**[CAD/FEA Integration with STEP AP209 Technology and
Implementation]{.underline}**

Keith A. Hunten, P.E.

IPT Lead - Analysis Tools and Integration

Virtual Product Development Initiative

Lockheed Martin Tactical Aircraft Systems

[Introduction]{.underline}

The Design/Structural Analysis integration problem is typified by the
requirement to share geometric shape and analysis information in an
iterative environment. The integration is made more difficult when
composite structures become a part of the problem. Figure 1 illustrates
the interconnectivity that this paper addresses. Most production systems
currently employ specific point-to-point translators to enable this
process, and very few analysis systems are able to seamlessly return
geometric shape information to the design shape modeler. With composite
structures there are the additional problems of calculating true fiber
directions and ply flat patterns that are shared with the manufacturing
process. All of this information needs to be shared with commercial or
in-house detailed analysis codes such as those for fastened joints and
panel buckling.

![](media/image1.emf){width="3.4368055555555554in"
height="2.397222222222222in"}

Figure 1. Engineering design, analysis, and manufacturing information
interconnectivity.

In large scale industrial settings a standards-based solution to the
iterative design/analysis /manufacturing process is becoming an
imperative. Figure 2 illustrates the 'four-or-more' problem that is the
major drawback to the point translator approach. If a standard data
model (as in the right hand portion of figure 2) is used to provide
information integration there is a significant reduction in the number
of translators and in maintenance. In a large scale system such as that
represented in figure 6 there may well be dozens of applications that
are required to share information. The ISO 10303-209 STEP Application
Protocol (AP) Composite and Metallic Structural Analysis and Related
Design has been developed to address this approach to the
Design/Structural Analysis problem.

![](media/image2.emf){width="3.402083333333333in"
height="0.8902777777777777in"}

Figure 2. The 'four-or-more' problem.

[STEP Overview]{.underline}

ISO 10303 STEP ([ST]{.underline}andard for the [E]{.underline}xchange of
[P]{.underline}roduct Model Data) is the standard that provides a
complete, unambiguous, computer-interpretable definition of the physical
and functional characteristics of a product throughout its life cycle.
The standard has been created by a team of international experts from
disciplines such as aerospace, automotive, shipping, process plants,
CAD/CAE/CAM, academia, and government.

Figure 3 illustrates the various aspects of the STEP standard. The core
of the standard is a series of integrated data models that provide
resources for information such as product design, geometric and
topologic representation, and some specialized representations. These
data models are all written in EXPRESS, an implementation-independent
computer-sensible language that is also an ISO standard. There are then
Application Protocols (APs) that define application specific views of
the integrated resources in a clearly defined context. Some examples of
APs include AP202 Associative Draughting, AP203 Configuration Controlled
Design, and the subject of this paper, AP209 Composite and Metallic
Structural Analysis and Related Design. There are two implementation
methods defined within STEP, the first is a flat ASCII file (Physical
File), and the second a standardized application programming database
interface (STEP Data Access Interface (SDAI)). Finally, each AP has an
associated set of Conformance Testing documents to provide a method to
test and certify translators and interfaces.

![](media/image3.emf){width="5.990972222222222in"
height="3.4715277777777778in"}

Figure 3. The structure of the STEP standard.

The internal structure of an AP is illustrated in figure 4. The first
section of an AP describes what is in and out of scope for data
exchange. There is then an Application Activity Model (AAM) of the
process that the AP enables that is written in the IDEF0 modeling
language. The AAM is primarily used to set the context for the data
exchange and to provide a basis for data exchange requirements. The
Application Reference Model (ARM) is an information (data) model of all
of the information requirements of the AP defined in language that an
application expert would be familiar. The ARM is the part of an AP that
a reviewer or user would find most useful. Finally there is the
Application Interpreted Model (AIM) that is the result of the mapping of
the ARM requirements information model to the STEP integrated resources
information models. The AIM is written in EXPRESS and is useful only for
implementers. There are also definitions of conformance classes for
applications implementing the AP, and there are associated documents
that delineate the test cases/suites for certifying implementations.

![](media/image4.emf){width="5.995833333333334in"
height="3.5243055555555554in"}

Figure 4. The internal structure of an Application Protocol

[AP209 Scope]{.underline}

The scope of AP209 is illustrated in figure 5. A central theme to the
partitioning of information within AP209 is that there are separate
product definitions for the analysis and design disciplines. This
division is primarily a constraint from the Aerospace industry, however
similar requirements were noted from shipping, offshore, and automotive.
Both product definitions may be independently configuration controlled,
and many aspects of each are subject to approvals. Another crucial
concept is that the shape and analysis information is meant to be
implemented to enable bi-directional transfer to enable the feedback of
information in the iterative design/analysis environment.

The analysis discipline product definitions primarily concern finite
element models, analysis controls, and analysis outputs. Loads and
boundary conditions may be applied to either mesh or geometry. Linear
statics, modes, and frequency analysis types are supported. The scope of
the analysis options was decided upon merits of trading addressing all
analysis needs versus resources available to develop the standard.
Surveys showed that the scope selected typically will address 60 to 90
percent of the analysis needs of an enterprise. It should be noted that
AP209 was designed to be easily enhanced to support nonlinear analyses
with little or no disturbance to the existing data model. In fact
roughly 90 percent of the nonlinear problem is addressed at the present
time. The analysis report serves several purposes: first is to document
design and analysis decisions such as geometric and material
idealizations, and second to reference documents containing text and/or
graphical documentation of the model, analysis controls, and results.

The design discipline product definition is primarily concerned with
shape representation and assemblies thereof. The geometric shape
representations within AP209 are entirely interoperable with those in
AP203 that are currently being implemented by most CAD and CAE vendors.
There is one additional shape representation unique to AP209 that is
utilized to represent the shape of composite constituents such as plies
and sandwich cores.

The composite constituents contain geometric information, a variety of
laminate stacking tables definitions, and either an as-laid or as-draped
fiber orientation definition. Both part and zone ply table capabilities
are supported. Another important benefit of AP209 is the standardization
of an taxonomy of composite constituents. Definitions and illustrations
are given each of the constituents such as ply, core, and filament
laminate.

Material specifications and properties are represented both for
composite and homogeneous (metallic) materials. The specifications and
properties may be expressed either at the design level, or more
specialized analysis specifications and properties may be represented.

![](media/image5.emf){width="5.990972222222222in"
height="3.9090277777777778in"}

Figure 5. AP209 scope.

An important feature of AP209 is the sharing of information between the
design and analysis product definitions. The shape information is shared
at the lowest level allowing locations for nodes to be the same as
points defining curves, surfaces, and solids. Additional associativities
between nodes and elements may be forged to geometric aspects such as
curves and surfaces to facilitate processes such as mesh generation.
Both disciplines may also share composite constituents, material
properties, and material specifications. A final crucial concept is that
both disciplines share the same product structure definition capability.

[ISO Status of AP209]{.underline}

The AP209 standard passed the ISO Committee Draft (CD) international
ballot in October 1996 with thirteen of eighteen P-members voting.
Eleven countries agreed, and two disagreed. AP209 has also been part of
a focused effort to ensure the maximum degree of interoperability (data
sharing) between STEP APs. Issues regarding AP interoperability were
submitted as CD ballot comments. No substantial technical issues were
raised against the CD document, and resolution of all ballot comments is
complete. The AP209 document is currently being prepared for
distribution as a Draft International Standard (DIS), with a target
release date for international DIS balloting beginning in June 1997.

[Information Integration with AP209]{.underline}

The integration of tools (applications) in a large-scale system is
illustrated in figure 6. There are five major groups of applications
represented: CAD-based shape design, composite producibility and
optimization, analysis model creation and post-processing, a
configuration control and archival management system to enable the use
of many different Finite Element Analysis (FEA) tools, and detail
analysis tools such as the panel analysis applications illustrated.
AP209 technology is utilized throughout to provide bi-directional
sharing of information.

The CAD-based shape design tools today often have at least some level of
functionality of Finite Element Model (FEM) generation capability. The
use of AP209 provides a standardized format so that the mesh information
and any related geometric associativities created in the CAD tool may be
shared with each of the other processes in figure 6. The composite shape
and structure information may also be associated and shared. This
combination of associated shape, mesh, and composites information
enables applications such as automated composite analysis material
property generation for finite elements, that is a task previously
impossible without the information integration offered by AP209. A
typical automated property routine would loop though all composite plies
associated with an element and use the ply thickness, orientation, and
material property information to calculate elastic response matrices.

![](media/image6.emf){width="5.999305555555556in"
height="3.9291666666666667in"}

Figure 6. Large scale system integration with AP209.

Composites producability and optimization tools stand to benefit most
from AP209 technology as the ability for the tools to share ply shape
and structure table information in a standardized format has not been
available before. There are two paradigms for composite structure and
shape representation within AP209: ply by ply stacking to define the
entire part, and zones of constant laminates (either at a point or over
an area on a surface). A part may be described by both methods to
maximize flexibility in the composite product development process. An
example of the need for dual representation is designing and analyzing a
part by area zones, and then deriving the ply boundaries for
manufacturing, and then the flat patterns for a fabric cutting machine.

An area of information management that has long been neglected is the
configuration control and management of FEA. The combination of product
structure, work authorization, and configuration management data
structures in AP209 offer the capability to manage a wide variety of
CAD/CAE information. An application to manage and archive AP209
information provides the engineer with more options than may be
available with current generation point-tot-point translators. An
example of this utility would be SPAM ([S]{.underline}tiffened
[P]{.underline}anel [A]{.underline}nalysis [M]{.underline}odeler), that
was originally written to output ABAQUS information. Engineers at a
different corporate site wanted to use SPAM, but only had ANSYS
available. Conversion of SPAM to AP209 in combination with the
management and translation application would allow the use of the tool
with a wider variety of solvers without further modification of the
detail analysis tool providing a significant resource and maintenance
cost savings.

Having a standardized shape, analysis, and composites database enables
other processes than those that have been classically involved in the
Design/Analysis process. An example of this is composite failure
analyses that require analysis, shape, and detail analysis input to
perform the task.

![](media/image7.emf)

[Future Engineering Analysis Development]{.underline}

There is currently a new work item (NWI) being initiated in the ISO
Engineering Analysis (EA) committee to build upon AP209 to create a
suite of EA APs. An EA Core ARM is being developed that will unify
various analysis disciplines (figure 7). The requirements model in the
EA C-ARM will be completely mappable to that in AP209 assuring
interoperability with other disciplines. To date three other APs have
been scoped for implementation within the EA Suite. The first will be a
material services AP that will provide a standard to represent
properties and allowables for materials, adhesives, and standard
fasteners. A second AP will be created to represent structured and
unstructured finite difference aerodynamic and thermodynamic
information. The last AP will be created to represent information to
perform the electro-mechanical sub-systems integration and analysis
tasks such as control laws and state space analyses. The intent is to
provide an interoperating suite of EA APs that will share information in
a multi-disciplinary environment.

[AP209 Implementations]{.underline}

To date there have been three successful pilot implementations of AP209,
and two more are underway. The pilots completed to date were performed
by three teams of companies: one under the auspices of the PDES, Inc.
consortium, another under a contract from the US Airforce Manufacturing
Technologies Directoriate's PDES Application Protocol Suite for
Composites (PAS-C) program, and the third under contract from the US
Army Tank Command (TACOM). Subsequently two more efforts are underway: a
Phase two pilot under PDES, Inc., and the Defense Advance Research
Program Administration (DARPA) MADE (Manufacturing Development)
Integrated Product Data Environment (IPDE) program being worked at
Boeing. The successes of these pilots have proven the effectiveness and
accuracy of the AP209 data exchange standard.

![](media/image8.emf){width="5.997222222222222in"
height="4.435416666666667in"}

Figure 8. Shape representations from the TACOM AP209 pilot.

The initial PDES, Inc. FEA pilot team included participants from Boeing,
Ford, General Motors International Technegroup Incorporated (ITI-OH),
Lockheed Martin, MacNeal Schwendler Corporation, and Northrop Grumman.
The exchanges centered upon the analysis of a metallic automotive engine
crankshaft. A solid model of the crankshaft was transferred from
ComputerVision (CV) to PATRAN where an idealized analysis shape and the
derived analysis model were created. The model was subsequently analyzed
in MSC/NASTRAN, and also written out in AP209 format and read into CV
Stresslab where an identical analysis was performed. During each step in
the demonstration information was appended to an AP209 Physical File
repository and displayed in an AP209 Visualizer application created by
ITI-OH. Note that the AP209 visualizer had support from the TACOM and
PAS-C pilots as well. Thus at the end of the cycle there were analysis
results available in CV Stresslab, PATRAN, and in the AP209 visualizer
demonstrating the sharing of analysis information. A video documenting
this project is available from PDES, Inc.

The TACOM pilot concentrated on the design and analysis of a composite
upper hull of an armored vehicle. The participants included South
Carolina Research Authority (SCRA), Lockheed Martin, and MacNeal
Schwendler Corporation. Figure 8 illustrates the various shape
representations of the nose of the composite armored vehicle (CAV) that
were represented in a single AP209 repository throughout the life cycle
of the pilot. The solid model of the nose CAV was transferred out of
Intergraph and into PATRAN, as were the surface/wireframe
representations of the ply boundaries. The ply boundaries were also put
through a ply merger and appended to an AP209 repository of the solid
model shape. A finite element model of the nose was then made in PATRAN,
and output to AP209 format and appended to the AP209 repository. An
application developed under the pilot was then run to automatically
generate the material response matrices from the plies and elements that
were then passed back to PATRAN. The analysis was then performed in
ABAQUS, translated back into PATRAN, and then into AP209 format and
appended to the repository. The completed repository was then read back
into Intergraph. In the end there were three applications able to
visualize the analysis output: PATAN, Intergraph, and the AP209
visualizer.

The PAS-C program AP209 pilot was performed with AP232 (Technical Data
Packaging Core Information and Exchange) to show how the two APs
cooperated in performing a configuration controlled design and analysis
modification to a horizontal stabilizer skin of an airlifter. Both AP209
and AP232 were primarily developed under the PAS-C program. The PAS-C
pilot began with a metallic horizontal stabilizer skin native CAD
(Unigraphics) and AP209 files with related configuration control
information being transmitted to a subcontractor via AP232. The
subcontractor then took the AP209 shape of the metallic skin and used it
as a basis to create a hat-stiffened composite replacement skin design.
The composite design was first created using a zone composite
description, and then converted to a ply description. The shape
information was shared with PATRAN to create a finite element model, and
the zone descriptions paired with the finite element model used to
automatically create the skin elastic response matrices. The analyses of
the metallic skin (again in AP209 format) was used as a basis for loads
and boundary conditions to analyze the replacements composite skin. The
composite shape, FEM, composite plies and zones, and analysis
information was aggregated in an AP209 repository in a similar fashion
to the last two pilots. Analysis results were viewed both in PATRAN and
the AP209 visualizer. Finally the revised versions of the shape and
analysis models were packaged in AP232 format and returned to the prime
contractor. A video documenting this pilot is currently in production.

The Phase two PDES, Inc. EA pilot has been underway since October 1997.
The scope of the pilot is to expand the richness of AP209
implementations completed in the Phase one FEA pilot, and to extend the
implementations to include panel and finite difference aerodynamic
information. The aero data will then be coupled with structural data to
enable a loosely coupled un-trimmed aeroelastic analysis. The
participants include Boeing (including the MADE IPDE work related in the
next paragraph), Lockheed Martin, MacNeal Schwendler, and NASA Lewis.

The DARPA/Boeing MADE IPDE contract is to provide an AP209 based
coupling between structural and aerodynamic analysis. The team includes
Boeing, Arizona State University, and MacNeal Schwendler Corporation.
The structural tools involved include MSC/PATRAN and MSC/NASTRAN, and
the aerodynamic tool is the Boeing A502 panel aerodynamic application.
The project includes both Physical File and SDAI data sharing
implementations, and includes an innovative approach to integrating
applications with multiple APs. A typical analysis iteration involves
reading in the AP209 file of A502 panels and pressures into MSC/PATRAN,
reading in the AP209 file of FEM and analysis results into MSC/PATRAN,
mapping the pressures from the A502 model onto the structural model,
analyzing the FEM with MSC/NASTRAN, mapping the deflections back onto
the A502 mesh in PATRAN, and writing out the A502 panel model in an
AP209 file for another aerodynamic analysis with A502. To date the AP209
Physical File based implementation has successfully demonstrated five
iterations to a converged aeroelastic analysis of a composite VTOL
aricraft wing.

[Conclusions]{.underline}

The ISO 10303 STEP AP209 emerging standard has received widespread
review during the last six years since the inception of the project.
Many pilot implementations have proven that AP209 capabilities are
mature enough for large scale commercial implementations. Current
efforts underway will ensure that AP209 will function interoperably
within a suite of EA APs that address the multi-disciplinary analysis
problems that are increasingly facing engineers. Work with AP232 and
other AP interoperability projects have ensured data sharing with many
other STEP APs. Finally, it is clear that the scope of AP209 provides an
effective standards-based solution to the majority of the iterative
structural Design/Analysis integration problems.

[Trademark Acknowledgments]{.underline}

NASTRAN is a registered trademark of NASA. MSC/NASTRAN is an enhanced,
proprietary version developed and maintained by MacNeal Schwendler
Corporation.

PATRAN is a registered trademark of the MacNeal Schwendler Corporation.

Unigraphics is a registered trademark of the Electronic Data
Corporation.

Computervision is a registered trademark of the Computervision
Corporation.

Stresslab is a registered trademark of the Computervision Corporation.

Intergraph is a registered trademark of the Intergraph Corporation.

[Abbreviations List]{.underline}

STEP, Standard for the Exchange of Product Model Data

AP, Application Protocol

ARM, Application Reference Model

AIM, Application Interface Model

FEA, Finite Element Analysis

SPAM, Stiffened Panel Analysis Modeler