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Analysis of Radial and Tangential Static Forces for Critical
Fillet Stress Studies of Crankshaft
Pranav B. Patel
1, Kamlesh C. Patel
2, Devendra A. Patel
3, Ankit J. Desai
4 1,3,4Assistant Professor at Mechanical Engineering Department- CGPIT, Bardoli- 3943502Assistant Professor at Mechanical Engineering Department- Government Polytechnic College- Valsad-396001
Abstract—In this paper crankshaft analysis is presented.
In crankshaft analysis, critical stress region is fillet area, so material optimization at fillet area is required. Analysis of the crankshaft is difficult due to complicated geometry and the complex torque imposed by the cylinder pressure, but here optimized meshing and accurate simulation of boundary condition along with ability to apply complex torque, provided by various FEM packages have helped the designer to carry torsional vibration analysis with investigation of critical stresses. Large memory &disc space as computing resource is required for solution of FEM problem. Bending vibration of crankshaft is cause by the radial forces on crankpin. Maximum force applied at radial crankpin is required to detect maximum bending deflection of crankshaft. Dynamic response and investigation of critical stresses are found out by incorporating the boundary conditions at the journal bearing positions. And tangential and radial forces on corresponding nodes. To validate the work holtzer method calculation is done with comparison of analysis result. Holtzer method is solved for those parameter which having lumped masses, so crank throw is modeled as lumped masses. By the work out this method, eventually natural frequency is found.
Keywords— Crankshaft analysis, Holtzer method, Radial
forces, Tangential forces.
I. INTRODUCTION
Here crankshaft vibration analysis is solved by the finite element analysis (FEA) packages. FEA is the rigorous tool to sharply analyse solid body parts. For a crankshaft vibration analysis, sharp knowledge of finite element method (FEM) theory and mechanical vibration theory are very important thing because wrongly meshed and wrongly applied boundary condition leads to incorrect result.
To predict dynamic behaviour of any system, the systems around the model have to be considered and simulated mathematically. It contains forces, constraints, reactions applied by external system on the system under consideration. In the terminology of FEM it is called ‘Boundary Conditions’, on the basis of which the model is solved. The crankshaft is in contact with cylinder block, connecting rod, damper pulley and vehicle load through clutch.
So after modeling and meshing it is important task ahead of analyst to mathematically model the boundary conditions. Their accurate models are required because a sight error in them cause changes in final results. Dynamic response and investigation of critical stresses are found out by incorporating the boundary conditions at the journal bearing positions. And tangential and radial forces on corresponding nodes.
II. SOLID MODELING OF CRANKSHAFT
To carry out FEM analysis of any component, the solid model of the same is essential. It is also called body in white. So the solid model of Crankshaft is require and this can be done in special CAD package like Pro-E Wildfire.[12]
Modeling Details: 2-D drawings: For generation of a 3-D model, 2-3-D orthographic views are required. The crankshaft is composed of following elements-
Flywheel end journals, Webs, Crankpins, Central Journal, Pulley side Journals, Flywheel end, Pulley end.
The 2-D drawings of every individual part and their assembly are collected from a company (name kept undisclosed).
International Journal of Emerging Technology and Advanced Engineering
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Finally boolean operation is performed to extract the required geometry. This process is repeated for each orientation of oil holes. [12]
Using similar techniques complete crankshaft is generated in 3-D model. Fig.1 shows a 3-D plot of the model used for a specific engine.
Building Clean Geometry: In short, clean geometry can be defined as a solid CAD model that maximizes the possibility for a’ mesh which in turn captures the features required for correct results. Two key points are made in this statement. First, the geometric features must not prevent the mesh from being created and must also contain surfaces of consistent size and shape ratios to prevent forcing high, aspect ratio elements and/or transitions between element
edges that may compromise accuracy. Second,
simplification or manipulation of features in an attempt to clean up the geometry should not reduce the structural integrity of the part. The best mesh is the smallest model that yields correct data. Consequently, manipulation of the model, either by adjusting dimensions or suppressing features far from any area of interest, is acceptable, as effects local to the simplification will most likely not affect the global behavior of the system. However, care should be taken when adjusting a model near an area of concern.
The best safeguard against the need to clean up geometry near an area of interest is to not create a problem in the first place. Many designers make dimensions and feature size choices based on convenience. Consequently, it is not surprising that short edges or sliver surfaces appear randomly in a model. If the feature choices are made with the knowledge of downstream needs, many of the modeling issues that plague the automeshers and analysts can’ be avoided.
[image:2.612.339.549.131.427.2]The primary causes of short edges are the misalignment of features and the proximity of fillet edges to other edges. Some commonly created short edges that could have been eliminated with proper planning of geometry are shown in the three illustrations appearing in this section. [12]
Fig. 1 Model of Crankshaft
III. FEMESH GENERATION
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Mesh Generation: While meshing can be used for a wide variety of applications, the principal application of interest is the finite element method. Surface domains may be subdivided into triangle or quadrilateral shapes, while volumes may be subdivided primarily into tetrahedra or hexahedra shapes. The shape and distribution of the elements is ideally defined by automatic meshing algorithms.
The automatic mesh generation problem is that of attempting to define a set of nodes and elements in order to best describe a geometric domain, subject to various element size and shape criteria. Geometry is most often composed of vertices, curves, surfaces and solids as described by a CAD or solids modeling package.
Many applications use a "bottom-up" approach to mesh generation. Vertices are first meshed, followed by curves, then surfaces and finally solids. The input for the subsequent meshing operation is the result of the previous lower dimension meshing operation.
Mesh Density: The art of using FEM lies in choosing the correct mesh density required to solve a problem. If the mesh is too coarse, then the element will not allow a correct solution to be obtained. Alternatively, if the mesh is too fine, the cost of analysis in computing time can be out of proportion to the results obtained. A fine mesh is required where there are high parameter gradients and strain and a course mesh is sufficient in areas that have result contours of reasonably constant slope. [13]
Fig. 2 Meshed model of whole assembly generated in Hypermesh
IV. RADIAL FORCES
We get radial and tangential force values from ANSYS macro. Further we apply these forces on crankshaft and solve it with ANSYS solver.
[image:3.612.324.573.270.462.2]To get the effect of bending forces on the crankshaft, we have applied the radial forces Fr on the crankpin positions and the displacement constraints is applied at the multiple journal bearing positions. The study of maximum stress distributions around the fillet which may be stress concentration region is our objective.
[image:3.612.71.261.468.697.2]Fig. 3 shows application of radial force.
Fig. 3 Boundary Conditions For Radial Stress Analysis.
[image:3.612.324.571.491.689.2]International Journal of Emerging Technology and Advanced Engineering
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Plot For Deformation Due To Radial Forces:
[image:4.612.49.299.176.382.2]From fig. 4 it is found the maximum deflection is 0.022mm and minimum deflection is 0 mm.
Fig. 5 Stress due to radial forces
Plot For Stress Due To Radial Forces:
[image:4.612.324.569.271.666.2]From fig. 5 it is found the maximum von mises stress value is 20.464 N/mm2 and minimum stress value is 0.19E-4 N/mm2.
Fig. 6 Radial Stress Concentration
Enlarged view of Radial Stress Concentration:
Fig. 6. shows stress concentration at fillet area at flywheel and crankpin position.
V. TANGENTIAL FORCES
We get tangential force values from ANSYS macro, and further we apply these forces on crankshaft. To get the effect of torsional forces on the crankshaft, we have applied the tangential forces Ft on the crankpin positions and the displacement constraints is applied at the end of one side journal bearing positions to see the effect of toque developed by tangential forces at different lobes of crankshaft. The study of maximum stress distributions around the crankpin positions, which may be stress concentration region is our objective.
Fig. 7 Application of tangential force.
[image:4.612.51.283.443.632.2]International Journal of Emerging Technology and Advanced Engineering
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Plot for Deformation Due To Tangential Forces:
[image:5.612.51.300.178.380.2]From fig. 8 it is found the maximum deflection is 0.022mm and minimum deflection is 0 mm.
Fig. 9 Stress Due To Tangential Forces
Plot for Stress Due To Tangential Forces:
From Fig. 9 it is found the maximum von mises stress value is 20.464 N/mm2 and minimum stress value is 0.19E-4 N/mm2
Fig. 10 Tangential Stress Concentration
Enlarged view of Tangential Stress Concentration: Fig. 10 shows large view of tangential stress concentration.
VI. MATERIAL OPTIMIZATION
Material Optimisation To study the effect of radial and tangential forces on different material conditions for same geometrical parameters of crankshaft and to study stress distribution around the stress concentration area like fillet stresses is our objective for material optimization study. From fig. 11, fig. 12, fig. 13, fig. 14. It is found that the red region shows stress affected area due to stress concentration near the fillet region, which is shifting its position due to material change conditions.
[image:5.612.324.533.297.441.2]1) For 40 Cr 4 MO3:
Fig. 11 stress concentration near fillet area for 40 Cr 4 MO3
2) MED Carbon, B, Mn, V, Alloy:
[image:5.612.325.535.306.573.2] [image:5.612.48.291.442.625.2]International Journal of Emerging Technology and Advanced Engineering
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[image:6.612.51.266.132.476.2]3) Med. Carbon, V, Alloys:
Fig. 13 stress concentration near fillet area for Med. Carbon, V, Alloys
4) Cast Iron:
Fig. 14 stress concentration near fillet area for Cast Iron
VII. CONCLUSION
Experimental validation of crankshaft is done using FFT
analyser. The values of FFT output and Modal frequency calculated from ANSYS and Hypermesh validates the results as both are matching.
The mode shape calculation of different systems of component is done using modal analysis. The effect of flywheel and pulley shows the natural frequency is decreasing due to additional masses at the end of crankshaft.
As the stress concentration area for radial forces is fillet and for tangential force it is crankpin positions. Both the stresses plot study shows the critical stress region.
As the crankshaft is already optimised at the fillet area at the end, keeping all geometrical parameter of crankshaft same, we studied the maximum stress area for the different materials used for four to five currently vehicles on road.
We conclude our results and discussion by viewing
displacement plot for different mode shapes that the natural frequency is affected or decreased due to the addition of pulley and flywheel. So the resonance condition is more critical for the combined assembly. The Vonmises stress plot concludes that during maximum rpm or maximum torque condition failure will take place near the fillet area.
REFERENCES
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[8] Peter J. Carrato, Chung C.Fu., “Modal Analysis Techniques for Torsional Vibration of Disel Crankshafts”, SAE paper, 861225, pp.4.955-4.963. 1986.
[9] Edward P. Petkus, Stephen F., “A Simple Algorithm for Torsional Vibration Analysis”, SAE paper, 870996, pp.3.156-3.163, 1987. [10] V. Prakash, D.N.Venkatesh, “The Effect of Bearing Stiffness on
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[15] Singiresu S. Rao, “Mechnical Vibrations”, Pearson Education Pte. Ltd., Indian Branch Delhi, 2004.
[16] J.N. Reddy, “An Introduction to the Finite Element Method”, Tata Mcgraw Hill, 2nd edition, 2003.