As ACCS is completely integrated within ANSYS Workbench, one simply needs to run Workbench to have access to it. For step-by-step tutorials, please refer to the Workshops section.
A typical Workbench ACCS workflow for composite structures looks as follows:
Fig. 3.1.1 Typical cure simulation workflow for composites in Workbench.¶
The material properties are defined in the Engineering Data module. A shell model is generated in DesignModeler or in SpaceClaim or in any other CAD tool, then it is worked out in ACP (Pre) module to build a solid finite element model of the composite structure that will be transferred to the “Transient Thermal” module where the temperature distribution will be computed throughout the cure cycle for every element as well as the degree of cure, the state of the material, the glass transition temperature and the instantaneous heat of reaction. The temperature distribution is then transferred to the “Static Structural” module where the distortions will be computed using the previously computed temperature and the material properties.
During curing or crystallization processes of polymers, the material, initially liquid, transforms into a solid. The several parameters used in the material models that will used by ACCS to describe these processes are typically calibrated using experimental data from Differential Scanning Calorimetry (DSC) tests, rheometers, Thermo-mechanical analyzers (TMA), and Dynamic Mechanical Analysis (DMA) tests performed on polymer-based single-component or polymeric reinforced composite materials. Within Engineering Data, Ansys provides only a limited set of exemplary-only material cards, LMAT has the ability to provide services for the realization of specific ready-to-use material cards in XML format for Engineering Data to support process simulations through ACCS.
In prepreg fabrics impregnated with thermoset resins, the initial as-received resin’s degree of cure is not 0; instead the resin is received in a partially cured state with a low degree of curing and the curing reaction is continued later after shape forming. Initially, the resin is composed of short monomers in a state preceeding polymerization and flows like a liquid. With heating and time, the thermoset reaction begins: monomers start forming longer polymer chains with crosslinking bonds between the chains (degrees of curing around 0.2-0.6). The extent of the crosslink network determines the resin’s ability to flow. At about a degree of cure of usually 0.5-0.6, the resin reaches a gelled state (gellation) where resin flow stops, and the resin behaves like a semi-solid gel material. The increase in the degree of cure slows as it approaches a maximum where most of the potential crosslinks are formed and the resin is transformed into a solid material state. Subsequent curing beyond this point will see a continual rise in degrees of cure and a rise in mechanical properties until plateauing – at this point, the thermoset matrix is considered fully cured.
Unlike thermosets, thermoplastics do not cure and can be easily melted with heat (between 135 °C and 250 °C): in the case of PEEK a crystallization equation describes the melting process. PEEK is a semi-crystalline thermoplastic polymer, which means that a portion of its molecules aligns and forms crystals while the rest remains amorphous.
From these considerations, it is clear that the first task in the modelling of the cure kinetics or crystallization processes with ACCS is to correctly define the material properties in the material cards.
Fig. 3.2.1 Common material properties specific for ACCS material cards in Engineering Data¶
Fig. 3.2.2 Thermoset material properties specific for ACCS material cards in Engineering Data¶
Fig. 3.2.3 Thermoplastics material properties specific for ACCS material cards in Engineering Data¶
In the list of Fig.:numref:Materials, the basic material properties that users should start with are the cure kinetic model or the crystallization equation, respectively for thermosets (ACCS – Thermosets - Cure Kinetic) and thermoplastics (ACCS – Thermoplastics – Crystallization Kinetic). Several cure kinetic equations models are available for thermosets for representing the evolution of the degrees of cure of the polymer (the Kamal-Sourour equation is one of the most common cure kinetics model in practice), while for describing the melting and crystallization process of thermoplastics only the material model for PEEK is available. For more details about the cure kinetic models and the available crystallization model, please refer to their sections in the theory documentation.
The total heat of reaction or melting, the ACCS-Common properties controlling the glass transition temperature, the levels of degrees of curing (initial, gelation, and final), and a smoothing width (for controlling the evolution of properties) must be included in the ACCS material card. For thermoset materials, advanced users have also the ability to include a diffusion limitation formulation (Proportional Diffusion Limitation or Parallel Diffusion Limitation): in its final part the curing reaction can become controlled mainly by diffusion, hence a diffusion limitation will be able to capture the shift from a chemically controlled reaction to a diffusion-controlled reaction.
After definition of the curing or melting/crystallization process, users must choose one of the two ways to define the composite material properties.
#. The first one is available for both thermosets and thermoplastics and consists in defining the composite material using separate fiber and matrix properties: in this case all the resin thermal and mechanical properties must be added from the thermoset or thermoplastic material cards sections in addition to defining the fibers common properties. It is useful to silence some messages from the Ansys solver that some properties are missing by homogenizing the glassy properties when defined as fiber and matrix (please refer to the ACCS Component Properties subsection of the Getting Started section).
#. The second way, currently possible only for thermosets, is to define the composite material using directly homogenized lamina properties. In this second case the orthotropic lamina thermal or mechanical properties must be included, please note that the thermal and mechanical of the glassy state (at the level of the cured composite material) are not defined within the ACCS material card properties in this case but must be taken directly from standard Ansys density and orthotropic thermal / mechanical material properties (Linear Elastic and Physics Properties), which must then be added to the ACCS card.
The chemical reaction of the curing process results in a shrinkage of the material. Therefore, among the mechanical properties available for thermosets users must also define cure shrinkage behavior (ultimately controlling the presence of residual stresses after curing and, thus, warpage). During polymerization, thermosetting resins undergo a significant increase in density and a corresponding reduction in volume, commonly referred to as ‘cure shrinkage’. One effect of resin cure shrinkage is both in-plane and through-thickness reductions in part dimensions. The shrinkage happening in thermoplastics is derived directly from the implemented material model. Please refer to the Theory Documentation section for more information regarding the ‘cure shrinkage’. Analogously to chemically induced strains, the thermal strains must be also defined through the specification of the opportune coefficient of thermal expansions for fibers and resin or directly at the lamina level. Chemical induced strains and thermal strains are ultimately responsible for the presence of warpage in the composite part and, therefore, for the presence of residual stresses.
Optionally, the user may want to include viscoelastic effects in the case of thermosets materials. To do so, the user can include one of the available models (Maxwell, Power Law, Prony, Extended Standard Non-Linear). Adding one will include the needed relevant properties. With a Maxwell viscoelastic material model when a material is put under a constant stress, the strain has two components, an elastic component which occurs instantaneously and relaxes immediately upon release of the stress, and a second viscous component that grows with time as long as the stress is applied. The Maxwell model, while inaccurate, can be used to describe the mechanical response of low cross-linked polymers since it gives the steady-state creep behavior. More general viscoelastic behavior can be represented by the Prony series (note that a Prony series expansion mathematically expresses the Generalized Maxwell model), having multiple terms to define the moduli relaxation as a function of time and that can be easily fitted, or the more complex Extended Standard Non-Linear Model. Please note that viscoelastic effects must be defined in the ACCS material card but also enabled within Mechanical through the “ViscoElasticity Behaviour?” dropdown menu which allows to enable/disable viscoelasticity without the need to modify the materials in Engineering Data, see Fig.3.9 for reference. The presence of viscoelastic effects will be responsible for the relaxation of the material with the progression of time.
The fundamental need in establishing cure dependence is to predict the instantaneous modulus at certain cure level and an approximation of the relaxation behavior at that cure level. The time and temperature dependent modulus of a thermo-rheologically simple linear viscoelastic material at any temperature (within the range) can be estimated from the measured modulus at a known reference temperature by using the time-temperature superposition principle. Including the “Liquid Time Shift”, “Rubbery Time Shift” and “Glassy Time Shift” properties, also available among viscoelastic effects for thermosets, allows to include temperature and/or degree of cure time shifts. The time shift of properties uses a combination of the WLF equation developed by Williams, Landel and Ferry and a linear formulation. This procedure shifts relaxation effects for amorphous polymers obtained at elevated temperatures to a reference temperature and, therefore, enables the building of a reference master curve to account for temperature effects on the stress relaxation. Similarly, the degree of cure time shift is an expression for describing stress relaxation time as a function of degree of cure for those cases where the relaxation time strongly depends on cure state and where becomes important capturing the viscoelastic effects during the curing process itself. The properties at a lower or higher temperature can be obtained by shifting the master curve left or right on the frequency axis, respectively. The discrete shift factors are recorded and fit to the shift continuous mathematical model. Please refer to section 8.4.5 and 8.4.6 for the details for the equations governing temperature time shift and degree of cure time shift respectively.
Note
The automatic inclusion of properties is only available for Engineering Data cells connected to an “ACP (Pre)” module, an ANSYS thermal module or an ANSYS structural module.
Warning
When opening in ANSYS 2024 R1 a project which was created with an earlier release of ACCS, the material properties must be updated. WB will present the user with a warning messagebox as illustrated below. The user can click on the button to check if the materials need to be upgraded and if it is the case they should click on the button to start the upgrade process.
Fig. 3.2.4 Warning message about ACCS extension upgrade¶
Note
If in Engineering Data the materials were introduced using the fibre/matrix formulation, the user can add equivalent glassy properties to fix solve issues (Mechanical displaying question mark on solution and nothing else seems missing). Simply click on the button . ACCS will only use the properties defined by fibre/matrix formulation and not the homogeneized ones.
The ACCS solution is also integrated within Mechanical and is therefore available in the Transient Thermal and Static Structural analysis systems in the form of an additional tab in the ribbon as show in the figure below.
Fig. 3.3.1 ACCS features in the Mechanical menu ribbon.¶
Adding ACCS to the analysis invokes the ANSYS solver with chemical cure and cure shrinkage routines for materials with defined cure kinetics properties within the Engineering Data module. Once in Workbench Mechanical the user can initiate ACCS by clicking on the “Add Cure Simulation” button as shown in the figures below for the Transient Thermal and Static Structural modules.
Fig. 3.3.2 Initiating ACCS from the toolbar adds an “ANSYS Composite Cure Simulation” item to the current thermal analysis.¶
Fig. 3.3.3 Initiating ACCS from the toolbar adds an “ANSYS Composite Cure Simulation” item to the current structural analysis.¶
Fig. 3.3.4 Details of the options for “ANSYS Composite Cure Simulation” item for a thermal analysis.¶
Fig. 3.3.5 Details of the options for “ANSYS Composite Cure Simulation” item for a FULL structural analysis.¶
The “ViscoElasticity Behaviour?” dropdown menu allows to enable/disable viscoelasticity without the need to modify the materials in Engineering Data.
Fig. 3.3.6 Details of the options for “ANSYS Composite Cure Simulation” item for a FAST structural analysis.¶
When performing a Full Cure Simulation, the button “Copy Analysis Settings” allows the user to copy relevant analysis settings between two analyses easy and fast.
Fig. 3.4.1 This pop up window appears when selecting the “copy Analysis Settings” feature.¶
The lamination process usually involves the placing of composite layers over a mold. After the curing cycle is finished, the part is taken off the mold. Is in this phase of the process where the most relevant permanent deformations occur since the part is without the form constrictions. To simulate that step, ACCS has a boundary condition called “Support Remover” which delete every node that is scoped to it from it predefined displacement constraint. It is important to remark that the support remover is only needed for frictionless supports because you cannot enable/disable it per load step as other supports do.
Fig. 3.5.1 Details of the Support Remover options¶
Including the ACCS feature into the analysis opens the possibility to add cure simulation specific post-processing options like Material State, Degree of Cure, Glass Transition Temperature and Cure Shrinkage in all cartesian directions. These options can be found by selecting the “Add Results” and the “Add Extra Results” buttons, as shown in the following image:
Fig. 3.6.1 Results available during both the Thermal and Mechanical analyses.¶
There are two main transitions that can be distinguished during the curing process of a thermosetting resin. The first one is gelation and the second one is vitrification occurring when the material Tg reaches the cure temperature
Fig. 3.6.2 Plot of an empirical curve (blue) and a simplified curve (red dots) used by ACCS to describe the different material states.¶
This result shows the develope of the curing reaction in the material domain. See Fig. 5.1.1 to see a the dependence of the degree of cure and the temperature in time.
The Heat of Reaction is shown in the Thermoset domain and the plot shows the evolution of it in the time window.
Once the model is solved, the results can be reviewed by clicking on them. Here in the example, an exothermic reaction can be seen in the temperature profile. In many cases, the exothermic reaction a risk to the process. Excessive heat can cause inhomogeneous cure (check the Degree of Cure result) and can damage the structural materials (mainly the resin itself, but also polymeric sandwich cores; or heat-sensitive fibers, such as natural fibers), as well as the auxiliary materials (e.g. the vacuum bag).
Fig. 3.6.3 Solution plots example. Exotherms and material states can be post processed from thermal simulation.¶
Fig. 3.6.4 Extra results only available during the Mechanical analysis.¶
Warning
Strain Results: It is important to note that the normal and shear strain results in mechanical do not only contain the elastic strains but also the cure shrinkage. To view on the elastic strains, please add the “Elastic Strain” results available in the “Extra Results” menu.
The export compensated geometry button adds an object which automatically compensates the process induced distortions for the selected faces. The process induced distortions (deformations) of the structural simulation are inverted and added to the nominal geometry. The compensated geometry can be exported as STL, RSO or point cloud. The options of the support remover are:
Output File Path: the file path where the file will be saved
Scoping Method and Geometry: the geometrical entities which will be exported
Fig. 3.7.1 Options of the compensated surface export item.¶
Fig. 3.7.2 Compensated geometry (orange) and nominal shape (grey).¶
The compensated STL geometry can be natively imported into SpaceClaim to morph the starting mold geometry and realize a tool compensation with a Class A finish, further details and a complete example is given in the ACCS tutorial on the ALH.
ACCS does not support Ansys RSM (Remote Solve Manager).
ACCS does not support coupled simulations in Ansys Mechanical, the transient thermal analysis to predict the evolution of degree of curing and thermal behavior during processing is independent of the downstream structural simulation and, therefore, the two simulations are sequentially coupled.
The viscoelasticity (Prony) implementation is currently implemented only for small-deformation studies.
to check if the materials need to be upgraded and if it is the case they should click on the button 
to start the upgrade process.
. ACCS will only use the properties defined by fibre/matrix formulation and not the homogeneized ones.
button as shown in the figures below for the Transient Thermal and Static Structural modules.
allows the user to copy relevant analysis settings between two analyses easy and fast.
which delete every node that is scoped to it from it predefined displacement constraint. It is important to remark that the support remover is only needed for frictionless supports because you cannot enable/disable it per load step as other supports do.
adds an object which automatically compensates the process induced distortions for the selected faces. The process induced distortions (deformations) of the structural simulation are inverted and added to the nominal geometry. The compensated geometry can be exported as STL, RSO or point cloud. The options of the support remover are:
