22nd CAD-FEM Users Meeting 2004 International Congress on FEM Technology with ANSYS CFX & ICEM CFD Conference November 10-12, 2004, International Congress Center Dresden, Germany 1

2.5.15

ESAComp and FE Software Integration

Harri Katajisto, Markku Palanter

Componeering Inc., Helsinki, Finland

Summary

ESAComp is software for analysis and design of laminated composite structures. In the design process of composite structures, it is used together with general purpose finite element software. ESAComp provides tools for the conceptual and preliminary design of structures, as well as for detailed post processing of FE results. Two-way interfaces between ESAComp and FE tools make the data transfer fluent. Supported FE packages include ABAQUS, ANSYS, I-DEAS, MSC.Nastran/Patran and EMRC/NISA. Current work focuses on further integration with ANSYS and MSC.Nastran/Patran.

Keywords

composite material, laminate, finite element analysis, ESAComp, ANSYS, MSC.Patran, MSC.Nastran

1. Using ESAComp with FE Software

Conceptual and preliminary design of layered composite structures are among the main application areas of the ESAComp software [1,2]. Export interfaces have been developed to allow easy and error free transfer of material data and laminate lay-ups into finite element software tools used in structural and thermal analyses. In the post processing of FE results, the detailed laminate analysis and result visualization capabilities of ESAComp are indispensable. The FE import interfaces of ESAComp facilitate this phase. First the integration between ESAComp and FE software was realized purely using standard text input and output formats of the supported FE tools. In this approach, the FE program and ESAComp are used as separate applications. The currently supported FE packages include ABAQUS, ANSYS, I-DEAS, MSC.Nastran (and other compatible NASTRAN releases) and EMRC/NISA. Two-way data exchange is provided for all these FE tools (currently export only for NISA). The FE export interface allows transferring ESAComp laminate definitions together with the associated material data into the FE program. ESAComp supports the layered shell element types of the FE programs. For some FE packages there is also the possibility to use a general shell element. In this case, ESAComp exports the laminate stiffness matrices instead of the material data and lay-up. Material data can also be exported for solid elements. (Figure 1) The FE import interface facilitates detailed post processing of FEA results in ESAComp. ESAComp reads output files created by the supported FE packages. The data imported into ESAComp are resultant forces and moments or corresponding strain state of a shell element. The user selects from ESAComp the laminate structure that corresponds to the results. A failure analysis can be performed

22nd CAD-FEM Users Meeting 2004 International Congress on FEM Technology with ANSYS CFX & ICEM CFD Conference November 10-12, 2004, International Congress Center Dresden, Germany 2

for the whole set of imported data to identify the criticality of the data points (element, integration point or node), their potential failure modes and critical layers. For a single data point selected from the set, a load response or failure analysis can be performed to see the layer level response. (Figure 2) Figure 1. ESAComp FE export interface: export main dialog (ABAQUS), parameters window for selected element type (ANSYS SHELL 181), and FE input file generated by ESAComp (MSC.Nastran PCOMP). Figure 2. ESAComp FE import interface: FPF failure analysis results for a set of imported FE data and through-the-thickness stress distribution for a selected element.

22nd CAD-FEM Users Meeting 2004 International Congress on FEM Technology with ANSYS CFX & ICEM CFD Conference November 10-12, 2004, International Congress Center Dresden, Germany 3

While the above described approach for interfacing FE packages is still feasible in many cases, the recent development work has focused on further integration of ESAComp with major FE tools. The interface with MSC.Patran Laminate Modeler already allows launching of ESAComp from the MSC.Patran user interface to perform detailed post processing. Similar capabilities for ANSYS have been realized on prototype level with further possibility to show results computed with ESAComp over the model geometry as contour plots. Compared to the earlier import interfaces, a major difference in these new interfaces is that material and laminate-lay-ups are also imported from FE software to ESAComp. Furthermore, the imported result data does not need to be associated with a single laminate lay-up. Hence, post processing of a complex model in one ESAComp analysis run becomes possible.

2. Interfacing with ANSYS

ANSYS is widely used in FE analyses of composite structures. ANSYS Parametric Design Language (APDL) provides means to build FE models in an effective way. A model written with APDL can be easily modified and fast what-if studies can be performed. ESAComp supports the creation of ANSYS models with the export of material data and laminate lay-ups for solid (SOLID 46 and 64) and shell elements (SHELL 91, 99 and 181). When dealing with composite structures, post processing is often the biggest challenge of the FE analysis. With the standard ANSYS composites capabilities extraction of failure analysis results is tedious and the results available are inadequate for demanding projects. The shortcomings can be overcome by using ESAComp for performing the detailed laminate analysis based on shell element forces and moments computed by ANSYS. The standard ANSYS to ESAComp interface allows post processing of shell model results using ESAComp analyses. The post processed results are displayed in ESAComp as layer charts and numeric tables. Since no material or laminate lay-up data is imported from ANSYS, the user must associate the result data with corresponding laminate in ESAComp.

2.1 Enhanced ANSYS Interface The so-called enhanced ANSYS interface automates the data transfer between the two software packages. The enhanced interface makes it possible to transfer material data, laminate lay-ups and results from ANSYS to ESAComp. Furthermore, the failure results computed by ESAComp can be returned to ANSYS to be displayed as contour plots. These capabilities can be accessed directly from the ANSYS user interface. In the current implementation, it is necessary to go to the ESAComp user interface only for viewing through-the-thickness layer charts and to set some option settings. The interface has been developed by Componeering Inc. in collaboration with DYNE Design Engineering GmbH (CH). The interface module will be commercially available by the end of 2004. A flow chart illustrating the enhanced ANSYS interface is presented in Figure 3. ESAComp can be used interactively as a design and analysis tool, especially in the preliminary design phase, and purely as a post processing code that runs in batch mode in the background. The enhanced interface is used through ANSYS command prompt by two commands. The ansystoesa command executes an APDL macro that gets all material values, section types with associated section data, and shell element resultants of the model. Laminate section types and results are linked to the corresponding element and stored in a file. Section data are stored in a separate file. It includes section type identifications and lay-up definitions: layer thicknesses and orientations, and material identifications. Material values are stored in a third file. These files are used as an input for ESAComp failure analysis that is run in batch mode. The APDL macro further reads the analysis results into ANSYS.

22nd CAD-FEM Users Meeting 2004 International Congress on FEM Technology with ANSYS CFX & ICEM CFD Conference November 10-12, 2004, International Congress Center Dresden, Germany 4

FE Pre processor FE Solve FE Post processor

ESAComp

ANSYS

Material selection, Preliminary design

Use ansystoesacommand to: write text file containing

all:- materials- laminates- N11, N22 and N12- M11, M22 and M12- Q13 and Q23

launch ESAComp

write text file containing:

- laminate definitions

- material data- options related to

FEA

write text file containing:

- 1/RF- failure

modes- critical

layers

Failure analysis (FPF, wrinkling, ILS,) in batch mode with user default analysis options

Use esaplotcommand to : create 1/RF

contour plots with

- failure modes

- critical layers

Figure 3. Enhanced ANSYS interface flow chart. The esaplot command executes an APDL macro that creates laminate level failure result contours based on ESAComp results. Inverse reserve factor, 1/RF, is used for indicating the criticality of the load case in each element. 1/RF is equivalent to the max strain/stress failure criteria values or Tsai-Wu strength ratio in ANSYS. Besides layer FPF failure, ESAComp results may contain information on failure modes like wrinkling, core shear, and interlaminar shear (ILS) failure. In addition to 1/RF contours, failure mode and critical layer of the element can be displayed. The enhanced interface supports shell 181 elements. Supported material models/types are orthotropic reinforced ply, isotropic homogeneous core, and orthotropic honeycomb core. Possible shell node offsets in the FE model are taken into account. ESAComp analysis options, such as the failure criterion to be applied, are set in ESAComp and saved as user options. The application of the enhanced ANSYS interface is illustrated with a design project by Componeering Inc. for a Finnish customer, ADR-Haanp chemicals hauling company. The ANSYS FE model of a glass fiber reinforced (GFRP) trailer tank is presented in Figure 4. The model has been constructed using shell 181 elements. The model includes fifteen laminate section types. Eight different load cases had to be studied. Several design and analysis cycles were required before achieving a satisfactory structure. 1/RF contours of the GFRP tank are presented in Figure 5 corresponding a case where the 30 m2 tank is filled with a substance having specific gravity of 2 kg/dm3. Figure 6 illustrates the tank end area. Element section types, 1/RF contours, failure modes, and critical layers are shown.

22nd CAD-FEM Users Meeting 2004 International Congress on FEM Technology with ANSYS CFX & ICEM CFD Conference November 10-12, 2004, International Congress Center Dresden, Germany 5

Figure 4. A trailer tank made of steel and an FE model of the GFRP counterpart under development. (Photo courtesy of ADR-Haanp Oy)

Figure 5. ESAComp failure analysis results (1/RF) of the GFRP trailer tank shown as ANSYS contour plot.

22nd CAD-FEM Users Meeting 2004 International Congress on FEM Technology with ANSYS CFX & ICEM CFD Conference November 10-12, 2004, International Congress Center Dresden, Germany 6

Figure 6. Detailed post processing for a part of the FE model. Failure modes and critical layers determined by ESAComp are shown as ANSYS plots.

3. Interfacing with MSC.Patran/Nastran

ESAComp includes a two-way interface for MSC.Software products through MSC.Patran. A direct interface for MSC.Nastran is also available.

3.1 MSC.Patran Laminate Modeler The ESACompMSC.Patran interface has been developed jointly with MSC.Software. It is available in the software versions ESAComp 3.0 / MSC.Patran 2003 and newer. The interface is in MSC.Patran under the Laminate Modeler module. However, export to ESAComp does not require use of the ply based modeling concept offered by Laminate Modeler. Element level results from any model having layered shell elements (defined with PCOMP in MSC.Nastran) can be exported to ESAComp for post processing. In ESAComp, the MSC.Patran interface is licensed as an add-on module. In practice, the interface works as follows. After solving the model, elements to be studied are selected using the MSC.Patran user interface. Export to ESAComp is selected from the Laminate Modeler menus and ESAComp is launched by MSC.Patran. Besides the forces and moments of the selected elements, the laminate lay-ups and associated material data are automatically transferred to ESAComp. Post processing is performed in ESAComp as with the standard interfaces. (Figure 7) The interface capabilities will be enhanced to allow transfer of ESAComp results back to MSC.Patran to be displayed as contour plots in a similar way as described in the previous section for ANSYS.

22nd CAD-FEM Users Meeting 2004 International Congress on FEM Technology with ANSYS CFX & ICEM CFD Conference November 10-12, 2004, International Congress Center Dresden, Germany 7

Figure 7. MSC.Patran Laminate Modeler to ESAComp interface.

3.2 MSC.Nastran

Laminate export from ESAComp to MSC.Nastran provides the alternatives of using layered definition (PCOMP) or general shell definition (PSHELL) in which case ESAComp computes the stiffness matrices. In the latter option, the advanced method used in ESAComp for the plate transverse shear stiffness computation can be utilized [3]. The current implementation of the MSC.Nastran to ESAComp interface uses the punch file. This approach has many disadvantages. Therefore, support for the OP2 file will be realized in ESAComp.

3.3 Global Ply ID

Real composite structures have varying laminate lay-ups and thicknesses, reinforcement patches and layer drop-offs. A consecutive through-the-thickness layer numbering at one point is not compatible with another point. To overcome this problem, global ply ids are used for referring to the physical plies of the structure. The ply based modeling approach of MSC.Patran Laminate Modeler uses inherently global ply ids. Recently the possibility for using global ply id has also been introduced in MSC.Nastran in the form of PCOMPG layered shell definition. The global ply id concept will be introduced in ESAComp to allow transfer of ply id information both ways through the interfaces with MSC.Patran and MSC.Nastran. On the level of ESAComp, the global ply id will be an alternative representation for the consecutive layer numbering. Hence, in an ESAComp layer chart showing laminate through-the-thickness distributions of stresses/strains/etc. the layers can be identified with global ply ids. Similarly, the critical layers indicated by a failure analysis can be given in terms of global ply ids.

4. General Improvements in ESAComp FE Post Processing

The global ply id concept mentioned in the previous section is not restricted to use with MSC.Software products. The ESAComp implementation will be on general level and thus allows the use of this

22nd CAD-FEM Users Meeting 2004 International Congress on FEM Technology with ANSYS CFX & ICEM CFD Conference November 10-12, 2004, International Congress Center Dresden, Germany 8

feature with other FE products when such modeling approach is introduced in them. Some modification of the ESAComp import interface for the particular program is naturally needed to take advantage of this feature. Another general improvement planned for ESAComp FE post processing is introduced in the following.

4.1 Automatic Recognition of Imported Materials

ESAComp ply material description includes plenty of composites specific data whereas the material descriptions of FE programs are typically limited to mechanical properties that are necessary in the model solving and in the limited composites post processing. The new advanced interfaces for MSC.Patran and ANSYS that allow import of material data together with FEA results introduce a problem in this respect. To perform post processing properly, ESAComp needs information on the type of material (reinforced, homogeneous core, honeycomb core,) and the form of reinforcement (unidirectional, other). For instance, if the imported sandwich construction is interpreted as solid laminate, no wrinkling analysis will be performed. While the material descriptions of FE codes may be expanded with user/application specific data, it cannot be expected that the material data has always been exported from ESAComp to the FE code. Post processing with ESAComp should be possible also in such cases. The simplest approach is that the user manually completes the material data after it has been imported to ESAComp. This is time consuming and does not allow automated post processing as ESAComp batch runs. Therefore, some heuristic rules will be introduced so that ESAComp can automatically recognize imported materials. Another approach that will be introduced later on is based on matching of imported materials with material data already stored in ESAComp. The name of the material can be used for this purpose, but for added confidence equivalence of the mechanical data can be checked as well. When the imported material is replaced with material specified in ESAComp, all composites specific data becomes available in the further analyses.

5. Future Work

The future work related to ESAComp-FE integration can be summarized as follows: Finalization and release of the enhanced ANSYS interface. ESAComp can be run in batch mode

using ANSYS APDL macros and results can be shown as ANSYS contour plots. Text labels can be shown in the contour plots to indicate failure modes and critical layers.

Extension of the MSC.Patran Laminate Modeler interface to allow importing of ESAComp post processing results to MSC.Patran and displaying them as contour plots.

Improving the MSC.Nastran to ESAComp interface. Introduction of global ply id in ESAComp to support, for instance, MSC.Nastran/Patran. Recognition of material types (reinforced, homogeneous/honeycomb core, unidirectional) with

heuristic rules when importing data to ESAComp. Alternatively, replacing imported material with material specified in ESAComp.

Regarding support for additional FE software, it has been decided that an export interface for LS-DYNA will be developed in the near future.

References

[1] Palanter, M.: Specialized Software Tools for the Design of Composite Structures, Proceedings of the 20th CAD-FEM Users Meeting 2002, Friedrichshafen, October 9-11, 2002

[2] ESAComp web site: www.componeering.com/esacomp/ [3] Skytt, V. et al: Transverse Shear in Laminate Analyses, Proceedings of European

Conference on Spacecraft Structures, Materials & Mechanical Testing, Toulouse, December 11-13, 2002.