INVESTIGATION OF FATIGUE CRACK GROWTH IN AEROSPACE …ijsetr.org/wp-content/uploads/2017/05/IJSETR-VOL-6-ISSUE-5-940-947.… · The main aim of this project is to try and do analysis

International Journal of Science, Engineering and Technology Research (IJSETR)

Volume 06, Issue 05, May 2017, ISSN: 2278 -7798

940

All Rights Reserved © 2017 IJSETR

INVESTIGATION OF FATIGUE CRACK GROWTH IN AEROSPACE

BRACKET BY USING FEA

NATI KRISHNA KANTH 1, RAJASEKHAR SANMALA

2

Nati Krishna kanth is currently pursuing master’s degree program in CAD/CAM in KITS Engineering College, Divili, Kakinada, Andhra Pradesh.

Sanmala. Rajasekhar is working as Associate Professor in Mechanical Engineering KITS Engineering College, Divili, Kakinada, Andhra Pradesh.

Abstract

The main aim of this project is to try and do analysis on a crack which propagates and grows throughout a typical within the design of bracket. FEA ANSYS 15.0 was used thus the coming up with a process of solving with which the design was tired in

CATIA and used to simulate crack growth in ansys and to compute the stresses and thus the stress-intensity factor at different conditions. In this project we had chosen a bracket design and was selected a crack growth then it was investigated with the

assistance of simulating software package. This design configuration was utilized by engineers since the engineers generally discover this sort of crack in brackets and different parts. The stress intensity factor was near the crack tip is compared against the yield strength of the material. Here the Mode I stress-intensity issue is compared against the material’s wear loaded in

various conditions for getting better result. The results show that the bracket will tolerate little cracks within the structure which we have designed by using CATIA. The strength of the structure is usually recommended to be assessed inside the long run and

that we had pointed out K1 k2 K3 values in conjunction with J-Integral. Key Words: Crack analysis, Bracket, design, and etc… --------------------------------------------------------------------***---------------------------------------------------------------------- 1. INTRODUCTION Fatigue is that the formation of a crack owing to cyclic elastic loading well at intervals the planning stress levels.

Most dynamically loaded welded structures are expressly designed for fatigue by checking the stress vary at crucial

details under some fatigue design loading. the stress vary at the crucial details is checked by comparison to AN S-N

curve that relates the life (N) to the strain vary (S). totally different S-N curves could also be used reckoning on

applicable codes or specifications. till recently, most ships weren't expressly designed for fatigue. Instead, the

allowable peak stress was controlled in a trial to indirectly avoid in depth fatigue cracking. Consequently, many ships, particularly commercial bulk carriers and tanker ships, exhibit in depth fatigue cracking. Among the main points that exhibit cracking on ships are: 1) Brackets at the intersections of girders with web frames or bulkheads; 2) The intersection of longitudinal stiffeners with crosswise web frames or bulkheads;

3) Hatch openings 4) Butt welds in hull plates, stiffeners, or girders; and 5) Drain holes and weld-access holes in stiffeners and girders. Because of the extremely redundant nature of ship structure, these fatigue cracks are generally not a threat to structural integrity. Therefore, the detection and repair of occasional fatigue cracks could also be tolerated as a part of routine maintenance. Repairs are usually created by arc gouging a v-shaped weld preparation on the length of the crack and welding. Alternative strategies like modifying the detail by adding soft toes, brackets, insert plates or doublers plates may additionally be used.

Unfortunately, fatigue cracks are of times repaired while not

comfortable thought of the performance beyond the repair.

Poorly designed or dead repairs can lead to fast reinitiating of

fatigue cracks at the situation of the repair. In some cases

individual ships are reported to possess thousands of cracks. In

these cases, the repair prices could also be staggering. 1.1 CALCULATION OF STRESS INTENSITY

FACTORS (SIF) USING THE FINITE

ELEMENT METHOD When a crack exists in a structure, stress is targeted at the tip however the strain concentration do not account for the fracture behavior at the tip of a crack as a result of as the radius of the curvature of the crack tip approaches zero, the strain level may become infinity, that isn't a true property of a loaded structure. As another to explain the structural strength at the crack tip appropriately, the stress-intensity issue, K, is a parameter to characterize “the stress field before a sharp crack during a test specimen or a support. The parameter, K, is expounded to the nominal stress level (σ) within the structural member and therefore the size of the crack (a), and has units of . In general, the relation is represented by where P could be a geometrical parameter depends on the

structural member and crack. Consistent with Barsom , “all

structural members or check specimens that have flaws may be

loaded to numerous levels of K. {this is this is often this may

be} analogous to the situation wherever flawless structural or

mechanical members can be loaded to numerous levels of

stress, σ”. the strain field close to crack tips may be classified

as Mode I: gap mode, Mode II: sliding and Mode III: tearing,

that every of them is characterized by a “local mode of

deformation” as illustrated. The gap mode I, is expounded to

native displacement within which the crack surfaces move

directly apart (symmetric with relation



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to the x-y and x-z planes). The slippy mode, II, is

expounded with local displacement within which the crack surfaces slide over each other perpendicular to the vanguard of the crack (symmetric with relation to the x-y plane and

skew-symmetric with relation to the x-z plane). The tearing mode, III, is expounded with native displacement local the crack surfaces slide with respect to each other parallel to the

leading edge (skew-symmetric with relation to the x-y and x-z planes). though these 3 modes may be superposed to “describe the foremost general case of crack tip

deformation and stress fields”, Mode I is that the primary focus of this paper.

Fig: 1 The three basic modes of crack surface displacements In general, stress-intensity issue depends on the strain

iatrogenic on a structure, the crack size and also the pure

mathematics of the crack. The stress-intensity issue

equation for associate degree embedded circular crack is

given by

If the crack occurs at the corner of a beam, as shown in

Figure 3, the KI expression would be

It is the free surface correction factor, that is added for each free

surface at that a crack would possibly originate. KI is accumulated by as a result of there are 2 free-surface

corrections for a corner crack. Current software computer-aided design packages vary from

2nd vector-based drafting systems to 3D solid and surface

modelers. fashionable CAD packages also can ofttimes permit

rotations in 3 dimensions, permitting viewing of a designed

object from any desired angle, even from the within looking.

Some CAD software is capable of dynamic mathematic

modeling, during which case it's going to be marketed as

CADD — computer-aided design and drafting. CAD is employed within the design of tools and machinery

and within the drafting and design of every kind of

buildings, from little residential sorts (houses) to the most

important industrial and industrial structures (hospitals and

factories). CAD is especially used for detailed engineering of 3D

models and/or 2nd drawings of physical elements, however

it's also used throughout the engineering process from

conceptual style and layout of products, through strength

and dynamic analysis of assemblies to definition of producing strategies of elements. It also can be accustomed

design objects. CATIA-V5 is that the industry’s factual

standard 3D mechanical design suit. it's the world’s leading

CAD/CAM /CAE software system, offers a broad vary of

integrated solutions to hide all aspects of product design

and producing. much of its success is attributed to its

technology that spurs its customer’s to a lot of quickly and

systematically innovate a replacement strong, parametric,

feature based mostly model. as a result of that CATIA-V5

is unmatched during this field, altogether processes,

altogether countries, altogether reasonably corporations on

the provision chains. Catia-v5 is additionally the proper

resolution for the producing enterprise, with associative

applications, strong responsiveness and web connectivity

that create it the ideal flexible engineering resolution to

accelerate innovations. Catia-v5 provides simple to use

resolution tailored to the wants of little medium sized

enterprises moreover as massive industrial companies

altogether industries, commodity, fabrications and

assembly. Electrical and physical science goods,

automotive, aerospace, building and plant style. it's user

friendly solid and surface modeling is done simply.

Fig: 2 Drafted Model of Bracket in CATIA

Table: 1 MATERIAL PROPERTY

Fig: 3 Model Developed in CATIA



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ADVANTAGES OF FEA The FEM is based on the concept of discretization. Nevertheless as either a variation or residual approach, the technique recognizes the multi dimensional continuity of the body not only does the idealizations portray the body as

continuous but it also requires no separate interpolation process to extend the approximate solution to every point within the continuum. Despite the fact that the solution is obtained at a finite number of discrete node points, the formation of field variable models inherently provides a solution at all other locations in the body. In contrast to other variation and residual approaches, the FEM does not

require trail solutions, which must all, apply to the entire multi dimensional continuum. The use of separate sub-regions or the finite elements for the separate trial solutions thus permits a greater flexibility in considering continua of the shape. Some of the most important advantages of the FEM derive from the techniques of introducing boundary conditions. This is another area in which the method differs from other variation or residual approaches. Rather than

requiring every trial solution to satisfy the boundary conditions, one prescribes the conditions after obtaining the algebraic equations for assemblage.

Fig: 4 Imported model to ANSYS

Fig: 7 Development of Crack in ANSYS

Fig: 8 Applying the Forces

TITANIUM MATERIAL

Fig: 9 Deformation at 500 N of Load (Titanium)

Fig: 10 Strain at 500 N of Load (Titanium)

Fig: 5 Mesh Developed in ANSYS

Fig: 11 Stress at 500 N of Load (Titanium)

Fig: 6 Crack Developing in ANSYS Fig: 12 K1 value at 2000 N of load (Titanium



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Fig: 13 K2 value at 2000 N of load (Titanium)

Fig: 14 K3 value at 2000 N of load (Titanium)

Fig: 15 J-Integral value at 2000 N of load (Titanium)

Fig: 16 K1 VALUE AT 2000 N OF LOAD Fig: 17 K2 VALUE AT 2000 N OF LOAD Fig: 18 K3 VALUE AT 2000 N OF LOAD

Fig: 19 J-INTEGRAL VALUE AT 2000 N OF LOAD ALUMINIUMMATERIAL

Fig: 20 K1 value at 2000N of load (Aluminum) Fig: 21 K2 value at 2000N of load (Aluminium) Fig: 22 K3 value at 2000N of load (Aluminum)

Fig: 23 J-Integral value at 2000N of load (Aluminium) Fig: 24 K1 VALUE AT 2000 N OF LOAD



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Fig: 30 Stress at 500 N of Load (Gray Cast Iron)

Fig: 25 K2 VALUE AT 2000 N OF LOAD

Fig: 31 K1 value at 2000N of load (Gray Cast Iron)



Fig: 27 J-INTEGRAL VALUE AT 2000 N OF LOAD

GRAY CAST IRON MATERIAL


Fig: 28 Deformations at 500 N of Load (Gray Cast Iron)

Fig: 34 J-Integral value at 2000N of load (Gray Cast

Iron)

Fig: 29 Strain at 500 N of Load (Gray Cast Iron)




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Fig: 38 J-INTEGRAL VALUE AT 2000 N OF LOAD

GRAPHITE MATERAL

Fig: 39 Deformation at 500 N of Load (Graphite)

Fig: 40 Strain at 500 N of Load (Graphite)

Fig: 41 Stress at 500 N of Load (Graphite)

Fig: 42 k1 value at 2000N of load (Graphite)

Fig: 43 K2 value at 2000N of load (Graphite)

Fig: 44 K3 value at 2000N of load (Graphite) Fig: 45 J-Integral value at 2000N of load (Graphite) Fig: 46 K1 VALUE AT 2000 N OF LOAD



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Fig: 48 K3 VALUE AT 2000 N OF LOAD Fig: 49 J-INTEGRAL VALUE AT 2000 N OF LOAD

RESULTS GRAPH REPRASENTING LOAD VS K1

Graph & Table 1 K1 values at Different Loads

of Different Materials GRAPH REPRASENTING LOAD VS K2 Graph & Table 2 K2 values at Different Loads

of Different Materials GRAPH REPRASENTING LOAD VS K3

Graph & Table 3 K3 values at Different Loads of Different Material



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GRAPH REPRASENTING LOAD VS J-INTEGRAL Graph & Table 4 J-Integral values at Different loads

of Different Materials CONCLUSION By investigation of the crack analysis done on completely

different materials I will conclude that by considering stress

intensity factors and J-integrals that Ti alloy has additional

withstanding capability wherever because the alternative

materials even have the potential of withstanding however

not the maximum amount as Ti alloy. In this work a trial has been created to seek out the method

of crack propagation and stress distribution during a typical

bracket region bracket by victimisation ANSYS and

CATIA. this sort of research is additional economic and time saving development and might be accustomed monitor

the cracks in numerous elements of region structures and

elements. The first step of the associate degreealysis consisted of

victimisation ANSYS to perform elastic stress analysis on

an un-cracked bracket to spot the high stress regions. In step 2, the un-cracked model was foreign to CATIA

associate degreed an initial crack of easy pure mathematics

was introduced and several other ANSYS files were created with crack. Step 3 of the analysis consists of victimisation

ANSYS to perform elastic stress analysis of the

antecedently cracked bracket created by ANSYS. For the model of cracks, the results show within the Mode I

stress intensity factors for the cracked model area unit

below the materials fracture toughness. Therefore, it seems that the bracket will tolerate little corner cracks within the

structure. The analysis procedure so are often accustomed

ceaselessly monitor the brackets and to require applicable

call on time of replacement of such brackets.

REFERENCES [[1] FRANC3D & ANSYS Tutorial. September 2010.

http://www.fracanalysis.com/Franc3D Documentation. [2] Honnorat, Yves. "Issues and breakthrough in manufacture of turbo engine titanium parts." Materials Science and Engineering, A213, 1996: 115-123. [3] J.P.Immarigeon, R.T.Holt, A.K. Koul, L.W.Zhao, Wallace and J.C. Beddoes , Lightweight Materials for Aircraft Applications, NRC Institute for Aerospace Research, 1995.

[4] Titanium. http://en.wikipedia.org/wiki/Titanium (accessed January 12, 2011). [5] Barsom, M. John, Rolfe and T. Stanley Fracture and Fatigue Control in Structures: Application of Fracture Mechanics, Philadelphia, 1999. [6] C.P.Paris, and G.C Sih, “Stress Analysis of Cracks,” in Fracture Toughness Testing and Its Applications, ASTM STP 381, American Society for Testing and Materials, Philadelphia, 1965. [7] B.J.Carter, P.A. Wawrzynek, and A.R.Ingraffea, Automated 3D Crack Growth Simulation, Cornell Fracture Group, 2003. BIOGRAPHIES

1. ................................................................................................................................... N

Nati Krishna kanth is currently pursuing master’s degree

program in CAD/CAM in KITS Engineering College,

Divili, Kakinada, Andhra Pradesh.

2. ................................................................................................................................... S

Sanmala. Rajasekhar is working as Associate Professor in

Mechanical Engineering KITS Engineering College, Divili,

Kakinada, Andhra Pradesh.

Documents

INVESTIGATION OF FATIGUE CRACK GROWTH IN AEROSPACE …ijsetr.org/wp-content/uploads/2017/05/IJSETR-VOL-6-ISSUE-5-940-947.… · The main aim of this project is to try and do analysis