The cca-configuration.xml File

The CCA components are configured through the use of an XML file, cca-configuration.xml. This file must be present in the job directory of any CCA analysis. At the moment, this file must be edited using a text editor to set the various configuration options before any CCA analysis is performed.

A Brief Note About XML Files

XML stands for eXtensible Markup Language, and is similar to HTML, the format that most worldwide web documents use. All CCA configuration and data files are written in XML. At the moment, these files must be edited using a text editor (such as Notepad, EMACS, vi, etc.). If you are unfamiliar with XML, the following section will give you an overview of “rules” that should be observed when working with these files.

Elements

The core structural forms in XML files are elements. Elements are essentially containers for data. Consider composite materials: a basic prepreg consists of a fibre component and a matrix component. A material element, then, would contain information relating to that particular material, whether it was a fibre, matrix, or prepreg.

Elements are specified by tags. A tag is just a way of indicating what element you are dealing with. There are start tags and end tags, which make up the container that is an element.

Start tags always begin with a “<”, and at some point end with a “>”. The start tag for the material element could be:

<material>

End tags usually begin with “</” followed by the element name, then a “>”. The end tag for the material element could be:

</material>

Thus, everything between the start tag and end tag is information that belongs to that particular element.

Sometimes, elements are contained in a single set of “<” and “>”. Such an element might be:

<material ...some information... />

Note that this is a complete element. The end tag is replaced with just “/>”, and the “>” for the start tag is not used. This form is used when no data (text or other elements) appear between the start and end tags.

Data

Data can be passed to elements in two ways. One way is to simply include text or other elements between the start and end tags of a parent element:

<material>AS4/3501-6
    <matrix>3501-6</matrix>
    <fibre>AS4</fibre>
</material>

In the above example, the material “AS4/3501-6” has a matrix element “3501-6” and a fibre element “AS4”. The XML is formatted with the indentation to emphasize the hierarchal or object-oriented nature of the data.

Data can also be passed to elements using attributes. Attributes appear within the start tags of elements:

<material name="AS4/3501-6" matrix="3501-6" fibre="AS4" />

In this example, the same data is passed to the material element, just in a different form. The material has a name attribute equal to “AS4/3501-6”, a matrix attribute equal to “3501-6”, and a fibre attribute equal to “AS4”. Attribute names appear as-is, but the attribute data must be enclosed within quotation marks. Note that the end tag is the “/>” form, since no other data is contained within the start and end tags.

These forms can be combined:

<material name="AS4/3501-6" >
    <matrix name="3501-6" />
    <fibre name="AS4" />
</material>

Again, the same information is passed to the material element, just in a different structure.

It is this last syntax that CCA uses. Attributes are used to describe elements, but often elements are contained within other elements (as in the matrix and fibre elements being contained within the material element in the above example).

Comments

Comments in XML files are contained within special start and end tags. Comments are always preceded by the “<!–” tag, and are always terminated by the “–>” tag. Everything in a comment container is ignored by CCA. Note that due to limitations in the XML parser (the code that reads the XML files), comments cannot exceed 8192 characters in length. For longer comments, use multiple “<!– –>” pairs.

<!-- This is a comment -->

Required Elements and Attributes

The file cca-configuration.xml requires the following elements and attributes:

<configuration> ... </configuration>

This is the “wrapper” container for the cca-configuration.xml file. All the configuration data must be within this container or an error will be written to the screen and the analysis will end.

<directory type= “data” path= “mydata” />

This element specifies the path of the CCA data files, relative to the current (i.e., job) directory. If the path attribute is left as “”, then the current directory is assumed.

<directory type= “output” path= “” />

This element specifies the path of the output files, relative to the current (i.e., job) directory. If the path attribute is left as “”, then the current directory is assumed.

<model_units system= “SI|Imperial|USCS” />

This element specifies the unit system used in the FE data files (not the CCA data files). Specify only one of the three unit systems. The SI units are m, kg, s, and the Imperial and USCS (US Customary System) are in (not feet), lbs, sec.

<analysis_code engine= “ABAQUS” />

This element specifies the analysis engine. Currently only ABAQUS and MARC are supported.

<debug screen= “false” file= “false” filename= “debug.csv” debug_element= “1” />

The CCA components are still in development. These options allow some debug information to be printed to screen or file. Most users will not use any of these functions. Note that for ABAQUS, the debug element can be specified as the global element number, or as an instance number of the form PartName.LocalElementID (e.g., Part.12)

<user_material id= “some_id”>...</user_material>

Each user material must be specified within a user_material container. The id is either a text-based identifier (for ABAQUS) or a numerical identifier (for MSC.Marc). Up to 20 different user materials can be specified, and at a minimum there must be one.

The following elements should be specified within the user_material container:

<composite_file name= “AS4-3501-6.xml” />

For each CCA data file that is a composite material, but not for individual matrices or fibres, an element must contain the filename of that material. These files must be located in the directory specifed in the <directory type= "data" path= "" /> element. Without these entries in the cca-configuration.xml file, the CCA component will not be able to locate the material data files.

<initial_doc DOC= “0.001” />

For each user material, you must specify the initial degree of cure. For autocatalytic reactions, this is typically non-zero – usually 0.001 or higher if the material has been characterized at CMT.

<smearing A= “1.0” B= “0.0” />

For each user material, you must specify the smearing parameters. These parameters are used in determining the effective in-plane properties of composites for thermal and flow analyses. Neither MSC.Marc nor ABAQUS support composite sections (or element configurations) so smearing factors must be used for directional material parameters such as conductivity and permeability.

The “A” and “B” parameters account for material properties according to the following relationship (conductivity is used as an example):

Where is the longitudinal conductivity, and is the transverse conductivity for a single ply. For a unidirectional lay-up, which is the default if nothing is specified, the parameters are A=1.0, B=0. For a cross-ply or quasi-orthotropic lay-up the values are A=0.5, B=0.5.

<fbc_override Ex="1.0E9" Ey="1.0E9" Ez="1.0E4"/>

In flow analyses, any layup other than unidirectional will result in complex in-plane fibre bed properties. As previously discussed, the analysis engines do not support “composite” sections in flow analyses, so the fibre bed stiffness properties must be given to the engine separately. At the moment (subject to change), the tensile properties of the fibre bed are input in this manner.