been observed that maximum

10,671 mm deformation has occurred during z direction. The result obtained in the

experiment is approximately 10 mm. Therefore, the approximate values as visual and

quantitative results were obtained in the analysis.

7. OPTIMIZATIONS

7.1. Mesh Optimizations

What is important is to see the accuracy of the results obtained and how the size of the

mesh element on the blade affects the results of the analysis. For this purpose, the maximum

Von Misses stress on the blade was examined using with one edge size is 1,6 mm, 1mm,

0,8mm, 0,5mm, 0,3 mm hexahedral mesh. In the examination of Table 7, it is seen that as the

mesh density increases, the amount of stress reaches to the regime after increasing a certain

amount. When we take into account the time relation of the process result, it was preferred for

the analysis that the edge length of the hexahedral mesh element was 0.5 mm.

Element Size 1,6 1 0,8 0,5 0,3

Number of Elements 400 1240 1950 9920 41184

Solution Time(sec) 150 275 305 600 3260

Max. Von Misses

Stress (MPa)

499,14 529,98 531,68 533,54 534,5

Table 5: Effect of Mesh Density on Analysis Result

23

7.2. Different Velocities

Velocity (m/sec) Von Misses Stress (MPa) Total Displacement(mm)

7 362,16 0,19828

10 374,81 0,83727

12 381,48 1,0715

15 385,69 1,2651

20 410,9 2,1403

50 486,92 6,9084

100 516,48 18,717

115 522,69 21,584

150 532,26 29,453

200 534,2 37,06

Table 6: Analysis in Different Velocities

Independent of the experimental speed, different velocities were analyzed. The yield

strength of the material is 380 MPa. When the ball hits the blade at a speed of approximately

12 m / sec, this von misses curve is equal to its yield stress. And after this speed, plastic

deformation starts in the material. As our impact speed increases, the deformation in our

material increases.

24

8. COMMENTS

Along with the developing technology, analysis has allowed engineering to go forward

and offer the opportunity to examine real situations with less cost. We can get answers in

short time by modeling different situations in computer software. In the face of a case we will

face in real life, it allows us to understand how the material will react and take precautions. In

this study where finite element method is used and impact analysis is performed, the changes

resulting from metal ball impact of a prototype compressor piece of blade were investigated.

Deformation stress and strain values were obtained and the results showed similar behavior

with experimental results. In our model, the maximum deformation occurred in 0.4

milliseconds. In order to obtain correct results in Ansys software, mesh optimization has been

done. Finally, unlike the speed at which the experiment was performed, different behaviors of

the material were analyzed by impact analysis at different speeds.

25

REFERANCES

[1] Url-1 < http://aviationknowledge.wikidot.com/aviation:foreign-object-damage >, date

retrieved 5.12.2018.

[2] Chen, R., Lv, F., Li, Q., Fu, G., Wang, H., Chai, Z., & Xu, Z. (2009, July). Failure

analysis on foreign object damage of aero-engine compressor blade. In 2009

8th International Conference on Reliability, Maintainability and Safety (pp.

1085-1088). IEEE.

[3] Url-2 < https://fodprevention.com/foreign-object-damage-also-abbreviated-as-fod/ >,

date retrieved 5.12.2018.

[4] Url-3 <https://www.imagenesmy.com/imagenes/bird-strike-db.html >, date retrieved

5.12.2018.

[5] Bachtel, B. (1998). Foreign object debris and damage prevention. Aero Magazine. [on-

linemagazine,URL:http://www.boeing.com/commercial/aeromagazine/aero

_01/textonly/s01txt. html].

[6]Url-4<https://www.elektrikport.com/universite/sonlu-elemanlar-analizi-yuksek-

maliyetten-yuksek-verime-dogru-yolculuk/8947#ad-image-0 >, date

retrieved 6.12.2018.

[7] Url-5 < http://feaforall.com/why-do-fea-engineers-use-1d-2d-3d-elements >, date

retrieved 7.12.2018.

[8] Url-6 < http://makinacitu.blogspot.com/2014/02/mesh-parametreleri.html >, date retrieved

10.12.2018.

[9] Url-7 < https://www.azom.com/article.aspx?ArticleID=8764 >, date retrieved 14.12.2018.

[10] Defense, A. T. I. Maraging Steels for Defense: ATI C-200TM/C-250TM/C-300TM/C-

350TM Alloys. Technical Data Sheet, 10.