Finite Element Analysis and Optimization of I.C. Engine Piston Using RADIOSS and OptiStruct Vivek Zolekar Student M. Tech. Mechanical (CAD/CAM) SGGSIE&T Nanded - 431 606 Dr. L.N. Wankhade Professor Department of Production Engineering SGGSIE&T Nanded - 431 606 Abbreviations: FEA- Finite Element Analysis CAD- Computer Aided Design CAE- Computer Aided Engineering. Keywords: FEA, HyperMesh, RADIOSS, OptiStruct Abstract In this paper, the wok is carried out to measure the stress and temperature distribution on the top surface of the piston. In I.C. Engine piston is most complex and important part therefore for smooth running of vehicle piston should be in proper working condition. Pistons fail mainly due to mechanical stresses and thermal stresses. Analysis of piston is done with boundary conditions, which includes pressure on piston head during working condition and uneven temperature distribution from piston head to skirt. The analysis predicts that due to temperature whether the top surface of the piston may be damaged or broken during the operating conditions, because damaged or broken parts are so expensive to replace and generally are not easily available. The CAD model is created using CATIA V5 tool. CAD model is imported into the HyperMesh for geometry cleaning and meshing purpose. The FEA is performed by using RADIOSS. The topology optimization of the model is done using OptiStruct module of HyperWorks software. 1. Introduction Engine pistons are one of the most complex components among all automotive and other industry field components. The engine can be called the heart of a vehicle and the piston may be considered the most important part of an engine. There are lots of research works proposing, for engine pistons, new geometries, materials and manufacturing techniques, and this evolution has undergone with a continuous improvement over the last decades and required thorough examination of the smallest details. Notwithstanding all these studies, there are a huge number of damaged pistons. Damage mechanisms have different origins and are mainly wear, temperature, and fatigue related. The fatigue related piston damages play a dominant role mainly due to thermal and mechanical fatigue, either at room or at high temperature. This paper describes the displacement and stress distribution on piston of internal combustion engine by using FEA. The FEA is performed by CAD and CAE software. The main objectives are to investigate and analyze the thermal stress distribution of piston at the real engine condition during combustion process. The paper describes the FEA technique to predict the higher stress and critical region on the component. The optimization is carried out to reduce the stress concentration on the piston. With using CATIA software the structural model of a piston will be developed. Furthermore, the FEA performed with using software Simulate to Innovate 1
HyperWorks. Optimization of piston is carried out by topology criteria from the result designable and non designable area is investigated. Applying different boundary conditions displacement and stress distribution is calculated. Softwares used are CATIAV5 for geometry creation, HyperMesh for meshing, RADIOSS for analysis, OptiStruct for optimization and HyperView for post processing. 2. Process Methodology 3D model of piston is imported into the HyperMesh for preprocessing. Preprocessing of model consist of meshing, selection of material properties, creation of load collectors and apply boundary conditions on model. Then model is exported to RADIOSS for solving problem. Results of solution plotted in HyperView which is well known postprocessor of HyperWorks software. For the optimization purpose topology optimization criteria is selected. According to topology criteria the designable and non designable space is generated and subsequently element density contour plot is generate in HyperView. Figure No. 1 shows Flow chart of process methodology of I.C. Engine Piston Analysis and Optimization. Import the geometry into the Geometry Clean Up and Meshing Selection Of Material Model Creation of Load Collectors Apply Boundary Conditions Export to RADIOSS for Solution Plotting Result in HyperView Optimization Fig.1. Flow chart of Process Methodology Simulate to Innovate 2
3. Finite Element Modeling: Finite Element Modeling is important preprocessing stage of analysis of piston. In this stage piston model is imported into HyperMesh for preprocessing. Preprocessing consist of meshing and applying material properties and boundary conditions. After completion of preprocessing finite element model is export to RADIOSS for analysis purpose. 3.1 Meshing of piston model: For meshing purpose model is imported into the HyperMesh. As the model is solid therefore PSOLID element is selected. Meshing of model is done with help of auto mesh command. As our area of interest is mainly concentrate on the displacement and stress distribution therefore 3D meshing type is selected. Meshing parameters are illustrated in Table No. 1, while figure no. 2 showss model after meshing in HyperMesh. Element Mesh Type Element type Element size PSOLID 3D Volume tetra Tetrahedral 5 mm Table No. 1 Meshing Parameters Fig.2. Meshing of Piston 3.2 Material Properties and Boundary Conditions Aluminum alloy is selected as material from the design data book. Generally in this material aluminum is the main component in addition to main component aluminum it consists of copper 4-5%, ferrous 1.3%, silicon 16-18%, magnesium 0.45-65%, zinc 1.5% and nickel 0.1%. Simulate to Innovate 3
Table No. 2 & 3 shows the structural and chemical properties of aluminum alloy. Structural Properties of Aluminum Alloy: Material Young s Modulus E (N/mm 2 ) Poisson s Ratio µ Density (ρ) kg/m 3 Coefficient of thermal Expansion A ( / k) Thermal Conductivity K (W/m k) Al Alloy 8.2 10 10 0.33 2713 18 10-6 134 Table No. 2. Structural Property of Aluminum Alloy. Chemical Composition of Aluminum Alloy: Material Al Cu Mg Si Zn Fe Ni Al Alloy Balanced 4-5 0.45-0.65 16-18 1.5 1.3 0.1 Table No. 3. Chemical Composition of Material in percentage In combustion chamber due to Explosion of gases, pressure will be applied on the surface of the piston. That pressure force will be taken as mechanical load applying on the piston and same will be taken as Boundary condition in structural analysis. Pressure acting on piston head = 35 10 5 N/m 2. Fixed support has given at surface of pin hole, because the piston will move from TDC to BDC with the help of fixed support at pin hole. The thermal boundary conditions consist of applying thermal properties and temperature. Temperature is applied on piston head and which is equal to 800k. Pressure 35 10 5 N/m 2 Temperature 800 k Table No. 4. Boundary conditions Figure 3 shows the Finite Element Model of piston after applying material properties and boundary conditions. After the pre processing model is exported to RADIOSS and HyperView for solution and plotting of result respectively. Simulate to Innovate 4
Fig.3. Finite Element Model of piston after applying boundary conditions 4. Analysis Results & Discussions From the result it can be conclude that the piston head is critical part in I..C. Engine piston. Figure 4 show the maximum deflection in the piston geometry due to the application of gas pressure is 0.5636mm, which is observed at the central portion of the piston crown. Figure 5 show the distribution of Von mises stresses induced within the piston body. The maximum values of equivalent stresses are goes up to 987.1 MPa. Table No. 5 shows the resultss of displacement and Von Mises stress, Maximum Displacement (mm) Stress (M Pa) 0.5636 987.1 Table No. 5 Results of analysis Fig.4. Displacement of Piston Fig.5. Von Mises Stress distribution Simulate to Innovate 5
5. Optimization Optimization is a process of finding an optimal solution satisfying a given number of constraints. An optimization problem mainly consists of three components: a) Design Variables b) Design Objective c) Design Constraints Topology Optimization deals with the removal of redundant material based on a set of objectives and constraints. Design variable for topology optimization is density of each element. In case of Topology optimization run in OptiStruct, the software calculates the density of each element on a scale of 0-1. Elements with density 0 represent state of void, whereas elements with density 1 represents state of solid. Intermediate densities represent fictitious material. In case of any Topology optimization problem complete FE model is divided into design and non design space. Choice of design and non design space is solely dependent on the user. In this study a part of piston head and pin holes are kept into non design space so as to not alter the bolt locations and to give optimization software a direction to remove the redundant material. Optimization parameters for the problem are as following: a) Design variables: Density of each element b) Design constraints: Volume c) Design objective: Minimum weighted compliance In this paper our area of interest is to find out the designable and non designable space. Following results are generated after solving the model in OptiStruct module, results are generated into the HyperWorks postprocessor i.e. HyperView Fig.6. Non Designable space Fig.7. Designable Space 5.1 Optimization Result and Discussion Density plot for the model is obtained after a topology optimization run. These density values help in finding the redundant locations so as to remove the unnecessary material. In order to achieve viable results, elements having density values less than 0.2 are removed. Simulate to Innovate 6
Fig.8. Optimization result 6. Benefits Summary This optimization technique gives flexibility to the designer to choose the concept as per the requirement. This method has offered considerable saving in terms of evaluating various concepts without actually building any prototype. Further it reduced the time required to arrive at the best design thus shortening the product design cycle time. We can generate designable and non designable space as per our requirement. Due to CAE process it helps to reduce design cycle time, number of prototypes and more importantly, testing time and its associated costs. As the meshing, analysis and optimization carried out in same environment of HyperWorks software, so there is less possibility of data loss during the analysis and we get accurate result. 7. Future Plans For further development work, RADIOSS can be used efficiently to study Fluid Structure Interaction (FSI) Analysis i.e. coupled field analysis of same problem. After topology optimization of piston we are planning to do the Shape optimization for further improvement. 8. Conclusions The structural and thermal analysis of piston carried out in this paper by applying the boundary conditions from that following conclusion are made, 1. By using the simple concepts of FEA we were able to find critical areas of failure of model. 2. The piston experiences maximum stress in the region where the combustion of the fuel takes place, i.e. at the piston head. 3. Topology optimization using Altair's optimization software OptiStruct found to be very useful for generating new concept designs in less time. Simulate to Innovate 7
REFERENCES: 1. Altair HyperWorks help manual and Tutorials. 2. A.R. Bhagat, Y.K. Jibhakate, Thermal analysis and optimization of I.C. Engine piston using finite element method, International Journal of Modern Engineering Research (IJMER) Vol.2, ISSN: 2249-6645. 3. Vinod Junju, M.V. Mallikarjun and Venkata Ramesh Mamilla, Thermo mechanical analysis of diesel engine piston using ceramic crown, International Journal of Emerging trends in Engineering and Development, ISSN 2249-6149. 4. Bhaumik Patel, Ashwin Bhabhor, Thermal analysis of a piston of reciprocating air compressor, International Journal of Advanced Engineering Research and Studies E-ISSN2249 8974. 5. Design Data book, The McGraw-Hill Publication. Simulate to Innovate 8