The Application of ABAQUS for CATIA V5 for Analyses in the Pre-Design and Design Phase

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1 The Application of ABAQUS for CATIA V5 for Analyses in the Pre-Design and Design Phase Fabien Debarle PSA Peugeot Citroën - 18 rue des Fauvelles La Garenne Colombes - France Mathieu Durix Digital Product Simulation - 2/4, rue Hans List Croissy sur Seine - France Abstract: In the automotive industry, engineers need to explore a wide range of solutions depending on many parameters and constraints. Therefore, they need to perform nonlinear analysis based on a parameterized CAD model linked to a 3D PLM tool. ABAQUS for CATIA V5 (AFC) helps to perform this type of analysis relatively easily and early in the product lifecycle. Including nonlinear ABAQUS analysis in the pre-design phase improves the effectiveness of the design and enables rapid design iterations at an early stage, where they are least expensive. Iterations are performed from a fully parameterized CAD model which integrates different design architectures. The analyses in the CATIA V5 tree are generated automatically in AFC thanks to Knowledgeware and Visual Basic for Application (VBA). The pre-design results are provided to a design group as one of the criteria for creating the final design. Once the final design is done, AFC coupled to VBA and publications give us the opportunity to perform all the linear and non linear analyses very easily. PSA Peugeot Citroën is a member of the AFC Customer Review Team, a consortium of six companies that are helping to define the product vision and requirements. In this context PSA Peugeot Citroën asked for API openings and knowledge in AFC to be able to perform this kind of approach. This paper presents one of the models on which we use VB scripting. Keywords: Design and pre-design phase, Plasticity, Bolt Loading, Post-processing, Assembly Deformation. 1. Introduction In the automotive industry, it is necessary to perform nonlinear Finite Element Analysis (FEA) based on CAD models created in a 3D Product Lifecycle Management (PLM) tool, such as CATIA V5, early in the product lifecycle. These CAD models are often parameterized so that they can be modified easily to accommodate model changes from a number of sources. For example, we want to perform several analyses of different candidate CAD solutions in the pre ABAQUS Users Conference 161

2 design phase to determine the appropriate CAD model to recommend to the design group for further refinement as part of the overall chassis design. At this early stage in the product lifecycle, the model geometry is based on an initial design that is fully parameterized. The initial design necessarily uses a simplified geometry, because the values of many parameters are not yet known. The goal of FEA in the pre-design phase is to define a model that meets several stress, strain, displacement, and fatigue requirements in pre-determined critical regions of the model. The model presented here (see Figure 1), the knuckle assembly, is a part of the chassis. Performing FEA on the final or nearly final design can be a difficult and extensive process. Consequently, such results on the full model sometimes are obtained only in the later stages of the product lifecycle. In the pre-design phase valuable results can be obtained based on the simplified model geometry. The results from pre-design analysis enable design engineers to propose necessary design modifications at the time when changes are least expensive and most effective. Previous studies have compared the analysis inaccuracies between these simplified models and their corresponding complete models, and the inaccuracies have been determined to be acceptable. To perform these analyses, we developed a workbench in CATIA V5 from which we have access to the parameterized CAD model. At any time, we can choose to switch from one architecture to another: for example, we can switch from a knuckle assembly with a clamp piece to a knuckle assembly without a clamp piece (see Figure 2). We simulate the performance of the knuckle under bolt preloading and service loading conditions. Our goal is to determine the values and locations of the maximum stresses and strains. Once we have obtained these results for a given pre-design model, we can analyze the results and modify the design to implement possible improvements. The mechanical analysis is initialized using ABAQUS for CATIA V5. 2. Knuckle assembly workbench As explained previously, we developed a specific workbench in CATIA V5 dedicated to the knuckle assembly. It makes extensive use of Knowledgeware and Visual Basic (VB) scripting. All of the Graphical User Interfaces (GUIs), are specified by PSA Peugeot Citroën (see an example Figure 3). Thanks to this approach, the workbench is usable by any design engineer. In the knuckle assembly workbench, the design engineer defines the following: - the CAD architecture and the geometric parameters - the material properties - the mesh sizes - the boundary conditions - the load cases (static analysis, modal analysis, ) ABAQUS Users Conference

3 Once the FEA model is defined completely, the input files are generated and submitted from the knuckle assembly workbench onto ABAQUS remote servers. 3. CAD model In the pre-design phase, the parameterized CAD model is geometrically simplified but still physically representative of the actual knuckle assembly. The model is defined in CATIA V5 using the Part Design, Assembly Design, and Knowledgeware workbenches. For example, the knuckle with a clamp piece is an assembly of seven parts, as shown in Figure 4: - The knuckle - The shock damper - The clamp piece - Two nuts - Two bolts The most influential parameters have been identified previously through numerical simulations. The CAD model is built so that these parameters can be modified easily as the design changes. 4. Material properties The material properties can be specified in a GUI or imported from a file written in an ABAQUS format. 5. Meshing The user provides some information about the desired mesh size, and then the mesh is generated automatically in the background in the Advanced Meshing Tools workbench (FMS/FMD) in CATIA V5 in two steps: - First, a surface mesh is created using a local mapped mesh and local element size at the surface using the FMS module. - Next, tetrahedron filler meshing is performed using the FMD module to generate the actual parabolic tetrahedral elements (C3D10M) needed for the structural analysis. We use a surface mesh and tetrahedron filler, because this approach enables control of surface mesh quality and limits the total number of elements in the model. The mesh specifications are associated with geometric entities of the CAD model. The mesh specifications persist even as the geometry is modified so that the mesh is rebuilt automatically after any modifications ABAQUS Users Conference 163

4 6. Preprocessing using ABAQUS for CATIA V5 We use ABAQUS for CATIA V5 (AFC) to generate the mechanical analysis properties and simulation history, including the following: - Nonlinear materials - Bolt tightening connections between the knuckle and the clamp piece - Contact between the knuckle, the clamp piece, the bolts, and the shock damper - Boundary conditions (see Figure 5) - Load cases imported from an existing file that comes from a separate program The order of steps for the mechanical simulation history is as follows: Step 1: Contact initialization and bolt tightening between the knuckle and the clamp piece Step 2: Bolt tightening fixed Step 3: Service loading Step 4: Service loading Step 5: We are able to generate the input files with much of the necessary analysis data. Because some additional features are necessary to completely define the analysis model, we extend the ABAQUS input file using VB scripting to complete the analysis model. For example, because we need to perform several separate analyses, we split the input file generated by AFC into several input files into which we add the *RESTART,READ command (see Figure 6). Thanks to this approach, we do not need to perform the initialization steps for each service loading analyses. 7. FE Analysis Because we are running ABAQUS/Standard on remote servers, the job submission is done automatically via LSF software that we interfaced with AFC. 8. Postprocessing using ABAQUS for CATIA V5 As noted in the introduction section, the goal of this analysis is to determine whether the knuckle assembly model has, for example, areas of excessive stress and plastic strain. Postprocessing is performed in AFC (viewing the minimum and maximum principal stresses, Von Mises stresses, PEEQ, ; see Figure 7) ABAQUS Users Conference

5 The maximum stresses often occur on the surfaces. The stress and strain results are calculated by ABAQUS at the integration points of solid elements. These integration points are only a small distance from the surface. In areas of high stress gradients, extrapolating the integration point results to the surface nodes indicates results that are inaccurate. One of the most effective ways of determining the surface results is to use surface skinning, a thin layer of membrane elements positioned at the surface of a solid body. The strains in this membrane correspond to the strains experienced at the surface in the solid model. Surface skinning is not yet available in AFC with M3D6 elements, so this postprocessing technique is performed using a separate program. 9. Results and parameter modifications All of the results can be used to classify the parameter sets tested as either acceptable or unacceptable. Because of this procedure, we can determine an acceptable design of the knuckle assembly that responds to all of the modeling constraints very early in the product lifecycle. When the analysis results for the initial design show excessive strains for example in a critical area, we can modify geometric parameters in the CATIA V5 PLM model in an effort to improve the design. Because of the associativity between the CAD model and the analysis model, we are able to perform modeling and analysis iterations with minimal additional effort. 10. Analyses in the design phase Up to this point, we discussed only simplified and parameterized CAD models used to perform analyses in the pre-design phase. In the design phase, we need to perform the same analyses that were performed in the pre-design phase but on a final design. Switching from a simplified predesign model to a more complicated final design is made possible in the knuckle assembly workbench thanks to CATIA publications. We only need to assign all of the needed publications to geometric parts of the model (for example, a face used in a contact definition). A specific GUI in the knuckle assembly workbench enables us to switch easily from a pre-design model to a final design. It takes just a few minutes to replace the simplified CAD model with a final design CAD model. Mesh specifications have to be made, and then all the ABAQUS input files can be generated automatically and submitted on the remote servers. 11. Conclusions We can state that ABAQUS for CATIA V5 is very useful for performing advanced nonlinear analyses based on a parameterized CATIA V5 CAD model or on a final design (coming from CATIA V4 or V5). While some of the features needed to perform the simulation completely within AFC are not yet available, we are able to define a full analysis model using AFC coupled to few additional developments ABAQUS Users Conference 165

6 The value in this approach is that everything defined within AFC maintains associativity with the CAD model and is updated automatically after any design modifications. Consequently : - We are able to evaluate the knuckle assembly design based on pre-determined critical parameters and perform several design modifications and subsequent ABAQUS analyses to determine an acceptable design. - We are able to evaluate the knuckle assembly design by performing several analyses on a final design in a very easy and fast way (more than 30 different analyses may be necessary to evaluate the knuckle assembly). AFC enables design engineers to explore a wide range of solutions easily and early in the product lifecycle, and also to evaluate a final design later in the product lifecycle. 12. Figures Figure 1 Origin of the studied geometry ABAQUS Users Conference

7 Clamp piece Figure 2. a. Knuckle with a clamp piece b. Knuckle without a clamp piece Figure 3. Example of graphic user interface specified by PSA Peugeot Citroën 2006 ABAQUS Users Conference 167

8 Shock damper body Clamp piece Knuckle Figure 4. CAD model assembly. Kinematic and distributing couplings Forces Clamp Forces Figure 5. Boundary conditions ABAQUS Users Conference

9 ABAQUS for CATIA Step 1: Contact initialization and bolt tightening Step 2: Bolt tightening fixed Step 3: Service loading Step 4: Service loading Step 5: SPLIT + MODIFICATIONS *RESTART,WRITE Step 1: Contact initialization and bolt tightening Step 2: Bolt tightening fixed *RESTART,READ,STEP=2 Step 3: Service loading *RESTART,READ,STEP=2 Step 4: Service loading *RESTART,READ,STEP=2 Step 5: Service loading Figure 6 : Example of modifications on the input file using VBA Figure 7. Sample of analysis results 2006 ABAQUS Users Conference 169