Curing Temperature

Curing Temperature Setup

Description

Define temperature fields for composite curing simulation. Invoke when user needs temperature initialization, temperature changes, or thermal fields for curing steps.

Initial Conditions

The initial temperature is set for all nodes in both instances (tool-1 and P8-1) at the start of the analysis:

*Initial Conditions, type=TEMPERATURE
_PickedSet333, 25.

• _PickedSet333: Node set covering ALL nodes in both instances (tool-1 and P8-1).
• Initial temperature: 25°C (room temperature).

_PickedSet333 Definition

The node set _PickedSet333 is defined using generated node ranges for both instances:

*Nset, nset=_PickedSet333, internal, instance=tool-1, generate
    1,  2691,     1
*Nset, nset=_PickedSet333, internal, instance=P8-1, generate
    1,  5445,     1    # (or 3025 for 4-ply model)

• tool-1: Nodes 1 to 2691 (all tool nodes).
• P8-1: Nodes 1 to 5445 (all composite nodes for 8-ply model) or 1 to 3025 (for 4-ply model).
• The generate option creates a sequential node set from the start to end label with the given increment.

Temperature in Each Step

The temperature is updated in each step of the curing cycle using the *Temperature predefined field. The temperature drives the UMAT material response (curing kinetics and glass transition).

vis Step (Viscous State)

*Temperature
_PickedSet333, 150.

• Temperature changes from 25°C to 150°C.
• At 150°C, the resin is in a low-viscosity state, allowing flow and compaction.
• The UMAT subroutine recognizes this as the viscous state.

rub Step (Rubbery State)

*Temperature
_PickedSet333, 180.

• Temperature changes from 150°C to 180°C.
• At 180°C, the cure reaction progresses and the material transitions to a rubbery state.
• The UMAT subroutine recognizes this as the rubbery state.

glassy Step (Glassy State)

*Temperature
_PickedSet333, 25.

• Temperature changes from 180°C to 25°C (cooling to room temperature).
• As the material cools below its glass transition temperature (Tg), it transitions to a glassy state.
• The UMAT subroutine recognizes this as the glassy state.

sp Step (Springback)

*Temperature
_PickedSet333, 25.

• Temperature maintained at 25°C.
• The tool is removed (via Model Change) and the composite undergoes springback at room temperature.

Temperature Schedule Summary

Temperature as a Predefined Field

Temperature is a predefined field in Abaqus, applied to all nodes in the model:

• The *Temperature keyword assigns a uniform temperature to all nodes in the specified set.
• The temperature is ramped linearly from the previous step's value to the new value over the step time.
• The UMAT subroutine receives the current temperature at each integration point and uses it to:
  • Determine the material state (viscous, rubbery, or glassy).
  • Compute the degree of cure (cure kinetics).
  • Update the glass transition temperature (Tg).
  • Calculate thermal strains and cure shrinkage strains.

UMAT and Temperature Interaction

The UMAT subroutine uses temperature as the primary driver for material state transitions:

1. Viscous state (high temperature, ~150°C): Low resin viscosity, resin flow and compaction occur. The material is soft and deformable.
2. Rubbery state (intermediate temperature, ~180°C): Cure reaction advances, cross-linking increases. The material becomes rubbery and begins to develop stiffness.
3. Glassy state (low temperature, ~25°C): Below Tg, the material is rigid and glassy. Residual stresses are locked in during this phase.

The state variables (SDV1-SDV4) are updated based on the temperature history, tracking:

• Degree of cure progression
• Glass transition temperature evolution
• Current material state
• Accumulated cure strain

Notes

• The temperature values (25, 150, 180, 25°C) represent a typical three-step curing cycle. Adjust based on the specific resin system and cure schedule.
• The temperature is applied uniformly to all nodes. For spatially varying temperature fields, use a field variable or mapped temperature data.
• The _PickedSet333 node set must include all nodes in both instances to ensure uniform temperature application.
• When changing the mesh (e.g., from 8-ply to 4-ply), update the node range for P8-1 in _PickedSet333 accordingly (5445 for 8-ply, 3025 for 4-ply).
• The temperature ramp rate is controlled by the step time. Ensure the step time is sufficient for the cure reaction to complete (especially in the rub step).