Virtual Product Development for HCV -FUPD Structure

Transcription

1 Virtual Product Development for HCV -FUPD Structure Shailesh Kadre Principal CAE Analyst Mahindra Engineering Services #128/A, Sanghavi Compound, Chinchwad Pune, Ravindra Kumar Senior CAE-Analyst Mahindra Engineering Services #128/A, Sanghavi Compound, Chinchwad Pune, Shreyas Shingavi CAE-Analyst Mahindra Engineering Services #128/A, Sanghavi Compound, Chinchwad Pune, Patil Manojkumar M. Mahindra Engineering Services #128/A, Sanghavi Compound, Chinchwad Pune, Abbreviations: HCV: Heavy commercial vehicles FUPD: Front Underrun Protection Device Keywords: HCV, FUPD, Optimization, Topology Optimization, ECE- 93. Abstract The issue of 'compatibility' in a collision between a passenger car and a truck is more important than in a collision between passenger cars in consideration of the severity of injuries of car occupants. In 1994 the ECE regulation regarding front under run protection devise (FUPD) was enacted in Europe. This regulation prevents an expansion of damage caused when a car undergoes the truck frame, and make installation of FUPD on medium and large trucks mandatory. This paper outlines the methodology used to generate optimal design concepts for FUPD and its components by using various optimization tools of HyperWorks. During this whole design process, it was ensured that the structural performance of newly designed FUPD to be better than baseline design. Stress based constraints were imposed for various operating load cases on the chassis. Topology optimization was performed for the various components for durability and stiffness requirements. New design concepts for the FUPD structure were developed using load path analysis with current space claim using topology optimization with single die as manufacturing constraint. These optimized designs were finalized on the basis of manufacturing feasibility and other practical limitations. The final designs were validated by performing non-linear analyses. Introduction: New competitive products must meet the growing demands of the market. They must be light-weighted, resource-efficient, durable, stable, and have a low noise emission. At the same time, the product must be introduced quickly into the market. These demands can only be met if structural optimization tools were used in addition to established CAE, CAD, DMU, and PDM systems. Variation calculations and improvements carried out on the digital prototype at a very early project stage. Accordingly, the number of required prototypes can be reduced which results in possible time and cost savings. The new optimization tools will then speed up the product development process and improve its efficiency. Light-weighted, stiff and durable structures will offer end users in the automotive and supplier industry, the aerospace and machine manufacturing industry as well as in the engineering service a decisive edge over their competitors. Optimization is the act of obtaining the best result under given circumstances. In design, construction, and maintenance of any engineering system, engineers have to take many technological and managerial decisions at several stages. Large motor vehicles, for example cargo vehicles, today built with a relatively high ground clearance. One of the major reasons for this is the need for using the vehicles on uneven surfaces. At the front of the vehicle, the ground clearance is normally in the order of about mm. Simulation Driven Innovation 1

2 Process Methodology 1A) Determine available space envelope for component 1B) Loads applied as per ECE-93 Standard 2) First rough solid model design 3) Non linear analysis of First rough solid model Is Model Safe? No Yes 4) Linear analysis of first rough solid model 5) Overall topology optimization 6) Second (Manufacturable) design by using topology optimization result 7) Linear analysis of Manufacturable design Is Model safe? Yes No 8) Shape optimization 9) Non linear analysis of shape optimized model STOP Figure 1: Flow chart of Optimization methodology Simulation Driven Innovation 2

3 The optimization methodology Weight optimizing structural components for heavy trucks is becoming more and more important in today s economy. However performing the optimization is not an easy task. One needs to have the following knowledge and tools to be able to perform weight optimization of structural component. Step 1: First rough solid model: This is the very first version of the design. At this stage, the component must be over designed, since the next step is topology optimization and this can only take the redundant material out of the design looks like the maximum available space envelope. However, the attachment points to the other component must be clearly defined. This step is divided in to two steps. Step 1A: Maximum available space envelope This will enable the analyst to consider the whole set of geometric possibilities during optimization. Optimum designs have the correct geometry for the loads that they carry. To be able to capture the available domains for the correct geometry one has to know what the maximum available space envelope for the design is. It is very important to calculate this envelope accurately. If it is understood the solution domain considered for optimum design would be just a subset of the full possible domain. If the envelope is overestimated, the optimized component would interfere with the other components during certain operating conditions and this is not acceptable. The method used by the author is to find the all the components near to the FUPD brackets by taking the full front Assembly into consideration Figure 2: Max. Available space envelope for FUPD bracket Step 1B: Determine the load as per ECE-93 Standard- The outline of the ECE-93 is shown below As this regulation considers prevention of the car under running a truck. A basic function it stipulates only the requirement of strength that defines the displacement amount again the static load replacing the collision, and does not stipulate any collision characteristics. Hence this study aims only to meet ECE regulation, requirement for the strength, to lessen the severity of injuries of passenger car occupants. Simulation Driven Innovation 3

4 Figure 3: Outline of ECE-93 Standard Figure 4: Applied Boundary conditions Step 2: Non-linear analysis of first rough solid model: The nonlinear analysis of the first rough solid model is carried out to ensure that it is of adequate strength before going to optimization Load TABLE I NON-LINEAR ANALYSIS: DISPLCEMENT SUMMERY This displacement is taken as reference for further analysis P1 1 P2 1 Simulation Driven Innovation 4

5 TABLE II NON-LINEAR ANALYSIS: EQUIVALENT PLASTIC STRAIN SUMMERY Load Case Factor of safety FUPD Tube Side Cast Bracket Support Clamp Bracket Frame rail P P Figure 5: Displacement Plots after P1 loading (80 kn) Figure 6: Displacement Plots after P2 loading (160 kn) Simulation Driven Innovation 5

6 Step 3: Overall topology optimization in Altair OptiStruct For topology optimization density method is used. In this method the material density of each element is directly used as the design variable, and varies continuously between 0 and 1; these represent the state of void and solid, respectively. For achieving certain objective function while observing the design constraints. Some examples for the possible objective function are min. compliance, max resonance frequency, least fluid resistance etc. The min. weighted compliance was the objective function for the optimization. The constrain is to reduce mass. The commercially available software package used to perform topology optimization with relative ease, is Altair Optistruct. Firstly, the side cast bracket is finely meshed as in case of the topology optimization the solver cannot move the grid points in the model but can assign the different densities to the model. Design Variables: Element density Constraints: Mass of design space < 50 % Objective: Min (weighted compliance =1.0 x load case x load case 2) Manufacturing & Packing constraint: Material distribution cast single die. Figure 6: Displacement Plots after P2 loading (160 kn) Linear Static Analysis of Manufacturable design The obtained Manufacturable design model is analyzed by linear static analysis solver and the results obtained will be compared with the base line design the compared results are as follows Simulation Driven Innovation 6

7 Linear Static Analysis TABLE III LINEAR ANALYSIS: DISPLACEMENT SUMMERY Load P1 Load P2 Load Displacement fraction compared with rough solid model The comparison of von Mises stress that of rough solid model and manufacturable design is shown below Shape optimization TABLE III LINEAR ANALYSIS: STRESS SUMMERY % deviation 80kN 160kN FUPD Tube 2 5 Side cast bracket Shape optimization is part of the field of optimal control theory. The typical problem is to find the shape, which is optimal in that it minimizes a certain cost functional while satisfying given constraints. In many cases, the functional being solved depends on the solution of a given partial differential equation defined on the variable domain. Topology optimization is, in addition, concerned with the number of connected components/boundaries belonging to the domain. Such methods are needed since typically shape optimization methods work in a subset of allowable shapes, which have fixed topological properties, such as having a fixed number of holes in them. Topological optimization techniques can then help work around the limitations of pure shape optimization. Simulation Driven Innovation 7

8 Figure 6: Final optimized shapes Nonlinear analysis of final shape optimized design To verify that the final design obtained is up to the mark, so that the non-linear analysis is performed to evaluate the displacements as well as the plastic strains. Since maximum stress did not change, there was no need for modifying the third design to get the required strength. The final shape of the side cast bracket is shown in Figure. The new set of loads obtained at the previous step, is used to analyze the stress levels, thus reliability, in the component as the last step. If the stress levels are not acceptable, then, partial topology and partial shape optimization can be performed until the calculated reliability of the component meets the required reliability. Non-linear Static Analysis- Displacement Summary TABLE IV NON-LINEAR ANALYSIS: DISPLACEMENT SUMMERY Load Displacement (% ) P P Simulation Driven Innovation 8

9 Equivalent Plastic strain Summary TABLE V NON-LINEAR ANALYSIS: EQUIVALENT PLASTIC STRAIN SUMMARY Load Case Min factor of safety (%) FUPD Side Cast Bracket Support Clamp Bracket Frame rail P P Conclusion: Attempt is made to study Optimization of a FUPD under load cases as per ECE-93 standard using topology and shape optimization. Following are the conclusions drawn from analysis, 1. The loads are applied as per ECE-93 standard. 2. Further, these loads are used in FE analysis of FUPD structure and stresses are found out for each load i.e. P1 and P2, results shows maximum stresses are found near holes and corners but are within limits. 3. The optimized FUPD holding bracket is manufacturable and the shape will not interfere with the operation of other nearby components. 4. All the steps of the optimization methodology are described clearly. This methodology can be used to optimize any structure. The Side cast bracket is optimized to show application of this methodology. 5. The topology optimization and shape optimization are advanced function of Altair OptiStruct both are reviewed and explained in detail to empower design/analysis specialist with these very useful tools to optimize any geometry. Future plan: Next step for optimization will be integrating Equivalent static load method (ESLM), RADIOSS non-linear and Altair Optistruct; to perform optimization efficiently for complex loading events. ACKNOWLEDGEMENTS The author would like to thank the following for their valuable technical inputs 1. Jaideep Bhat, Sr. Manager, Frame & Suspension Systems CAE, Navistar Inc., USA. 2. Deepak Nidgalkar, Group Head- CAE, Mahindra Engineering Service Ltd. The authors would also like to thank Mahindra Engineering Services Ltd. for sponsoring this project. Simulation Driven Innovation 9

10 REFERENCES [1] Caner Demirdogen.Weight Optimized design of a front suspension component for commercial heavy truck Technical report, SAE Documents [2] Basavaraju Raju. Numerical and experimental verification of optimum design obtained from topology optimization Technical report, SAE Documents [3] Masatoshi Shimoda Non-parametric shape optimization method for rigidity design of automotive sheet metal structures Technical report, SAE Documents [4] L.S. Rajaram, Optimization of Caliper housing using FEM Technical report, SAE Documents [5] Danial Blower Analysis of Truck- light weight vehicle crash data for truck aggressivity reduction Technical report, SAE Documents [6] Ccline Adalian Improvement of car-to-truck compatibility in head-on collisions Technical report, SAE Documents 98-S4-O-12. [7] Dinesh Redkar Non Linear Analysis of Farm Tractor Front axle uses Abaqus/CAE Technical report Mahindra & Mahindra ltd Tractor division. [8] Lance Proctor Shape optimization in MSC/NASTRAN and MSC/PATRAN Sr. Technical Representative The MacNeal-Schwendler Corporation Grapevine, Texas Simulation Driven Innovation 10