Fea for Backhoe

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This chapter describes the methodology adopted for static finite element analysis of the

boom, arm, bucket and swing link of the backhoe excavator in ANSYS. Furthermore;

boundary conditions, meshed models, and results of boom, arm, bucket and swing link

are presented and discussed. FEA of all four parts of backhoe excavator attachment are

done by considering the maximum breakout force configuration as calculated and

presented in chapter 7.

8.1 Introduction to finite element method

The finite element method is an approximate numerical procedure for analyzing large

structures and continua. The finite element method became popular with the

advancements in digital computers since they allow engineers to solve large systems of

equations quickly and efficiently. The finite element method is a very useful tool for the

solution of many types of engineering problems such as the analysis of the structures,

heat transfer and fluid flow. The method is also used in the design of air frames, ships,

electric motors, heat engines and spacecraft. The finite element method is also used for

analyzing the behavior of components of biological systems. In most structural analysis

applications it is necessary to compute displacements and stresses at various points of

interest. The finite element method is a very valuable tool for studying the behavior of

structures. In the finite element method, the finite element model is created by dividing

the structure in to a number of finite elements. Each element is interconnected by nodes.

The selection of elements for modeling the structure depends upon the behavior and

geometry of the structure being analyzed. The modeling pattern, which is generally called

mesh for the finite element method, is a very important part of the modeling process. The

results obtained from the analysis depend upon the selection of the finite elements and the

mesh size. Although the finite element model does not behave exactly like the actual

structure, it is possible to obtain sufficiently accurate results for most practical

applications. Once the finite element model has been created, the equilibrium equations

can easily be solved using digital computers without having to solve a large number of

partial differential equations by hand. The deflections at each node of the finite element

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respect to the overall model dimensions and do not play a substantial role in the

simulation results can be avoided or suppressed.

8.3 Analysis assumptions The stress analysis that ANSYS simulations provides is appropriate only for linear

material properties. These properties are where the stresses are directly proportional

to the strain in the material (no permanent yielding of the material). Linear behavior

results when the slope of the material stresses-strain curve in the elastic region

(measured as the Modulus of Elasticity) is constant.

The total deformation is assumed to be small in comparison to the part thickness. Asfor an example, while studying the deflection of the beam, the calculateddisplacement must be less than the minimum cross-section of the beam.

The results are temperature independent. The temperature is assumed not to affectthe material properties.

Inertia of the component is neglected as the acceleration of the parts is less than 0.05m/sec2in the field.

Minimum element size allows automatic refinement in small areas.

8.4 FEA of backhoe excavator parts

Here, intention to perform static FEA is to know the developed stresses are within the safe

stress limit of the material used for backhoe excavator attachments. Based on this analysis

one can identify that the optimization of backhoe mechanism is possible or not.

The presented work includes the static FEA of bucket, arm, boom and swing link by

applying boundary conditions as calculated in chapter 7 using ANSYS workbench software,

in which the elements generated by the software itself and they are tetrahedron in shape. The

material properties are considered as discussed in chapter 5. Fine meshing is performed for

analysis of all the parts of the backhoe attachment which provides accurate results. The post

processing includes the results of Von Misses stresses and displacement developed with the

application of known boundaryconditions.

Von Misses stresses is used as a criterion in determining the onset of failure in

ductile materials, and the materials in the presented study for the parts of the bucket, arm,

boom and swing link are of ductile materials, so the design of all parts should be on the

basis of Von Misses stresses acting on the parts.

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The failure criterion states that the Von Misses stresses VM should be less than the

yield stresses y of the material by taking appropriate safety factor into consideration.

This indicates for the design of a part to be safe, the following condition must be satisfied

(Tirupathi R. Chandrupatla et al., 2005).Design stress for ductile material,

VM y

Safety factor

. (8.1)

The backhoe parts gets deformation as the load applied on them. The deformation or

displacement of the backhoe part should be less than that of the minimum thickness of plate

used in the parts of backhoe attachment to be analyzed for safe stress condition. The next

section presents the FE analysis of the bucket.

8.4.1 FEA of the bucket

Materials used for the parts of the bucket assembly are listed in table 5.1 of chapter 5.

Properties of the materials used to model the bucket are listed in table 5.2 and table 5.3.

Only the bushes used in the bucket assembly are made up of the material IS 2062 (Yield

strength, y = 250 MPa), and rest of the parts of the bucket are made up of HARDOX 400

(Yield strength, y = 1000 MPa). Fig. 8.1 shows the boundary conditions applied to

bucket as calculated for maximum breakout force configuration and presented in Fig. 7.7

(section 7.4.1) of chapter 7.

Fig. 8.1 Boundary conditions applied to the bucket

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Fig. 8.2 Mesh view of the bucket

Fig. 8.3 Maximum Von Misses stresses of the bucket

Fig. 8.2 shows the mesh view of the bucket with 52219 nodes and 9636 elements.

Fig. 8.3 shows the results of the static force analysis as Von Misses stresses on the

bucket. Analysis shows the maximum Von Misses stresses (VM ) is acting at the leap

plate near teeth and it is 203.67 MPa. Minimum Von Misses stresses are acting at the

bush of the mounting lug and it is 0.51909 MPa.

All parts of the bucket are made up of HARDOX 400 material except the bushes

used in mounting lugs are made up of IS 2062 material. The maximum Von Misses

stresses are acting at the leap plate made up of HARDOX 400 material with the yield

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strength of 1000 MPa, by taking safety factor as 2, equation (8.1) yields the safe stress of

= 500 MPa, this clearly indicates VM

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Fig. 8.6 Mesh view of the arm

Materials used for the parts of the arm assembly are listed in table 5.4 of chapter 5.

Properties of the materials used to model the arm assembly are listed in table 5.2, 5.3 and

table 5.5. The bushes and the collar used in the arm assembly are made up of the material IS

2062 (Yield strength, y = 250 MPa), mounting lugs of the cylinders are made of HAROX

400 (Yield strength, y = 1000 MPa), and rest of the parts of the arm are made up of

SAILMA 450HI (Yield strength, y = 450 MPa). Fig. 8.5 shows the boundary conditions

calculated for maximum breakout configuration to carry out the static analysis of arm as

presented in Fig. 7.8 (section 7.4.2) of chapter 7.

Fig. 8.7 Maximum Von Misses stresses of the arm

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Fig. 8.8 Enlarged view of maximum stresses of the arm

Fig. 8.6 shows the mesh view of the arm with 44126 nodes and 8670 elements. Fig.

8.7 shows the results of the Von Misses stresses on arm assembly. As it can be seen from

the Fig. 8.7 that the maximum Von Misses stresses (VM ) is acting at the arm cylinder

mounting lug and it is 239.39 MPa. Fig 8.8 shows enlarge view of arm at which the

maximum stresses are produced.

The arm cylinder mounting lugs are made up from HARDOX 400 with yield

strength of 1000 MPa, by taking safety factor as 2, equation (8.1) yields the safe stress of

= 500 MPa, this clearly indicates VM

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Fig 8.9 shows the maximum displacement on arm is 0.35945 mm which is very less

compare to minimum thickness of plate used in the arm. Therefore, the arm is safe in

8.4.3 FEA of the boom

Fig. 8.10 Boundary conditions applied to the boom

Fig. 8.11 Mesh view of the boom

Materials used for the parts of the boom assembly are listed in table 5.6 of chapter

5. Properties of the materials used to model the boom assembly are listed in table 5.2, 5.3

and table 5.5. The bushes, and the collar used in the boom assembly are made up of the

material IS 2062 (Yield strength = y = 250 MPa), the mounting lugs are made of the

HARDOX 400 material with the yield strength of 1000 MPa and rest of the parts of the

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boom are made up of SAILMA 450HI (Yield strength = y = 450 MPa). Fig. 8.10 shows

the boundary conditions of the boom as calculated for maximum breakout configuration

to carry out the static analysis of boom as presented in Fig. 7.9 (section 7.4.3) of chapter

7.

Fig. 8.12 Maximum Von Misses stresses of the boom

Fig. 8.13 Enlarged view of maximum stresses of the boom

Fig. 8.11 shows the mesh view of the boom with 31855 nodes and 4647 elements. Fig.

8.12 shows the results of the Von Misses stresses on boom assembly. As it can be seen

from the Fig. 8.12 that the maximum Von Misses stress VM is acting on the mounting

lug and it is 246.71 MPa. Fig 8.13 shows enlarged view at which maximum stresses are

produced.

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The boom cylinder mounting lugs are made up of HARDOX 400 with yield

strength of 1000 MPa, by taking safety factor as 2, equation (8.1) yields the safe stress of

= 500 MPa, this clearly indicates VM

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Materials used for the parts of the swing link assembly are listed in table 5.8 of

chapter 5. Properties of the materials used to model the swing link assembly are listed in

table 5.2, 5.3 and table 5.5. The bushes are made up of the material IS 2062 (Yield

strength, y = 250 MPa), the mounting lugs are made of the material HARDOX 400

(yield strength, y 1000 MPa) and rest of the parts of the swing link are made up of

SAILMA 450HI (Yield strength, y = 450 MPa). Fig. 8.15 shows the boundary

conditions of the swing link as calculated for maximum breakout configuration to carry

out the static analysis of swing link as presented in Fig. 7.10 (section 7.4.4) of chapter 7.

Fig. 8.16 Mesh view of the swing link

Fig. 8.17 Maximum Von Misses stresses of the swing link

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Fig. 8.18 Enlarged view of maximum stresses of the swing link

Fig. 8.16 shows the mesh view of the boom with 47376 nodes and 25387 elements.

Fig. 8.17 shows the results of the Von Misses stresses on swing link. As it can be seen

from the Fig. 8.17 that the maximum Von Misses stresses VM is acting on the cylinder

mounting lug and it is 119.83 MPa. Fig. 8.18 shows the enlarged view of maximum

The boom cylinder mounting lugs are made up of HARDOX 400 with yield

strength of 1000 MPa, by taking safety factor as 2, equation (8.1) yields the safe stress of

= 500 MPa, this clearly indicates VM

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condition.

8.4.5 FEA of the backhoe assembly

Fig. 8.20 Boundary conditions applied to the backhoe assembly

Fig. 8.21 Mesh view of the backhoe assembly

In the earlier sections, the Finite Element Analysis of each part of backhoe

excavator is carried out, now in this section the Finite Element Analysis of full assembly

is performed. As we can see in the Fig 8.20 the whole assembly acts as the cantilever

beam with one free end and one fixed end. Fig 8.20 shows the load applied to the full

assembly of backhoe attachment with appropriate constaints.

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Fig. 8.22 Maximum Von Misses stresses of the backhoe assembly

Fig.8.23 Enlarged view of maximum stresses of the backhoe assembly

Fig. 8.21 shows the mesh view of the boom with 151910 nodes and 47749 elements.Fig 8.22 shows the maximum Von Misses stresses produced in the backhoe attachment

assembly. Maximum Von Misses stresses acting on the bucket is 252.3 MPa. The

maximum Von Misses stresses is acting at the intersection of mounting lug and top

bucket plate as shown in Fig. 8.23, which is made up of HARDOX 400 material with the

yield strength of 1000 MPa. By taking safety factor as 2, equation (5.1) yields = 500

MPa, this clearly indicates VM

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Fig. 8.24 Maximum displacement of the backhoe assembly

Fig. 8.24 shows the maximum displacement in the excavator assembly reported is

3.41 mm at bucket end. The maximum displacement of the excavator assembly is less

than the minimum thickness of plate used in backhoe assembly. Therefore, the backhoe

8.5 Stress analysis of backhoe parts with consideration of welding

In this setion the Finite Element Analysis is carried out for each part and the full assembly

of the backhoe excavator with welding consideraton. Now, introducing welding to the

each part of the excavator with the help of WLDMENT tool of the Autodesk Inventor

2011.

Welding proportions considered as per the thickness of the parts to be weld based

on industry practice. Then the parts with welding is analysed with FEA approach using

ANSYS. After this analysis, the effect of generated stresses on the backhoe parts with

welding consideration can be evaluated. The residual stresses generated in the welding at

weld joints. Here it is considered that the generated residual stresses will be removed with

the application of stress relieving process performed after the welding provided at each

weld joint of the backhoe parts.

Here, the boundary conditions and material properties used for the purpose of

analysis are remains same as the used in previous sections in which FEA of backhoe

attachment parts carried out without welding consideration.

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8.5.1 FEA of the bucket with welding

Fig. 8.25 Maximum Von Misses stresses of the bucket with welding

Fig. 8.26 Maximum displacement of the bucket with welding

Fig. 8.25 shows the maximum Von Misses stresses acting at the leap plate near

teeth on the bucket with welding is of 178.33 MPa, moreover; all parts of the bucket are

made up of HARDOX 400 material except the bushes used in mounting lugs are made up

of IS 2062 material. The leap is made up of HARDOX 400 material with the yield

strength of 1000 MPa. By taking safety factor as 2, equation (8.1) yields = 500 MPa,

this clearly indicates that VM

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Fig. 8.26 shows the maximum displacement produced in the bucket with welding,

which is 2.245 mm and it is less than the thickness of the plate used in bucket, so the

of the bucket with welding is less than the displacement of the bucket without welding.

8.5.2 FEA of the Arm with welding

Fig. 8.27 Maximum Von Misses stresses of the arm with welding

Fig. 8.28 Maximum displacement of the arm with welding

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Fig. 8.27 shows the results of the Von Misses stresses on arm with welding. As it

can be seen from Fig. 8.27 that the maximum Von Misses stresses is acting at the arm

cylinder mounting lug and it is 212.46 MPa. The arm cylinder mounting lug is made up of

HARDOX 400 material with the yield strength of 1000 MPa. By taking safety factor as 2,

equation (8.1) yields = 500 MPa, this clearly indicates that VM

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Fig. 8.30 Enlarge view of maximum Von Misses stresses of the boom with welding

Fig. 8.31 Maximum displacement of the arm with welding

Fig. 8.30 shows enlarge view of maximum Von Misses stresses of the boom with

welding. Fig. 8.31 shows the maximum displacement in the boom reported is 1.968 mm

at the boom to arm joint. The maximum displacement is very less compare to minimum

thickness of plate used in the boom so the boom is safe in deflection for given loading

conditions. Maximum displacement of the boom after welding is less than the

displacement of the boom without welding.

8.5.4 FEA of the swing link with welding

Fig. 8.32 shows the results of the Von Misses stresses on swing link with welding. As it

can be seen from the Fig. 8.32 that the maximum Von Misses stresses is acting on the

boom cylinder mounting lug and it is 119.29 MPa on swing link.

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Fig. 8.32 Maximum Von Misses stresses of the swing link with welding

Fig. 8.33 Enlarged view of maximum Von Misses stresses of the swing link

Fig. 8.34 Maximum displacement of the swing link with welding

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The boom cylinder mounting lug welded on swing link is made up of HARDOX

400 material with the yield strength of 1000 MPa. By taking safety factor as 2, equation

(8.1) yields = 500 MPa, this clearly indicates that VM

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Fig. 8.36 Enlarged view of maximum stresses of the backhoe assembly with welding

Fig. 8.37 Maximum displacement of the backhoe assembly with welding

Fig. 8.36 shows the enlarged view of excavator assembly where maximum stresses

are produced. Fig. 8.37 shows the maximum displacement in the excavator assembly

reported is 3.2302 mm at bucket end. The maximum displacement of the excavator

assembly is less than the minimum thickness of plate used in the backhoe attachment, so

the design is safe for deflection.

8.6 Summary

In the first section of this chapter, the introduction of Finite Element Method is explained,

second section explains the FEA procedure in ANSYS software, analysis assumptions are

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included in section three, in the fourth section FEA of backhoe excavator parts is carried

out without welding consideration and in the fifth section stress analysis of backhoe parts

performed with welding consideration. FEA results of backhoe attachment parts and of

backhoe assembly shows the stresses developed are 203.67 MPa, 239.39 MPa, 246.71

MPa, 119.83, and 252.3 MPa for bucket, arm, boom, swing link and backhoe assembly

respectively without welding consideration, where as with welding consideration the

stresses developed are 178.33 MPa, 212.46 MPa, 242.41 MPa, 119.29 MPa and 241.87

MPa respectively. The produced stresses in the various parts of the backhoe attachement

are within stress limit, therefor all parts of backhoe attachment are safe in strength for

applied known boundary conditions. The results clearly depict that the developed stresses

in backhoe parts without welding are less than than the stresses developed in backhoe

parts with welding, therefore we can say that the welding strengthen the backhoe parts

and its assembly.

The developed backhoe mechanism should be weight optimized for better

controlling during excavation task as well as to reduce the initial cost of the mechanism.

The next chapter 9 includes the structural optimiaztion of the backhoe attachment without

and with consideration of welding. The weight optimized backhoe excavator attachment

also checked for strength using FE analysis approach.

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