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Optimization of knuckle joint by using finite element analysis and its experimental validation
Mr.Nitin Paraji Jondhale P G Student
S.N.D.C.O.E.&R.C Yeola [email protected]
Prof.Karwande A.H Asst.Professor
S.N.D.C.O.E.&R.C Yeola [email protected]
ABSTRACT
The aim of this paper is to study and calculate the stresses in Knuckle joint using analytical method and its validation through experiment. A knuckle joint is used to connect two rods under tensile load. These joints are used for different types of connections e.g. tie rods, tension links in bridge structure. In this, one of the rods has an eye at the rod end and the other one is forked with eyes at both the legs. In this study, modeling and analysis of a knuckle joint is performed by using Finite Element Method. The commercial finite element package ANSYS version 16 will be used for the solution of the problem. The knuckle joint takes tensile loads often, thus there is a need for quality design tools. The modeling of the knuckle joint is done using 3D software. Here CATIA or Cre-O will be used for modeling. The simulation part will be carried out using the Analysis software, ANSYS.
With the Boundary constrains and the tensile load applied, the knuckle joint is analyzed and the values are tabulated. FEA results for tensile loading then validated with tensile testing results at UTM.
Keywords
FEM, UTM, Tensile Testing, Experimental Validation.
1. INTRODUCTION
Knuckle joint is a type of mechanical joint used in structures, to connect two intersecting cylindrical rods, whose axes lie on the same plane. It permits some angular movement between the cylindrical rods (in their plane). It is specially designed to withstand tensile loads. Knuckle joint is named so because it is free to rotate about the axis of a knuckle pin.
Figure 1.Typical Knuckle Joint
It is basically a tensile joint. However, if the joint is guided, it may support a compressible load. This joint can be readily
disconnected for adjustments or repairs. The common examples of the knuckle joints are link of a roller chain, tension link in a bridge structure, tie rod joint of roof truss, tie rod joint of jib crank, etc. A typical knuckle joint consists of three parts: an eye, a fork, and a knuckle pin. The end of one rod is formed into an eye and the end of other rod is formed into fork with an eye in each of the fork leg. The eye is inserted into the fork and after aligning the holes in the eye and fork, the knuckle pin is inserted through them. The knuckle pin has a head at one end and at the other end it is secured by a collar and a taper pin or split pin. The simple definition of stress is that force divided by area. If the force is perpendicular to the area and pulling away from it, the stress is tensile. If the force is perpendicular to area and pushing towards it, the stress is compressive. Coaxial holes are provided in the fork end, eye end and collar. The fork end and the eye end are held together in position by means of a knuckle pin. The knuckle pin is held in its position with the help of a collar and a taper pin. The assembled view of a knuckle joint is shown in the image below. Both the fork end and the eye end are capable of rotating in their planes about the axis of the knuckle pin.
2. PROBLEM STATEMENT
To suggest appropriate material for Knuckle joint with cost effectiveness and to increasing the life of knuckle joint used for Mahindra tractor.
2.1 Need of Study
To decide the best suitable material for Knuckle joint from available materials for same load carrying capacity.
To reduce cost of knuckle joint.
To improve the life of knuckle joint.
To analyze the stresses using Ansys software calculations.
To modify the geometry if necessary
2.2 Aim
To find out Alternative Material to minimize cost and weight of knuckle joint and also increase the life of joint and for that the study of different type of material is carried out.
4 MATERIAL SELECTIONS BY FINITE ELEMENT ANALYSIS
4.1 Tool Used
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Here Ansys 16.0 is used for analyzing natural frequencies and static deflection. CAD modeling is done in Catia software and .stp file were imported in ANSYs for analysis. Ansys Mechanical software is a comprehensive FE analysis (finite element) tool for structural analysis, including linear, nonlinear and dynamic studies. The engineering simulation product provides a complete set of elements behavior, material models and equation solvers for a wide range of mechanical design problems. In addition, ANSYS Mechanical offers thermal analysis and coupled-physics capabilities involving acoustic, piezoelectric, thermal structural and thermo-electric analysis. With a solid foundation of element and material technology, ANSYS structural analysis software offers various advanced modeling methods for different kinds of applications. In addition, ANSYS finite element analysis (FEA) tools offer advanced capabilities that enable simulation of a variety of physics phenomena, such as thermal stress, electromechanical, structural acoustics, mass diffusion and simple thermal fluid analysis.
4.2 Static Analysis
A static structural analysis determines the displacements, stresses, strains, and forces in structures or components caused by loads that do not induce significant inertia and damping effects. Steady loading and response conditions are assumed; that is, the loads and the structure's response are assumed to vary slowly with respect to time. A static structural load can be performed using the ANSYS solver.
The types of loading that can be applied in a static analysis include:
1) Externally applied forces and pressures.
2) Steady-state inertial forces (such as gravity or rotational velocity).
3) Imposed (nonzero) displacements.
4) Temperatures (for thermal strain).
Static analysis of knuckle joint design is performed using ANSYS 16.0 to find the static deflection and stress for corresponding pay load. The Static Analysis involves following major steps.
4.2. Pre-Processing
Geometry Modeling
Meshing
Material
Contact Definition
Loading and boundary condition
Solution
4.3. Post-Processing
Deformation
Stresses
4.4. Geometry Details
CAD Modeling of any project is one of the most time consuming process. One cannot shoot directly from the form sketches to Finite Element Model. CAD (Geometry) Modeling is the base of any project. Finite Element software will consider shapes, whatever is made in CAD model. CAD modeling of the knuckle joint is performed by using Catia.
Fig.2.Knuckle Joint.
Knuckle joint is another promising joint to join rods and carry axial force. It is named so because of its freedom to move or rotate around the pin which joins two rods. A knuckle joint is understood to be a hinged joint in which projection in one part enters the recess of the other part and two are held together by passing a pin through coaxial holes in two parts. This joint cannot sustain compressive force because of possible rotation about the pin. There are most common in steering and drive train applications where it needs to move something but also need to allow for offset angles. A knuckle joint is used when two or more rods subjected to tensile and compressive forces are fastened together such that their axes are not in alignment but meet in a point. This type of joint allows a small angular movement of one rod relative to another. The joint can be easily connected and disconnected. Knuckle joint is found in valve rods, braced girders, links of suspension chains, elevator chains, etc. The knuckle joint assembly consists of following major components:
Single eye.
Double eye or fork.
Knuckle pin.
Table.1.Specification of Knuckle joint.
1 Rod diameter b 40mm
2 Load applied P 50KN
3 Diameter of knuckle pin (dp) = d, dp
40mm
4 Thickness of single eye ( b)
1.25d = 1.25x40, b
= 50mm
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5
Thickness of fork (a) 0.75d = 0.75x40, a
= 30mm
6 Outer diameter of eye (d1)
2d = 2x40, D = 80mm
Table .2 Material Properties
Material Property
Unit Structu ral Steel
AL Stainless Steel
Teflo n
Gray Iron
Modulus of Elasticity
GPa 200 71 193 0.5 110
Poisson‟s Ratio
-
0.3 0.27 0.31 .46 0.28
Mass Density
kg/
m3
7750 275 0
7750 2100 7200
Material Strength
MPa 250 280 207 150 190
Fig.3.FE Modeling details; Nodes: 33674, Elements:
191244
4.5. Meshing
Meshing involves division of the entire of model into small pieces called elements. This is done by meshing. It is
convenient to select the free mesh because the has sharp curves, so that shape of the object will not alter. To mesh the plate the element type must be decided first. SOLID187 is used here for meshing plates.
4.5.1 Solid187 Element Description
SOLID187 element is a higher order 3-D, 10-node element.
SOLID187 has a quadratic displacement behavior and is well suited to modeling irregular meshes (such as those produced from various CAD/CAM systems).The element is defined by 10 nodes having three degrees of freedom at each node:
translations in the nodal x, y, and z directions. The element has plasticity, hyper elasticity, creep, stress stiffening, large deflection, and large strain capabilities. It also has mixed formulation capability for simulating deformations of nearly incompressible elastoplastic materials, and fully incompressible hyperplastic materials. The geometry, node locations, and the coordinate system for this element are shown in Figure: SOLID187 Geometry. In addition to the nodes, the element input data includes the orthotropic or anisotropic material properties. Orthotropic and anisotropic material directions correspond to the element coordinate directions.
Fig.5.SOLID187 Geometry
4.5.2 Solid187 Assumptions and Restrictions
The element must not have a zero volume.
Elements may be numbered either as shown in Figure: SOLID187 Geometry or may have node L below the I, J, K plane.
An edge with a removed midside node implies that the displacement varies linearly, rather than parabolically, along that edge. See Quadratic Elements (Midside
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Nodes) in the Modeling and Meshing Guide for information about using midside nodes.
When mixed formulation is used (KEYOPT(6) = 1 or 2), no midside nodes can be missed.
If you use the mixed formulation (KEYOPT(6) = 1 or 2), the damped eigensolver is not supported. You must use the sparse solver (default).
Fig.6. FE Modeling details; Nodes: 33674, Elements:
191244
5. LOADS AND BOUNDARY
CONDITIONS
Eye end is fixed in all directions and force is applied on fork end. Below fig. shows loads and bc's knuckle joint. Same bc's are applied for cases of material models.
Fig.7. Knuckle joint Model bc's
6. TOTAL DEFORMATION
Steel have observed less deformation compared o othermaterial. Apart from this AL material, also shows very low deformation
Table No.3.Total Deformation
Total Deformation(mm)
Material Eye
Steel 0.053
AL 0.148
Stainless Steel 0.055
Teflon 20.537
CI 0.096
7. EXPERIMENTAL WORK
A based FEA result, AL alloy material was proposed and hence physical model of AL alloy mentioned below was considered to prepare. The manufacturing of knuckle joint was done at „FINE CASTING INTERPRISES‟. Refer below snap for the industry details. AL Alloy material composition:
Grade 2024 was considered as per available in market.
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The drawing of all three components was made in catia for making pattern for casting process. Refer below drawing details as below.
The knuckle joint was made using sand casting process.
7.1. Sand Casting Process
Table.No.4. Result
Sand casting, the most widely used casting process, utilizes expendable sand molds to form complex metal parts that can be made of nearly any alloy. Because the sand mold must be destroyed in order to remove the part, called the casting, sand casting typically has a low production rate. The sand casting process involves the use of a furnace, metal, pattern, and sand mold. The metal is melted in the furnace and then ladled and poured into the cavity of the sand mold, which is formed by the pattern. The sand mold separates along a parting line and the solidified casting can be removed.
7.2. Machining process
Machining is the broad term used to describe removal of material from a workpiece, it covers several processes, which we usually divide into the following categories:
• Cutting, generally involving single-point or multipoint cutting tools, each with a clearly defined geometry.
• Abrasive processes, such as grinding.
• Nontraditional machining processes, utilizing electrical, chemical, and optimal sources of energy.
Knuckle Joint
Experimental Results
ANSYS Results
Percentage Difference
Static Deformation(mm) 0.148 0.140 5%
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It is important to view machining, as well as all manufacturing operations, as a system consisting of the work piece, the tool and the machine. The introduction topic in this section covers primers on topics like mechanics & shear bending in machining, and heat in machining. The traditional machining includes primers on turning, milling, drilling, and grinding. It also includes computer applications which are being supported by the primers. The nontraditional machining includes primers on the topics like ECM, EDM, AFM, USM.
The final job is the tested on UTM to calculate deformation of joint for 50KN load. Below the industry certificate for successfully completing manufacturing of knuckle joint.
7.3. Tensile Testing
7.3.1. Universal Testing Machine
A universal testing machine (UTM), also known as a universal tester, materials testing machine or materials test frame, is used to test the tensile strength and compressive strength of materials. An earlier name for a tensile testing machine is a tensometer. The "universal" part of the name reflects that it can perform many standard tensile and compression tests on materials, components, and structures (in other words, that it is versatile).
8. RESULT
Validation of FEA and Experimental results by correlating AL alloy deformation observed in FEA and comparing with experimental measured deformation in tensile testing.
Table No.5. the load vs. deflection data from FEA and experimental.
FEA Experimental
Load(N) Deflection(mm)
5000 0.0148 0.0138
10000 0.0297 0.0277
15000 0.0445 0.0415
20000 0.0594 0.0554
25000 0.0742 0.0692
30000 0.0891 0.0831
35000 0.1039 0.0969
40000 0.1187 0.1107
45000 0.1336 0.1246
50000 0.1484 0.1400
Fig.8.Load Vs Delction Graph
With current load of 50KN, the knuckle joint does cross yield point and hence graph showing linear behavior.
CONCLUSION
Knuckle joint was analysis for five different material.
Static deformation of AL allot knuckle joint was validated with experimental. Good agreement is observed for experimental measure static deformation in UTM and FEA results. The results are validated and hence we can conclude that the ANSYS results are reliable and can be applied for complicated analysis.
Deformation of steel and AL material are very less co pared to Teflon and CI.
Steel FOS are higher than min requirement of 3, however the material cost and mass of steel is higher compared all other material.
Material cost of Teflon is less compared all other material along with FOS and hence Teflon will not be good material even having less mass.
Steel and CI having similar FOS and mass of knuckle also seems comparative and hence both material were not recommended.
AL is having highest FOS and less mass compared to steel and CI and hence based FEA study we recommended to manufacture knuckle joint in future with AL material.
AL material is sustaining tensile loading of 50KN with min FOS of 3.5
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