Validation Report: Additional Data Mapping to help. Moldflow® Structural Alliance 2012 Validation

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  • Autodesk Moldflow Structural Alliance 2012

    Validation Report: Additional Data Mapping to Structural Analysis Packages

    Mapping process-induced stress data from Autodesk Moldflow Insight Dual Domain and 3D meshes to a structural analysis mesh

    Mapping coefficients of thermal expansion from Autodesk Moldflow Insight and Autodesk Moldflow Adviser Dual Domain and 3D meshes to a structural analysis mesh

    Workflow and settings Comparison validation of warpage prediction

    and thermal stress analysis with DS Simulia Abaqus

    Comparison validation of warpage prediction with Autodesk Simulation Multiphysics after mapping

  • VALIDATION REPORT: ADDITIONAL DATA MAPPING TO STRUCTURAL ANALYSIS PACKAGES

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    Contents Introduction ....................................................................................................................... 3

    Background....................................................................................................................... 3

    Different mesh focus ..................................................................................................... 3

    Mapping strategy .......................................................................................................... 4

    Workflow and Settings ..................................................................................................... 5

    Workflow ....................................................................................................................... 5

    Autodesk Moldflow Structural Alliance with DS Simulia Abaqus 6.9 and 6.10 .............. 7

    Create Anchor Points for Warpage Analysis............................................................. 7

    Autodesk Moldflow Structural Alliance built-in Export Wizard ................................... 8

    Autodesk Moldflow Structural Alliance built-in Import Wizard ................................. 10

    Autodesk Moldflow Structural Alliance with Autodesk Simulation Multiphysics and Simulation Mechanical ................................................................................................ 11

    Create Anchor Points for Warp Analysis ................................................................ 12

    Plastic Material Selection ....................................................................................... 13

    Export to Autodesk Moldflow .................................................................................. 14

    Validation Examples ....................................................................................................... 14

    Process-induced stress mapping validation ................................................................ 14

    Validation with DS Simulia Abaqus ......................................................................... 15

    Validation with Autodesk Simulation Multiphysics .................................................. 21

    Conclusion .............................................................................................................. 23

    Mapping validation for Coefficients of Thermal Expansion (CTE) ............................... 23

    Validation with DS Simulia Abaqus ......................................................................... 23

  • VALIDATION REPORT: ADDITIONAL DATA MAPPING TO STRUCTURAL ANALYSIS PACKAGES

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    Introduction The Autodesk Moldflow Structural Alliance 2012 release supports additional important data sets which can be mapped to a structural analysis mesh, to enable a structural analysis package to predict injection molding process-induced deformation, such as warpage, final residual stress within the molded plastic part; and thermal stresses based on the correct property data predicted by Autodesk Moldflow Adviser and Autodesk Moldflow Insight.

    In-cavity residual stress for Dual Domain mesh models and initial stress for 3D mesh models are among these new data sets which can be mapped to a structural analysis mesh. These process-induced stresses are the driving factor for plastic part warpage after ejection. The stresses will find a new equilibrium state in an unconstrained condition and become part of the final stress remaining in a molded plastic part, which can be calculated in a structural analysis.

    Coefficient of thermal expansion (CTE) data is another new data set which can be mapped to a structural analysis mesh. This data mapping enables a structural analysis to account correctly for a distributed CTE due to fiber orientation of a fiber-filled material across a molded plastic part. (Future work is planned to handle distributed CTE due to crystalline morphology of a semi-crystalline material.)

    Although the process-induced stress data sets are always essential to both non-fiber-filled and fiber-filled materials for a warpage prediction and a further stress analysis in a structural analysis package, the CTE data are mainly for injection molded fiber-filled composites in which the CTE tensor is distributed non-uniformly across the molded part due to fiber orientation. When even a single set of anisotropic CTE data is measured and introduced for a non-fiber-filled material, the first principal direction is changing during the polymer melt flow before it solidifies due to cooling from mold halves. These CTE data, coupled with the mechanical properties of the molded part, are used to calculate the in-cavity residual stress or initial stress (depending on mesh type) induced by the molding process.

    The mechanical properties have been mapped in previous releases of Autodesk Moldflow Structural Alliance software. Now the mechanical properties will be coupled with process-induced stress and/or CTE data in a structural analysis. In this release, the mapping of these additional data sets is implemented according to the same approach, which will be explained in the next section, with some consideration of various tensor conventions in different structural analysis packages.

    Background Different mesh focus In order to catch the high gradient changes across the part thickness in a flow analysis of the injection molding process, multiple layers are used in Autodesk Moldflows mesh models, as shown in Figure 1. A midplane triangular element is similar to a 3-node shell element with thickness as a geometric property, whereas a Dual Domain mesh is characterized with two matching triangular elements on the top and bottom surfaces with multiple layers in between. In a symmetric cooling condition, the number of layers is reduced to half for more efficient calculation.

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    Even with a 3D solid mesh, the number of layers of tetrahedral elements across the thickness should be controlled; six layers are used by default, whereas for fiber orientation calculation, it is suggested to double the default number of layers in order to catch the profiled fiber tensor changes.

    Figure 1. Autodesk Moldflows midplane and Dual Domain triangular element with multiple layers (left), and default number of layers of tetrahedral elements in a solid 3D mesh (right).

    These mesh models can be and have been directly passed to structural analysis packages in the past, but they triggered many warning messages indicating that the element aspect ratios were too high and they were not suitable for accurate structural analysis. On the other hand, major structural analysis packages have many high-order and multi-layered element types that are capable of handling profiled variables within each element, as shown in Figure 2. Their element types are developed for different purposes, and the number of element types grows with required research in the finite element method. However, a common requirement for most structural analysis element types is that the aspect ratio needs to be kept low.

    Figure 2. Element types of typical structural analysis that require low aspect ratio.

    Mapping strategy The difficulty in interfacing between Autodesk Moldflow analyses and all of these structural packages was to keep up with all these element types without violating their basic aspect ratio requirement for accuracy. A clear strategy would be mapping the distributed values from one type of mesh to another. However, what could be a generic approach that fits most of the element types?

    In reviewing these element types, it is found that most of the element types have integration points inside their element domain, as illustrated in Figure 3. These are Gauss integration points used for increasing the accuracy by capturing the distribution within the element domain. In order to develop a generic approach suitable for most the structural analysis packages without going into the details of each element type, the method selected was to map the required values to these integration points of a target mesh.

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    Figure 3. Gauss integration points in a hex element of a structural analysis.

    Having this mapping strategy, the remaining work is to calculate all of these distributed data, which are mostly tensor data, at those Gauss integration points. However, most structural analysis packages do not take input at Gauss integration points, and even if a special arrangement can be made for taking these data from input files, the amount of data would be huge. Therefore this mapping strategy needs to be coupled with an Application Programming Interface (API) in order to achieve seamless and smooth data transfer. This API has been implemented as a dynamic linking library, that is, the Autodesk Moldflow Structural Alliance package, which can be connect