STATIC ANALYSIS OF MINI HYDRAULIC BACKHOE ... Int. J. Mech. Eng. & Rob. Res. 2012 Bhaveshkumar P...

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Int. J. Mech. Eng. & Rob. Res. 2012 Bhaveshkumar P Patel and J M Prajapati, 2012

STATIC ANALYSIS OF MINI HYDRAULICBACKHOE EXCAVATOR ATTACHMENT USING FEA

APPROACH

Bhaveshkumar P Patel1* and J M Prajapati2

*Corresponding Author: Bhaveshkumar P Patel,[email protected]

An excavator is a typical hydraulic heavy-duty human-operated machine used in general versatileconstruction operations, such as digging, ground leveling, carrying loads, dumping loads andstraight traction. Normally backhoe excavators are working under worst working conditions.Due to severe working conditions, excavator parts are subjected to high loads and must workreliably under unpredictable working conditions. Thus, it is necessary for the designers to providenot only a equipment of maximum reliability but also of minimum weight and cost, keepingdesign safe under all loading conditions. The force analysis and strength analysis are importantsteps in the design of excavator parts. Finite Element Analysis (FEA) is the most powerfultechnique used to evaluate strength of the structures working under high loads. This paperfocuses on the solid modeling of the mini hydraulic backhoe excavator intended for light dutyexcavation task and its FE analysis for strength evaluation. It also includes the effect of thewelding on the developed stresses in backhoe excavator parts.

Keywords: Backhoe excavator, FEA

INTRODUCTIONEarth moving excavation represents a hugepotential and a favourable approach for manyearthmoving operations includingconstruction, mining, agricultural, forestry,military applications and especially for cleaningup hazardous areas (Nareshkumar, 2006).

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Int. J. Mech. Eng. & Rob. Res. 2012

1 Mechanical Engineering Department, JJT University, Jhunjhunu 333001, Rajasthan, India.2 Mechanical Engineering Department, Faculty of Engineering & Technology, M S University of Baroda, Vadodara 390002, Gujarat,

India.

Rapidly growing rate of industry of earthmoving machines is assured through the highperformance construction machineries withcomplex mechanism and automation ofconstruction activity (Mehta, 2008). Hoes areused primarily to excavate below the naturalsurface of the ground on which the machine

Research Paper

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rests. A hoe is sometimes referred to by other

names, such as backhoe or back shovels(Peurifoy and Schexnayder, 2006). Since thelate 50’s hydraulics have been the systems ofchoice where high force-to-weight ratios arerequired.

The skilled operator also cannot know aboutthe terrain condition, soil parameters, and thesoil-tool interaction forces exerted duringexcavation operation are required to findbecause these forces helpful for better designof the tool, backhoe parts and for trajectory

planning. The design of all excavationmachinery and the attachments are very as pertheir functional requirements and depends ontheir applications (Bhaveshkumar andPrajapati, 2011b).

An excavator is a typical hydraulic heavy-duty human-operated machine used ingeneral versatile construction operations. In

the toxic or hazardous environment, dirtyplaces and worst working area it is verydifficult to perform excavation task by humanoperator. To avoid this problem one of the bestsolution is automation of the excavationmachine.

Herein the greatest opportunity to developa backhoe excavator attachment, which can

perform the digging operation in autonomousmode to fulfill the operational functionality withbetter strength, higher durability and reliability.Presented work emphasize on FEA of such adeveloped mini hydraulic backhoe excavatorattachment for light duty construction work. The

next section covers the problems concernedwith the backhoe excavators used as earthmoving machine.

PROBLEM FORMULATIONThis digging task is repetitive in nature andduring the operation the entire l inkmechanism working under the dynamicalcondition. Some time due to impropercontrolling of the dynamic forces the backhoemechanism may failed. Higher damage rateslead to higher maintenance downtime (lowermachine availability) which subtracts from thenet capacity of the machine to produce(Andrew, 2002).

The excavator mechanism must workreliably under unpredictable workingconditions. Poor strength properties of theexcavator parts like boom, arm and bucketlimit the life expectancy of the excavator.Therefore, excavator parts must be strongenough to cope with caustic workingconditions of the excavator (Mehmet, 2005).Terrains are of different kind and exerted siol-tool interaction forces may very as per theterrain condition. Therefore it is challanging jobto design such a excavator which can workunder unpredictable working environment andalso prolong all kind of forces without any kindof failure. For design engineer it is not enoughto provide rubust design but also taking careof the weight of the attachmet for bettercontrolling during excavation operation.

During the work cycle a backhoe mustaccelerate, move at constant speed, anddecelerate. This time-varying position andorientation of the backhoe is termed as itsdynamic behavior. Time-varying torques areapplied at the joints (by the joint actuators) tobalance out the internal and external forces.The internal forces are caused by motion(velocity and acceleration) of links. Inertial,Coriolis, and frictional forces are some of the

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internal forces. The external forces are theforces exerted by the environment. Theseinclude the “load” and gravitational forces. Asa result, links and joints have to withstandstresses caused by force/torque balanceacross these (Mittal and Nagtath, 2008).

Earth moving process passages hugechallenges to scientist and researchers dueto the complexicity of the dynamicalenvironment, in particular era of design,dynamics and controlling of the excavationprocess of an excavator (Bhaveshkumar andPrajapati, 2011b).

UTILITY OF FEAThe strength analysis is an important step inthe design of excavator parts. Finite ElementAnalysis (FEA) is the most powerful techniquein strength calculations of the structuresworking under known load and boundaryconditions. One can determine the criticalloading conditions of the excavator byperforming static force analysis of themechanism involved for different pistondisplacements. The boundary conditions forstrength analysis will be determined accordingto the results of static force analysis. In general,Computer Aided Drawing (CAD) model of theparts to be analyzed must be prepared priorto the FEA. Preparation of the CAD model canbe done either using a commercial FEAprogram or using a separate commercialprogram, which is specialized for CAD(Bhaveshkumar and Prajapati, 2011a).

The finite element method is an approximatenumerical procedure for analyzing largestructures and continua. In the finite elementmethod, the finite element model is createdby dividing the structure in to a number of finite

elements. Each element is interconnected bynodes. The selection of elements for modellingthe structure depends upon the behaviour andgeometry of the structure being analyzed. Themodelling pattern, which is generally calledmesh for the finite element method, is a veryimportant part of the modelling process. Theresults obtained from the analysis dependupon the selection of the finite elements andthe mesh size. Although the finite elementmodel does not behave exactly like the actualstructure, it is possible to obtain sufficientlyaccurate results for most practical applications.Once the finite element model has beencreated, the equilibrium equations can easilybe solved using digital computers withouthaving to solve a large number of partialdifferential equations by hand. The deflectionsat each node of the finite element model areobtained by solving the equilibrium equations.The stresses and strains then can be obtainedfrom the stress-strain and strain-displacementrelations (Reena, 2005). Due to number ofassumptions considered in design procedure,the design becomes idealized; hence thequality of the result is depend on the skill andexpertise of the person (Bhaveshkumar et al.,2011).

ASSUMPTIONSThe following are the assumptions made in theanalysis of the mini hydraulic backhoeexcavator.

• The stress analysis that ANSYS simulationsprovides is appropriate only for linearmaterial properties. These properties arewhere the stress is directly proportional tothe strain in the material (no permanentyielding of the material). Linear behaviour

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results when the slope of the material stress-strain curve in the elastic region (measuredas the Modulus of Elasticity) is constant.

• The total deformation is assumed to besmall in comparison to the part thickness.As for an example, while studying thedeflection of the beam, the calculateddisplacement must be less than theminimum 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 theacceleration of the parts is less than 0.05m/sec2 in the field.

• Minimum element size allows automaticrefinement in small areas (Reena, 2005).

ANALYSIS OF BACKHOEEXCAVATOR PARTSA backhoe excavator attachment havingbasically four links of bucket, arm, boom andswing link connected to each other in series.One more link namely fixed link connected withthe structure of excavator on rear site. Herethe static analysis is performed for all the partsof the mini hydraulic backhoe excavatorattachment and stress analysis carried outbased on FEA approach using ANSYSsoftware.

Von Misses stress is used as a criterion indetermining the onset of failure in ductilematerials, and the materials in the presentedstudy for the parts of the bucket, arm, boomand swing link are ductile materials, so thedesign of all parts should be on the basis ofVon Misses stresses acting on the parts.

The failure criterion states that the Von Missesstress should be less than the yield stress ofthe material by taking appropriate safety factorinto consideration. This indicates for thedesign of a part to be safe the followingcondition must be satisfied (Tirupathi andAshok, 2005).

Design Stress (for ductile materials),

FactorSafetyy

VM

...(1)

Static force analysis is carried out basedon the digging froce calculation according toSAE J1179 standards but entire calculationsare not a part of this paper, it is taken from thereference (Bhaveshkumar and Prajapati,2012). Stress analysis performed for bucket,arm, boom and swing link based on loadingconditions obtained from the static froceanalysis. The next section covers the stressanalysis of the bucket.

Analysis of the Bucket

Here the static analysis is utilized to carry outthe Finite Element Analysis for various partsof the backhoe attachment to know thedeveloped stress level for known boundaryand loading conditions.

Figure 1 shows static force analysis ofbucket calculated for the maximum breakoutforce configuration. Figure 2 indicate theboundary and loading conditions applicatedfor the bucket. Figure 3 shows the mesh viewof the bucket with 52219 nodes and 9636elements.

Figure 4 shows the Von Misses stressesdeveloped in the bucket and Figure 5 showsthe enlarged view of the same. Maximum VonMisses stress acting on the bucket is 203.67

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MPa, moreover; all parts of the bucket aremade up of HARDOX 400 material except thebushes used in mounting lugs are made up ofIS 2062 material.

Figure 1: Static Force Analysis of Bucket

Figure 2: Boundary Conditions for Bucket

Figure 3: Mesh View of Bucket

Figure 4: Von Misses Stresses of Bucket

Figure 5: Enlarged View of MaximumStresses of Bucket

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The maximum Von Misses stress is actingat the leap plate near teeth as shown in Figure4, which is made up of HARDOX 400 materialwith the yield strength of 1000 MPa, by takingsafety factor as 2, Equation (1) yields = 203.67MPa, [

y] = (

y/Safety factor) = 500 MPa, this

clearly indicates VM

< [y], so the design of

the bucket is safe.

Figure 6 shows the displacement of thebucket after application of known boundaryand loading condition.

Figure 6: Displacement of Bucket

It clearly depicts that the maximumdisplacement occurs at the tip of the teeth as2.3255 mm which is less than the minimumthickness of plate used in the bucket. It alsoindicate that the maximum displacement of thebucket is within the limit of acceptance,therefore the design of the bucket is safe forapplied static load.

Analysis of the Arm

Figure 7 shows the static analysis of arm ofthe backhoe excavator. Figure 8 shows theboundary and loading conditions applied to thearm. Figure 9 shows the mesh view of the armwith 44126 nodes and 8670 elements.

Figure 7: Static Force Analysis for Arm

Figure 8: Boundary Conditions for Arm

Figure 9: Mesh View of Arm

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Figure 10 shows the results of the VonMisses stresses on arm assembly. As it canbe seen from the Figure 10 that the maximumVon Misses stress is acting at the arm cylindermounting lug and it is 239.39 MPa. Figure 11shows enlarged view of the arm at which themaximum stress is produced.

made up of HARDOX 400) is 1000 MPa.Equation (1) yields [

y] = 500 MPa (safety

factor = 2), and VM

= 239.39 MPa (Figure10), so

VM < [

y] and this indicates that the

design of the arm is safe. Figure 12 showsthe maximum displacement of 0.35945 mmoccurs at the free end of the arm (A

3 point)

which is far less than the minimum platethickness used in the arm therefore the designof the arm is safe for static condition.

Figure 10: Von Misses Stresses of Arm

Figure 11: Enlarged View of MaximumStresses of Arm

Now, yield strength of the materialHARDOX 400 (because maximum VonMisses stress is acting at the mounting lug,

Figure 12: Displacement of Arm

Analysis of the Boom

Figure 13 shows the static force analysis ofthe boom to determine the boundary condition

Figure 13: Static Analysis of Boom

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for performing stress analysis of the boom.Figure 14 shows the boundary conditions ofthe boom as calculated. Figure 15 shows themesh view of the boom with 31855 nodes and4647 elements.

be seen from the Figure 16 that the maximumVon Misses stress is acting on the mountinglug and it is 246.71 MPa. Now, yield strengthof the material HARDOX 400 (Becausemaximum Von Misses stress is acting on themounting lug, made up of HARDOX 400) is1000 MPa. Equation (1) yields [

y] = 500 MPa

(safety factor = 2), and VM

= 246.71 MPa(Figure 16), so

VM < [

y] and this indicates

that the design of the boom is safe. Figure 17shows the enlarged view of the boom at whichthe maximum stress developed. Figure 18depict that the maximum displacement of

Figure 14: Boundary Conditions for Boom

Figure 15: Mesh View of Boom

Figure 13 shows the static force analysisof the boom to determine the boundarycondition for performing stress analysis of theboom. Figure 14 shows the boundaryconditions of the boom as calculated. Figure15 shows the mesh view of the boom with31855 nodes and 4647 elements.

Figure 16 shows the results of the VonMisses stresses on boom assembly. As it can

Figure 16: Von Misses Stresses of Boom

Figure 17: Enlarged View of MaximumStresses of Boom

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Figure 22 shows the results of the Von Missesstresses developed on swing link. As it canbe seen from the Figure 22 that the maximumVon Misses stress is acting on the cylindermounting lug and it is 119.83 MPa. Figure 23shows the Enlarged view of maximum stressdeveloped on the swing link.

Now, yield strength of the materialHARDOX 400 (Because maximum VonMisses stress is acting at the cylinder mountinglug, made up of HARDOX 400) is 1000 MPa.

1.9982 mm occurs at the free end of the boom(A

2 point) is very less than that of the minimum

thickness of the plate used in the boom,therefore the boom is safe for the given staticloading condition.

Analysis of the Swing Link

Figure 19 shows the static force analysis ofthe swing link. Figure 20 shows the boundaryconditions of the swing link as calculated andFigure 21 shows the mesh view of the swinglink with 47376 nodes and 25387elements.

Figure 18: Displacements of Boom

Figure 19: Static Force Analysisof Swing Link

Figure 20: Boundary Conditionsfor Swing Link

Figure 21: Mesh View of Swing Link

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Figure 22: Von Misses Stressesof Swing Link

Figure 23: Enlarged View of MaximumStresses of Swing Link

Equation (1) yields [y] = 500 MPa (safety

factor = 2), VM

and = 119.83 MPa, so VM

<[

y] and this indicates that the design of the

swing link is safe.

Figure 24 depict that the maximumdisplacement of 0.068247 mm occurs at hingejoint of the boom (A

2 point) is very less than

Figure 24: Displacements of Swing Link

that of the minimum thickness of the plate usedin the swing link, therefore the swing link is safefor the given static loading condition.

Analysis of the Backhoe ExcavatorAttachment Assembly

Figure 25 shows the boundary conditions ofthe backhoe excavator attachment. Figure 26shows the mesh view of the boom with 151910nodes and 47749 elements.

Figure 25: Boundary Conditionsof Backhoe Excavator

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Figure 27 shows the maximum Von Missesstresses produced in the backhoe attachmentassembly. Maximum Von Misses stress actingon the bucket is 252.3 MPa. The maximumVon Misses stress is acting at the intersectionof mounting lug and top bucket plate as shownin Figure 27, which is made up of Hardox 400material with the yield strength of 1000 MPa,by taking safety factor as 2, Equation (1) yields

VM = 252.3 MPa [

y] = 500 MPa, this clearly

indicates VM

< [y], so the stresses produced

in the assembly of the backhoe are within thelimits and the design is safe. Figure 28 showsthe enlarged view of excavator assemblywhere maximum stress is produced.

Analysis of the Backhoe ExcavatorAttachment with Considerationof Welding

Now, welding is introducing to each part of theexcavator with the help of WLDMENT tool ofthe Autodesk Inventor 2011. Then the partswith welding are analyzed with FEA approachusing ANSYS and procedure for analysisremain same as discussed in above sections.

Strength of the material for the weldingshould be less than the strength of the basemetal. A soft electrode is a filler material withyield strength less than parent material. Theseelectrodes reduce the level of residual tensionin the weld and hence the tendency of thematerial to develop cracks in cold state(Bhaveshkumar and Prajapati, 2011b).Therefore it is very important to carry out thestress analysis of backhoe excavator parts andits assembly with application of welding.

Figure 26: Mesh View of BackhoeExcavator

Figure 27: Von Misses Stressesof Backhoe Excavator

Figure 28: Enlarged View of MaximumStresses of Backhoe Excavator

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Based on this analysis we can know the effectof the welding on the stress produced in theparts of excavator.

The Table 1 shows the comparison ofstresses produced in the parts with weldingand without welding.

to perform the structural optimization of theexcavator attachment for weight reduction.Optimization can help to reduce the initial costof the attachment as well as to improve thefunctionality in context of controlling of theexcavation operation.

REFERENCES1. Andrew Hall (2002), “Characterizing the

Operation of a Large Hydraulic Excavator”,p. 1, Thesis of Master of Philosophy,School of Engineering, The University ofQueensland Brisbane, Australia.

2. Bhaveshkumar P Patel and Prajapati J M(2011a), “A Review on FEA andOptimization of Backhoe Attachment inHydraulic Excavator”, IACSITInternational Journal of Engineering andTechnology, Vol. 3, No. 5, pp. 505-511.

3. Bhaveshkumar P Patel and Prajapati J M(2011b), “Soil-Tool Interaction as a Reviewfor Digging Operation of Mini HydraulicExcavator”, International Journal ofEngineering Science and Technology,Vol. 3, No. 2, pp. 894-901.

4. Bhaveshkumar P Patel and Prajapati J M(2012), “Evaluation of Bucket Capacity,Digging Force Calculations and StaticForce Analysis of Mini Hydraulic BackhoeExcavator”, Machine Design—TheJournal of Faculty of Technical Sciences,Vol. 4, No. 1, pp. 59-66.

5. Bhaveshkumar P Patel, Prajapati J M andSandipkumar P Parmar (2011), “A Reviewon FEA and Genetic Algorithm Approachfor Structural Optimization”, GlobalJournal of Mechanical Engineering andComputational Science, Vol. 1, No. 4,pp. 29-32.

1. Bucket 203.67 178.33

2. Arm 239.39 212.46

3. Boom 246.71 242.41

4. Swing link 119.83 119.29

5. Backhoe Assembly 252.30 241.87

Table 1: Comparision of StressesProduced in Backhoe Modelwith and Without Welding

Part Name

Maximum Von MissesStresses (MPa)

S.No.

BackhoeModel

WithoutWelding

Backhoe ModelWith Welding

CONCLUSIONThe mini hydraulic backhoe excavatorattachment is developed to perform excavationtask for light duty construction work. Based onstatic force analysis finite element analysis iscarried out for individual parts as well as thewhole assembly of the backhoe excavator withand without consideration of welding. It isclearly depicted that the stresses produced inthe parts of the backhoe excavator attachmentare within the safe limit of the material stressesfor the case of with and without considerationof welding. The result shows the maximumstresses produced in the parts with welding isless than the parts without welding, it clearlydepict that the welding strengthen the parts.Based on results also we can conclude thatthe maximum stresses produced in the partsare very less compare to limiting (safe) stressof the parts material, therefore there is a scope

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6. Mehmet Yener (2005), “Design of aComputer Interface for Automatic FiniteElement Analysis of an Excavator Boom”,pp. 1-4 and 68-69, MS Thesis, TheGraduate School of natural and AppliedSciences of Middle East TechnicalUniversity.

7. Mehta Gaurav K (2008), “Design andDevelopment of an ExcavatorAttachment”, p. 1, M.Tech DissertationThesis, Nirma University, Institute ofTechnology, Ahmedabad.

8. Mittal R K and Nagtath I J (2008),“Robotics and Control”, 9th Reprint, pp. 70and 190, Tata McGraw-Hill PublishingCompany Limited.

9. Nareshkumar N Oza (2006), “FiniteElement Analysis and Optimization of anEarthmoving Equipment Attachment –

Backhoe”, pp. 5-6 and 38-68, M.TechDissertation Thesis, Nirma University,Institute of Technology, Ahmedabad.

10. Peurifoy Robert L and Schexnayder JClifford (2006), Construction, Planning,Equipment and Methods, 6th Edition,pp. 229-267, Tata McGraw-Hill Publica-tion, New Delhi.

11. Reena Trivedi (2005), “Calculation ofStatic Forces and Finite ElementAnalysis of Attachment of an Excavator”,M.Tech Thesis, Nirma University,Institute of Science and Technology,Ahmedabad.

12. Tirupathi R Chandrupatla and Ashok GBelegundu (2005), “Introduction to FiniteElements in Engineering”, PearsonEducation Publication India Branch,Delhi, India.

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